module c

import strings
import v3.flat
import v3.types

// gen_expr_lvalue emits expr lvalue output for c.
fn gen_expr_lvalue(mut g FlatGen, id flat.NodeId) {
    node := g.a.nodes[int(id)]
    if node.kind == .index {
        base_id := g.a.child(&node, 0)
        base_type := g.tc.resolve_type(base_id)
        if base_type is types.Map {
            c_key := g.tc.c_type(base_type.key_type)
            c_val := g.tc.c_type(base_type.value_type)
            zero := if base_type.value_type is types.Array {
                c_elem := g.tc.c_type(base_type.value_type.elem_type)
                '&(${c_val}[]){array_new(sizeof(${c_elem}), 0, 0)}'
            } else {
                '&(${c_val}[]){0}'
            }
            g.write('(*(${c_val}*)map__get_or_set(&')
            g.gen_expr(base_id)
            g.write(', &(${c_key}[]){')
            g.gen_expr(g.a.child(&node, 1))
            g.write('}, ${zero}))')
            return
        }
    }
    g.gen_expr(id)
}

fn (mut g FlatGen) gen_split_array_append_expr_stmt(node flat.Node) bool {
    if node.kind != .infix || node.op != .pipe || node.children_count < 2 {
        return false
    }
    append_id := g.a.child(&node, 0)
    append := g.a.nodes[int(append_id)]
    if append.kind != .infix || append.op != .left_shift || append.children_count < 2 {
        return false
    }
    lhs_id := g.a.child(&append, 0)
    lhs_arr_type := types.unwrap_pointer(g.tc.resolve_type(lhs_id))
    lhs_arr := array_like_type(lhs_arr_type) or { return false }
    lhs_is_ptr := g.tc.resolve_type(lhs_id) is types.Pointer
    amp := if lhs_is_ptr { '' } else { '&' }
    c_elem := g.tc.c_type(lhs_arr.elem_type)
    g.write('array_push(${amp}')
    gen_expr_lvalue(mut g, lhs_id)
    g.write(', &(${c_elem}[]){(')
    g.gen_expr(g.a.child(&append, 1))
    g.write(' ${g.op_str(node.op)} ')
    g.gen_expr(g.a.child(&node, 1))
    g.writeln(')});')
    return true
}

// gen_node emits node output for c.
fn (mut g FlatGen) gen_node(id flat.NodeId) {
    if int(id) < 0 || int(id) >= g.a.nodes.len {
        return
    }
    node := g.a.nodes[int(id)]
    g.in_return = false
    match node.kind {
        .fn_decl, .c_fn_decl {
            return
        }
        .expr_stmt {
            child_id := g.a.child(&node, 0)
            if int(child_id) < 0 || int(child_id) >= g.a.nodes.len {
                return
            }
            child := g.a.nodes[int(child_id)]
            if g.is_runtime_array_flags_stmt(child_id) {
                return
            }
            if child.kind == .or_expr {
                g.gen_or_expr_stmt(child)
                return
            } else if g.gen_split_array_append_expr_stmt(child) {
                return
            } else if child.kind == .infix && child.op == .left_shift {
                lhs_id := g.a.child(&child, 0)
                if child.value == 'push_many' {
                    g.gen_array_push_many_stmt(lhs_id, g.a.child(&child, 1))
                } else if child.value == 'push' {
                    push_rhs_id := g.a.child(&child, 1)
                    mut c_elem := if child.typ.len > 0 {
                        g.tc.c_type(g.tc.parse_type(child.typ))
                    } else {
                        'string'
                    }
                    lhs_arr_type := types.unwrap_pointer(g.usable_expr_type(lhs_id))
                    if lhs_arr := array_like_type(lhs_arr_type) {
                        push_rhs_clean := types.unwrap_pointer(g.usable_expr_type(push_rhs_id))
                        if rhs_arr := array_like_type(push_rhs_clean) {
                            if g.tc.c_type(lhs_arr.elem_type) !in ['array', 'Array']
                                && g.tc.c_type(lhs_arr.elem_type) == g.tc.c_type(rhs_arr.elem_type) {
                                g.gen_array_push_many_stmt(lhs_id, push_rhs_id)
                                return
                            }
                        } else if rhs_fixed := array_fixed_type(push_rhs_clean) {
                            if g.tc.c_type(lhs_arr.elem_type) !in ['array', 'Array']
                                && g.tc.c_type(lhs_arr.elem_type) == g.tc.c_type(rhs_fixed.elem_type) {
                                g.gen_array_push_many_stmt(lhs_id, push_rhs_id)
                                return
                            }
                        }
                        c_elem = g.tc.c_type(lhs_arr.elem_type)
                    }
                    lhs_is_ptr := g.tc.resolve_type(lhs_id) is types.Pointer
                    amp := if lhs_is_ptr { '' } else { '&' }
                    g.write('array_push(${amp}')
                    gen_expr_lvalue(mut g, lhs_id)
                    g.write(', &(${c_elem}[]){')
                    if lhs_arr := array_like_type(lhs_arr_type) {
                        g.gen_expr_with_expected_type(push_rhs_id, lhs_arr.elem_type)
                    } else {
                        g.gen_expr(push_rhs_id)
                    }
                    g.writeln('});')
                } else {
                    lhs_type := g.usable_expr_type(lhs_id)
                    clean := types.unwrap_pointer(lhs_type)
                    if lhs_arr := array_like_type(clean) {
                        rhs_id := g.a.child(&child, 1)
                        rhs_type := g.usable_expr_type(rhs_id)
                        rhs_clean := types.unwrap_pointer(rhs_type)
                        if rhs_arr := array_like_type(rhs_clean) {
                            if g.tc.c_type(lhs_arr.elem_type) !in ['array', 'Array']
                                && g.tc.c_type(lhs_arr.elem_type) == g.tc.c_type(rhs_arr.elem_type) {
                                g.gen_array_push_many_stmt(lhs_id, rhs_id)
                            } else {
                                c_elem := g.tc.c_type(lhs_arr.elem_type)
                                lhs_is_ptr := g.tc.resolve_type(lhs_id) is types.Pointer
                                amp := if lhs_is_ptr { '' } else { '&' }
                                g.write('array_push(${amp}')
                                gen_expr_lvalue(mut g, lhs_id)
                                g.write(', &(${c_elem}[]){')
                                g.gen_expr_with_expected_type(rhs_id, lhs_arr.elem_type)
                                g.writeln('});')
                            }
                        } else if rhs_fixed := array_fixed_type(rhs_clean) {
                            if g.tc.c_type(lhs_arr.elem_type) !in ['array', 'Array']
                                && g.tc.c_type(lhs_arr.elem_type) == g.tc.c_type(rhs_fixed.elem_type) {
                                g.gen_array_push_many_stmt(lhs_id, rhs_id)
                            } else {
                                c_elem := g.tc.c_type(lhs_arr.elem_type)
                                lhs_is_ptr := g.tc.resolve_type(lhs_id) is types.Pointer
                                amp := if lhs_is_ptr { '' } else { '&' }
                                g.write('array_push(${amp}')
                                gen_expr_lvalue(mut g, lhs_id)
                                g.write(', &(${c_elem}[]){')
                                g.gen_expr_with_expected_type(rhs_id, lhs_arr.elem_type)
                                g.writeln('});')
                            }
                        } else {
                            c_elem := g.tc.c_type(lhs_arr.elem_type)
                            lhs_is_ptr := g.tc.resolve_type(lhs_id) is types.Pointer
                            amp := if lhs_is_ptr { '' } else { '&' }
                            g.write('array_push(${amp}')
                            gen_expr_lvalue(mut g, lhs_id)
                            g.write(', &(${c_elem}[]){')
                            g.gen_expr(rhs_id)
                            g.writeln('});')
                        }
                    } else {
                        g.gen_expr(child_id)
                        g.writeln(';')
                    }
                }
            } else {
                g.gen_expr(child_id)
                g.writeln(';')
            }
        }
        .decl_assign {
            g.gen_decl_assign(node)
        }
        .assign, .selector_assign {
            g.gen_assign(node)
        }
        .index_assign {
            g.gen_index_assign(node)
        }
        .return_stmt {
            g.in_return = true
            if g.cur_fn_ret is types.Enum {
                g.expected_enum = g.cur_fn_ret.name
            }
            if node.children_count > 0 && g.has_pending_defers() {
                g.gen_return_with_defers(node)
                g.expected_enum = ''
                return
            }
            g.gen_all_defers()
            if node.children_count > 0 {
                ret_id := g.a.child(&node, 0)
                if int(ret_id) < 0 || int(ret_id) >= g.a.nodes.len {
                    g.gen_default_return_stmt()
                    g.expected_enum = ''
                    return
                }
                ret_node := g.a.nodes[int(ret_id)]
                if ret_node.kind == .call {
                    fn_n := g.a.child_node(&ret_node, 0)
                    if fn_n.value == 'error' || fn_n.value == 'error_with_code' {
                        if g.cur_fn_ret_is_optional {
                            ct := g.optional_type_name(g.cur_fn_ret)
                            g.write('return ')
                            g.gen_optional_error_from_call(ct, ret_node)
                            g.writeln(';')
                        } else {
                            g.write('return ')
                            g.gen_expr(ret_id)
                            g.writeln(';')
                        }
                        return
                    }
                }
                if g.cur_fn_ret_is_optional {
                    ct := g.optional_type_name(g.cur_fn_ret)
                    base := g.cur_fn_ret_base
                    if g.expr_is_optional_literal(ret_id, g.cur_fn_ret) {
                        g.write('return ')
                        g.gen_expr(ret_id)
                        g.writeln(';')
                        return
                    }
                    if base is types.MultiReturn && node.children_count > 1 {
                        base_ct := g.tc.c_type(base)
                        g.write('return (${ct}){.ok = true, .value = (${base_ct}){')
                        for i in 0 .. node.children_count {
                            if i > 0 {
                                g.write(', ')
                            }
                            child_id := g.a.child(&node, i)
                            if i < base.types.len {
                                g.gen_expr_with_expected_type(child_id, base.types[i])
                            } else {
                                g.gen_expr(child_id)
                            }
                        }
                        g.writeln('}};')
                        return
                    }
                    if ret_node.kind == .none_expr {
                        g.writeln('return (${ct}){.ok = false};')
                        return
                    }
                    if base is types.Void {
                        g.writeln('return (${ct}){.ok = false};')
                    } else if base is types.ArrayFixed {
                        // The optional's `.value` is a fixed-array member, which can't be set
                        // in the compound literal; build via a temp + memcpy.
                        g.write('return ({ ${ct} __opt = {.ok = true}; memcpy(__opt.value, ')
                        g.gen_fixed_array_copy_source(ret_id, base)
                        g.writeln(', sizeof(__opt.value)); __opt; });')
                    } else {
                        raw_expr_type := g.tc.resolve_type(ret_id)
                        expr_type := g.usable_expr_type(ret_id)
                        call_ret_type := g.local_fn_call_return_type(ret_id, ret_node)
                        decl_ret_type := g.declared_call_return_type(ret_id)
                        if g.optional_result_matches_base(raw_expr_type, base)
                            || g.optional_result_matches_base(expr_type, base)
                            || g.optional_result_matches_base(call_ret_type, base)
                            || g.optional_result_matches_base(decl_ret_type, base) {
                            g.write('return ')
                            g.gen_expr(ret_id)
                            g.writeln(';')
                        } else {
                            mut expr_value_type := expr_type
                            if expr_type is types.OptionType {
                                expr_value_type = expr_type.base_type
                            } else if expr_type is types.ResultType {
                                expr_value_type = expr_type.base_type
                            }
                            base_ct := g.tc.c_type(base)
                            expr_ct := g.tc.c_type(expr_value_type)
                            struct_init_ct := if ret_node.kind == .struct_init {
                                g.struct_init_c_type_name(ret_node.value)
                            } else {
                                ''
                            }
                            if expr_ct != base_ct && struct_init_ct != base_ct
                                && !g.type_names_match(expr_value_type, base)
                                && !g.expr_is_nil_pointer_payload(ret_id, base)
                                && !g.type_can_wrap_as_sum(expr_value_type, base)
                                && !g.types_numeric_compatible(expr_value_type, base)
                                && !g.call_constructs_type(ret_id, base)
                                && !g.clone_call_matches_base(ret_node, base)
                                && expr_value_type !is types.Primitive
                                && expr_value_type !is types.Unknown {
                                g.writeln('return (${ct}){.ok = false};')
                            } else {
                                g.write('return (${ct}){.ok = true, .value = ')
                                g.gen_expr_with_expected_type(ret_id, base)
                                g.writeln('};')
                            }
                        }
                    }
                } else if g.cur_fn_ret is types.MultiReturn {
                    if node.children_count > 1 {
                        ct := g.tc.c_type(g.cur_fn_ret)
                        ret_types := g.cur_fn_ret.types
                        if g.multi_return_types_have_fixed_array(ret_types) {
                            g.gen_multi_return_temp_return(ct, ret_types, node)
                        } else {
                            g.write('return (${ct}){')
                            for i in 0 .. node.children_count {
                                if i > 0 {
                                    g.write(', ')
                                }
                                g.gen_expr(g.a.child(&node, i))
                            }
                            g.writeln('};')
                        }
                    } else {
                        expr_type := g.usable_expr_type(ret_id)
                        if expr_type is types.MultiReturn {
                            g.write('return ')
                            g.gen_expr(ret_id)
                            g.writeln(';')
                        } else {
                            ct := g.tc.c_type(g.cur_fn_ret)
                            g.write('return (${ct}){')
                            g.gen_expr(ret_id)
                            g.writeln('};')
                        }
                    }
                } else if ret_node.kind == .assoc {
                    g.gen_return_assoc(ret_node)
                } else if g.cur_fn_ret is types.ArrayFixed
                    && g.tc.c_type(g.cur_fn_ret) in g.fixed_array_ret_wrappers {
                    g.write('return ')
                    g.gen_fixed_array_return_wrap(g.cur_fn_ret, ret_id)
                    g.writeln(';')
                } else {
                    g.write('return ')
                    // Most interface returns are already boxed by the transform pass into
                    // a `(Iface){._typ = N, ._object = ...}` literal, in which case
                    // gen_interface_value_expr is a no-op (the value is already an
                    // interface) and we emit it directly. IError is intentionally left
                    // unboxed by the transform, so box the concrete error here. Never emit
                    // a zeroed `(Iface){0}` — that drops `_typ`/`_object` and makes every
                    // dispatch through the returned interface panic as "not implemented".
                    if g.cur_fn_ret is types.Interface {
                        if !g.gen_interface_value_expr(ret_id, g.cur_fn_ret) {
                            g.gen_expr(ret_id)
                        }
                    } else {
                        g.gen_expr(ret_id)
                    }
                    g.writeln(';')
                }
            } else {
                g.gen_default_return_stmt()
            }
            g.expected_enum = ''
        }
        .defer_stmt {
            if node.value == 'function' {
                if count_name := g.fn_defer_counts[int(id)] {
                    g.writeln('${count_name}++;')
                }
                g.fn_defers << id
            } else {
                g.defers << g.a.child(&node, 0)
            }
        }
        .for_stmt {
            g.gen_for(node)
        }
        .for_in_stmt {
            g.gen_for_in(node)
        }
        .break_stmt {
            if node.value.len > 0 {
                g.writeln('goto ${c_name(node.value)}_break;')
            } else {
                g.writeln('break;')
            }
        }
        .continue_stmt {
            if node.value.len > 0 {
                g.writeln('goto ${c_name(node.value)}_continue;')
            } else {
                g.writeln('continue;')
            }
        }
        .block {
            g.writeln('{')
            g.tc.push_scope()
            defer_start := g.defers.len
            g.indent++
            for i in 0 .. node.children_count {
                g.gen_node(g.a.child(&node, i))
            }
            g.gen_defers_from(defer_start)
            g.trim_defers(defer_start)
            g.indent--
            g.tc.pop_scope()
            g.writeln('}')
        }
        .if_expr {
            g.gen_if(node)
        }
        .assert_stmt {
            g.write('if (!(')
            g.gen_expr(g.a.child(&node, 0))
            g.writeln(')) {')
            g.indent++
            g.writeln('fprintf(stderr, "assert failed\\n");')
            g.writeln('exit(1);')
            g.indent--
            g.writeln('}')
        }
        .goto_stmt {
            g.writeln('goto ${c_name(node.value)};')
        }
        .label_stmt {
            old_indent := g.indent
            g.indent = 0
            g.writeln('${c_name(node.value)}: ;')
            g.indent = old_indent
        }
        .empty, .asm_stmt {}
        else {
            // NOTE: match_stmt is intentionally absent — the transformer lowers every
            // match into an if/else-if chain (see transform.lower_match_stmts), so the
            // backend never sees one. Match lowering lives in the transformer, not here.
            eprintln('gen_node: unsupported node kind: ${node.kind}')
        }
    }
}

// has_pending_defers reports whether has pending defers applies in c.
fn (g &FlatGen) has_pending_defers() bool {
    return g.defers.len > 0 || g.fn_defers.len > 0
}

// gen_return_with_defers emits return with defers output for c.
fn (mut g FlatGen) gen_return_with_defers(node flat.Node) {
    ret_id := g.a.child(&node, 0)
    if int(ret_id) < 0 || int(ret_id) >= g.a.nodes.len {
        g.gen_all_defers()
        g.gen_default_return_stmt()
        return
    }
    ret_node := g.a.nodes[int(ret_id)]
    if ret_node.kind == .assoc {
        tmp := g.tmp_name()
        g.gen_assoc_return_tmp(ret_node, tmp)
        g.gen_all_defers()
        g.writeln('return ${tmp};')
        return
    }
    if g.cur_fn_ret is types.ArrayFixed && g.tc.c_type(g.cur_fn_ret) in g.fixed_array_ret_wrappers {
        wrapper := fixed_array_ret_wrapper_name(g.tc.c_type(g.cur_fn_ret))
        tmp := g.tmp_name()
        g.write('${wrapper} ${tmp} = ')
        g.gen_fixed_array_return_wrap(g.cur_fn_ret, ret_id)
        g.writeln(';')
        g.gen_all_defers()
        g.writeln('return ${tmp};')
        return
    }
    ct := g.return_c_type()
    if g.cur_fn_ret is types.MultiReturn && node.children_count > 1 {
        ret_types := g.cur_fn_ret.types
        if g.multi_return_types_have_fixed_array(ret_types) {
            tmp := g.gen_multi_return_temp(ct, ret_types, node)
            g.gen_all_defers()
            g.writeln('return ${tmp};')
            return
        }
    }
    expr := g.return_expr_string(node, ret_id, ret_node, ct)
    tmp := g.tmp_name()
    g.writeln('${ct} ${tmp} = ${expr};')
    g.gen_all_defers()
    g.writeln('return ${tmp};')
}

// gen_fixed_array_return_wrap emits a fixed-array return value wrapped in its
// return-wrapper struct: `({ Wrapper __fa_ret; memcpy(__fa_ret.ret_arr, <expr>,
// sizeof(...)); __fa_ret; })`. C cannot return raw arrays, so the array is copied
// into the wrapper's `ret_arr` field and the struct is returned by value.
fn (mut g FlatGen) gen_fixed_array_return_wrap(ret_type types.Type, ret_id flat.NodeId) {
    wrapper := fixed_array_ret_wrapper_name(g.tc.c_type(ret_type))
    g.write('({ ${wrapper} __fa_ret; memcpy(__fa_ret.ret_arr, ')
    g.gen_fixed_array_copy_source(ret_id, ret_type)
    g.write(', sizeof(__fa_ret.ret_arr)); __fa_ret; })')
}

fn (mut g FlatGen) gen_default_return_stmt() {
    if g.cur_fn_ret_is_optional {
        ct := g.optional_type_name(g.cur_fn_ret)
        g.writeln('return (${ct}){.ok = true};')
    } else if g.cur_fn_name == 'main' {
        g.writeln('return 0;')
    } else if g.cur_fn_ret is types.Void {
        g.writeln('return;')
    } else {
        g.write('return ')
        g.gen_default_value_for_type(g.cur_fn_ret)
        g.writeln(';')
    }
}

// return_c_type supports return c type handling for FlatGen.
fn (mut g FlatGen) return_c_type() string {
    if g.cur_fn_ret_is_optional {
        return g.optional_type_name(g.cur_fn_ret)
    }
    return g.tc.c_type(g.cur_fn_ret)
}

// return_expr_string supports return expr string handling for FlatGen.
fn (mut g FlatGen) return_expr_string(node flat.Node, ret_id flat.NodeId, ret_node flat.Node, ct string) string {
    if ret_node.kind == .call {
        fn_n := g.a.child_node(&ret_node, 0)
        if fn_n.value == 'error' || fn_n.value == 'error_with_code' {
            if g.cur_fn_ret_is_optional {
                return g.optional_error_from_call_string(ct, ret_node)
            }
            return g.expr_to_string(ret_id)
        }
    }
    if g.cur_fn_ret_is_optional {
        base := g.cur_fn_ret_base
        if g.expr_is_optional_literal(ret_id, g.cur_fn_ret) {
            return g.expr_to_string(ret_id)
        }
        if base is types.MultiReturn && node.children_count > 1 {
            base_ct := g.tc.c_type(base)
            mut parts := []string{cap: int(node.children_count)}
            for i in 0 .. node.children_count {
                child_id := g.a.child(&node, i)
                if i < base.types.len {
                    parts << g.expr_to_string_with_expected_type(child_id, base.types[i])
                } else {
                    parts << g.expr_to_string(child_id)
                }
            }
            return '(${ct}){.ok = true, .value = (${base_ct}){${parts.join(', ')}}}'
        }
        if ret_node.kind == .none_expr {
            return '(${ct}){.ok = false}'
        }
        if base is types.Void {
            return '(${ct}){.ok = false}'
        }
        if base is types.ArrayFixed {
            // The optional's `.value` is a fixed-array member, which can't be set in a compound
            // literal; build via a temp + memcpy (mirrors the direct return path) so a deferred
            // return saves the array value instead of dropping it to `{.ok = false}`.
            src := g.fixed_array_copy_source_string(ret_id, base)
            return '({ ${ct} __opt = {.ok = true}; memcpy(__opt.value, ${src}, sizeof(__opt.value)); __opt; })'
        }
        raw_expr_type := g.tc.resolve_type(ret_id)
        expr_type := g.usable_expr_type(ret_id)
        call_ret_type := g.local_fn_call_return_type(ret_id, ret_node)
        decl_ret_type := g.declared_call_return_type(ret_id)
        if g.optional_result_matches_base(raw_expr_type, base)
            || g.optional_result_matches_base(expr_type, base)
            || g.optional_result_matches_base(call_ret_type, base)
            || g.optional_result_matches_base(decl_ret_type, base) {
            return g.expr_to_string(ret_id)
        }
        mut expr_value_type := expr_type
        if expr_type is types.OptionType {
            expr_value_type = expr_type.base_type
        } else if expr_type is types.ResultType {
            expr_value_type = expr_type.base_type
        }
        base_ct := g.tc.c_type(base)
        expr_ct := g.tc.c_type(expr_value_type)
        struct_init_ct := if ret_node.kind == .struct_init {
            g.struct_init_c_type_name(ret_node.value)
        } else {
            ''
        }
        if expr_ct != base_ct && struct_init_ct != base_ct
            && !g.type_names_match(expr_value_type, base)
            && !g.expr_is_nil_pointer_payload(ret_id, base)
            && !g.type_can_wrap_as_sum(expr_value_type, base)
            && !g.types_numeric_compatible(expr_value_type, base)
            && !g.call_constructs_type(ret_id, base) && !g.clone_call_matches_base(ret_node, base)
            && expr_value_type !is types.Primitive && expr_value_type !is types.Unknown {
            return '(${ct}){.ok = false}'
        }
        return '(${ct}){.ok = true, .value = ${g.expr_to_string_with_expected_type(ret_id, base)}}'
    }
    if g.cur_fn_ret is types.MultiReturn {
        if node.children_count > 1 {
            mut parts := []string{cap: int(node.children_count)}
            for i in 0 .. node.children_count {
                parts << g.expr_to_string(g.a.child(&node, i))
            }
            return '(${ct}){${parts.join(', ')}}'
        }
        expr_type := g.usable_expr_type(ret_id)
        if expr_type is types.MultiReturn {
            return g.expr_to_string(ret_id)
        }
        return '(${ct}){${g.expr_to_string(ret_id)}}'
    }
    if g.cur_fn_ret is types.Interface {
        // Box the concrete value the same way the direct return path does, so a deferred return
        // preserves `_typ`/`_object` instead of zeroing the interface.
        return g.interface_value_to_string(ret_id, g.cur_fn_ret)
    }
    return g.expr_to_string(ret_id)
}

fn (g &FlatGen) local_fn_call_return_type(call_id flat.NodeId, call_node flat.Node) types.Type {
    if call_node.kind != .call || call_node.children_count == 0 {
        return types.Type(types.void_)
    }
    mut node_type := types.Type(types.void_)
    if name := g.tc.resolved_call_name(call_id) {
        if ret := g.tc.fn_ret_types[name] {
            return ret
        }
    }
    if call_node.typ.len > 0 {
        node_type = g.tc.parse_type(call_node.typ)
        if node_type is types.OptionType || node_type is types.ResultType {
            return node_type
        }
    }
    fn_node := g.a.child_node(&call_node, 0)
    if fn_node.kind == .selector {
        if ret := g.selector_call_return_type(fn_node) {
            return ret
        }
        return node_type
    }
    if fn_node.kind != .ident {
        return node_type
    }
    if ret := g.tc.fn_ret_types[fn_node.value] {
        return ret
    }
    cfn := c_name(fn_node.value)
    if cfn != fn_node.value {
        if ret := g.tc.fn_ret_types[cfn] {
            return ret
        }
    }
    if ret := g.fn_decl_return_type_for_call_name(fn_node.value) {
        return ret
    }
    if typ := g.tc.cur_scope.lookup(fn_node.value) {
        return fn_type_return_type(typ)
    }
    typ := g.tc.resolve_type(g.a.child(&call_node, 0))
    ret_type := fn_type_return_type(typ)
    if ret_type !is types.Void {
        return ret_type
    }
    return node_type
}

// declared_call_return_type returns the *declared* return type of a (possibly
// lowered) call's target function, preserving type aliases. Method calls are
// lowered to ident calls (`Recv__method(recv, ...)`) before codegen, and the
// call node's own `.typ` annotation has aliases resolved away (e.g. `?NodeId`
// becomes `?int`), which makes the optional C type name appear to differ from
// the callee's signature. The declared type read from `fn_ret_types`/the fn decl
// keeps the alias, so propagating `return call()` is recognised as valid.
fn (g &FlatGen) declared_call_return_type(call_id flat.NodeId) types.Type {
    if int(call_id) < 0 {
        return types.Type(types.void_)
    }
    call_node := g.a.nodes[int(call_id)]
    if call_node.kind != .call || call_node.children_count == 0 {
        return types.Type(types.void_)
    }
    fn_node := g.a.child_node(&call_node, 0)
    if fn_node.kind == .selector {
        if ret := g.selector_call_return_type(fn_node) {
            return ret
        }
    } else if fn_node.kind == .ident {
        if ret := g.tc.fn_ret_types[fn_node.value] {
            return ret
        }
        cfn := c_name(fn_node.value)
        if cfn != fn_node.value {
            if ret := g.tc.fn_ret_types[cfn] {
                return ret
            }
        }
        if ret := g.fn_decl_return_type_for_call_name(fn_node.value) {
            return ret
        }
    }
    // Indirect call through an fn-pointer value (local var, param, or struct field
    // like `h.f()`): the target isn't a declared function/method, so resolve its type
    // and read the fn type's return. Unwrap alias (`type MakeArr = fn () [2]string`)
    // and pointer layers first. Lets fixed-array-returning callbacks unwrap `.ret_arr`
    // at the call site whether reached through a local, a param, or a struct field.
    mut callee_t := types.unwrap_pointer(g.tc.resolve_type(g.a.child(&call_node, 0)))
    for callee_t is types.Alias {
        callee_t = types.unwrap_pointer((callee_t as types.Alias).base_type)
    }
    if callee_t is types.FnType {
        return callee_t.return_type
    }
    return types.Type(types.void_)
}

fn (g &FlatGen) selector_call_return_type(fn_node flat.Node) ?types.Type {
    if fn_node.children_count == 0 || fn_node.value.len == 0 {
        return none
    }
    base_id := g.a.child(&fn_node, 0)
    base_node := g.a.nodes[int(base_id)]
    // A selector whose base names a type or an imported module is not a receiver method but a
    // static method (`Type.make()`) or import-qualified function (`mod.make()`); the base ident
    // has no value type, so resolve it the same way gen_call does and read the declared return
    // type. Without this a fixed-array such call's `_v_ret_*` wrapper is never unwrapped.
    if base_node.kind == .ident && base_node.value.len > 0 {
        base_is_local := g.tc.cur_scope.lookup(base_node.value) or { types.Type(types.void_) } !is types.Void
        if !base_is_local {
            if static_fn := g.static_method_fn_name(base_node.value, fn_node.value) {
                if ret := g.tc.fn_ret_types[static_fn] {
                    return ret
                }
            }
            if mod := g.import_alias_module(base_node.value) {
                if ret := g.tc.fn_ret_types['${mod}.${fn_node.value}'] {
                    return ret
                }
            }
        }
    }
    base_type0 := g.usable_expr_type(base_id)
    base_type := if base_type0 is types.Unknown || base_type0 is types.Void {
        g.tc.resolve_type(base_id)
    } else {
        base_type0
    }
    clean_type := types.unwrap_pointer(base_type)
    if fn_node.value == 'clone' && (clean_type is types.Array || clean_type is types.Map) {
        return base_type
    }
    mut receiver_name := clean_type.name()
    if clean_type is types.Struct {
        receiver_name = clean_type.name
    } else if clean_type is types.Interface {
        receiver_name = clean_type.name
    } else if clean_type is types.Alias {
        receiver_name = clean_type.name
    }
    if receiver_name.len == 0 {
        return none
    }
    if decl_key := g.interface_method_signature_key(receiver_name, fn_node.value) {
        if ret := g.tc.fn_ret_types[decl_key] {
            return ret
        }
    }
    method_name := '${receiver_name}.${fn_node.value}'
    if ret := g.tc.fn_ret_types[method_name] {
        return ret
    }
    if receiver_name.contains('.') {
        short_name := receiver_name.all_after_last('.')
        short_method := '${short_name}.${fn_node.value}'
        if ret := g.tc.fn_ret_types[short_method] {
            return ret
        }
    }
    return none
}

fn (g &FlatGen) fn_decl_return_type_for_call_name(name string) ?types.Type {
    if name.len == 0 {
        return none
    }
    // Indexed in collect_gen_info (register_fn_decl_ret_type); previously this scanned
    // every AST node per call (O(n^2)) and re-mangled each decl name with c_name.
    if rt := g.fn_decl_ret_types[name] {
        return rt
    }
    cname := c_name(name)
    if cname != name {
        if rt := g.fn_decl_ret_types[cname] {
            return rt
        }
    }
    return none
}

fn fn_type_return_type(typ types.Type) types.Type {
    if typ is types.FnType {
        return typ.return_type
    }
    if typ is types.Alias {
        return fn_type_return_type(typ.base_type)
    }
    return types.Type(types.void_)
}

// optional_error_from_call_string converts optional error from call string data for c.
fn (mut g FlatGen) optional_error_from_call_string(ct string, node flat.Node) string {
    orig := g.sb
    orig_line_start := g.line_start
    g.sb = strings.new_builder(64)
    g.line_start = true
    g.gen_optional_error_from_call(ct, node)
    result := g.sb.str()
    g.sb = orig
    g.line_start = orig_line_start
    return result
}

// expr_really_returns_optional supports expr really returns optional handling for FlatGen.
fn (g &FlatGen) expr_really_returns_optional(id flat.NodeId) bool {
    if int(id) < 0 {
        return false
    }
    node := g.a.nodes[int(id)]
    if node.kind == .none_expr {
        return true
    }
    if node.kind == .call {
        if fname := g.tc.resolved_call_name(id) {
            ret_type := g.tc.fn_ret_types[fname] or { return false }
            return ret_type is types.OptionType || ret_type is types.ResultType
        }
    }
    return false
}

// optional_result_matches_base supports optional result matches base handling for FlatGen.
fn (g &FlatGen) optional_result_matches_base(expr_type types.Type, base types.Type) bool {
    mut inner := types.Type(types.void_)
    if expr_type is types.OptionType {
        inner = expr_type.base_type
    } else if expr_type is types.ResultType {
        inner = expr_type.base_type
    } else {
        return false
    }
    if g.type_names_match(inner, base) {
        return true
    }
    // Aliases keep their declared name (e.g. `[]NodeId`) while `resolve_type` collapses
    // them to the underlying type (`[]int`), so a structural name comparison spuriously
    // fails. What actually matters for `return <call>;` is whether the C optional type
    // emitted for the call equals the one this function returns — compare those instead.
    return g.option_c_name_for_base(inner) == g.option_c_name_for_base(base)
}

fn (g &FlatGen) clone_call_matches_base(call_node flat.Node, base types.Type) bool {
    mut node := call_node
    for node.kind in [.expr_stmt, .paren] && node.children_count > 0 {
        node = *g.a.child_node(&node, 0)
    }
    if node.kind != .call || node.children_count == 0 {
        return false
    }
    fn_node := g.a.child_node(&node, 0)
    if fn_node.kind == .ident {
        base_ct := g.tc.c_type(types.unwrap_pointer(base))
        return (fn_node.value == 'array__clone' && base_ct == 'Array')
            || (fn_node.value == 'map__clone' && base_ct == 'map')
    }
    if fn_node.kind != .selector || fn_node.value != 'clone' || fn_node.children_count == 0 {
        return false
    }
    base_id := g.a.child(fn_node, 0)
    receiver_type0 := g.usable_expr_type(base_id)
    receiver_type := if receiver_type0 is types.Unknown || receiver_type0 is types.Void {
        g.tc.resolve_type(base_id)
    } else {
        receiver_type0
    }
    clean_receiver := types.unwrap_pointer(receiver_type)
    clean_base := types.unwrap_pointer(base)
    if g.type_names_match(clean_receiver, clean_base) {
        return true
    }
    receiver_ct0 := g.tc.c_type(clean_receiver)
    base_ct0 := g.tc.c_type(clean_base)
    if receiver_ct0.len > 0 && base_ct0.len > 0 && receiver_ct0 == base_ct0 {
        return true
    }
    receiver := if clean_receiver is types.Alias {
        clean_receiver.base_type
    } else {
        clean_receiver
    }
    expected := if clean_base is types.Alias {
        clean_base.base_type
    } else {
        clean_base
    }
    if expected is types.Array || expected is types.Map {
        receiver_ct := g.tc.c_type(receiver)
        expected_ct := g.tc.c_type(expected)
        if receiver_ct.len > 0 && receiver_ct == expected_ct {
            return true
        }
    }
    if receiver is types.Array && expected is types.Array {
        return g.type_names_match(receiver.elem_type, expected.elem_type)
    }
    if receiver is types.Map && expected is types.Map {
        return g.type_names_match(receiver.key_type, expected.key_type)
            && g.type_names_match(receiver.value_type, expected.value_type)
    }
    return false
}

// option_c_name_for_base returns the C optional type name used for a `?base`/`!base`
// value, mirroring optional_type_name without its side effects.
fn (g &FlatGen) option_c_name_for_base(base types.Type) string {
    if base is types.Void || base is types.Primitive || base is types.Enum {
        return 'Optional'
    }
    return 'Optional_' + g.tc.c_type(base).replace('*', 'ptr').replace(' ', '_')
}

fn (g &FlatGen) expr_is_nil_pointer_payload(id flat.NodeId, base types.Type) bool {
    if !g.type_accepts_nil_pointer(base) {
        return false
    }
    return g.expr_is_nil_value(id)
}

fn (g &FlatGen) type_accepts_nil_pointer(typ types.Type) bool {
    if typ is types.Pointer {
        return true
    }
    if typ is types.Alias {
        return g.type_accepts_nil_pointer(typ.base_type)
    }
    return false
}

fn (g &FlatGen) expr_is_nil_value(id flat.NodeId) bool {
    if int(id) < 0 || int(id) >= g.a.nodes.len {
        return false
    }
    node := g.a.nodes[int(id)]
    match node.kind {
        .nil_literal {
            return true
        }
        .expr_stmt {
            if node.children_count == 0 {
                return false
            }
            return g.expr_is_nil_value(g.a.child(&node, 0))
        }
        .block {
            if node.children_count == 0 {
                return false
            }
            return g.expr_is_nil_value(g.a.child(&node, node.children_count - 1))
        }
        .cast_expr, .as_expr {
            if node.children_count == 0 {
                return false
            }
            return g.expr_is_nil_value(g.a.child(&node, 0))
        }
        else {
            return false
        }
    }
}

// usable_expr_type supports usable expr type handling for FlatGen.
fn (g &FlatGen) usable_expr_type(id flat.NodeId) types.Type {
    if int(id) >= 0 && int(id) < g.a.nodes.len {
        node := g.a.nodes[int(id)]
        if node.kind in [.expr_stmt, .paren] && node.children_count > 0 {
            return g.usable_expr_type(g.a.child(&node, 0))
        }
        if node.kind == .ident {
            if typ := g.cur_param_types[node.value] {
                return typ
            }
            if typ := g.tc.cur_scope.lookup(node.value) {
                if typ !is types.Void {
                    return typ
                }
            }
        }
        if node.kind == .index && node.children_count > 0 {
            base_type0 := g.usable_expr_type(g.a.child(&node, 0))
            base_type := types.unwrap_pointer(base_type0)
            is_slice := node.value == 'range'
                || (node.children_count > 1 && g.a.child_node(&node, 1).kind == .range)
            if is_slice {
                if base_type is types.Array {
                    return base_type
                }
                if base_type is types.ArrayFixed {
                    return types.Type(types.Array{
                        elem_type: base_type.elem_type
                    })
                }
                if base_type is types.String {
                    return types.Type(types.String{})
                }
            }
            if base_type is types.Array {
                return base_type.elem_type
            }
            if base_type is types.ArrayFixed {
                return base_type.elem_type
            }
            if base_type is types.Map {
                return base_type.value_type
            }
            if base_type is types.String {
                return types.Type(types.u8_)
            }
        }
        if node.kind == .call && node.children_count > 0 {
            fn_node := g.a.child_node(&node, 0)
            if fn_node.kind == .ident {
                if typ := g.tc.cur_scope.lookup(fn_node.value) {
                    ret := fn_type_return_type(typ)
                    if ret !is types.Unknown && ret !is types.Void {
                        return ret
                    }
                }
                if ret := g.fn_decl_return_type_for_call_name(fn_node.value) {
                    if ret !is types.Unknown && ret !is types.Void {
                        return ret
                    }
                }
            }
        }
    }
    if typ := g.tc.expr_type(id) {
        if typ !is types.Unknown && typ !is types.Void {
            return typ
        }
    }
    return g.tc.resolve_type(id)
}

// type_names_match returns type names match data for FlatGen.
fn (g &FlatGen) type_names_match(a types.Type, b types.Type) bool {
    a_name := a.name()
    b_name := b.name()
    if a_name.len == 0 || b_name.len == 0 {
        return false
    }
    if a_name == b_name {
        return true
    }
    return a_name.all_after_last('.') == b_name.all_after_last('.')
}

// type_can_wrap_as_sum returns type can wrap as sum data for FlatGen.
fn (g &FlatGen) type_can_wrap_as_sum(actual types.Type, expected types.Type) bool {
    expected0 := if expected is types.Alias { expected.base_type } else { expected }
    if expected0 !is types.SumType {
        return false
    }
    actual0 := if actual is types.Alias { actual.base_type } else { actual }
    if actual0 is types.SumType {
        return false
    }
    sum_type := expected0 as types.SumType
    sum_name := g.resolve_sum_name(sum_type.name)
    variant := g.resolve_variant(sum_name, actual0.name())
    variants := g.tc.sum_types[sum_name] or { return false }
    return variant in variants
}

// types_numeric_compatible supports types numeric compatible handling for FlatGen.
fn (g &FlatGen) types_numeric_compatible(a types.Type, b types.Type) bool {
    _ = g
    return (a.is_integer() || a.is_float()) && (b.is_integer() || b.is_float())
}

// call_constructs_type updates call constructs type state for FlatGen.
fn (g &FlatGen) call_constructs_type(id flat.NodeId, target types.Type) bool {
    if int(id) < 0 {
        return false
    }
    node := g.a.nodes[int(id)]
    if node.kind != .call || node.children_count == 0 {
        return false
    }
    fn_node := g.a.child_node(&node, 0)
    if fn_node.kind != .ident {
        return false
    }
    target_name := target.name()
    if target_name.len == 0 {
        return false
    }
    short_target := target_name.all_after_last('.')
    return fn_node.value == target_name || fn_node.value == short_target
}

// is_runtime_array_flags_stmt reports whether is runtime array flags stmt applies in c.
fn (g &FlatGen) is_runtime_array_flags_stmt(id flat.NodeId) bool {
    if int(id) < 0 {
        return false
    }
    node := g.a.nodes[int(id)]
    if node.kind != .call || node.children_count == 0 {
        return false
    }
    fn_node := g.a.child_node(&node, 0)
    if fn_node.kind != .selector || fn_node.value !in ['set', 'clear']
        || fn_node.children_count == 0 {
        return false
    }
    flags_node := g.a.child_node(fn_node, 0)
    if flags_node.kind != .selector || flags_node.value != 'flags' || flags_node.children_count == 0 {
        return false
    }
    owner_id := g.a.child(flags_node, 0)
    owner_type := types.unwrap_pointer(g.tc.resolve_type(owner_id))
    return owner_type is types.Array || owner_type.name() == 'strings.Builder'
}

fn (g &FlatGen) multi_return_expr_type(id flat.NodeId) ?types.MultiReturn {
    rtype := g.tc.resolve_type(id)
    if rtype is types.MultiReturn {
        return rtype
    }
    utype := g.usable_expr_type(id)
    if utype is types.MultiReturn {
        return utype
    }
    return none
}

// gen_decl_assign emits decl assign output for c.
fn (mut g FlatGen) gen_decl_assign(node flat.Node) {
    if node.children_count >= 3 {
        if _ := g.multi_return_expr_type(g.a.child(&node, 1)) {
            g.gen_multi_return_decl(node)
            return
        }
    }
    mut bad_decl_child := node.children_count % 2 == 1
    for i in 0 .. node.children_count {
        if int(g.a.child(&node, i)) < 0 {
            bad_decl_child = true
        }
    }
    if bad_decl_child {
        mut parts := []string{}
        for i in 0 .. node.children_count {
            child_id := g.a.child(&node, i)
            if int(child_id) < 0 {
                parts << '${i}:empty'
            } else {
                child := g.a.nodes[int(child_id)]
                parts << '${i}:${child.kind}:${child.value}:${child.typ}'
            }
        }
        panic('internal error: odd decl_assign in ${g.cur_fn_name}: count=${node.children_count} typ=${node.typ} value=${node.value} children=${parts.join('|')}')
    }
    decl_prefix := if node.value == 'static' { 'static ' } else { '' }
    mut i := 0
    for i < node.children_count {
        lhs_id := g.a.child(&node, i)
        rhs_id := g.a.child(&node, i + 1)
        lhs := g.a.nodes[int(lhs_id)]
        rhs := g.a.nodes[int(rhs_id)]
        lhs_is_defer_capture := lhs.kind == .ident && lhs.value in g.defer_capture_types
        if rhs.kind == .array_literal {
            elem_type := if rhs.children_count > 0 {
                g.tc.resolve_type(g.a.child(&rhs, 0))
            } else {
                types.Type(types.int_)
            }
            if !lhs_is_defer_capture {
                g.write('${decl_prefix}Array ')
            }
            g.gen_decl_lhs(lhs_id)
            g.write(' = ')
            g.gen_array_literal_value(rhs, elem_type)
            g.writeln(';')
            if lhs.kind == .ident {
                g.tc.cur_scope.insert(lhs.value, types.Type(types.Array{
                    elem_type: elem_type
                }))
            }
        } else if rhs.kind == .or_expr {
            g.gen_decl_or_expr(lhs, rhs)
        } else if rhs.kind == .array_init {
            raw_init_type := g.tc.parse_type(rhs.value)
            init_type := raw_init_type
            if init_type is types.ArrayFixed {
                g.gen_fixed_array_zero_init_decl(lhs_id, init_type, decl_prefix,
                    lhs_is_defer_capture)
                if lhs.kind == .ident {
                    g.tc.cur_scope.insert(lhs.value, raw_init_type)
                }
            } else {
                c_elem := g.tc.c_type(init_type)
                mut init_len := '0'
                mut init_cap := '0'
                mut init_val := ''
                for j in 0 .. rhs.children_count {
                    child := g.a.child_node(&rhs, j)
                    if child.kind == .field_init {
                        if child.value == 'len' {
                            init_len = g.expr_to_string(g.a.child(child, 0))
                        } else if child.value == 'cap' {
                            init_cap = g.expr_to_string(g.a.child(child, 0))
                        } else if child.value == 'init' {
                            init_val = g.expr_to_string(g.a.child(child, 0))
                        }
                    }
                }
                lhs_str := g.decl_lhs_str(lhs_id)
                if lhs_is_defer_capture {
                    g.writeln('${lhs_str} = array_new(sizeof(${c_elem}), ${init_len}, ${init_cap});')
                } else {
                    g.writeln('${decl_prefix}Array ${lhs_str} = array_new(sizeof(${c_elem}), ${init_len}, ${init_cap});')
                }
                if init_val.len > 0 {
                    g.writeln('for (int _ai = 0; _ai < ${lhs_str}.len; _ai++) ((${c_elem}*)${lhs_str}.data)[_ai] = ${init_val};')
                }
                if lhs.kind == .ident {
                    g.tc.cur_scope.insert(lhs.value, types.Type(types.Array{
                        elem_type: init_type
                    }))
                }
            }
        } else if init_type := g.fixed_array_zero_init_block_type(rhs) {
            g.gen_fixed_array_zero_init_decl(lhs_id, init_type, decl_prefix, lhs_is_defer_capture)
            if lhs.kind == .ident {
                g.tc.cur_scope.insert(lhs.value, init_type)
            }
        } else if rhs.kind == .map_init {
            v_type := g.tc.resolve_type(rhs_id)
            c_typ := g.tc.c_type(v_type)
            if !lhs_is_defer_capture {
                g.write('${decl_prefix}${c_typ} ')
            }
            g.gen_decl_lhs(lhs_id)
            g.write(' = ')
            g.gen_expr_with_expected_type(rhs_id, v_type)
            g.writeln(';')
            if lhs.kind == .ident {
                g.tc.cur_scope.insert(lhs.value, v_type)
            }
            if rhs.children_count > 0 {
                if v_type is types.Map {
                    c_key := g.tc.c_type(v_type.key_type)
                    c_val := g.tc.c_type(v_type.value_type)
                    for j := 0; j < rhs.children_count; j += 2 {
                        g.write('map__set(&')
                        g.gen_decl_lhs(lhs_id)
                        g.write(', &(${c_key}[]){')
                        g.gen_expr(g.a.child(&rhs, j))
                        g.write('}, &(${c_val}[]){')
                        g.gen_expr(g.a.child(&rhs, j + 1))
                        g.writeln('});')
                    }
                }
            }
        } else {
            v_type := if node.typ.len > 0 {
                g.tc.parse_type(node.typ)
            } else if rhs.kind == .if_expr {
                g.if_expr_type(&rhs)
            } else {
                g.usable_expr_type(rhs_id)
            }
            if fixed := array_fixed_type(v_type) {
                lhs_str := g.decl_lhs_str(lhs_id)
                if !lhs_is_defer_capture {
                    c_elem, dims := g.fixed_array_decl_parts(fixed)
                    g.writeln('${decl_prefix}${c_elem} ${lhs_str}${dims};')
                }
                g.gen_fixed_array_copy_from_node(lhs_str, rhs_id, fixed)
                if lhs.kind == .ident {
                    g.tc.cur_scope.insert(lhs.value, v_type)
                }
                i += 2
                continue
            }
            ct0 := g.tc.c_type(v_type)
            ct := if v_type is types.OptionType || v_type is types.ResultType {
                g.optional_type_name(v_type)
            } else {
                ct0
            }
            if ct.starts_with('fn_ptr:') {
                fp_name := g.resolve_fn_ptr_type(ct)
                if !lhs_is_defer_capture {
                    g.write('${decl_prefix}${fp_name} ')
                }
            } else {
                if !lhs_is_defer_capture {
                    g.write('${decl_prefix}${ct} ')
                }
            }
            g.gen_decl_lhs(lhs_id)
            g.write(' = ')
            g.gen_decl_init_expr(rhs_id, rhs, v_type, ct, !lhs_is_defer_capture)
            g.writeln(';')
            if lhs.kind == .ident {
                g.tc.cur_scope.insert(lhs.value, v_type)
            }
        }
        i += 2
    }
}

fn (mut g FlatGen) gen_fixed_array_zero_init_decl(lhs_id flat.NodeId, init_type types.ArrayFixed, decl_prefix string, lhs_is_defer_capture bool) {
    c_elem, dims := g.fixed_array_decl_parts(init_type)
    lhs_str := g.decl_lhs_str(lhs_id)
    if g.fixed_array_len_is_zero(init_type) {
        if !lhs_is_defer_capture {
            g.writeln('${decl_prefix}${c_elem} ${lhs_str}${dims};')
        }
    } else if lhs_is_defer_capture {
        g.writeln('memset(${lhs_str}, 0, sizeof(${lhs_str}));')
    } else {
        g.writeln('${decl_prefix}${c_elem} ${lhs_str}${dims} = {0};')
    }
}

fn (mut g FlatGen) fixed_array_zero_init_block_type(node flat.Node) ?types.ArrayFixed {
    if node.kind != .block || node.children_count != 1 {
        return none
    }
    stmt_id := g.a.child(&node, 0)
    if int(stmt_id) < 0 {
        return none
    }
    stmt := g.a.nodes[int(stmt_id)]
    expr_id := if stmt.kind == .expr_stmt && stmt.children_count == 1 {
        g.a.child(&stmt, 0)
    } else {
        stmt_id
    }
    if int(expr_id) < 0 {
        return none
    }
    expr := g.a.nodes[int(expr_id)]
    if expr.kind != .array_init || expr.children_count != 0 {
        return none
    }
    typ := g.tc.parse_type(expr.value)
    if typ is types.ArrayFixed {
        return typ
    }
    return none
}

// gen_decl_init_expr emits decl init expr output for c.
fn (mut g FlatGen) gen_decl_init_expr(rhs_id flat.NodeId, rhs flat.Node, v_type types.Type, c_type string, is_declaration bool) {
    if g.is_json_decode_call_expr(rhs_id) {
        g.write('(${c_type}){0}')
        return
    }
    if rhs.kind == .int_literal && rhs.value == '0' && g.is_aggregate_zero_init_type(v_type, c_type) {
        if is_declaration {
            g.write('{0}')
        } else {
            g.write('(${c_type}){0}')
        }
        return
    }
    g.gen_expr_with_expected_type(rhs_id, v_type)
}

// gen_multi_return_decl emits multi return decl output for c.
fn (g &FlatGen) multi_return_types_have_fixed_array(ret_types []types.Type) bool {
    for typ in ret_types {
        if _ := array_fixed_type(typ) {
            return true
        }
    }
    return false
}

fn (mut g FlatGen) gen_multi_return_temp(ct string, ret_types []types.Type, node flat.Node) string {
    tmp := g.tmp_name()
    g.writeln('${ct} ${tmp};')
    for i in 0 .. node.children_count {
        field := '${tmp}.arg${i}'
        child_id := g.a.child(&node, i)
        if i < ret_types.len {
            if fixed := array_fixed_type(ret_types[i]) {
                g.gen_fixed_array_copy_from_node(field, child_id, fixed)
                continue
            }
            g.write('${field} = ')
            g.gen_expr_with_expected_type(child_id, ret_types[i])
            g.writeln(';')
            continue
        }
        g.write('${field} = ')
        g.gen_expr(child_id)
        g.writeln(';')
    }
    return tmp
}

fn (mut g FlatGen) gen_multi_return_temp_return(ct string, ret_types []types.Type, node flat.Node) {
    tmp := g.gen_multi_return_temp(ct, ret_types, node)
    g.writeln('return ${tmp};')
}

fn (mut g FlatGen) gen_fixed_array_copy_from_node(dst string, rhs_id flat.NodeId, fixed types.ArrayFixed) {
    g.write('memmove(${dst}, ')
    g.gen_fixed_array_data_arg(rhs_id, fixed)
    g.writeln(', sizeof(${dst}));')
}

fn (mut g FlatGen) gen_multi_return_decl(node flat.Node) {
    rhs_id := g.a.child(&node, 1)
    rhs_multi := g.multi_return_expr_type(rhs_id) or { return }
    rhs_type := types.Type(rhs_multi)
    ct := g.tc.c_type(rhs_type)
    tmp := g.tmp_name()
    g.write('${ct} ${tmp} = ')
    g.gen_expr_with_expected_type(rhs_id, rhs_type)
    g.writeln(';')
    num_lhs := node.children_count - 1
    multi_types := rhs_multi.types.clone()
    for j in 0 .. num_lhs {
        lhs_idx := if j == 0 { 0 } else { j + 1 }
        lhs_id := g.a.child(&node, lhs_idx)
        lhs := g.a.nodes[int(lhs_id)]
        if lhs.kind == .ident && lhs.value == '_' {
            continue
        }
        field_type := if j < multi_types.len {
            g.tc.c_type(multi_types[j])
        } else {
            'int'
        }
        lhs_name := c_name(lhs.value)
        if j < multi_types.len {
            if fixed := array_fixed_type(multi_types[j]) {
                c_elem, dims := g.fixed_array_decl_parts(fixed)
                g.writeln('${c_elem} ${lhs_name}${dims};')
                g.writeln('memmove(${lhs_name}, ${tmp}.arg${j}, sizeof(${lhs_name}));')
                if lhs.kind == .ident {
                    g.tc.cur_scope.insert(lhs.value, multi_types[j])
                }
                continue
            }
        }
        g.writeln('${field_type} ${lhs_name} = ${tmp}.arg${j};')
        if lhs.kind == .ident {
            inner := if j < multi_types.len {
                multi_types[j]
            } else {
                types.Type(types.int_)
            }
            g.tc.cur_scope.insert(lhs.value, inner)
        }
    }
}

// gen_assign emits assign output for c.
fn (mut g FlatGen) gen_assign(node flat.Node) {
    if node.children_count >= 3 {
        rhs_id := g.a.child(&node, 1)
        if _ := g.multi_return_expr_type(rhs_id) {
            g.gen_multi_return_assign(node)
            return
        }
    }
    mut i := 0
    for i < node.children_count {
        lhs := g.a.nodes[int(g.a.child(&node, i))]
        if lhs.kind == .ident && lhs.value == '_' {
            g.write('(void)(')
            g.gen_expr(g.a.child(&node, i + 1))
            g.writeln(');')
        } else if node.op == .left_shift_assign && lhs.kind == .ident {
            if node.value == 'push_many' {
                g.gen_array_push_many_stmt(g.a.child(&node, i), g.a.child(&node, i + 1))
            } else if node.value == 'push' {
                lhs_id := g.a.child(&node, i)
                rhs_id := g.a.child(&node, i + 1)
                lhs_arr_type := types.unwrap_pointer(g.usable_expr_type(lhs_id))
                if lhs_arr := array_like_type(lhs_arr_type) {
                    push_rhs_clean := types.unwrap_pointer(g.tc.resolve_type(rhs_id))
                    if rhs_arr := array_like_type(push_rhs_clean) {
                        if g.tc.c_type(lhs_arr.elem_type) !in ['array', 'Array']
                            && g.tc.c_type(lhs_arr.elem_type) == g.tc.c_type(rhs_arr.elem_type) {
                            g.gen_array_push_many_stmt(lhs_id, rhs_id)
                            i += 2
                            continue
                        }
                    } else if rhs_fixed := array_fixed_type(push_rhs_clean) {
                        if g.tc.c_type(lhs_arr.elem_type) !in ['array', 'Array']
                            && g.tc.c_type(lhs_arr.elem_type) == g.tc.c_type(rhs_fixed.elem_type) {
                            g.gen_array_push_many_stmt(lhs_id, rhs_id)
                            i += 2
                            continue
                        }
                    }
                    lhs_is_ptr := g.tc.resolve_type(g.a.child(&node, i)) is types.Pointer
                    amp := if lhs_is_ptr { '' } else { '&' }
                    c_elem := g.tc.c_type(lhs_arr.elem_type)
                    g.write('array_push(${amp}${c_name(lhs.value)}, &(${c_elem}[]){')
                    g.gen_expr_with_expected_type(g.a.child(&node, i + 1), lhs_arr.elem_type)
                    g.writeln('});')
                } else {
                    // Array appends are annotated by the transformer; an un-annotated
                    // `<<=` here is the integer bit-shift-assign operator.
                    g.gen_expr(g.a.child(&node, i))
                    g.write(' <<= ')
                    g.gen_expr(g.a.child(&node, i + 1))
                    g.writeln(';')
                }
            } else {
                g.gen_expr(g.a.child(&node, i))
                g.write(' <<= ')
                g.gen_expr(g.a.child(&node, i + 1))
                g.writeln(';')
            }
        } else {
            rhs_id := g.a.child(&node, i + 1)
            rhs_node := g.a.nodes[int(rhs_id)]
            if rhs_node.kind == .or_expr {
                g.gen_assign_or_expr(node, i, rhs_node)
                i += 2
                continue
            }
            lhs_id := g.a.child(&node, i)
            if rhs_node.kind == .array_literal {
                lhs_type := types.unwrap_pointer(g.tc.resolve_type(lhs_id))
                if lhs_type is types.ArrayFixed {
                    // A fixed-array field/var can't be `=`-assigned an array literal (which
                    // lowers to a dynamic `Array`); memcpy the element bytes instead.
                    g.write('memcpy(')
                    g.gen_expr(lhs_id)
                    g.write(', ')
                    g.gen_fixed_array_data_arg(rhs_id, lhs_type)
                    g.write(', sizeof(')
                    g.gen_expr(lhs_id)
                    g.writeln('));')
                    i += 2
                    continue
                }
                elem_type := if rhs_node.children_count > 0 {
                    g.tc.resolve_type(g.a.child(&rhs_node, 0))
                } else if lhs_arr := array_like_type(lhs_type) {
                    lhs_arr.elem_type
                } else {
                    types.Type(types.int_)
                }
                g.gen_expr(g.a.child(&node, i))
                g.write(' = ')
                g.gen_array_literal_value(rhs_node, elem_type)
                g.writeln(';')
            } else {
                lhs_type := g.usable_expr_type(lhs_id)
                rhs_type := g.usable_expr_type(rhs_id)
                if node.op == .assign {
                    if lhs_fixed := array_fixed_type(lhs_type) {
                        if _ := array_fixed_type(rhs_type) {
                            dst := g.expr_to_string(lhs_id)
                            g.writeln('memmove(${dst}, ${g.expr_to_string(rhs_id)}, sizeof(${dst}));')
                            i += 2
                            continue
                        } else if rhs_node.kind == .array_init || rhs_node.kind == .array_literal
                            || rhs_node.kind == .postfix {
                            dst := g.expr_to_string(lhs_id)
                            g.write('memmove(${dst}, ')
                            g.gen_fixed_array_data_arg(rhs_id, lhs_fixed)
                            g.writeln(', sizeof(${dst}));')
                            i += 2
                            continue
                        }
                    }
                }
                if node.op == .plus_assign && (lhs_type is types.String || rhs_type is types.String) {
                    g.gen_expr(g.a.child(&node, i))
                    g.write(' = string__plus(')
                    g.gen_expr(g.a.child(&node, i))
                    g.write(', ')
                    g.gen_expr(rhs_id)
                    g.writeln(');')
                    i += 2
                    continue
                }
                if method_name := g.assign_struct_operator_method(lhs_type, node.op) {
                    g.gen_expr(lhs_id)
                    g.write(' = ${c_name(method_name)}(')
                    g.gen_expr(lhs_id)
                    g.write(', ')
                    g.gen_expr(rhs_id)
                    g.writeln(');')
                    i += 2
                    continue
                }
                if lhs_type is types.Enum {
                    g.expected_enum = lhs_type.name
                }
                if g.assign_lhs_needs_deref(g.a.child(&node, i), lhs_type, rhs_type, node.op) {
                    g.write('*')
                }
                g.gen_expr(g.a.child(&node, i))
                g.write(' ${g.op_str(node.op)} ')
                if _ := fn_type_from(lhs_type) {
                    if c_abi_fn := g.assign_lhs_c_abi_fn_ptr_type(lhs_id) {
                        if g.gen_callback_fn_value_for_field_c_abi(rhs_id, lhs_type, c_abi_fn) {
                            g.writeln(';')
                            g.expected_enum = ''
                            i += 2
                            continue
                        }
                    }
                    g.gen_expr_with_expected_type(rhs_id, lhs_type)
                } else {
                    g.gen_expr(rhs_id)
                }
                g.writeln(';')
                g.expected_enum = ''
            }
        }
        i += 2
    }
}

fn (g &FlatGen) assign_lhs_c_abi_fn_ptr_type(lhs_id flat.NodeId) ?string {
    if int(lhs_id) < 0 || int(lhs_id) >= g.a.nodes.len {
        return none
    }
    lhs := g.a.nodes[int(lhs_id)]
    if lhs.kind != .selector || lhs.children_count == 0 || lhs.value.len == 0 {
        return none
    }
    base_id := g.a.child(&lhs, 0)
    base_type := types.unwrap_pointer(g.usable_expr_type(base_id))
    mut clean := base_type
    if base_type is types.Alias {
        clean = base_type.base_type
    }
    if clean is types.Struct {
        return g.struct_field_c_abi_fn_ptr_type(clean.name, lhs.value)
    }
    return none
}

fn (g &FlatGen) assign_struct_operator_method(lhs_type types.Type, op flat.Op) ?string {
    clean := types.unwrap_pointer(lhs_type)
    if clean !is types.Struct {
        return none
    }
    op_symbol := assign_struct_operator_symbol(op) or { return none }
    method_name := '${clean.name()}.${op_symbol}'
    if method_name in g.tc.fn_param_types || method_name in g.tc.fn_ret_types {
        return method_name
    }
    cmethod_name := c_name(method_name)
    if cmethod_name in g.tc.fn_param_types || cmethod_name in g.tc.fn_ret_types {
        return cmethod_name
    }
    return none
}

fn assign_struct_operator_symbol(op flat.Op) ?string {
    match op {
        .plus_assign { return '+' }
        .minus_assign { return '-' }
        .mul_assign { return '*' }
        .div_assign { return '/' }
        .mod_assign { return '%' }
        else {}
    }

    return none
}

// assign_lhs_needs_deref supports assign lhs needs deref handling for FlatGen.
fn (g &FlatGen) assign_lhs_needs_deref(lhs_id flat.NodeId, lhs_type types.Type, rhs_type types.Type, op flat.Op) bool {
    if op != .assign {
        return false
    }
    lhs := g.a.nodes[int(lhs_id)]
    if lhs.kind != .ident {
        return false
    }
    if lhs_type is types.Pointer {
        return lhs_type.base_type.name() == rhs_type.name()
    }
    return false
}

// gen_multi_return_assign emits multi return assign output for c.
fn (mut g FlatGen) gen_multi_return_assign(node flat.Node) {
    rhs_id := g.a.child(&node, 1)
    rhs_multi := g.multi_return_expr_type(rhs_id) or { return }
    rhs_type := types.Type(rhs_multi)
    ct := g.tc.c_type(rhs_type)
    tmp := g.tmp_name()
    g.write('${ct} ${tmp} = ')
    g.gen_expr_with_expected_type(rhs_id, rhs_type)
    g.writeln(';')
    num_lhs := node.children_count - 1
    multi_types := rhs_multi.types.clone()
    for j in 0 .. num_lhs {
        lhs_idx := if j == 0 { 0 } else { j + 1 }
        lhs_id := g.a.child(&node, lhs_idx)
        lhs := g.a.nodes[int(lhs_id)]
        if lhs.kind == .ident && lhs.value == '_' {
            continue
        }
        if j < multi_types.len {
            if _ := array_fixed_type(multi_types[j]) {
                dst := g.expr_to_string(lhs_id)
                g.writeln('memmove(${dst}, ${tmp}.arg${j}, sizeof(${dst}));')
                continue
            }
        }
        gen_expr_lvalue(mut g, lhs_id)
        g.writeln(' = ${tmp}.arg${j};')
    }
}

// gen_decl_lhs emits decl lhs output for c.
fn (mut g FlatGen) gen_decl_lhs(id flat.NodeId) {
    node := g.a.nodes[int(id)]
    if node.kind == .ident {
        g.write(c_name(node.value))
    } else {
        g.gen_expr(id)
    }
}

// decl_lhs_str supports decl lhs str handling for FlatGen.
fn (mut g FlatGen) decl_lhs_str(id flat.NodeId) string {
    node := g.a.nodes[int(id)]
    if node.kind == .ident {
        return c_name(node.value)
    }
    return g.expr_to_string(id)
}

// gen_assign_or_expr emits assign or expr output for c.
fn (mut g FlatGen) gen_assign_or_expr(node flat.Node, lhs_idx int, or_node flat.Node) {
    expr_id := g.a.child(&or_node, 0)
    or_body_id := g.a.child(&or_node, 1)
    or_body := g.a.nodes[int(or_body_id)]
    tmp := g.tmp_name()
    expr_type := g.tc.resolve_type(expr_id)
    opt_ct := g.optional_type_name(expr_type)
    g.write('${opt_ct} ${tmp} = ')
    g.gen_expr(expr_id)
    g.writeln(';')
    g.writeln('if (${tmp}.ok) {')
    g.indent++
    g.gen_expr(g.a.child(&node, lhs_idx))
    g.writeln(' = ${tmp}.value;')
    g.indent--
    g.writeln('} else {')
    g.tc.push_scope()
    g.tc.cur_scope.insert('err', types.Type(types.Struct{
        name: 'IError'
    }))
    g.indent++
    g.writeln('IError err = ${tmp}.err;')
    if or_node.value == '!' || or_node.value == '?' {
        if g.cur_fn_ret_is_optional {
            fn_opt_ct := g.optional_type_name(g.cur_fn_ret)
            g.writeln('return (${fn_opt_ct}){.ok = false, .err = err};')
        } else {
            g.writeln('panic(IError__str(err));')
        }
    } else {
        for j in 0 .. or_body.children_count {
            child_id := g.a.child(&or_body, j)
            g.gen_node(child_id)
        }
    }
    g.indent--
    g.tc.pop_scope()
    g.writeln('}')
}

// gen_decl_or_expr emits decl or expr output for c.
fn (mut g FlatGen) gen_decl_or_expr(lhs flat.Node, or_node flat.Node) {
    expr_id := g.a.child(&or_node, 0)
    or_body_id := g.a.child(&or_node, 1)
    or_body := g.a.nodes[int(or_body_id)]
    expr_node := g.a.nodes[int(expr_id)]
    if expr_node.kind == .index {
        base_type := g.tc.resolve_type(g.a.child(&expr_node, 0))
        clean := types.unwrap_pointer(base_type)
        if clean is types.Map {
            g.gen_decl_or_map_index(lhs, expr_node, clean, or_body)
            return
        }
    }
    tmp := g.tmp_name()
    expr_type := g.tc.resolve_type(expr_id)
    opt_ct := g.optional_type_name(expr_type)
    val_ct, val_type := g.optional_value_ct(expr_type)
    g.tc.cur_scope.insert(lhs.value, val_type)
    g.write('${opt_ct} ${tmp} = ')
    if g.is_json_decode_call_expr(expr_id) {
        g.write('(${opt_ct}){0}')
    } else {
        g.gen_expr_with_expected_type(expr_id, expr_type)
    }
    g.writeln(';')
    g.writeln('${val_ct} ${c_name(lhs.value)};')
    g.writeln('if (${tmp}.ok) {')
    g.indent++
    g.writeln('${c_name(lhs.value)} = ${tmp}.value;')
    g.indent--
    g.writeln('} else {')
    g.tc.push_scope()
    g.tc.cur_scope.insert('err', types.Type(types.Struct{
        name: 'IError'
    }))
    g.indent++
    g.writeln('IError err = ${tmp}.err;')
    if or_node.value == '!' || or_node.value == '?' {
        if g.cur_fn_ret_is_optional {
            fn_opt_ct := g.optional_type_name(g.cur_fn_ret)
            g.writeln('return (${fn_opt_ct}){.ok = false, .err = err};')
        } else {
            g.writeln('panic(IError__str(err));')
        }
    } else if or_body.children_count > 0 {
        for i in 0 .. or_body.children_count {
            child_id := g.a.child(&or_body, i)
            child := g.a.nodes[int(child_id)]
            if i == or_body.children_count - 1 && child.kind == .expr_stmt {
                inner := g.a.child_node(&child, 0)
                if inner.kind == .call && g.is_noreturn_call(inner) {
                    g.gen_node(child_id)
                } else {
                    g.write('${c_name(lhs.value)} = ')
                    g.gen_expr(g.a.child(&child, 0))
                    g.writeln(';')
                }
            } else {
                g.gen_node(child_id)
            }
        }
    }
    g.indent--
    g.tc.pop_scope()
    g.writeln('}')
}

// gen_decl_or_map_index emits decl or map index output for c.
fn (mut g FlatGen) gen_decl_or_map_index(lhs flat.Node, expr_node flat.Node, m types.Map, or_body flat.Node) {
    tmp := g.tmp_name()
    c_val := g.tc.c_type(m.value_type)
    c_key := g.tc.c_type(m.key_type)
    g.tc.cur_scope.insert(lhs.value, m.value_type)
    g.write('void* ${tmp} = map__get_check(&')
    g.gen_expr(g.a.child(&expr_node, 0))
    g.write(', &(${c_key}[]){')
    g.gen_expr(g.a.child(&expr_node, 1))
    g.writeln('});')
    g.writeln('${c_val} ${c_name(lhs.value)};')
    g.writeln('if (${tmp}) {')
    g.indent++
    g.writeln('${c_name(lhs.value)} = *(${c_val}*)${tmp};')
    g.indent--
    g.writeln('} else {')
    g.indent++
    if or_body.children_count > 0 {
        for i in 0 .. or_body.children_count {
            child_id := g.a.child(&or_body, i)
            child := g.a.nodes[int(child_id)]
            if i == or_body.children_count - 1 && child.kind == .expr_stmt {
                inner := g.a.child_node(&child, 0)
                if inner.kind == .call && g.is_noreturn_call(inner) {
                    g.gen_node(child_id)
                } else {
                    g.write('${c_name(lhs.value)} = ')
                    g.gen_expr(g.a.child(&child, 0))
                    g.writeln(';')
                }
            } else {
                g.gen_node(child_id)
            }
        }
    }
    g.indent--
    g.writeln('}')
}

fn (g &FlatGen) is_json_decode_call_expr(id flat.NodeId) bool {
    if int(id) < 0 || int(id) >= g.a.nodes.len {
        return false
    }
    node := g.a.nodes[int(id)]
    if node.kind == .call && node.children_count > 0 {
        target := g.call_target_name(g.a.child(&node, 0))
        if target in ['decode', 'json.decode', 'json2.decode'] {
            return true
        }
        if g.call_has_selector_name(g.a.child(&node, 0), 'decode') {
            return true
        }
    }
    for i in 0 .. node.children_count {
        if g.is_json_decode_call_expr(g.a.child(&node, i)) {
            return true
        }
    }
    return false
}

// is_noreturn_call reports whether is noreturn call applies in c.
fn (g &FlatGen) is_noreturn_call(node &flat.Node) bool {
    if node.kind != .call || node.children_count == 0 {
        return false
    }
    fn_node := g.a.child_node(node, 0)
    return fn_node.value in ['panic', 'exit']
}

// tmp_name supports tmp name handling for FlatGen.
fn (mut g FlatGen) tmp_name() string {
    g.tmp_count++
    return '_t${g.tmp_count}'
}

// gen_or_expr emits or expr output for c.
fn (mut g FlatGen) gen_or_expr(node flat.Node) {
    expr_id := g.a.child(&node, 0)
    or_body_id := g.a.child(&node, 1)
    or_body := g.a.nodes[int(or_body_id)]
    expr_node := g.a.nodes[int(expr_id)]
    if expr_node.kind == .index {
        base_type := g.tc.resolve_type(g.a.child(&expr_node, 0))
        clean := types.unwrap_pointer(base_type)
        if clean is types.Map {
            g.gen_or_map_index(expr_node, clean, or_body)
            return
        }
    }
    tmp := g.tmp_name()
    expr_type := g.tc.resolve_type(expr_id)
    opt_ct := g.optional_type_name(expr_type)
    val_ct, val_type := g.optional_value_ct(expr_type)
    val := g.tmp_name()
    g.write('({${opt_ct} ${tmp} = ')
    g.gen_expr_with_expected_type(expr_id, expr_type)
    g.write('; ${val_ct} ${val}; if (${tmp}.ok) { ${val} = ${tmp}.value; } else { IError err = ${tmp}.err; (void)err; ')
    // Bind `err` (IError) in a *temporary* cgen scope so the or-body's own string
    // interpolations and selector accesses resolve `err`'s type correctly (without this
    // an `${err}` inside the or-body falls back to `int__str(err)`). The scope is popped
    // afterwards so an outer local named `err` keeps its real type — e.g.
    // `err := 1; _ := maybe() or { 0 }; println('${err}')` must still see `err` as int.
    g.tc.push_scope()
    g.tc.cur_scope.insert('err', g.tc.parse_type('IError'))
    g.gen_or_body_value(or_body, val, val_type)
    g.tc.pop_scope()
    g.write(' } ${val};})')
}

// gen_or_body emits or body output for c.
fn (mut g FlatGen) gen_or_body(or_body flat.Node) {
    if or_body.children_count == 1 {
        last_id := g.a.child(&or_body, or_body.children_count - 1)
        last := g.a.nodes[int(last_id)]
        if last.kind == .expr_stmt {
            g.gen_expr(g.a.child(&last, 0))
        } else {
            g.gen_expr(last_id)
        }
    } else {
        g.write('({')
        for i in 0 .. or_body.children_count {
            child_id := g.a.child(&or_body, i)
            child := g.a.nodes[int(child_id)]
            if i == or_body.children_count - 1 && child.kind == .expr_stmt {
                g.gen_expr(g.a.child(&child, 0))
                g.write(';')
            } else {
                g.gen_node(child_id)
            }
        }
        g.write('})')
    }
}

fn (mut g FlatGen) gen_or_body_value(or_body flat.Node, value_name string, value_type types.Type) {
    for i in 0 .. or_body.children_count {
        child_id := g.a.child(&or_body, i)
        child := g.a.nodes[int(child_id)]
        is_last := i == or_body.children_count - 1
        if is_last && child.kind == .expr_stmt {
            expr_id := g.a.child(&child, 0)
            if g.expr_is_error_call(expr_id) && g.cur_fn_ret_is_optional {
                fn_opt_ct := g.optional_type_name(g.cur_fn_ret)
                g.write('return ')
                g.gen_optional_error_from_call(fn_opt_ct, g.a.nodes[int(expr_id)])
                g.write(';')
            } else if g.tc.resolve_type(expr_id) is types.Void {
                // A diverging/void or-body tail (e.g. `panic(..)`/`exit(..)`) yields no
                // value; emit it as a bare statement instead of assigning void.
                g.gen_expr(expr_id)
                g.write(';')
            } else {
                g.write('${value_name} = ')
                g.gen_expr_with_expected_type(expr_id, value_type)
                g.write(';')
            }
        } else {
            g.gen_node(child_id)
        }
    }
}

fn (g &FlatGen) expr_is_error_call(id flat.NodeId) bool {
    if int(id) < 0 || int(id) >= g.a.nodes.len {
        return false
    }
    node := g.a.nodes[int(id)]
    if node.kind != .call || node.children_count == 0 {
        return false
    }
    fn_node := g.a.child_node(&node, 0)
    return fn_node.value == 'error' || fn_node.value == 'error_with_code'
}

// gen_or_map_index emits or map index output for c.
fn (mut g FlatGen) gen_or_map_index(expr_node flat.Node, m types.Map, or_body flat.Node) {
    tmp := g.tmp_name()
    c_val := g.tc.c_type(m.value_type)
    c_key := g.tc.c_type(m.key_type)
    val := g.tmp_name()
    g.write('({void* ${tmp} = map__get_check(&')
    g.gen_expr(g.a.child(&expr_node, 0))
    g.write(', &(${c_key}[]){')
    g.gen_expr(g.a.child(&expr_node, 1))
    g.write('}); ${c_val} ${val}; if (${tmp}) { ${val} = *(${c_val}*)${tmp}; } else { ')
    g.gen_or_body_value(or_body, val, m.value_type)
    g.write(' } ${val};})')
}

// gen_or_expr_stmt emits or expr stmt output for c.
fn (mut g FlatGen) gen_or_expr_stmt(node flat.Node) {
    expr_id := g.a.child(&node, 0)
    or_body_id := g.a.child(&node, 1)
    or_body := g.a.nodes[int(or_body_id)]
    tmp := g.tmp_name()
    expr_type := g.tc.resolve_type(expr_id)
    opt_ct := g.optional_type_name(expr_type)
    g.writeln('${opt_ct} ${tmp} = ')
    g.gen_expr_with_expected_type(expr_id, expr_type)
    g.writeln(';')
    g.writeln('if (!${tmp}.ok) {')
    g.tc.push_scope()
    g.tc.cur_scope.insert('err', types.Type(types.Struct{
        name: 'IError'
    }))
    g.indent++
    g.writeln('IError err = ${tmp}.err;')
    if node.value == '!' || node.value == '?' {
        if g.cur_fn_ret_is_optional {
            fn_opt_ct := g.optional_type_name(g.cur_fn_ret)
            g.writeln('return (${fn_opt_ct}){.ok = false, .err = err};')
        } else {
            g.writeln('panic(IError__str(err));')
        }
    } else {
        for i in 0 .. or_body.children_count {
            g.gen_node(g.a.child(&or_body, i))
        }
    }
    g.indent--
    g.tc.pop_scope()
    g.writeln('}')
}