module markused

import v3.flat
import v3.types

const trace_markused = false

// mark_used updates mark used state for markused.
pub fn mark_used(a &flat.FlatAst, tc &types.TypeChecker) map[string]bool {
    return mark_used_with_test_files(a, tc, map[string]bool{})
}

pub fn mark_used_for_tests(a &flat.FlatAst, tc &types.TypeChecker, test_files []string) map[string]bool {
    mut file_map := map[string]bool{}
    for file in test_files {
        file_map[file] = true
    }
    return mark_used_with_test_files(a, tc, file_map)
}

fn mark_used_with_test_files(a &flat.FlatAst, tc &types.TypeChecker, test_files map[string]bool) map[string]bool {
    mut cur_module := ''
    mut imports := map[string]string{}
    mut fn_decls := map[string]FnDeclInfo{}
    mut fn_decl_lists := map[string][]FnDeclInfo{}
    mut struct_decls := map[string]StructDeclInfo{}
    mut const_decls := map[string]ConstDeclInfo{}

    // Reverse index: short name (after last '.') -> list of full qualified names
    mut suffix_map := map[string][]string{}

    mut fn_count := 0
    mut fn_with_dot := 0
    mut contains2_total := 0
    for node_idx, node in a.nodes {
        if node.kind == .file {
            cur_module = ''
            continue
        }
        if node.kind == .module_decl {
            cur_module = node.value
            continue
        }
        if node.kind == .import_decl {
            imports[node.typ] = node.value
            continue
        }
        if node.kind == .struct_decl {
            full_name := qualify_fn(cur_module, node.value)
            info := StructDeclInfo{
                node_id: flat.NodeId(node_idx)
                module:  cur_module
            }
            struct_decls[full_name] = info
            if node.value !in struct_decls {
                struct_decls[node.value] = info
            }
            continue
        }
        if node.kind == .const_decl {
            for i in 0 .. node.children_count {
                field_id := a.child(&node, i)
                field := a.node(field_id)
                if field.kind != .const_field || field.children_count == 0 {
                    continue
                }
                info := ConstDeclInfo{
                    expr_id: a.child(field, 0)
                    module:  cur_module
                }
                const_decls[field.value] = info
                full_name := qualify_fn(cur_module, field.value)
                if full_name != field.value {
                    const_decls[full_name] = info
                }
            }
            continue
        }
        if node.kind == .fn_decl {
            has_dot := node.value.contains('.')
            if trace_markused {
                fn_count++
                if has_dot {
                    fn_with_dot++
                    if fn_with_dot <= 5 {
                        eprintln('  fn with dot: "${node.value}"')
                    }
                }
            }
            info := FnDeclInfo{
                node_id: flat.NodeId(node_idx)
                module:  cur_module
            }
            add_fn_decl_info(mut fn_decls, mut fn_decl_lists, node.value, info)
            lowered_name := markused_c_name(node.value)
            if lowered_name != node.value {
                add_fn_decl_info(mut fn_decls, mut fn_decl_lists, lowered_name, info)
            }
            qname := qualify_fn(cur_module, node.value)
            if qname != node.value {
                add_fn_decl_info(mut fn_decls, mut fn_decl_lists, qname, info)
                lowered_qname := markused_c_name(qname)
                if lowered_qname != qname {
                    add_fn_decl_info(mut fn_decls, mut fn_decl_lists, lowered_qname, info)
                }
            }
            // Build suffix_map entries
            if has_dot {
                if trace_markused {
                    contains2_total++
                }
                short := node.value.all_after_last('.')
                add_suffix_candidate(mut suffix_map, short, node.value)
                if qname != node.value {
                    add_suffix_candidate(mut suffix_map, short, qname)
                }
            }
            if qname != node.value && qname.contains('.') {
                short := qname.all_after_last('.')
                add_suffix_candidate(mut suffix_map, short, qname)
            }
        }
    }

    // BFS from main
    mut used := map[string]bool{}
    mut queue := []string{}
    queue << 'main'
    used['main'] = true
    enqueue_main_module_roots(fn_decls, mut used, mut queue)
    enqueue_auto_roots(fn_decls, mut used, mut queue)
    enqueue_export_roots(a, mut used, mut queue)
    enqueue_veb_handler_roots(a, tc, mut used, mut queue)
    enqueue_test_file_roots(a, test_files, mut used, mut queue)
    queue << 'time.Time.new'
    used['time.Time.new'] = true
    used['Time.new'] = true
    queue << 'gen_expr_lvalue'
    used['gen_expr_lvalue'] = true
    queue << 'c.gen_expr_lvalue'
    used['c.gen_expr_lvalue'] = true
    queue << 'gen_assign'
    used['gen_assign'] = true
    queue << 'c.gen_assign'
    used['c.gen_assign'] = true
    for seed in ['__new_array', 'new_array_from_c_array', 'array.get', 'array.set', 'array.push',
        'array.push_many', 'array.slice', 'array.clone', 'array.delete', 'array.ensure_cap',
        'string.==', 'string.<', 'string.free', 'string.all_before', 'string.all_before_last',
        'string.all_after', 'string.all_after_last', 'string.substr', 'string__substr', 'u8.vstring',
        '[]rune.string', 'map.set', 'map.exists', 'map.get', 'map.get_check', 'map.get_and_set',
        'map.delete', 'map.clone', 'map.clear', 'memdup', 'strings.Builder.write_ptr',
        'strings.Builder.write_runes', 'strings.Builder.free', 'strconv.format_int',
        'strconv.format_uint', 'bool.str', 'ptr_str', 'strconv__f32_to_str_l',
        'strconv__f64_to_str_l', 'sync.new_channel_st', 'sync.Channel.push', 'sync.Channel.pop',
        'sync.Channel.close', 'sync.Channel.len', 'sync.Channel.closed', 'new_channel_st',
        'Channel.push', 'Channel.pop', 'Channel.close', 'Channel.len', 'Channel.closed', 'panic',
        'u8.is_letter', 'u8.is_capital', 'string.is_capital', 'string.to_lower_ascii',
        'rune.to_lower', 'Array_u8__bytestr', 'Array_u8__hex', 'data_to_hex_string',
        'map_hash_string', 'map_hash_int_1', 'map_hash_int_2', 'map_hash_int_4', 'map_hash_int_8',
        'map_eq_string', 'map_eq_int_1', 'map_eq_int_2', 'map_eq_int_4', 'map_eq_int_8',
        'map_clone_string', 'map_clone_int_1', 'map_clone_int_2', 'map_clone_int_4',
        'map_clone_int_8', 'map_free_string', 'map_free_nop', '[]string.join', 'Array_string__join',
        'exit', 'v_exit'] {
        queue << seed
        used[seed] = true
    }

    if trace_markused {
        eprintln('markused: fn_count:')
        eprintln(fn_count.str())
        eprintln('fn_with_dot:')
        eprintln(fn_with_dot.str())
        eprintln('contains2_total:')
        eprintln(contains2_total.str())
        eprintln('markused: main in fn_decls: ${'main' in fn_decls}')
        eprintln('markused: fn_decls count: ${fn_decls.len}')
        eprintln('markused: suffix_map count: ${suffix_map.len}')
        mut total_suffix_entries := 0
        for _, vals in suffix_map {
            total_suffix_entries += vals.len
        }
        eprintln('total suffix_map entries (sum of array lens):')
        eprintln(total_suffix_entries.str())
    }

    mut suffix_hits := 0
    // mut suffix_misses := 0
    mut in_cg := 0
    mut not_in_cg := 0
    mut total_callees := 0
    collector := CallCollector{
        a:            a
        tc:           tc
        fn_decls:     fn_decls
        struct_decls: struct_decls
        const_decls:  const_decls
    }
    enqueue_detected_runtime_helpers(a, tc, mut used, mut queue)
    enqueue_function_value_selectors(a, collector, fn_decls, mut used, mut queue)
    // Methods used as values (`recv.method` passed as a callback) are reachable only
    // through a wrapper cgen generates later. The checker records them per enclosing
    // function in `method_values_by_fn`; they are seeded inside the BFS below (only when
    // that function is reached), so an unreachable function's method value never forces an
    // otherwise-unused specialization to be transformed/emitted.
    enqueue_initializer_calls(a, collector, imports, fn_decls, mut used, mut queue)
    enqueue_top_level_calls(a, collector, fn_decls, mut used, mut queue)
    // Interface dispatch reachability: calling an interface method `Foo.m` may
    // dispatch to any concrete `T.m` for a type `T` that implements `Foo`. Those
    // concrete methods are only referenced from the generated dispatch switch, so
    // without this they would be pruned and produce undefined-symbol errors.
    mut iface_impls := map[string][]string{}
    mut checked_iface_impls := map[string]bool{}
    mut processed_nodes := []bool{len: a.nodes.len}
    mut calls := []string{cap: 128}
    mut qi := 0
    for qi < queue.len {
        name := queue[qi]
        qi++
        prev_len := queue.len
        fn_infos := fn_decl_infos_for_queue_name(name, fn_decl_lists, a)
        if fn_infos.len == 0 {
            not_in_cg++
            if trace_markused && qi <= 10 {
                eprintln('BFS qi=${qi.str()} name="${name}" in_cg=false')
            }
            continue
        }
        for fn_info in fn_infos {
            if trace_markused && qi <= 10 {
                eprintln('BFS qi=${qi.str()} name="${name}" in_cg=true')
            }
            in_cg++
            node_key := int(fn_info.node_id)
            if node_key < 0 || node_key >= processed_nodes.len {
                continue
            }
            if processed_nodes[node_key] {
                continue
            }
            processed_nodes[node_key] = true
            // This function is reachable, so any methods it uses as *values* (recorded by
            // the checker per enclosing function) are reachable too -- mark them so they
            // survive pruning (cgen emits a wrapper that calls them).
            if mvs := tc.method_values_by_fn[node_key] {
                for mkey in mvs {
                    enqueue(mkey, mut used, mut queue)
                    lowered_mv := markused_c_name(mkey)
                    if lowered_mv != mkey {
                        enqueue(lowered_mv, mut used, mut queue)
                    }
                    mv_short := mkey.all_after_last('.')
                    if cands := suffix_map[mv_short] {
                        for cand in cands {
                            if cand == mkey || cand.ends_with('.${mkey}') {
                                enqueue(cand, mut used, mut queue)
                            }
                        }
                    }
                }
            }
            calls.clear()
            node := a.node(fn_info.node_id)
            receiver_name, receiver_struct := receiver_info(a, node)
            collector.collect_calls(node, fn_info.module, imports, receiver_name, receiver_struct, mut
                calls)
            total_callees += calls.len
            for callee in calls {
                if !valid_symbol_name(callee) {
                    continue
                }
                mut found_direct := false
                if callee_info := fn_decls[callee] {
                    found_direct = true
                    if enqueue(callee, mut used, mut queue) {
                        if trace_markused && qi == 1 {
                            eprintln('main: all_fns hit: "${callee}"')
                        }
                    }
                    add_safe_decl_alias(callee, callee_info, a, mut used)
                } else if callee in tc.fn_ret_types {
                    found_direct = true
                    if enqueue(callee, mut used, mut queue) {
                        if trace_markused && qi == 1 {
                            eprintln('main: resolved hit: "${callee}"')
                        }
                    }
                }
                if !found_direct || !callee.contains('.') {
                    short := callee.all_after_last('.')
                    if suffix_candidates := suffix_map[short] {
                        for candidate in suffix_candidates {
                            if candidate in fn_decls || candidate in tc.fn_ret_types {
                                if enqueue(candidate, mut used, mut queue) {
                                    suffix_hits++
                                }
                            }
                        }
                    }
                }
                if callee.contains('.') {
                    recv := callee.all_before_last('.')
                    method := callee.all_after_last('.')
                    ensure_iface_impls(recv, fn_info.module, tc, mut iface_impls, mut
                        checked_iface_impls)
                    if impls := iface_impls[recv] {
                        for impl in impls {
                            impl_method := '${impl}.${method}'
                            enqueue(impl_method, mut used, mut queue)
                            short_impl := '${impl.all_after_last('.')}.${method}'
                            if short_impl != impl_method {
                                enqueue(short_impl, mut used, mut queue)
                            }
                        }
                    }
                }
            }
        }
        new_added := queue.len - prev_len
        if trace_markused && qi <= 10 {
            eprintln('  -> added ${new_added.str()} new entries, queue now ${queue.len.str()}')
        }
    }
    if trace_markused {
        eprintln('total_callees:')
        eprintln(total_callees.str())
        eprintln('markused: in_cg:')
        eprintln(in_cg.str())
        eprintln('not_in_cg:')
        eprintln(not_in_cg.str())
        eprintln('queue.len:')
        eprintln(queue.len.str())
        eprintln('markused: suffix_hits:')
        eprintln(suffix_hits.str())
        eprintln('markused: total used: ${used.len}')
    }
    return used
}

// ensure_iface_impls supports ensure iface impls handling for markused.
fn ensure_iface_impls(recv string, cur_module string, tc &types.TypeChecker, mut iface_impls map[string][]string, mut checked map[string]bool) {
    if recv.len == 0 {
        return
    }
    iface_name := interface_name_for_receiver(recv, cur_module, tc) or { return }
    if iface_name in checked {
        return
    }
    checked[iface_name] = true
    if recv != iface_name {
        checked[recv] = true
    }
    mut impls := []string{}
    for struct_name, _ in tc.structs {
        if tc.named_type_implements_interface(struct_name, iface_name) {
            impls << struct_name
        }
    }
    iface_impls[recv] = impls
    if iface_name != recv {
        iface_impls[iface_name] = impls
        checked[iface_name] = true
    }
}

fn interface_name_for_receiver(recv string, cur_module string, tc &types.TypeChecker) ?string {
    if recv in tc.interface_names {
        return recv
    }
    if recv.contains('.') {
        return none
    }
    if cur_module.len > 0 && cur_module != 'main' && cur_module != 'builtin' {
        qname := '${cur_module}.${recv}'
        if qname in tc.interface_names {
            return qname
        }
    }
    return none
}

// add_suffix_candidate updates add suffix candidate state for markused.
fn add_suffix_candidate(mut suffix_map map[string][]string, short string, name string) {
    if !valid_symbol_name(short) || !valid_symbol_name(name) {
        return
    }
    mut candidates := suffix_map[short] or { []string{} }
    candidates << name
    suffix_map[short] = candidates
}

fn add_fn_decl_info(mut fn_decls map[string]FnDeclInfo, mut fn_decl_lists map[string][]FnDeclInfo, name string, info FnDeclInfo) {
    fn_decls[name] = info
    mut infos := fn_decl_lists[name] or { []FnDeclInfo{} }
    infos << info
    fn_decl_lists[name] = infos
}

fn fn_decl_infos_for_queue_name(name string, fn_decl_lists map[string][]FnDeclInfo, a &flat.FlatAst) []FnDeclInfo {
    infos := fn_decl_lists[name] or { return []FnDeclInfo{} }
    if infos.len <= 1 {
        return infos
    }
    mut exact_infos := []FnDeclInfo{}
    for info in infos {
        node := a.node(info.node_id)
        if fn_decl_key_is_exact_for_info(name, node.value, info.module) {
            exact_infos << info
        }
    }
    return exact_infos
}

fn fn_decl_key_is_exact_for_info(name string, decl_name string, module_name string) bool {
    qname := qualify_fn(module_name, decl_name)
    if name == qname {
        return true
    }
    lowered := markused_c_name(qname)
    return lowered != qname && name == lowered
}

fn add_safe_decl_alias(callee string, callee_info FnDeclInfo, a &flat.FlatAst, mut used map[string]bool) {
    alias := a.node(callee_info.node_id).value
    if alias == callee || alias in used {
        return
    }
    if fn_decl_key_is_exact_for_info(callee, alias, callee_info.module) {
        return
    }
    used[alias] = true
}

// valid_symbol_name supports valid symbol name handling for markused.
fn valid_symbol_name(name string) bool {
    return name.len > 0 && name.len < 512
}

// markused_clone_bool_map returns a value clone even when the source is passed
// from a `mut map` parameter. v3 self-host cgen otherwise infers a `map*` local
// for `param.clone()` in a few recursive markused scanners.
fn markused_clone_bool_map(src map[string]bool) map[string]bool {
    return src.clone()
}

fn markused_clone_string_map(src map[string]string) map[string]string {
    return src.clone()
}

// enqueue_initializer_calls supports enqueue initializer calls handling for markused.
fn enqueue_initializer_calls(a &flat.FlatAst, collector CallCollector, imports map[string]string, fn_decls map[string]FnDeclInfo, mut used map[string]bool, mut queue []string) {
    mut cur_module := ''
    mut calls := []string{cap: 32}
    for node in a.nodes {
        match node.kind {
            .module_decl {
                cur_module = node.value
            }
            .const_decl, .global_decl {
                for i in 0 .. node.children_count {
                    field := a.child_node(&node, i)
                    if field.children_count == 0 {
                        continue
                    }
                    calls.clear()
                    collector.collect_calls(field, cur_module, imports, '', '', mut calls)
                    for callee in calls {
                        if callee_info := fn_decls[callee] {
                            enqueue(callee, mut used, mut queue)
                            add_safe_decl_alias(callee, callee_info, a, mut used)
                        } else {
                            enqueue(callee, mut used, mut queue)
                        }
                    }
                }
            }
            else {}
        }
    }
}

fn enqueue_top_level_calls(a &flat.FlatAst, collector CallCollector, fn_decls map[string]FnDeclInfo, mut used map[string]bool, mut queue []string) {
    if markused_has_entry_main(a) {
        return
    }
    mut calls := []string{cap: 32}
    for file_idx, file_node in a.nodes {
        if !markused_should_scan_top_level_file(a, file_idx, file_node) {
            continue
        }
        module_name := markused_top_level_file_module_name(a, file_node)
        file_imports := markused_top_level_file_imports(a, file_node)
        mut local_values := map[string]bool{}
        mut local_types := map[string]string{}
        for i in 0 .. file_node.children_count {
            child_id := a.child(&file_node, i)
            if int(child_id) < a.user_code_start {
                continue
            }
            child := a.node(child_id)
            if !markused_is_top_level_stmt(child) {
                continue
            }
            calls.clear()
            collector.collect_top_level_stmt_calls(child_id, module_name, file_imports, mut
                local_values, mut local_types, mut calls)
            for callee in calls {
                if callee_info := fn_decls[callee] {
                    enqueue(callee, mut used, mut queue)
                    add_safe_decl_alias(callee, callee_info, a, mut used)
                } else {
                    enqueue(callee, mut used, mut queue)
                }
            }
        }
    }
}

fn markused_has_entry_main(a &flat.FlatAst) bool {
    mut cur_module := ''
    for node in a.nodes {
        match node.kind {
            .file {
                cur_module = ''
            }
            .module_decl {
                cur_module = node.value
            }
            .fn_decl {
                if node.value == 'main' && (cur_module.len == 0 || cur_module == 'main') {
                    return true
                }
            }
            else {}
        }
    }
    return false
}

fn markused_should_scan_top_level_file(a &flat.FlatAst, file_idx int, file_node flat.Node) bool {
    if file_idx < a.user_code_start || file_node.kind != .file || file_node.children_count == 0 {
        return false
    }
    module_name := markused_top_level_file_module_name(a, file_node)
    return module_name.len == 0 || module_name == 'main'
}

fn markused_top_level_file_module_name(a &flat.FlatAst, file_node flat.Node) string {
    for i in 0 .. file_node.children_count {
        child := a.child_node(&file_node, i)
        if child.kind == .module_decl {
            return child.value
        }
    }
    return ''
}

fn markused_top_level_file_imports(a &flat.FlatAst, file_node flat.Node) map[string]string {
    mut imports := map[string]string{}
    for i in 0 .. file_node.children_count {
        child := a.child_node(&file_node, i)
        if child.kind == .import_decl {
            imports[child.typ] = child.value
        }
    }
    return imports
}

fn markused_is_top_level_stmt(node flat.Node) bool {
    return match node.kind {
        .expr_stmt, .assign, .decl_assign, .global_decl, .selector_assign, .index_assign,
        .for_stmt, .for_in_stmt, .if_expr, .match_stmt, .assert_stmt, .defer_stmt, .block {
            true
        }
        else {
            false
        }
    }
}

// enqueue supports enqueue handling for markused.
fn enqueue(name string, mut used map[string]bool, mut queue []string) bool {
    if !valid_symbol_name(name) {
        return false
    }
    if name in used {
        return false
    }
    used[name] = true
    queue << name
    return true
}

// FnDeclInfo stores fn decl info metadata used by markused.
struct FnDeclInfo {
    node_id flat.NodeId
    module  string
}

// StructDeclInfo stores struct decl info metadata used by markused.
struct StructDeclInfo {
    node_id flat.NodeId
    module  string
}

// ConstDeclInfo stores const decl info metadata used by markused.
struct ConstDeclInfo {
    expr_id flat.NodeId
    module  string
}

// CallCollector represents call collector data used by markused.
struct CallCollector {
    a            &flat.FlatAst      = unsafe { nil }
    tc           &types.TypeChecker = unsafe { nil }
    fn_decls     map[string]FnDeclInfo
    struct_decls map[string]StructDeclInfo
    const_decls  map[string]ConstDeclInfo
}

// enqueue_auto_roots supports enqueue auto roots handling for markused.
fn enqueue_auto_roots(fn_decls map[string]FnDeclInfo, mut used map[string]bool, mut queue []string) {
    for name, info in fn_decls {
        if !is_auto_root_fn(name) {
            continue
        }
        enqueue(name, mut used, mut queue)
        short_name := name.all_after_last('.')
        if short_name != name {
            enqueue(short_name, mut used, mut queue)
        }
        qualified_name := qualify_fn(info.module, short_name)
        if qualified_name != name {
            enqueue(qualified_name, mut used, mut queue)
        }
    }
}

fn enqueue_export_roots(a &flat.FlatAst, mut used map[string]bool, mut queue []string) {
    if a.export_fn_names.len == 0 {
        return
    }
    mut cur_module := ''
    for node in a.nodes {
        match node.kind {
            .file {
                cur_module = ''
            }
            .module_decl {
                cur_module = node.value
            }
            .fn_decl {
                qname := qualify_fn(cur_module, node.value)
                if qname in a.export_fn_names {
                    enqueue(qname, mut used, mut queue)
                }
            }
            else {}
        }
    }
}

fn enqueue_veb_handler_roots(a &flat.FlatAst, tc &types.TypeChecker, mut used map[string]bool, mut queue []string) {
    mut cur_module := ''
    for node in a.nodes {
        match node.kind {
            .file {
                cur_module = ''
            }
            .module_decl {
                cur_module = node.value
            }
            .fn_decl {
                if markused_fn_needs_implicit_veb_ctx(a, tc, cur_module, node) {
                    enqueue(qualify_fn(cur_module, node.value), mut used, mut queue)
                }
            }
            else {}
        }
    }
}

fn markused_fn_needs_implicit_veb_ctx(a &flat.FlatAst, tc &types.TypeChecker, cur_module string, node flat.Node) bool {
    return markused_fn_returns_veb_result(tc, node) && markused_fn_has_receiver_param(a, node)
        && !markused_fn_receiver_type_is_context(a, node) && !markused_fn_has_param(a, node, 'ctx')
        && markused_type_name_known_in_module(tc, cur_module, 'Context')
}

fn markused_fn_returns_veb_result(tc &types.TypeChecker, node flat.Node) bool {
    if node.typ == 'veb.Result' {
        return true
    }
    ret := tc.parse_type(node.typ)
    return ret.name() == 'veb.Result'
}

fn markused_fn_has_receiver_param(a &flat.FlatAst, node flat.Node) bool {
    if !node.value.contains('.') || node.children_count == 0 {
        return false
    }
    first := a.child_node(&node, 0)
    if first.kind != .param || first.typ.len == 0 {
        return false
    }
    receiver := node.value.all_before_last('.').all_after_last('.')
    param_type := first.typ.trim_left('&').all_after_last('.')
    return receiver == param_type
}

fn markused_fn_receiver_type_is_context(a &flat.FlatAst, node flat.Node) bool {
    if !markused_fn_has_receiver_param(a, node) {
        return false
    }
    first := a.child_node(&node, 0)
    return first.typ.trim_left('&').all_after_last('.') == 'Context'
}

fn markused_fn_has_param(a &flat.FlatAst, node flat.Node, name string) bool {
    for i in 0 .. node.children_count {
        param := a.child_node(&node, i)
        if param.kind == .param && param.value == name {
            return true
        }
    }
    return false
}

fn markused_type_name_known_in_module(tc &types.TypeChecker, module_name string, typ string) bool {
    qtyp := qualify_fn(module_name, typ)
    return qtyp in tc.type_aliases || qtyp in tc.structs || qtyp in tc.interface_names
        || qtyp in tc.enum_names || qtyp in tc.sum_types
}

fn enqueue_test_file_roots(a &flat.FlatAst, test_files map[string]bool, mut used map[string]bool, mut queue []string) {
    if test_files.len == 0 {
        return
    }
    for file_idx, file_node in a.nodes {
        if !is_user_test_file_node(a, file_idx, file_node, test_files) {
            continue
        }
        module_name := test_file_module_name(a, file_node)
        if module_name.len > 0 && module_name != 'main' {
            continue
        }
        mut decl_ids := []flat.NodeId{}
        markused_collect_test_harness_decl_ids(a, file_node, mut decl_ids)
        for child_id in decl_ids {
            child := a.node(child_id)
            if is_test_harness_root_name(child.value) {
                enqueue(qualify_fn(module_name, child.value), mut used, mut queue)
            }
        }
    }
}

fn markused_collect_test_harness_decl_ids(a &flat.FlatAst, node flat.Node, mut ids []flat.NodeId) {
    if node.kind != .file && node.kind != .block {
        return
    }
    for i in 0 .. node.children_count {
        child_id := a.child(&node, i)
        if int(child_id) < a.user_code_start {
            continue
        }
        child := a.node(child_id)
        if child.kind == .fn_decl {
            ids << child_id
        } else if child.kind == .block {
            markused_collect_test_harness_decl_ids(a, child, mut ids)
        }
    }
}

fn is_user_test_file_node(a &flat.FlatAst, file_idx int, file_node flat.Node, test_files map[string]bool) bool {
    if file_idx < a.user_code_start || file_node.kind != .file || file_node.children_count == 0 {
        return false
    }
    return test_files[file_node.value]
}

fn test_file_module_name(a &flat.FlatAst, file_node flat.Node) string {
    for i in 0 .. file_node.children_count {
        child := a.child_node(&file_node, i)
        if child.kind == .module_decl {
            return child.value
        }
    }
    return ''
}

fn is_test_harness_root_name(name string) bool {
    return name.starts_with('test_')
        || name in ['testsuite_begin', 'testsuite_end', 'before_each', 'after_each']
}

// enqueue_main_module_roots supports enqueue main module roots handling for markused.
fn enqueue_main_module_roots(fn_decls map[string]FnDeclInfo, mut used map[string]bool, mut queue []string) {
    for name, info in fn_decls {
        if info.module != 'main' || name != 'main' {
            continue
        }
        enqueue(name, mut used, mut queue)
    }
}

// is_auto_root_fn reports whether is auto root fn applies in markused.
fn is_auto_root_fn(name string) bool {
    short_name := name.all_after_last('.')
    return short_name == 'init'
}

// enqueue_detected_runtime_helpers supports enqueue detected runtime helpers handling for markused.
fn enqueue_detected_runtime_helpers(a &flat.FlatAst, tc &types.TypeChecker, mut used map[string]bool, mut queue []string) {
    mut needs_optional_helpers := false
    mut needs_string_interp_helpers := false
    mut needs_string_plus_helper := false
    mut needs_string_membership_helpers := false
    mut needs_new_map := false
    mut cur_module := ''
    mut imports := map[string]string{}
    for node in a.nodes {
        match node.kind {
            .file {
                cur_module = ''
                imports = map[string]string{}
            }
            .module_decl {
                cur_module = node.value
            }
            .import_decl {
                imports[node.typ] = node.value
            }
            .fn_decl {
                ret_type := tc.parse_type(node.typ)
                if ret_type is types.OptionType || ret_type is types.ResultType {
                    needs_optional_helpers = true
                }
            }
            .param, .field_decl, .field_init, .const_field {
                if type_string_needs_optional_helpers(node.typ) {
                    needs_optional_helpers = true
                }
            }
            .none_expr {
                needs_optional_helpers = true
            }
            .or_expr {
                needs_optional_helpers = true
                if node.children_count > 0 {
                    expr_id := a.child(&node, 0)
                    expr_type := tc.expr_type(expr_id) or { tc.resolve_type(expr_id) }
                    if type_needs_zero_map(expr_type) {
                        needs_new_map = true
                    }
                }
            }
            .call {
                if node.children_count > 0 {
                    fn_node := a.child_node(&node, 0)
                    if fn_node.kind == .ident
                        && (fn_node.value == 'error' || fn_node.value == 'error_with_code') {
                        needs_optional_helpers = true
                    }
                    if fn_node.kind == .ident && fn_node.value == 'flag_default_value' {
                        enqueue('escape_default_string', mut used, mut queue)
                    }
                    if fn_node.kind == .selector
                        && fn_node.value in ['trim_space', 'trim_space_left', 'trim_space_right', 'to_upper', 'to_upper_ascii', 'to_lower', 'to_lower_ascii'] {
                        enqueue('string.${fn_node.value}', mut used, mut queue)
                    }
                    if markused_call_lowers_to_join_path_single(a, fn_node, imports) {
                        enqueue('join_path_single', mut used, mut queue)
                        enqueue('os.join_path_single', mut used, mut queue)
                    }
                    if fn_node.kind == .ident
                        && fn_node.value in ['print', 'println', 'eprint', 'eprintln']
                        && node.children_count >= 2 {
                        enqueue_stringified_custom_str_method(a.child(&node, 1), cur_module, tc, mut
                            used, mut queue)
                    }
                }
            }
            .string_interp {
                needs_string_interp_helpers = true
                needs_string_plus_helper = true
                for i in 0 .. node.children_count {
                    enqueue_stringified_custom_str_method(a.child(&node, i), cur_module, tc, mut
                        used, mut queue)
                }
            }
            .assign {
                if node.op == .plus_assign && node.children_count == 2 {
                    lhs_id := a.child(&node, 0)
                    rhs_id := a.child(&node, 1)
                    rhs := a.node(rhs_id)
                    lhs_type := markused_membership_container_type(tc, tc.resolve_type(lhs_id))
                    rhs_type := markused_membership_container_type(tc, tc.resolve_type(rhs_id))
                    if lhs_type == 'string' || rhs_type == 'string'
                        || rhs.kind in [.string_literal, .string_interp] {
                        needs_string_plus_helper = true
                    }
                }
            }
            .in_expr {
                if node.children_count >= 2 {
                    rhs_id := a.child(&node, 1)
                    rhs_type := markused_membership_container_type(tc, tc.resolve_type(rhs_id))
                    if rhs_type == 'string' {
                        needs_string_membership_helpers = true
                    }
                }
            }
            .map_init {
                needs_new_map = true
            }
            .enum_decl {
                // A `[flag]` enum's synthesized `<Enum>__autostr` helper (emitted
                // unconditionally in cgen) builds its `Enum{.a | .b}` string with
                // `string__plus`. markused never walks that generated body, so without
                // seeding the helper here it can be pruned when the program has no other
                // string concatenation, leaving the autostr calling an undefined
                // `string__plus`.
                if node.typ == 'flag' {
                    needs_string_plus_helper = true
                }
            }
            else {}
        }
    }
    if needs_optional_helpers {
        for helper in ['IError.str', 'error', 'error_with_code'] {
            enqueue(helper, mut used, mut queue)
        }
    }
    if needs_string_interp_helpers {
        for helper in ['strings.new_builder', 'strings.Builder.write_string', 'strings.Builder.str',
            'string_plus_many'] {
            enqueue(helper, mut used, mut queue)
        }
    }
    if needs_string_plus_helper {
        enqueue('string__plus', mut used, mut queue)
    }
    if needs_string_membership_helpers {
        for helper in ['string__contains', 'string__contains_u8'] {
            enqueue(helper, mut used, mut queue)
        }
    }
    if needs_new_map {
        enqueue('new_map', mut used, mut queue)
    }
}

fn markused_call_lowers_to_join_path_single(a &flat.FlatAst, fn_node flat.Node, imports map[string]string) bool {
    if fn_node.kind == .ident {
        return fn_node.value == 'join_path'
    }
    if fn_node.kind != .selector || fn_node.value != 'join_path' || fn_node.children_count == 0 {
        return false
    }
    base_id := a.child(&fn_node, 0)
    if int(base_id) < 0 {
        return false
    }
    base := a.node(base_id)
    if base.kind != .ident {
        return false
    }
    return base.value == 'os' || imports[base.value] == 'os'
}

// enqueue_stringified_custom_str_method supports enqueue_stringified_custom_str_method handling.
fn enqueue_stringified_custom_str_method(expr_id flat.NodeId, cur_module string, tc &types.TypeChecker, mut used map[string]bool, mut queue []string) {
    mut typ := tc.expr_type(expr_id) or { tc.resolve_type(expr_id) }
    for _ in 0 .. 8 {
        if typ is types.Alias {
            typ = typ.base_type
            continue
        }
        if typ is types.OptionType {
            typ = typ.base_type
            continue
        }
        if typ is types.ResultType {
            typ = typ.base_type
            continue
        }
        break
    }
    match typ {
        types.Enum {
            enqueue_enum_str_method(typ.name, cur_module, tc, mut used, mut queue)
        }
        types.Struct {
            enqueue_structlike_str_method(typ.name, cur_module, tc, mut used, mut queue)
        }
        types.SumType {
            enqueue_structlike_str_method(typ.name, cur_module, tc, mut used, mut queue)
        }
        else {}
    }
}

// enqueue_enum_str_method supports enqueue enum str method handling for markused.
fn enqueue_enum_str_method(type_name string, cur_module string, tc &types.TypeChecker, mut used map[string]bool, mut queue []string) {
    for candidate in stringification_type_candidates(type_name, cur_module) {
        method := '${candidate}.str'
        if method in tc.fn_ret_types {
            enqueue(method, mut used, mut queue)
            lowered := markused_c_name(method)
            if lowered != method {
                enqueue(lowered, mut used, mut queue)
            }
        }
    }
}

// enqueue_structlike_str_method supports enqueue structlike str method handling for markused.
fn enqueue_structlike_str_method(type_name string, cur_module string, tc &types.TypeChecker, mut used map[string]bool, mut queue []string) {
    for candidate in stringification_type_candidates(type_name, cur_module) {
        lowered := '${markused_c_name(candidate)}__str'
        if lowered in tc.fn_ret_types {
            enqueue(lowered, mut used, mut queue)
        }
        method := '${candidate}.str'
        if method in tc.fn_ret_types {
            enqueue(method, mut used, mut queue)
        }
    }
}

// stringification_type_candidates supports stringification type candidates handling for markused.
fn stringification_type_candidates(type_name string, cur_module string) []string {
    if type_name.len == 0 {
        return []string{}
    }
    mut candidates := []string{cap: 2}
    candidates << type_name
    if !type_name.contains('.') && cur_module.len > 0 && cur_module != 'main'
        && cur_module != 'builtin' {
        candidates << '${cur_module}.${type_name}'
    }
    return candidates
}

// enqueue_function_value_selectors supports enqueue function value selectors handling for markused.
fn enqueue_function_value_selectors(a &flat.FlatAst, collector CallCollector, fn_decls map[string]FnDeclInfo, mut used map[string]bool, mut queue []string) {
    ignored_top_level_nodes := markused_ignored_top_level_nodes(a)
    ignored_fn_decl_nodes := markused_ignored_fn_decl_nodes(a)
    shadowed_value_idents := markused_shadowed_value_idents(collector)
    for node_idx, node in a.nodes {
        if node_idx < ignored_fn_decl_nodes.len && ignored_fn_decl_nodes[node_idx] {
            continue
        }
        if node_idx < ignored_top_level_nodes.len && ignored_top_level_nodes[node_idx] {
            continue
        }
        if node.kind == .ident && node.value.len > 0 {
            node_id := flat.NodeId(node_idx)
            is_shadowed := node_idx < shadowed_value_idents.len && shadowed_value_idents[node_idx]
            if is_shadowed {
                continue
            }
            if resolved := collector.tc.resolved_fn_value_name(node_id) {
                enqueue(resolved, mut used, mut queue)
                continue
            }
            if node.value in fn_decls && collector.node_is_fn_value(node_id) {
                enqueue(node.value, mut used, mut queue)
            }
            continue
        }
        if node.kind == .selector && node.children_count > 0 && node.value.len > 0 {
            base_id := a.child(&node, 0)
            if int(base_id) >= 0 && int(base_id) < shadowed_value_idents.len
                && shadowed_value_idents[int(base_id)] {
                continue
            }
            base := a.node(base_id)
            if base.kind == .ident && base.value.len > 0 {
                name := '${base.value}.${node.value}'
                if name in fn_decls {
                    enqueue(name, mut used, mut queue)
                }
            }
        }
    }
}

fn markused_ignored_fn_decl_nodes(a &flat.FlatAst) []bool {
    mut ignored := []bool{len: a.nodes.len}
    for node_idx, node in a.nodes {
        if node.kind == .fn_decl {
            markused_mark_node_subtree(a, flat.NodeId(node_idx), mut ignored)
        }
    }
    return ignored
}

fn markused_ignored_top_level_nodes(a &flat.FlatAst) []bool {
    if !markused_has_entry_main(a) {
        return []bool{}
    }
    mut ignored := []bool{len: a.nodes.len}
    for file_idx, file_node in a.nodes {
        if !markused_should_scan_top_level_file(a, file_idx, file_node) {
            continue
        }
        for i in 0 .. file_node.children_count {
            child_id := a.child(&file_node, i)
            if int(child_id) < a.user_code_start {
                continue
            }
            child := a.node(child_id)
            if !markused_is_top_level_stmt(child) {
                continue
            }
            markused_mark_node_subtree(a, child_id, mut ignored)
        }
    }
    return ignored
}

fn markused_shadowed_value_idents(collector CallCollector) []bool {
    a := collector.a
    mut shadowed := []bool{len: a.nodes.len}
    for node in a.nodes {
        if node.kind != .fn_decl {
            continue
        }
        local_values := markused_local_value_names(a, &node)
        if local_values.len == 0 {
            continue
        }
        markused_mark_shadowed_idents(a, &node, local_values, mut shadowed)
    }
    for file_idx, file_node in a.nodes {
        if !markused_should_scan_top_level_file(a, file_idx, file_node) {
            continue
        }
        mut local_values := map[string]bool{}
        for i in 0 .. file_node.children_count {
            child_id := a.child(&file_node, i)
            if int(child_id) < a.user_code_start {
                continue
            }
            child := a.node(child_id)
            if !markused_is_top_level_stmt(child) {
                continue
            }
            if local_values.len > 0 {
                markused_mark_shadowed_idents(a, child, local_values, mut shadowed)
            }
            markused_mark_top_level_lhs_idents(a, child, mut shadowed)
            markused_add_top_level_lhs_names(a, child, mut local_values)
        }
    }
    return shadowed
}

fn markused_mark_shadowed_idents(a &flat.FlatAst, node &flat.Node, local_values map[string]bool, mut shadowed []bool) {
    if local_values.len == 0 {
        return
    }
    mut stack := []flat.NodeId{cap: int(node.children_count)}
    for i in 0 .. node.children_count {
        child_id := a.child(node, i)
        if int(child_id) >= 0 {
            stack << child_id
        }
    }
    for stack.len > 0 {
        id := stack.pop()
        idx := int(id)
        if idx < 0 || idx >= shadowed.len {
            continue
        }
        child := a.node(id)
        if child.kind == .ident && child.value in local_values {
            shadowed[idx] = true
        }
        for i in 0 .. child.children_count {
            next_id := a.child(child, i)
            if int(next_id) >= 0 {
                stack << next_id
            }
        }
    }
}

fn markused_mark_top_level_lhs_idents(a &flat.FlatAst, node &flat.Node, mut shadowed []bool) {
    if node.kind != .decl_assign {
        return
    }
    mut i := 0
    for i + 1 < node.children_count {
        lhs_id := a.child(node, i)
        idx := int(lhs_id)
        if idx >= 0 && idx < shadowed.len {
            lhs := a.node(lhs_id)
            if lhs.kind == .ident {
                shadowed[idx] = true
            }
        }
        i += 2
    }
}

fn markused_add_top_level_lhs_names(a &flat.FlatAst, node &flat.Node, mut local_values map[string]bool) {
    match node.kind {
        .decl_assign, .assign {
            mut i := 0
            for i + 1 < node.children_count {
                lhs_id := a.child(node, i)
                if int(lhs_id) >= 0 {
                    lhs := a.node(lhs_id)
                    if lhs.kind == .ident && lhs.value.len > 0 {
                        local_values[lhs.value] = true
                    }
                }
                i += 2
            }
        }
        .global_decl {
            for i in 0 .. node.children_count {
                field := a.child_node(node, i)
                if field.value.len > 0 {
                    local_values[field.value] = true
                }
            }
        }
        else {}
    }
}

fn markused_mark_node_subtree(a &flat.FlatAst, root flat.NodeId, mut marked []bool) {
    mut stack := [root]
    for stack.len > 0 {
        id := stack.pop()
        idx := int(id)
        if idx < 0 || idx >= marked.len || marked[idx] {
            continue
        }
        marked[idx] = true
        node := a.node(id)
        for i in 0 .. node.children_count {
            child_id := a.child(node, i)
            if int(child_id) >= 0 {
                stack << child_id
            }
        }
    }
}

// type_string_needs_optional_helpers returns type string needs optional helpers data for markused.
fn type_string_needs_optional_helpers(typ string) bool {
    return typ.len > 0 && (typ[0] == `?` || typ[0] == `!`)
}

// type_needs_zero_map returns type needs zero map data for markused.
fn type_needs_zero_map(typ types.Type) bool {
    mut clean := typ
    for _ in 0 .. 8 {
        if clean is types.Alias {
            clean = clean.base_type
            continue
        }
        if clean is types.OptionType {
            clean = clean.base_type
            continue
        }
        if clean is types.ResultType {
            clean = clean.base_type
            continue
        }
        break
    }
    return clean is types.Map
}

// markused_membership_container_type
// supports helper handling in markused.
fn markused_membership_container_type(tc &types.TypeChecker, typ types.Type) string {
    mut clean := typ.name().trim_space()
    for {
        if clean.starts_with('shared ') {
            clean = clean[7..].trim_space()
            continue
        }
        if clean.starts_with('&') {
            clean = clean[1..].trim_space()
            continue
        }
        if clean in tc.type_aliases {
            alias := tc.type_aliases[clean].trim_space()
            if alias == clean {
                break
            }
            clean = alias
            continue
        }
        break
    }
    return clean
}

// qualify_fn supports qualify fn handling for markused.
fn qualify_fn(mod string, name string) string {
    if mod.len == 0 || mod == 'main' || mod == 'builtin' {
        return name
    }
    return '${mod}.${name}'
}

// receiver_info supports receiver info handling for markused.
fn receiver_info(a &flat.FlatAst, node &flat.Node) (string, string) {
    mut receiver_struct := ''
    if node.value.contains('.') {
        receiver_struct = node.value.all_before_last('.')
    }
    for pi in 0 .. node.children_count {
        pc := a.child_node(node, pi)
        if pc.kind == .param {
            if receiver_struct.len > 0 {
                return pc.value, receiver_struct
            }
            clean_type := pc.typ.trim_left('&')
            if pc.value.len > 0 && clean_type.len > 0 && clean_type[0] >= `A`
                && clean_type[0] <= `Z` {
                return pc.value, clean_type
            }
        }
    }
    if receiver_struct.len == 0 {
        return '', ''
    }
    return '', receiver_struct
}

// collect_calls updates collect calls state for markused.
fn (c &CallCollector) collect_calls(node &flat.Node, cur_module string, imports map[string]string, receiver_name string, receiver_struct string, mut calls []string) {
    local_values := c.local_value_names(node)
    local_types := c.local_value_type_names(node, cur_module, imports)
    visible_local_idents := markused_visible_local_idents(c.a, node, local_values)
    mut stack := []flat.NodeId{cap: int(node.children_count)}
    for i in 0 .. node.children_count {
        child_id := c.a.child(node, i)
        if int(child_id) >= 0 {
            stack << child_id
        }
    }
    for stack.len > 0 {
        child_id := stack.pop()
        child := &c.a.nodes[int(child_id)]
        match child.kind {
            .ident {
                name_is_local := markused_ident_is_visible_local(child_id, child.value,
                    local_values, visible_local_idents)
                c.collect_fn_value_ident(child_id, child.value, cur_module, imports, name_is_local, mut
                    calls)
            }
            .selector {
                if !c.selector_base_is_local(child, local_values) {
                    c.collect_fn_value_selector(child_id, child, cur_module, imports, mut calls)
                } else if resolved := c.tc.resolved_fn_value_name(child_id) {
                    calls << resolved
                }
            }
            .call {
                mut resolved_call := ''
                if resolved := c.tc.resolved_call_name(child_id) {
                    resolved_call = resolved
                }
                if child.children_count > 0 {
                    callee_id := c.a.child(child, 0)
                    if int(callee_id) >= 0 {
                        callee := c.a.nodes[int(callee_id)]
                        if callee.kind == .ident && callee.value.len > 0 {
                            if resolved_call.len > 0 {
                                calls << resolved_call
                            }
                            if callee.value !in local_values {
                                calls << callee.value
                                qcallee := qualify_fn(cur_module, callee.value)
                                if qcallee != callee.value {
                                    calls << qcallee
                                }
                            }
                        } else if callee.kind == .selector && callee.value.len > 0 {
                            mut has_exact_selector_call := false
                            if callee.children_count > 0 {
                                base_id := c.a.child(&callee, 0)
                                if int(base_id) >= 0 {
                                    base := c.a.nodes[int(base_id)]
                                    has_exact_selector_call = c.collect_typed_receiver_method(base_id,
                                        callee.value, cur_module, imports, local_values,
                                        local_types, mut calls)
                                    if !has_exact_selector_call && base.kind == .ident
                                        && base.value in imports && base.value !in local_values {
                                        calls << imports[base.value] + '.' + callee.value
                                        has_exact_selector_call = true
                                    }
                                    if !has_exact_selector_call && resolved_call.len > 0 {
                                        calls << resolved_call
                                        has_exact_selector_call = true
                                    }
                                    if !has_exact_selector_call && base.kind == .ident
                                        && base.value in local_values && !(receiver_name.len > 0
                                        && base.value == receiver_name) {
                                        has_exact_selector_call = true
                                    }
                                    if !has_exact_selector_call {
                                        if base.kind == .ident && base.value.len > 0 {
                                            if receiver_name.len > 0 && base.value == receiver_name {
                                                calls << receiver_struct + '.' + callee.value
                                                qrecv := qualify_fn(cur_module, receiver_struct +
                                                    '.' + callee.value)
                                                if qrecv != receiver_struct + '.' + callee.value {
                                                    calls << qrecv
                                                }
                                            }
                                            mod_name := if base.value in imports {
                                                imports[base.value]
                                            } else {
                                                base.value
                                            }
                                            calls << mod_name + '.' + callee.value
                                            calls << qualify_fn(cur_module, base.value + '.' +
                                                callee.value)
                                            if base.value.len > 0 && base.value[0] >= `A`
                                                && base.value[0] <= `Z` {
                                                named_type := c.tc.parse_type(base.value)
                                                named_type_name := resolve_type_name(named_type)
                                                if named_type_name.len > 0 {
                                                    calls << named_type_name + '.' + callee.value
                                                }
                                            }
                                        } else if base.kind == .selector && base.children_count > 0 {
                                            inner_id := c.a.child(&base, 0)
                                            if int(inner_id) >= 0 {
                                                inner := c.a.nodes[int(inner_id)]
                                                if inner.kind == .ident && inner.value.len > 0 {
                                                    mod_name := if inner.value in imports {
                                                        imports[inner.value]
                                                    } else {
                                                        inner.value
                                                    }
                                                    calls << mod_name + '.' + base.value + '.' +
                                                        callee.value
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                            if !has_exact_selector_call {
                                calls << callee.value
                            }
                        } else if resolved_call.len > 0 {
                            calls << resolved_call
                        }
                    }
                } else if resolved_call.len > 0 {
                    calls << resolved_call
                }
                for ci in 1 .. child.children_count {
                    arg_id := c.a.child(child, ci)
                    if int(arg_id) >= 0 {
                        arg := c.a.nodes[int(arg_id)]
                        if arg.kind == .ident && arg.value.len > 0 {
                            arg_is_local := markused_ident_is_visible_local(arg_id, arg.value,
                                local_values, visible_local_idents)
                            c.collect_fn_value_ident(arg_id, arg.value, cur_module, imports,
                                arg_is_local, mut calls)
                        }
                    }
                }
            }
            .prefix {
                if child.op == .amp && child.children_count > 0 {
                    inner_id := c.a.child(child, 0)
                    if int(inner_id) >= 0 {
                        inner := c.a.nodes[int(inner_id)]
                        if inner.kind == .struct_init {
                            calls << 'memdup'
                        }
                    }
                }
            }
            .string_interp {
                calls << 'string_plus_many'
            }
            .infix {
                if child.op == .plus {
                    calls << 'string__plus'
                }
                if child.children_count >= 2 {
                    lhs_id := c.a.child(child, 0)
                    rhs_id := c.a.child(child, 1)
                    if child.op in [.dot, .amp] {
                        lhs_name := c.qualified_expr_name(lhs_id)
                        if lhs_name.len > 0 {
                            rhs := c.a.nodes[int(rhs_id)]
                            if rhs.kind == .call && rhs.children_count > 0 {
                                fn_node := c.a.child_node(&rhs, 0)
                                if fn_node.kind == .ident && fn_node.value.len > 0 {
                                    mod_name := if lhs_name in imports {
                                        imports[lhs_name]
                                    } else {
                                        lhs_name
                                    }
                                    calls << mod_name + '.' + fn_node.value
                                    calls << qualify_fn(cur_module, lhs_name + '.' + fn_node.value)
                                }
                            }
                        }
                    }
                    if int(lhs_id) >= 0 {
                        c.collect_struct_operator_call(lhs_id, child.op, cur_module, mut calls)
                    }
                }
            }
            .or_expr {
                if child.children_count > 0 {
                    expr_id := c.a.child(child, 0)
                    c.collect_zero_struct_default_calls(c.node_type(expr_id), cur_module, imports, mut
                        calls)
                }
            }
            .struct_init {
                c.collect_struct_default_calls(child, cur_module, imports, mut calls)
            }
            else {}
        }

        if child.children_count > 0 {
            mut j := int(child.children_count) - 1
            for j >= 0 {
                if child.kind == .decl_assign && j % 2 == 0 {
                    j--
                    continue
                }
                next_id := c.a.child(child, j)
                if int(next_id) >= 0 {
                    stack << next_id
                }
                j--
            }
        }
    }
}

fn (c &CallCollector) local_value_names(node &flat.Node) map[string]bool {
    return markused_local_value_names(c.a, node)
}

fn (c &CallCollector) local_value_type_names(node &flat.Node, cur_module string, imports map[string]string) map[string]string {
    mut result := map[string]string{}
    mut stack := []flat.NodeId{cap: int(node.children_count)}
    for i in 0 .. node.children_count {
        child_id := c.a.child(node, i)
        if int(child_id) >= 0 {
            stack << child_id
        }
    }
    for stack.len > 0 {
        id := stack.pop()
        child := c.a.node(id)
        if child.kind == .param && child.value.len > 0 && child.typ.len > 0 {
            result[child.value] = markused_resolve_imported_type_name(child.typ, imports)
        } else if child.kind == .decl_assign {
            mut i := 0
            for i + 1 < child.children_count {
                lhs_id := c.a.child(child, i)
                rhs_id := c.a.child(child, i + 1)
                if int(lhs_id) >= 0 && int(rhs_id) >= 0 {
                    lhs := c.a.node(lhs_id)
                    if lhs.kind == .ident && lhs.value.len > 0 {
                        type_name := if child.children_count == 2 && child.typ.len > 0 {
                            child.typ
                        } else {
                            c.top_level_decl_rhs_type_name(rhs_id, cur_module, imports)
                        }
                        if type_name.len > 0 {
                            result[lhs.value] = type_name
                        }
                    }
                }
                i += 2
            }
        }
        for i in 0 .. child.children_count {
            next_id := c.a.child(child, i)
            if int(next_id) >= 0 {
                stack << next_id
            }
        }
    }
    return result
}

fn markused_local_value_names(a &flat.FlatAst, node &flat.Node) map[string]bool {
    mut names := map[string]bool{}
    mut stack := []flat.NodeId{cap: int(node.children_count)}
    for i in 0 .. node.children_count {
        child_id := a.child(node, i)
        if int(child_id) >= 0 {
            stack << child_id
        }
    }
    for stack.len > 0 {
        id := stack.pop()
        child := a.node(id)
        if child.kind == .param && child.value.len > 0 {
            names[child.value] = true
        } else if child.kind == .decl_assign {
            mut i := 0
            for i < child.children_count {
                lhs_id := a.child(child, i)
                if int(lhs_id) >= 0 {
                    lhs := a.node(lhs_id)
                    if lhs.kind == .ident && lhs.value.len > 0 {
                        names[lhs.value] = true
                    }
                }
                i += 2
            }
        }
        for i in 0 .. child.children_count {
            next_id := a.child(child, i)
            if int(next_id) >= 0 {
                stack << next_id
            }
        }
    }
    return names
}

fn markused_visible_local_idents(a &flat.FlatAst, root &flat.Node, local_values map[string]bool) map[int]bool {
    mut visible_ids := map[int]bool{}
    if local_values.len == 0 {
        return visible_ids
    }
    mut locals := map[string]bool{}
    if root.kind == .fn_decl {
        for i in 0 .. root.children_count {
            child := a.child_node(root, i)
            if child.kind == .param && child.value.len > 0 {
                locals[child.value] = true
            }
        }
    }
    markused_collect_visible_local_idents(a, root, local_values, mut locals, mut visible_ids)
    return visible_ids
}

fn markused_ident_is_visible_local(id flat.NodeId, name string, local_values map[string]bool, visible_local_idents map[int]bool) bool {
    return name.len > 0 && name in local_values && int(id) in visible_local_idents
}

fn markused_collect_visible_local_idents(a &flat.FlatAst, node &flat.Node, local_values map[string]bool, mut locals map[string]bool, mut visible_ids map[int]bool) {
    for i in 0 .. node.children_count {
        child_id := a.child(node, i)
        if int(child_id) < 0 {
            continue
        }
        child := a.node(child_id)
        match child.kind {
            .fn_decl, .c_fn_decl, .fn_literal {
                continue
            }
            .block, .if_expr, .match_stmt, .for_stmt, .for_in_stmt {
                mut scoped := markused_clone_bool_map(locals)
                markused_collect_visible_local_idents(a, child, local_values, mut scoped, mut
                    visible_ids)
            }
            .decl_assign {
                mut i2 := 1
                for i2 < child.children_count {
                    rhs_id := a.child(child, i2)
                    if int(rhs_id) >= 0 {
                        markused_mark_visible_local_ident(a, rhs_id, local_values, locals, mut
                            visible_ids)
                        rhs := a.node(rhs_id)
                        markused_collect_visible_local_idents(a, rhs, local_values, mut locals, mut
                            visible_ids)
                    }
                    i2 += 2
                }
                i2 = 0
                for i2 + 1 < child.children_count {
                    lhs_id := a.child(child, i2)
                    lhs := a.node(lhs_id)
                    if lhs.kind == .ident && lhs.value in local_values && lhs.value in locals {
                        visible_ids[int(lhs_id)] = true
                    }
                    if lhs.kind == .ident && lhs.value.len > 0 {
                        locals[lhs.value] = true
                    }
                    i2 += 2
                }
            }
            else {
                if child.kind == .ident && child.value in local_values && child.value in locals {
                    visible_ids[int(child_id)] = true
                }
                markused_collect_visible_local_idents(a, child, local_values, mut locals, mut
                    visible_ids)
            }
        }
    }
}

fn markused_mark_visible_local_ident(a &flat.FlatAst, id flat.NodeId, local_values map[string]bool, locals map[string]bool, mut visible_ids map[int]bool) {
    node := a.node(id)
    if node.kind == .ident && node.value in local_values && node.value in locals {
        visible_ids[int(id)] = true
    }
}

fn (c &CallCollector) top_level_decl_rhs_type_name(rhs_id flat.NodeId, cur_module string, imports map[string]string) string {
    rhs := c.a.node(rhs_id)
    if rhs.kind == .struct_init && rhs.value.len > 0 {
        return c.struct_lookup_name(markused_resolve_imported_type_name(rhs.value, imports),
            cur_module)
    }
    type_name := resolve_type_name(c.node_type(rhs_id))
    if type_name.len > 0 {
        struct_type := c.struct_lookup_name(type_name, cur_module)
        if struct_type.len > 0 {
            return struct_type
        }
        return type_name
    }
    return ''
}

fn (c &CallCollector) collect_top_level_stmt_calls(id flat.NodeId, cur_module string, imports map[string]string, mut local_values map[string]bool, mut local_types map[string]string, mut calls []string) {
    if int(id) < 0 {
        return
    }
    node := c.a.node(id)
    match node.kind {
        .decl_assign, .assign {
            c.collect_top_level_assign_calls(node, cur_module, imports, mut local_values, mut
                local_types, mut calls)
        }
        .global_decl {
            c.collect_top_level_global_decl_calls(node, cur_module, imports, mut local_values, mut
                local_types, mut calls)
        }
        .block, .for_stmt, .for_in_stmt {
            mut nested_values := markused_clone_bool_map(local_values)
            mut nested_types := markused_clone_string_map(local_types)
            c.collect_top_level_child_calls(node, cur_module, imports, mut nested_values, mut
                nested_types, mut calls)
        }
        .if_expr, .match_stmt {
            c.collect_top_level_branch_calls(node, cur_module, imports, local_values, local_types, mut
                calls)
        }
        else {
            c.collect_top_level_expr_calls(id, cur_module, imports, local_values, local_types, mut
                calls)
        }
    }
}

fn (c &CallCollector) collect_top_level_child_calls(node &flat.Node, cur_module string, imports map[string]string, mut local_values map[string]bool, mut local_types map[string]string, mut calls []string) {
    for i in 0 .. node.children_count {
        child_id := c.a.child(node, i)
        if int(child_id) >= 0 {
            c.collect_top_level_stmt_calls(child_id, cur_module, imports, mut local_values, mut
                local_types, mut calls)
        }
    }
}

fn (c &CallCollector) collect_top_level_branch_calls(node &flat.Node, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string, mut calls []string) {
    for i in 0 .. node.children_count {
        child_id := c.a.child(node, i)
        if int(child_id) < 0 {
            continue
        }
        mut branch_values := local_values.clone()
        mut branch_types := local_types.clone()
        c.collect_top_level_stmt_calls(child_id, cur_module, imports, mut branch_values, mut
            branch_types, mut calls)
    }
}

fn (c &CallCollector) collect_top_level_assign_calls(node &flat.Node, cur_module string, imports map[string]string, mut local_values map[string]bool, mut local_types map[string]string, mut calls []string) {
    if node.kind !in [.decl_assign, .assign] {
        return
    }
    mut i := 0
    pre_values := markused_clone_bool_map(local_values)
    pre_types := markused_clone_string_map(local_types)
    for i + 1 < node.children_count {
        rhs_id := c.a.child(node, i + 1)
        if int(rhs_id) >= 0 {
            mut rhs_values := markused_clone_bool_map(pre_values)
            mut rhs_types := markused_clone_string_map(pre_types)
            c.collect_top_level_stmt_calls(rhs_id, cur_module, imports, mut rhs_values, mut
                rhs_types, mut calls)
        }
        i += 2
    }
    i = 0
    for i + 1 < node.children_count {
        lhs_id := c.a.child(node, i)
        rhs_id := c.a.child(node, i + 1)
        if int(lhs_id) >= 0 && int(rhs_id) >= 0 {
            lhs := c.a.node(lhs_id)
            if lhs.kind == .ident && lhs.value.len > 0 {
                local_values[lhs.value] = true
                type_name := c.top_level_decl_rhs_type_name(rhs_id, cur_module, imports)
                if type_name.len > 0 {
                    local_types[lhs.value] = type_name
                }
            }
        }
        i += 2
    }
}

fn (c &CallCollector) collect_top_level_global_decl_calls(node &flat.Node, cur_module string, imports map[string]string, mut local_values map[string]bool, mut local_types map[string]string, mut calls []string) {
    if node.kind != .global_decl {
        return
    }
    pre_values := markused_clone_bool_map(local_values)
    pre_types := markused_clone_string_map(local_types)
    for i in 0 .. node.children_count {
        field := c.a.child_node(node, i)
        if field.children_count == 0 {
            continue
        }
        expr_id := c.a.child(field, 0)
        if int(expr_id) >= 0 {
            mut rhs_values := markused_clone_bool_map(pre_values)
            mut rhs_types := markused_clone_string_map(pre_types)
            c.collect_top_level_stmt_calls(expr_id, cur_module, imports, mut rhs_values, mut
                rhs_types, mut calls)
        }
    }
    for i in 0 .. node.children_count {
        field := c.a.child_node(node, i)
        if field.value.len == 0 {
            continue
        }
        local_values[field.value] = true
        if field.children_count > 0 {
            expr_id := c.a.child(field, 0)
            type_name := c.top_level_decl_rhs_type_name(expr_id, cur_module, imports)
            if type_name.len > 0 {
                local_types[field.value] = type_name
            }
        }
    }
}

fn (c &CallCollector) collect_top_level_expr_calls(id flat.NodeId, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string, mut calls []string) {
    if int(id) < 0 {
        return
    }
    mut stack := [id]
    for stack.len > 0 {
        child_id := stack.pop()
        child := c.a.node(child_id)
        match child.kind {
            .ident {
                if child.value !in local_values {
                    c.collect_fn_value_ident(child_id, child.value, cur_module, imports, false, mut
                        calls)
                }
            }
            .selector {
                if !c.top_level_selector_base_is_local(child, local_values) {
                    c.collect_fn_value_selector(child_id, child, cur_module, imports, mut calls)
                }
            }
            .call {
                c.collect_top_level_call(child_id, child, cur_module, imports, local_values,
                    local_types, mut calls)
            }
            .prefix {
                if child.op == .amp && child.children_count > 0 {
                    inner_id := c.a.child(child, 0)
                    if int(inner_id) >= 0 {
                        inner := c.a.node(inner_id)
                        if inner.kind == .struct_init {
                            calls << 'memdup'
                        }
                    }
                }
            }
            .string_interp {
                calls << 'string_plus_many'
            }
            .infix {
                if child.op == .plus {
                    calls << 'string__plus'
                }
                if child.children_count >= 2 {
                    lhs_id := c.a.child(child, 0)
                    rhs_id := c.a.child(child, 1)
                    if child.op in [.dot, .amp] {
                        lhs_name := c.qualified_expr_name(lhs_id)
                        if lhs_name.len > 0 {
                            rhs := c.a.node(rhs_id)
                            if rhs.kind == .call && rhs.children_count > 0 {
                                fn_node := c.a.child_node(rhs, 0)
                                if fn_node.kind == .ident && fn_node.value.len > 0 {
                                    mod_name := if lhs_name in imports {
                                        imports[lhs_name]
                                    } else {
                                        lhs_name
                                    }
                                    calls << mod_name + '.' + fn_node.value
                                    calls << qualify_fn(cur_module, lhs_name + '.' + fn_node.value)
                                }
                            }
                        }
                    }
                    if int(lhs_id) >= 0 {
                        c.collect_struct_operator_call(lhs_id, child.op, cur_module, mut calls)
                    }
                }
            }
            .or_expr {
                if child.children_count > 0 {
                    expr_id := c.a.child(child, 0)
                    c.collect_zero_struct_default_calls(c.node_type(expr_id), cur_module, imports, mut
                        calls)
                }
            }
            .struct_init {
                c.collect_struct_default_calls(child, cur_module, imports, mut calls)
            }
            else {}
        }

        if child.children_count > 0 {
            mut j := int(child.children_count) - 1
            for j >= 0 {
                next_id := c.a.child(child, j)
                if int(next_id) >= 0 {
                    stack << next_id
                }
                j--
            }
        }
    }
}

fn (c &CallCollector) top_level_selector_base_is_local(node flat.Node, local_values map[string]bool) bool {
    return c.selector_base_is_local(&node, local_values)
}

fn (c &CallCollector) selector_base_is_local(node &flat.Node, local_values map[string]bool) bool {
    if node.children_count == 0 {
        return false
    }
    base_id := c.a.child(node, 0)
    if int(base_id) < 0 {
        return false
    }
    base := c.a.node(base_id)
    return base.kind == .ident && base.value in local_values
}

fn (c &CallCollector) collect_top_level_call(call_id flat.NodeId, call &flat.Node, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string, mut calls []string) {
    mut resolved_call := ''
    if resolved := c.tc.resolved_call_name(call_id) {
        resolved_call = resolved
    }
    if call.children_count == 0 {
        if resolved_call.len > 0 {
            calls << resolved_call
        }
        return
    }
    callee_id := c.a.child(call, 0)
    if int(callee_id) < 0 {
        return
    }
    callee := c.a.node(callee_id)
    if callee.kind == .ident && callee.value.len > 0 {
        if resolved_call.len > 0 {
            calls << resolved_call
        }
        if callee.value !in local_values {
            calls << callee.value
            qcallee := qualify_fn(cur_module, callee.value)
            if qcallee != callee.value {
                calls << qcallee
            }
        }
    } else if callee.kind == .selector && callee.value.len > 0 {
        c.collect_top_level_selector_call(callee, callee.value, resolved_call, cur_module, imports,
            local_values, local_types, mut calls)
    } else if resolved_call.len > 0 {
        calls << resolved_call
    }
    for ci in 1 .. call.children_count {
        arg_id := c.a.child(call, ci)
        if int(arg_id) >= 0 {
            arg := c.a.node(arg_id)
            if arg.kind == .ident && arg.value.len > 0 {
                if arg.value !in local_values {
                    c.collect_fn_value_ident(arg_id, arg.value, cur_module, imports, false, mut
                        calls)
                }
            }
        }
    }
}

fn (c &CallCollector) collect_top_level_selector_call(callee &flat.Node, method string, resolved_call string, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string, mut calls []string) {
    mut has_exact_selector_call := false
    if callee.children_count > 0 {
        base_id := c.a.child(callee, 0)
        if int(base_id) >= 0 {
            base := c.a.node(base_id)
            has_exact_selector_call = c.collect_top_level_typed_receiver_method(base_id, method,
                cur_module, imports, local_values, local_types, mut calls)
            if !has_exact_selector_call && base.kind == .ident && base.value in imports
                && base.value !in local_values {
                calls << imports[base.value] + '.' + method
                has_exact_selector_call = true
            }
            if !has_exact_selector_call && resolved_call.len > 0 {
                calls << resolved_call
                has_exact_selector_call = true
            }
            if !has_exact_selector_call {
                c.collect_top_level_selector_fallback(base, method, cur_module, imports,
                    local_values, mut calls)
            }
        }
    }
}

fn (c &CallCollector) collect_top_level_selector_fallback(base &flat.Node, method string, cur_module string, imports map[string]string, local_values map[string]bool, mut calls []string) {
    if base.kind == .ident && base.value.len > 0 {
        if base.value in local_values {
            return
        }
        if base.value in imports {
            return
        }
        mod_name := base.value
        calls << mod_name + '.' + method
        calls << qualify_fn(cur_module, base.value + '.' + method)
        if base.value.len > 0 && base.value[0] >= `A` && base.value[0] <= `Z` {
            named_type := c.tc.parse_type(base.value)
            named_type_name := resolve_type_name(named_type)
            if named_type_name.len > 0 {
                calls << named_type_name + '.' + method
            }
        }
    } else if base.kind == .selector && base.children_count > 0 {
        inner_id := c.a.child(base, 0)
        if int(inner_id) >= 0 {
            inner := c.a.node(inner_id)
            if inner.kind == .ident && inner.value.len > 0 {
                mod_name := if inner.value in imports {
                    imports[inner.value]
                } else {
                    inner.value
                }
                calls << mod_name + '.' + base.value + '.' + method
            }
        }
    }
}

fn (c &CallCollector) collect_top_level_typed_receiver_method(base_id flat.NodeId, method string, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string, mut calls []string) bool {
    type_name := c.top_level_receiver_type_name(base_id, cur_module, imports, local_values,
        local_types)
    if type_name.len == 0 {
        return false
    }
    method_name := c.typed_receiver_method_name(type_name, method, cur_module) or { return false }
    c.add_typed_receiver_method_name(method_name, mut calls)
    return true
}

fn (c &CallCollector) top_level_receiver_type_name(base_id flat.NodeId, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string) string {
    base := c.a.node(base_id)
    type_name := resolve_type_name(c.node_type(base_id))
    if type_name.len > 0 {
        struct_type := c.struct_lookup_name(type_name, cur_module)
        if struct_type.len > 0 {
            return struct_type
        }
        return type_name
    }
    if base.kind == .ident && base.value.len > 0 {
        if local_type := local_types[base.value] {
            return local_type
        }
        if base.value in local_values {
            return ''
        }
        if base.value in imports {
            return ''
        }
    }
    if base.kind == .ident && base.value.len > 0 {
        return c.value_type_name(base.value, cur_module, imports)
    }
    if base.kind == .selector {
        name := c.qualified_expr_name(base_id)
        if name.len > 0 {
            return c.value_type_name(name, cur_module, imports)
        }
    }
    return ''
}

// collect_struct_operator_call updates collect struct operator call state for markused.
fn (c &CallCollector) collect_struct_operator_call(lhs_id flat.NodeId, op flat.Op, cur_module string, mut calls []string) {
    lhs_type := c.node_type(lhs_id)
    lhs_name := resolve_type_name(lhs_type)
    struct_type := c.struct_lookup_name(lhs_name, cur_module)
    if struct_type.len == 0 {
        return
    }
    method_name := c.struct_operator_call_name(struct_type, op) or { return }
    c.add_operator_call_name(method_name, mut calls)
}

// struct_operator_call_name supports struct operator call name handling for CallCollector.
fn (c &CallCollector) struct_operator_call_name(struct_type string, op flat.Op) ?string {
    if op_name := markused_struct_operator_symbol(op) {
        if method_name := c.struct_operator_fn_name(struct_type, op_name) {
            return method_name
        }
    }
    match op {
        .gt, .ge, .le {
            if method_name := c.struct_operator_fn_name(struct_type, '<') {
                return method_name
            }
        }
        .ne {
            if method_name := c.struct_operator_fn_name(struct_type, '==') {
                return method_name
            }
        }
        else {}
    }

    return none
}

// markused_struct_operator_symbol supports markused struct operator symbol handling for markused.
fn markused_struct_operator_symbol(op flat.Op) ?string {
    match op {
        .plus { return '+' }
        .minus { return '-' }
        .mul { return '*' }
        .div { return '/' }
        .mod { return '%' }
        .eq { return '==' }
        .ne { return '!=' }
        .lt { return '<' }
        .gt { return '>' }
        .le { return '<=' }
        .ge { return '>=' }
        else {}
    }

    return none
}

// struct_operator_fn_name supports struct operator fn name handling for CallCollector.
fn (c &CallCollector) struct_operator_fn_name(struct_type string, op_name string) ?string {
    method_name := '${struct_type}.${op_name}'
    if c.is_known_fn_name(method_name) {
        return method_name
    }
    cmethod_name := markused_c_name(method_name)
    if c.is_known_fn_name(cmethod_name) {
        return cmethod_name
    }
    return none
}

// is_known_fn_name reports whether is known fn name applies in markused.
fn (c &CallCollector) is_known_fn_name(name string) bool {
    return name in c.fn_decls || name in c.tc.fn_ret_types || name in c.tc.fn_param_types
}

// struct_lookup_name supports struct lookup name handling for CallCollector.
fn (c &CallCollector) struct_lookup_name(type_name string, cur_module string) string {
    if type_name.len == 0 {
        return ''
    }
    if type_name.contains('.') {
        if type_name in c.struct_decls {
            return type_name
        }
        short_type := type_name.all_after_last('.')
        type_mod := type_name.all_before_last('.')
        if info := c.struct_decls[short_type] {
            if info.module == type_mod {
                return short_type
            }
        }
        if info := c.struct_decls[type_name] {
            if info.module == type_mod {
                return type_name
            }
        }
        return ''
    }
    if info := c.struct_decls[type_name] {
        if info.module.len == 0 || info.module == cur_module {
            return type_name
        }
    }
    if cur_module.len > 0 && cur_module != 'main' && cur_module != 'builtin' {
        qtype := '${cur_module}.${type_name}'
        if qtype in c.struct_decls {
            return qtype
        }
    }
    return ''
}

// add_operator_call_name updates add operator call name state for CallCollector.
fn (c &CallCollector) add_operator_call_name(method_name string, mut calls []string) {
    calls << method_name
    lowered := markused_c_name(method_name)
    if lowered != method_name {
        calls << lowered
    }
}

// qualified_expr_name supports qualified expr name handling for CallCollector.
fn (c &CallCollector) qualified_expr_name(id flat.NodeId) string {
    if int(id) < 0 {
        return ''
    }
    node := c.a.nodes[int(id)]
    match node.kind {
        .ident {
            return node.value
        }
        .selector {
            if node.children_count == 0 {
                return node.value
            }
            base := c.qualified_expr_name(c.a.child(&node, 0))
            if base.len == 0 {
                return node.value
            }
            return base + '.' + node.value
        }
        else {
            return ''
        }
    }
}

// collect_fn_value_ident updates collect fn value ident state for markused.
fn (c &CallCollector) collect_fn_value_ident(id flat.NodeId, name string, cur_module string, imports map[string]string, is_local_value bool, mut calls []string) {
    if is_local_value {
        return
    }
    if resolved := c.tc.resolved_fn_value_name(id) {
        calls << resolved
        return
    }
    if name.len == 0 || !c.name_may_reference_fn(name, cur_module, imports) {
        return
    }
    has_fn_decl := c.name_has_fn_decl(name, cur_module, imports)
    if !has_fn_decl && !c.node_is_fn_value(id) {
        return
    }
    c.add_fn_value_candidates(name, cur_module, imports, mut calls)
    c.add_const_alias_candidates(name, cur_module, imports, mut calls)
}

// collect_fn_value_selector updates collect fn value selector state for markused.
fn (c &CallCollector) collect_fn_value_selector(id flat.NodeId, node &flat.Node, cur_module string, imports map[string]string, mut calls []string) {
    if resolved := c.tc.resolved_fn_value_name(id) {
        calls << resolved
        return
    }
    if node.children_count == 0 {
        return
    }
    base := c.a.child_node(node, 0)
    if base.kind != .ident || base.value.len == 0 || node.value.len == 0 {
        return
    }
    name := '${base.value}.${node.value}'
    if !c.name_may_reference_fn(name, cur_module, imports) {
        return
    }
    has_fn_decl := c.name_has_fn_decl(name, cur_module, imports)
    if !has_fn_decl && !c.node_is_fn_value(id) {
        return
    }
    c.add_fn_value_candidates(name, cur_module, imports, mut calls)
    c.add_const_alias_candidates(name, cur_module, imports, mut calls)
    if base.value in imports {
        mod_name := imports[base.value]
        resolved_name := '${mod_name}.${node.value}'
        c.add_fn_value_candidates(resolved_name, cur_module, imports, mut calls)
        c.add_const_alias_candidates(resolved_name, cur_module, imports, mut calls)
    }
}

// name_may_reference_fn returns name may reference fn data for CallCollector.
fn (c &CallCollector) name_may_reference_fn(name string, cur_module string, imports map[string]string) bool {
    return c.name_has_candidate_decl(name, cur_module, imports, true)
}

// name_has_fn_decl returns name has fn decl data for CallCollector.
fn (c &CallCollector) name_has_fn_decl(name string, cur_module string, imports map[string]string) bool {
    return c.name_has_candidate_decl(name, cur_module, imports, false)
}

// name_has_candidate_decl returns name has candidate decl data for CallCollector.
fn (c &CallCollector) name_has_candidate_decl(name string, cur_module string, imports map[string]string, include_consts bool) bool {
    if c.candidate_matches_decl(name, include_consts) {
        return true
    }
    qname := qualify_fn(cur_module, name)
    if qname != name && c.candidate_matches_decl(qname, include_consts) {
        return true
    }
    if name.contains('.') {
        base := name.all_before_last('.')
        member := name.all_after_last('.')
        if base in imports {
            imported_name := imports[base] + '.' + member
            if c.candidate_matches_decl(imported_name, include_consts) {
                return true
            }
        }
    }
    return false
}

// candidate_matches_decl supports candidate matches decl handling for CallCollector.
fn (c &CallCollector) candidate_matches_decl(candidate string, include_consts bool) bool {
    if candidate in c.fn_decls {
        return true
    }
    return include_consts && candidate in c.const_decls
}

// node_is_fn_value supports node is fn value handling for CallCollector.
fn (c &CallCollector) node_is_fn_value(id flat.NodeId) bool {
    expr_type := c.node_type(id)
    return expr_type is types.FnType
}

// add_fn_value_candidates updates add fn value candidates state for CallCollector.
fn (c &CallCollector) add_fn_value_candidates(name string, cur_module string, imports map[string]string, mut calls []string) {
    if name.len == 0 {
        return
    }
    calls << name
    qname := qualify_fn(cur_module, name)
    if qname != name {
        calls << qname
    }
    if name.contains('.') {
        base := name.all_before_last('.')
        member := name.all_after_last('.')
        if base in imports {
            calls << imports[base] + '.' + member
        }
    }
}

// add_const_alias_candidates converts add const alias candidates data for markused.
fn (c &CallCollector) add_const_alias_candidates(name string, cur_module string, imports map[string]string, mut calls []string) {
    c.add_const_alias_candidate(name, imports, mut calls)
    qname := qualify_fn(cur_module, name)
    if qname != name {
        c.add_const_alias_candidate(qname, imports, mut calls)
    }
    if name.contains('.') {
        base := name.all_before_last('.')
        member := name.all_after_last('.')
        if base in imports {
            c.add_const_alias_candidate(imports[base] + '.' + member, imports, mut calls)
        }
    }
}

// add_const_alias_candidate converts add const alias candidate data for markused.
fn (c &CallCollector) add_const_alias_candidate(const_name string, imports map[string]string, mut calls []string) {
    info := c.const_decls[const_name] or { return }
    expr := c.a.node(info.expr_id)
    match expr.kind {
        .ident {
            c.add_fn_value_candidates(expr.value, info.module, imports, mut calls)
        }
        .selector {
            if expr.children_count > 0 {
                base := c.a.child_node(expr, 0)
                if base.kind == .ident && base.value.len > 0 && expr.value.len > 0 {
                    c.add_fn_value_candidates('${base.value}.${expr.value}', info.module, imports, mut
                        calls)
                    if base.value in imports {
                        c.add_fn_value_candidates('${imports[base.value]}.${expr.value}',
                            info.module, imports, mut calls)
                    }
                }
            }
        }
        else {}
    }
}

// node_type supports node type handling for CallCollector.
fn (c &CallCollector) node_type(id flat.NodeId) types.Type {
    if t := c.tc.expr_type(id) {
        return t
    }
    return c.tc.resolve_type(id)
}

fn (c &CallCollector) collect_typed_receiver_method(base_id flat.NodeId, method string, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string, mut calls []string) bool {
    type_name := c.receiver_type_name(base_id, cur_module, imports, local_values, local_types)
    if type_name.len == 0 {
        return false
    }
    method_name := c.typed_receiver_method_name(type_name, method, cur_module) or { return false }
    c.add_typed_receiver_method_name(method_name, mut calls)
    return true
}

fn (c &CallCollector) receiver_type_name(base_id flat.NodeId, cur_module string, imports map[string]string, local_values map[string]bool, local_types map[string]string) string {
    base := c.a.node(base_id)
    base_type := c.node_type(base_id)
    type_name := resolve_type_name(base_type)
    if type_name.len > 0 {
        return type_name
    }
    if base.kind == .ident && base.value.len > 0 {
        if local_type := local_types[base.value] {
            return local_type
        }
    }
    if base.kind == .ident && base.value.len > 0 {
        if base.value in local_values {
            return ''
        }
        return c.value_type_name(base.value, cur_module, imports)
    }
    if base.kind == .selector {
        name := c.qualified_expr_name(base_id)
        if name.len > 0 {
            return c.value_type_name(name, cur_module, imports)
        }
    }
    return ''
}

fn (c &CallCollector) typed_receiver_method_name(type_name string, method string, cur_module string) ?string {
    if type_name.len == 0 || method.len == 0 {
        return none
    }
    mut candidates := []string{cap: 4}
    if type_name.starts_with('map[') {
        candidates << markused_map_receiver_method_candidates(type_name, method, cur_module)
    } else if type_name.contains('.') {
        candidates << '${type_name}.${method}'
    } else {
        if cur_module.len > 0 && cur_module != 'main' && cur_module != 'builtin' {
            candidates << '${cur_module}.${type_name}.${method}'
        }
        candidates << '${type_name}.${method}'
    }
    for candidate in candidates {
        if c.is_known_fn_name(candidate) {
            return candidate
        }
        lowered := markused_c_name(candidate)
        if lowered != candidate && c.is_known_fn_name(lowered) {
            return lowered
        }
    }
    return none
}

fn markused_map_receiver_method_candidates(receiver_type string, method string, cur_module string) []string {
    clean_type := markused_clean_map_type(receiver_type)
    key_type := markused_map_key_type(clean_type)
    value_type := markused_map_value_type(clean_type)
    mut candidates := []string{}
    candidates << '${clean_type}.${method}'
    if key_type.len == 0 || value_type.len == 0 {
        return candidates
    }
    short_value := if value_type.contains('.') {
        value_type.all_after_last('.')
    } else {
        value_type
    }
    short_map := 'map[${key_type}]${short_value}'
    if short_map != clean_type {
        candidates << '${short_map}.${method}'
    }
    if value_type.contains('.') {
        mod_name := value_type.all_before_last('.')
        candidates << '${mod_name}.${short_map}.${method}'
    } else if cur_module.len > 0 && cur_module != 'main' && cur_module != 'builtin' {
        candidates << '${cur_module}.${short_map}.${method}'
    }
    return candidates
}

fn markused_clean_map_type(receiver_type string) string {
    mut clean := receiver_type.trim_space()
    for {
        if clean.starts_with('shared ') {
            clean = clean[7..].trim_space()
            continue
        }
        if clean.starts_with('&') {
            clean = clean[1..].trim_space()
            continue
        }
        break
    }
    return clean
}

fn markused_map_key_type(type_str string) string {
    if !type_str.starts_with('map[') {
        return ''
    }
    bracket_end := type_str.index(']') or { return '' }
    if bracket_end > 4 {
        return type_str[4..bracket_end]
    }
    return ''
}

fn markused_map_value_type(type_str string) string {
    if !type_str.starts_with('map[') {
        return ''
    }
    bracket_end := type_str.index(']') or { return '' }
    if bracket_end + 1 < type_str.len {
        return type_str[bracket_end + 1..]
    }
    return ''
}

fn (c &CallCollector) add_typed_receiver_method_name(method_name string, mut calls []string) {
    calls << method_name
    lowered := markused_c_name(method_name)
    if lowered != method_name {
        calls << lowered
    }
}

fn (c &CallCollector) value_type_name(name string, cur_module string, imports map[string]string) string {
    for candidate in c.value_name_candidates(name, cur_module, imports) {
        if typ := c.tc.file_scope.lookup(candidate) {
            type_name := resolve_type_name(typ)
            if type_name.len > 0 {
                return type_name
            }
        }
        if typ := c.tc.const_types[candidate] {
            type_name := resolve_type_name(typ)
            if type_name.len > 0 {
                return type_name
            }
        }
        if info := c.const_decls[candidate] {
            type_name := c.const_initializer_type_name(info)
            if type_name.len > 0 {
                return type_name
            }
        }
    }
    return ''
}

fn (c &CallCollector) const_initializer_type_name(info ConstDeclInfo) string {
    expr := c.a.node(info.expr_id)
    if expr.kind == .struct_init && expr.value.len > 0 {
        return c.struct_lookup_name(expr.value, info.module)
    }
    type_name := resolve_type_name(c.node_type(info.expr_id))
    if type_name.len > 0 {
        return type_name
    }
    return ''
}

fn (c &CallCollector) value_name_candidates(name string, cur_module string, imports map[string]string) []string {
    mut candidates := []string{cap: 3}
    qname := qualify_fn(cur_module, name)
    candidates << qname
    if qname != name {
        candidates << name
    }
    if name.contains('.') {
        base := name.all_before_last('.')
        member := name.all_after_last('.')
        if base in imports {
            candidates << '${imports[base]}.${member}'
        }
    }
    return candidates
}

fn markused_resolve_imported_type_name(name string, imports map[string]string) string {
    if !name.contains('.') {
        return name
    }
    base := name.all_before_last('.')
    member := name.all_after_last('.')
    if base in imports {
        return '${imports[base]}.${member}'
    }
    return name
}

// collect_zero_struct_default_calls updates collect zero struct default calls state for markused.
fn (c &CallCollector) collect_zero_struct_default_calls(typ types.Type, cur_module string, imports map[string]string, mut calls []string) {
    type_name := zero_value_struct_type_name(typ)
    if type_name.len == 0 {
        return
    }
    c.collect_struct_default_calls_for_type(type_name, cur_module, imports, mut calls)
}

// zero_value_struct_type_name supports zero value struct type name handling for markused.
fn zero_value_struct_type_name(typ types.Type) string {
    mut clean := typ
    for _ in 0 .. 8 {
        if clean is types.Alias {
            clean = clean.base_type
            continue
        }
        if clean is types.OptionType {
            clean = clean.base_type
            continue
        }
        if clean is types.ResultType {
            clean = clean.base_type
            continue
        }
        break
    }
    if clean is types.Struct {
        return clean.name
    }
    return ''
}

// collect_struct_default_calls updates collect struct default calls state for markused.
fn (c &CallCollector) collect_struct_default_calls(init &flat.Node, cur_module string, imports map[string]string, mut calls []string) {
    info := c.struct_decl_info(init.value, cur_module) or { return }
    mut set_fields := map[string]bool{}
    for i in 0 .. init.children_count {
        field := c.a.child_node(init, i)
        if field.kind == .field_init {
            set_fields[field.value] = true
        }
    }
    c.collect_struct_default_calls_from_info(info, set_fields, imports, mut calls)
}

// collect_struct_default_calls_for_type supports collect_struct_default_calls_for_type handling.
fn (c &CallCollector) collect_struct_default_calls_for_type(type_name string, cur_module string, imports map[string]string, mut calls []string) {
    info := c.struct_decl_info(type_name, cur_module) or { return }
    c.collect_struct_default_calls_from_info(info, map[string]bool{}, imports, mut calls)
}

// struct_decl_info supports struct decl info handling for CallCollector.
fn (c &CallCollector) struct_decl_info(type_name string, cur_module string) ?StructDeclInfo {
    struct_name := c.struct_lookup_name(type_name, cur_module)
    if struct_name.len == 0 {
        return none
    }
    return c.struct_decls[struct_name] or { none }
}

// collect_struct_default_calls_from_info supports collect_struct_default_calls_from_info handling.
fn (c &CallCollector) collect_struct_default_calls_from_info(info StructDeclInfo, provided map[string]bool, imports map[string]string, mut calls []string) {
    node := c.a.node(info.node_id)
    for i in 0 .. node.children_count {
        field := c.a.child_node(node, i)
        if field.kind != .field_decl || field.children_count == 0 || field.value in provided {
            continue
        }
        c.collect_calls(field, info.module, imports, '', '', mut calls)
    }
}

// resolve_type_name resolves resolve type name information for markused.
fn resolve_type_name(t types.Type) string {
    if t is types.Alias {
        return t.name
    } else if t is types.Struct {
        return t.name
    } else if t is types.Interface {
        return t.name
    } else if t is types.SumType {
        return t.name
    } else if t is types.Enum {
        return t.name
    } else if t is types.String {
        return 'string'
    } else if t is types.Array {
        return 'Array'
    } else if t is types.Map {
        return 'map[${t.key_type.name()}]${t.value_type.name()}'
    } else if t is types.Pointer {
        return resolve_type_name(t.base_type)
    } else if t is types.Primitive {
        props := int(t.props)
        sz := int(t.size)
        if props & 1 > 0 {
            return 'bool'
        }
        if props & 4 > 0 {
            if props & 8 > 0 {
                return match sz {
                    8 { 'u8' }
                    16 { 'u16' }
                    32 { 'u32' }
                    64 { 'u64' }
                    else { 'int' }
                }
            }
            return match sz {
                0 { 'int' }
                8 { 'i8' }
                16 { 'i16' }
                32 { 'i32' }
                64 { 'i64' }
                else { 'int' }
            }
        }
        if props & 2 > 0 {
            return match sz {
                32 { 'f32' }
                64 { 'f64' }
                else { 'f64' }
            }
        }
        return 'int'
    } else if t is types.ISize {
        return 'isize'
    } else if t is types.USize {
        return 'usize'
    } else if t is types.Rune {
        return 'rune'
    }
    return ''
}

// markused_c_name converts markused c name data for markused.
fn markused_c_name(name string) string {
    if name.starts_with('C.') {
        return name[2..]
    }
    if name == 'malloc' {
        return 'v_malloc'
    }
    if name == 'exit' {
        return 'v_exit'
    }
    if markused_c_name_is_plain(name) {
        return name
    }
    return name.replace('[]', 'Array_').replace('.-', '__minus').replace('.+', '__plus').replace('.==',
        '__eq').replace('.!=', '__ne').replace('.<=', '__le').replace('.>=', '__ge').replace('.<',
        '__lt').replace('.>', '__gt').replace('&', 'ptr').replace('[', '_').replace(']', '').replace(',',
        '_').replace(' ', '_').replace('.', '__')
}

// markused_c_name_is_plain converts markused c name is plain data for markused.
fn markused_c_name_is_plain(name string) bool {
    for i in 0 .. name.len {
        c := name[i]
        if (c >= `a` && c <= `z`) || (c >= `A` && c <= `Z`) || (c >= `0` && c <= `9`) || c == `_` {
            continue
        }
        return false
    }
    return true
}