// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module parser

import v.ast
import v.token
import v.util
import os

fn table_fn_lookup(table &ast.Table, name string) (ast.Fn, bool) {
    if name !in table.fns {
        return ast.Fn{}, false
    }
    return unsafe { table.fns[name] }, true
}

fn comptime_define_idx(attrs []ast.Attr) int {
    for idx in 0 .. attrs.len {
        if attrs[idx].kind == .comptime_define {
            return idx
        }
    }
    return ast.invalid_type_idx
}

fn type_method_name_pos(sym &ast.TypeSymbol, name string, fallback token.Pos) token.Pos {
    for method in sym.methods {
        if method.name == name {
            return method.name_pos
        }
    }
    return fallback
}

fn (mut p Parser) call_expr(language ast.Language, mod string) ast.CallExpr {
    first_pos := p.tok.pos()
    mut name := if language == .js { p.check_js_name() } else { p.check_name() }
    mut is_static_type_method := language == .v && name != '' && name[0].is_capital()
        && p.tok.kind == .dot
    if is_static_type_method {
        p.check(.dot)
        name = name + '__static__' + p.check_name()
    }
    mut fn_name := if language == .c {
        'C.${name}'
    } else if language == .js {
        'JS.${name}'
    } else if language == .wasm {
        'WASM.${name}'
    } else if mod != '' {
        '${mod}.${name}'
    } else {
        name
    }
    if language != .v {
        p.check_for_impure_v(language, first_pos)
    }
    mut or_kind := ast.OrKind.absent
    if fn_name == 'json.decode' || fn_name == 'C.va_arg' {
        p.expecting_type = true // Makes name_expr() parse the type `User` in `json.decode(User, txt)`
    }

    old_expr_mod := p.expr_mod
    defer {
        p.expr_mod = old_expr_mod
    }
    p.expr_mod = ''

    mut concrete_types := []ast.Type{}
    mut concrete_list_pos := p.tok.pos()
    if p.tok.kind == .lsbr {
        // `foo[int](10)`
        p.expr_mod = ''
        concrete_types = p.parse_concrete_types()
        concrete_list_pos = concrete_list_pos.extend(p.prev_tok.pos())
    }
    p.check(.lpar)
    args := p.call_args()
    if p.tok.kind != .rpar && !p.pref.is_vls {
        mut params := []ast.Param{}
        fn_info, has_fn_info := table_fn_lookup(p.table, fn_name)
        if has_fn_info {
            params = fn_info.params.clone()
        } else {
            mod_fn_info, has_mod_fn_info := table_fn_lookup(p.table, '${p.mod}.${fn_name}')
            if has_mod_fn_info {
                params = mod_fn_info.params.clone()
            }
        }
        min_required_params := min_required_call_args(params)
        if args.len < min_required_params && p.prev_tok.kind != .comma {
            pos := if p.tok.kind == .eof { p.prev_tok.pos() } else { p.tok.pos() }
            p.unexpected_with_pos(pos, expecting: '`,`')
        } else if args.len > params.len {
            ok_arg_pos := if params.len > 0 { args[params.len - 1].pos } else { args[0].pos }
            pos := token.Pos{
                ...ok_arg_pos
                col: u16(ok_arg_pos.col + ok_arg_pos.len)
            }
            p.unexpected_with_pos(pos.extend(p.tok.pos()), expecting: '`)`')
        } else {
            pos := if p.tok.kind == .eof { p.prev_tok.pos() } else { p.tok.pos() }
            p.unexpected_with_pos(pos, expecting: '`)`')
        }
    }
    last_pos := p.tok.pos()
    if p.tok.kind == .rpar {
        p.next()
    }
    mut pos := first_pos.extend(last_pos)
    mut or_stmts := []ast.Stmt{} // TODO: remove unnecessary allocations by just using .absent
    mut or_pos := p.tok.pos()
    mut or_scope := ast.empty_scope
    if p.tok.kind == .key_orelse {
        // `foo() or {}``
        or_kind = .block
        or_stmts, or_pos, or_scope = p.or_block(.with_err_var)
    }
    if p.tok.kind in [.question, .not] {
        is_not := p.tok.kind == .not
        // `foo()?`
        p.next()
        if p.inside_defer {
            p.error_with_pos('error propagation not allowed inside `defer` blocks',
                p.prev_tok.pos())
        }
        or_kind = if is_not { .propagate_result } else { .propagate_option }
        or_scope = p.scope
    }
    if p.is_imported_symbol(fn_name) {
        check := !p.imported_symbols_used[fn_name]
        fn_name = p.imported_symbols[fn_name]
        if check {
            p.register_used_import_for_symbol_name(fn_name)
        }
    }
    comments := p.eat_comments(same_line: true)
    pos.update_last_line(p.prev_tok.line_nr)
    return ast.CallExpr{
        name:               fn_name
        name_pos:           first_pos
        args:               args
        mod:                p.mod
        kind:               p.call_kind(fn_name)
        pos:                pos
        language:           language
        concrete_types:     concrete_types
        concrete_list_pos:  concrete_list_pos
        raw_concrete_types: concrete_types
        or_block:           ast.OrExpr{
            stmts: or_stmts
            kind:  or_kind
            pos:   or_pos
            scope: or_scope
        }
        scope:              p.scope
        comments:           comments
        is_return_used:     p.expecting_value
        is_static_method:   is_static_type_method
    }
}

fn min_required_call_args(params []ast.Param) int {
    if params.len == 0 {
        return 0
    }
    mut required := params.len
    mut idx := params.len - 1
    for idx >= 0 {
        if params[idx].typ.has_flag(.option) {
            required--
            idx--
            continue
        }
        break
    }
    return required
}

fn (mut p Parser) call_kind(fn_name string) ast.CallKind {
    if fn_name.len < 3 || fn_name.len > 20 {
        return .unknown
    }
    return match fn_name.len {
        3 {
            match fn_name {
                'str' {
                    .str
                }
                'map' {
                    .map
                }
                'any' {
                    .any
                }
                'all' {
                    .all
                }
                'pop' {
                    .pop
                }
                else {
                    .unknown
                }
            }
        }
        4 {
            match fn_name {
                'wait' {
                    .wait
                }
                'free' {
                    .free
                }
                'keys' {
                    .keys
                }
                'sort' {
                    .sort
                }
                'trim' {
                    .trim
                }
                'last' {
                    .last
                }
                'drop' {
                    .drop
                }
                'main' {
                    .main
                }
                'move' {
                    .move
                }
                else {
                    .unknown
                }
            }
        }
        5 {
            return match fn_name {
                'count' {
                    .count
                }
                'print' {
                    .print
                }
                'close' {
                    .close
                }
                'slice' {
                    .slice
                }
                'clone' {
                    .clone
                }
                'index' {
                    .index
                }
                'first' {
                    .first
                }
                'panic' {
                    .panic
                }
                'clear' {
                    .clear
                }
                'error' {
                    .error
                }
                else {
                    .unknown
                }
            }
        }
        6 {
            return match fn_name {
                'values' {
                    .values
                }
                'eprint' {
                    .eprint
                }
                'sorted' {
                    .sorted
                }
                'filter' {
                    .filter
                }
                'insert' {
                    .insert
                }
                'delete' {
                    .delete
                }
                'repeat' {
                    .repeat
                }
                '__addr' {
                    .addr
                }
                'malloc' {
                    .malloc
                }
                else {
                    .unknown
                }
            }
        }
        7 {
            return match fn_name {
                'prepend' {
                    .prepend
                }
                'writeln' {
                    .writeln
                }
                'println' {
                    .println
                }
                'try_pop' {
                    .try_pop
                }
                'reverse' {
                    .reverse
                }
                'reserve' {
                    .reserve
                }
                else {
                    .unknown
                }
            }
        }
        8 {
            return match fn_name {
                'try_push' {
                    .try_push
                }
                'eprintln' {
                    .eprintln
                }
                'pointers' {
                    .pointers
                }
                'contains' {
                    .contains
                }
                'pop_left' {
                    .pop_left
                }
                'type_idx' {
                    .type_idx
                }
                'C.va_arg' {
                    .va_arg
                }
                'JS.await' {
                    .jsawait
                }
                'grow_len' {
                    .grow_len
                }
                'grow_cap' {
                    .grow_cap
                }
                else {
                    .unknown
                }
            }
        }
        9 {
            return match fn_name {
                'type_name' {
                    .type_name
                }
                'main.main' {
                    .main_main
                }
                'push_many' {
                    .push_many
                }
                else {
                    .unknown
                }
            }
        }
        10 {
            return match fn_name {
                'last_index' {
                    .last_index
                }
                else {
                    .unknown
                }
            }
        }
        11 {
            return match fn_name {
                'delete_many' {
                    .delete_many
                }
                'delete_last' {
                    .delete_last
                }
                'json.decode' {
                    .json_decode
                }
                'json.encode' {
                    .json_encode
                }
                else {
                    .unknown
                }
            }
        }
        else {
            return match fn_name {
                'sort_with_compare' {
                    .sort_with_compare
                }
                'sorted_with_compare' {
                    .sorted_with_compare
                }
                'reverse_in_place' {
                    .reverse_in_place
                }
                'json.encode_pretty' {
                    .json_encode_pretty
                }
                'clone_to_depth' {
                    .clone_to_depth
                }
                else {
                    .unknown
                }
            }
        }
    }
}

@[inline]
fn (p &Parser) is_start_of_call_arg_expr() bool {
    if p.tok.kind == .name && p.peek_tok.kind == .string && p.tok.lit !in ['c', 'r', 'js'] {
        return false
    }
    return match p.tok.kind {
        .name, .number, .string, .chartoken, .dot, .at, .dollar, .amp, .mul, .not, .bit_not,
        .arrow, .minus, .lpar, .lsbr, .lcbr, .pipe, .logical_or, .question, .key_fn, .key_type,
        .key_struct, .key_none, .key_nil, .key_true, .key_false, .key_if, .key_match, .key_select,
        .key_lock, .key_rlock, .key_go, .key_spawn, .key_unsafe, .key_likely, .key_unlikely,
        .key_typeof, .key_sizeof, .key_isreftype, .key_offsetof, .key_dump, .key_mut, .key_shared,
        .key_atomic, .key_static, .key_volatile {
            true
        }
        else {
            false
        }
    }
}

@[inline]
fn (p &Parser) can_omit_comma_between_fn_params() bool {
    return p.tok.line_nr > p.prev_tok.line_nr
        && p.tok.kind in [.name, .key_mut, .key_shared, .key_atomic, .ellipsis]
}

fn (mut p Parser) call_args() []ast.CallArg {
    prev_inside_call_args := p.inside_call_args
    p.inside_call_args = true
    defer {
        p.inside_call_args = prev_inside_call_args
    }
    mut args := []ast.CallArg{}
    for p.tok.kind != .rpar {
        if p.tok.kind == .eof {
            return args
        }
        is_shared := p.tok.kind == .key_shared
        is_atomic := p.tok.kind == .key_atomic
        is_mut := p.tok.kind == .key_mut || is_shared || is_atomic
        if is_mut {
            p.next()
        }
        mut comments := p.eat_comments()
        arg_start_pos := p.tok.pos()
        mut array_decompose := false
        if p.tok.kind == .ellipsis {
            p.next()
            array_decompose = true
        }
        mut expr := ast.empty_expr
        if p.peek_tok.kind == .colon {
            // `foo(key:val, key2:val2)`
            expr = p.struct_init('void_type', .short_syntax, false)
        } else {
            expr = p.expr(0)
            if mut expr is ast.Ident {
                if p.is_imported_symbol(expr.name) && !p.imported_symbols_used[expr.name] {
                    // func call arg is another function call
                    // import term { bright_cyan, colorize } ... colorize(bright_cyan, 'hello')
                    p.register_used_import_for_symbol_name(p.imported_symbols[expr.name])
                }
            }
        }
        if array_decompose {
            expr = ast.ArrayDecompose{
                expr: expr
                pos:  p.tok.pos()
            }
        }
        if mut expr is ast.StructInit {
            expr.pre_comments << comments
            comments = []ast.Comment{}
        }
        pos := arg_start_pos.extend(p.prev_tok.pos())
        comments << p.eat_comments()
        args << ast.CallArg{
            is_mut:   is_mut
            share:    ast.sharetype_from_flags(is_shared, is_atomic)
            expr:     expr
            comments: comments
            pos:      pos
        }
        if p.tok.kind != .comma {
            if !p.is_start_of_call_arg_expr() {
                break
            }
            continue
        }
        p.next()
    }
    return args
}

struct ReceiverParsingInfo {
mut:
    name     string
    pos      token.Pos
    typ      ast.Type
    type_pos token.Pos
    is_mut   bool
    language ast.Language
}

fn (mut p Parser) fn_decl() ast.FnDecl {
    p.top_level_statement_start()
    start_pos := p.tok.pos()

    mut is_manualfree := p.is_manualfree
    mut is_deprecated := false
    mut is_direct_arr := false
    mut is_keep_alive := false
    mut is_exported := false
    mut is_unsafe := false
    mut is_must_use := false
    mut is_trusted := false
    mut is_noreturn := false
    mut is_ctor_new := false
    mut is_c2v_variadic := false
    mut is_c_extern := false
    mut is_markused := false
    mut is_ignore_overflow := false
    mut is_weak := false
    mut is_expand_simple_interpolation := false
    mut comments := []ast.Comment{}
    fn_attrs := p.attrs
    p.attrs = []
    for fna in fn_attrs {
        match fna.name {
            'noreturn' {
                is_noreturn = true
            }
            'manualfree' {
                is_manualfree = true
            }
            'deprecated' {
                is_deprecated = true
            }
            'direct_array_access' {
                if !p.pref.force_bounds_checking {
                    is_direct_arr = true
                }
            }
            'keep_args_alive' {
                is_keep_alive = true
            }
            'export' {
                is_exported = true
            }
            'wasm_export' {
                is_exported = true
            }
            'unsafe' {
                is_unsafe = true
            }
            'must_use' {
                is_must_use = true
            }
            'trusted' {
                is_trusted = true
            }
            'c2v_variadic' {
                is_c2v_variadic = true
            }
            'weak' {
                is_weak = true
            }
            'use_new' {
                is_ctor_new = true
            }
            'markused' {
                is_markused = true
            }
            'ignore_overflow' {
                is_ignore_overflow = true
            }
            'c_extern' {
                is_c_extern = true
            }
            'windows_stdcall' {
                p.note_with_pos('the tag [windows_stdcall] has been deprecated, it will be an error after 2022-06-01, use `[callconv: stdcall]` instead',
                    p.tok.pos())
            }
            '_fastcall' {
                p.note_with_pos('the tag [_fastcall] has been deprecated, it will be an error after 2022-06-01, use `[callconv: fastcall]` instead',
                    p.tok.pos())
            }
            'callconv' {
                if !fna.has_arg {
                    p.error_with_pos('callconv attribute is present but its value is missing',
                        p.prev_tok.pos())
                }
                if fna.arg !in ['stdcall', 'fastcall', 'cdecl'] {
                    p.error_with_pos('unsupported calling convention, supported are stdcall, fastcall and cdecl',
                        p.prev_tok.pos())
                }
            }
            'expand_simple_interpolation' {
                is_expand_simple_interpolation = true
            }
            else {}
        }
    }
    conditional_ctdefine_idx := comptime_define_idx(fn_attrs)
    is_pub := p.tok.kind == .key_pub
    if is_pub {
        p.next()
    }
    p.check(.key_fn)
    mut comments_before_key_fn := if p.pref.is_vls { p.cur_comments.clone() } else { [] }
    comments << p.eat_comments()
    p.open_scope()
    defer {
        p.close_scope()
    }
    language_tok_pos := p.tok.pos()
    mut language := p.parse_language()
    p.fn_language = language
    if language != .v {
        for fna in fn_attrs {
            if fna.name == 'export' {
                p.error_with_pos('interop function cannot be exported', fna.pos)
                break
            }
        }
    }
    if is_keep_alive && language != .c {
        p.error_with_pos('attribute [keep_args_alive] is only supported for C functions',
            language_tok_pos)
    }
    if language != .v {
        p.check_for_impure_v(language, language_tok_pos)
        if language == .c {
            is_unsafe = !is_trusted
        }
    }
    // Receiver?
    mut rec := ReceiverParsingInfo{
        typ:      ast.void_type
        language: language
    }
    mut is_method := false
    mut is_static_type_method := false
    mut params := []ast.Param{}
    if p.tok.kind == .lpar {
        is_method = true
        p.fn_receiver(mut params, mut rec) or { return ast.FnDecl{
            scope: unsafe { nil }
        } }

        // rec.language was initialized with language variable.
        // So language is changed only if rec.language has been changed.
        language = rec.language
        p.fn_language = language
    }
    mut name := ''
    mut type_sym := p.table.sym(rec.typ)
    mut name_pos := p.tok.pos()
    mut static_type_pos := p.tok.pos()
    if p.tok.kind == .name || is_ident_name(p.tok.lit) {
        mut check_name := ''
        // TODO: high order fn
        is_static_type_method = p.tok.lit.len > 0 && p.tok.lit[0].is_capital()
            && p.peek_tok.kind == .dot && language == .v // `fn Foo.bar() {}`
        if is_static_type_method {
            type_name := p.tok.lit // "Foo"
            static_type_pos = p.tok.pos()
            rec.typ = p.parse_type()
            p.check(.dot)
            check_name = p.check_name()
            name = type_name + '__static__' + check_name // "foo__bar"
            name_pos = name_pos.extend(p.prev_tok.pos())
        } else {
            check_name = if language == .js { p.check_js_name() } else { p.check_name() }
            name = check_name
        }

        if language == .v && !p.pref.translated && !p.is_translated && !p.builtin_mod
            && util.contains_capital(check_name) {
            p.error_with_pos('function names cannot contain uppercase letters, use snake_case instead',
                name_pos)
            return ast.FnDecl{
                scope: unsafe { nil }
            }
        }
        if is_method {
            mut is_duplicate := type_sym.has_method(name)
            // make sure this is a normal method and not an interface method
            if type_sym.kind == .interface && is_duplicate {
                if mut type_sym.info is ast.Interface {
                    // if the method is in info then its an interface method
                    is_duplicate = !type_sym.info.has_method(name)
                }
            }
            // when formatting, methods in mutually exclusive $if/$else branches
            // may appear as duplicates since all branches are parsed
            if is_duplicate && !p.pref.is_fmt {
                if type_sym.kind == .enum
                    && name in ['is_empty', 'has', 'all', 'set', 'set_all', 'clear', 'clear_all', 'toggle', 'zero', 'from'] {
                    name_pos = type_method_name_pos(type_sym, name, name_pos)
                    p.error_with_pos('duplicate method `${name}`, `${name}` is an enum type built-in method',
                        name_pos)
                } else {
                    p.error_with_pos('duplicate method `${name}`', name_pos)
                }
                return ast.FnDecl{
                    scope: unsafe { nil }
                }
            }
        }
        if !p.pref.is_fmt {
            if p.is_imported_symbol(name) {
                p.error_with_pos('cannot redefine imported function `${name}`', name_pos)
                return ast.FnDecl{
                    scope: unsafe { nil }
                }
            }
        }
    } else if p.tok.kind in [.plus, .minus, .mul, .power, .div, .mod, .lt, .eq]
        && p.peek_tok.kind == .lpar {
        name = p.tok.kind.str() // op_to_fn_name()
        if rec.typ == ast.void_type {
            p.error_with_pos('cannot use operator overloading with normal functions', p.tok.pos())
        }
        if type_sym.has_method(name) {
            p.error_with_pos('cannot duplicate operator overload `${name}`', p.tok.pos())
        }
        p.next()
    } else if p.tok.kind == .lsbr && p.peek_tok.kind == .rsbr && p.peek_token(2).kind == .lpar {
        name = '[]'
        if rec.typ == ast.void_type {
            p.error_with_pos('cannot use operator overloading with normal functions', p.tok.pos())
        }
        if type_sym.has_method(name) {
            p.error_with_pos('cannot duplicate operator overload `${name}`', p.tok.pos())
        }
        p.next()
        p.next()
    } else if p.tok.kind == .lsbr && p.peek_tok.kind == .rsbr && p.peek_token(2).kind == .assign
        && p.peek_token(3).kind == .lpar {
        name = '[]='
        if rec.typ == ast.void_type {
            p.error_with_pos('cannot use operator overloading with normal functions', p.tok.pos())
        }
        if type_sym.has_method(name) {
            p.error_with_pos('cannot duplicate operator overload `${name}`', p.tok.pos())
        }
        p.next()
        p.next()
        p.next()
    } else if p.tok.kind in [.ne, .gt, .ge, .le] && p.peek_tok.kind == .lpar {
        p.error_with_pos('cannot overload `!=`, `>`, `<=` and `>=` as they are auto generated from `==` and`<`',
            p.tok.pos())
    } else if p.tok.kind in [.plus_assign, .minus_assign, .div_assign, .mult_assign, .power_assign,
        .mod_assign] {
        extracted_op := match p.tok.kind {
            .plus_assign { '+' }
            .minus_assign { '-' }
            .div_assign { '/' }
            .mod_assign { '%' }
            .mult_assign { '*' }
            .power_assign { '**' }
            else { 'unknown op' }
        }

        if type_sym.has_method(extracted_op) {
            p.error('cannot overload `${p.tok.kind}`, operator is implicitly overloaded because the `${extracted_op}` operator is overloaded')
        }
        p.error('cannot overload `${p.tok.kind}`, overload `${extracted_op}` and `${p.tok.kind}` will be automatically generated')
    } else {
        p.error_with_pos('expecting method name', p.tok.pos())
        return ast.FnDecl{
            scope: unsafe { nil }
        }
    }
    // [T]
    _, mut generic_names := p.parse_generic_types()
    // generic names can be infer with receiver's generic names
    if is_method && rec.typ.has_flag(.generic) {
        sym := p.table.sym(rec.typ)
        mut rec_generic_types := []ast.Type{}
        match sym.info {
            ast.Struct {
                rec_generic_types = sym.info.generic_types.clone()
            }
            ast.Interface {
                rec_generic_types = sym.info.generic_types.clone()
            }
            else {}
        }

        if rec_generic_types.len > 0 {
            decl_generic_names := p.types_to_names(rec_generic_types, p.tok.pos(),
                'rec_generic_types') or { return ast.FnDecl{
                scope: unsafe { nil }
            } }
            fn_generic_names := generic_names.clone()
            generic_names = p.table.generic_type_names(rec.typ)
            mut is_structured_receiver_pattern := false
            if decl_generic_names.len != generic_names.len {
                structured_generic_names :=
                    p.table.structured_receiver_generic_pattern_names(rec.typ)
                if structured_generic_names.len > 0 {
                    generic_names = structured_generic_names.clone()
                    is_structured_receiver_pattern = true
                }
            }
            if decl_generic_names.len != generic_names.len && !is_structured_receiver_pattern {
                plural := if decl_generic_names.len == 1 { '' } else { 's' }
                p.error_with_pos('expected ${decl_generic_names.len} generic parameter${plural}, got ${generic_names.len}',
                    rec.type_pos)
            }
            for gname in fn_generic_names {
                if gname !in generic_names {
                    generic_names << gname
                }
            }
        }
    }
    if generic_names.len > 0 {
        for fna in fn_attrs {
            if fna.name == 'export' {
                p.error_with_pos('generic functions cannot be exported', fna.pos)
                break
            }
        }
    }
    // Params
    params_t, are_params_type_only, mut is_variadic, mut is_c_variadic := p.fn_params()
    if is_c2v_variadic {
        is_variadic = true
        is_c_variadic = true
    }
    params << params_t
    // Return type
    mut return_type_pos := p.tok.pos()
    mut return_type := ast.void_type
    // don't confuse token on the next line: fn decl, [attribute]
    same_line := p.tok.line_nr == p.prev_tok.line_nr
    // `fn foo()[` is usually a mistaken body opener; report it as such
    // instead of trying to parse `[` as a fixed array return type.
    invalid_body_opener := same_line && p.tok.kind == .lsbr && p.peek_tok.line_nr > p.tok.line_nr
    if invalid_body_opener {
        p.unexpected(got: '${p.tok} after function signature', expecting: '`{`')
    } else if (p.tok.kind.is_start_of_type() && (same_line || p.tok.kind != .lsbr))
        || (same_line && p.tok.kind == .key_fn) {
        // Disallow [T] as return type
        if p.tok.kind == .lsbr && p.peek_tok.kind == .name && p.peek_tok.lit.len == 1
            && p.peek_tok.lit[0].is_capital() {
            return_type_pos = return_type_pos.extend(p.peek_tok.pos()).extend(p.peek_token(2).pos())
            p.error_with_pos('invalid generic return, use `${p.peek_tok.lit}` instead',
                return_type_pos)
        }
        p.inside_fn_return = true
        return_type = p.parse_type()
        p.inside_fn_return = false
        return_type_pos = return_type_pos.extend(p.prev_tok.pos())

        if p.tok.kind in [.question, .not] {
            ret_type_sym := p.table.sym(return_type)
            p.error_with_pos('wrong syntax, it must be ${p.tok.kind}${ret_type_sym.name}, not ${ret_type_sym.name}${p.tok.kind}',
                return_type_pos)
        }
    }

    if p.tok.kind == .comma {
        mr_pos := return_type_pos.extend(p.peek_tok.pos())
        p.error_with_pos('multiple return types in function declaration must use parentheses, e.g. (int, string)',
            mr_pos)
    }
    mut type_sym_method_idx := 0
    no_body := p.tok.kind != .lcbr
    end_pos := p.prev_tok.pos()
    short_fn_name := name
    is_main := short_fn_name == 'main' && p.mod == 'main'
    if is_main {
        p.main_already_defined = true
    }
    is_test := (!is_method && params.len == 0) && p.inside_test_file
        && (short_fn_name.starts_with('test_') || short_fn_name.starts_with('testsuite_')
        || short_fn_name in ['before_each', 'after_each'])
    file_mode := p.file_backend_mode
    if is_main {
        if 'main.main' in p.table.fns {
            if '.' in os.args {
                p.error_with_pos('multiple `main` functions detected, and you ran `v .`
perhaps there are multiple V programs in this directory, and you need to
run them via `v file.v` instead',
                    name_pos)
            }
        }
    }
    if is_method && is_static_type_method {
        p.error_with_pos('cannot declare a static function as a receiver method', name_pos)
    }
    // Register
    if !are_params_type_only {
        for k, param in params {
            if p.scope.known_var(param.name) {
                p.error_with_pos('redefinition of parameter `${param.name}`', param.pos)
                return ast.FnDecl{
                    scope: unsafe { nil }
                }
            }
            effective_is_mut := if is_method && k == 0 {
                param.is_mut
            } else {
                p.scope_var_is_mut(param.is_mut)
            }
            is_stack_obj := !param.typ.has_flag(.shared_f) && (param.is_mut || param.typ.is_ptr())
            p.scope.register(ast.Var{
                name:          param.name
                typ:           param.typ
                generic_typ:   if param.typ.has_flag(.generic) { param.typ } else { ast.Type(0) }
                is_mut:        effective_is_mut
                is_auto_deref: param.is_mut
                is_stack_obj:  is_stack_obj
                pos:           param.pos
                is_used:       is_pub || no_body || (is_method && k == 0) || p.builtin_mod
                is_arg:        true
                ct_type_var:   if (!is_method || k >= 0) && param.typ.has_flag(.generic)
                    && !param.typ.has_flag(.variadic) {
                    .generic_param
                } else {
                    .no_comptime
                }
            })
        }
    }
    if is_method {
        // Do not allow to modify / add methods to types from other modules
        // arrays/maps dont belong to a module only their element types do
        // we could also check if kind is .array,  .array_fixed, .map instead of mod.len
        mut is_non_local := type_sym.mod.len > 0 && type_sym.mod != p.mod && type_sym.language == .v
        // check maps & arrays, must be defined in same module as the elem type
        if !is_non_local && !(p.builtin_mod && p.pref.is_fmt) && type_sym.kind in [.array, .map] {
            elem_type_sym := p.table.sym(p.table.value_type(rec.typ))
            is_non_local = elem_type_sym.mod.len > 0 && elem_type_sym.mod != p.mod
                && elem_type_sym.language == .v
        }
        if is_non_local && !(p.file_backend_mode == .js && type_sym.mod.starts_with('Promise')) {
            p.error_with_pos('cannot define new methods on non-local type ${type_sym.name}. Define an alias and use that instead like `type AliasName = ${type_sym.name}` ',
                rec.type_pos)
            return ast.FnDecl{
                scope: unsafe { nil }
            }
        }
        method := ast.Fn{
            name:          name
            file_mode:     file_mode
            params:        params
            return_type:   return_type
            is_variadic:   is_variadic
            generic_names: generic_names
            is_pub:        is_pub
            is_deprecated: is_deprecated
            is_noreturn:   is_noreturn
            is_unsafe:     is_unsafe
            is_must_use:   is_must_use
            is_main:       is_main
            is_test:       is_test
            is_keep_alive: is_keep_alive
            is_method:     true
            receiver_type: rec.typ
            //
            attrs:          fn_attrs
            is_conditional: conditional_ctdefine_idx != ast.invalid_type_idx
            ctdefine_idx:   conditional_ctdefine_idx
            //
            no_body:  no_body
            mod:      p.mod
            file:     p.file_path
            pos:      start_pos
            name_pos: name_pos
            language: language
            //
            is_expand_simple_interpolation: is_expand_simple_interpolation
        }
        type_sym_method_idx = type_sym.register_method(method)
        p.table.register_structured_receiver_method(method)
    } else {
        name = match language {
            .c { 'C.${name}' }
            .js { 'JS.${name}' }
            .wasm { 'WASM.${name}' }
            else { p.prepend_mod(name) }
        }

        if language == .v {
            existing, has_existing := table_fn_lookup(p.table, name)
            if has_existing {
                if existing.name != '' {
                    if file_mode == .v && existing.file_mode != .v {
                        // a definition made in a .c.v file, should have a priority over a .v file definition of the same function
                        if !p.pref.is_fmt {
                            name =
                                p.prepend_mod('pure_v_but_overridden_by_${existing.file_mode}_${short_fn_name}')
                        }
                    } else if !p.pref.translated {
                        p.table.redefined_fns << name
                    }
                }
            }
        }
        p.table.register_fn(ast.Fn{
            name:                  name
            file_mode:             file_mode
            params:                params
            return_type:           return_type
            is_variadic:           is_variadic
            is_c_variadic:         is_c_variadic
            generic_names:         generic_names
            is_pub:                is_pub
            is_deprecated:         is_deprecated
            is_noreturn:           is_noreturn
            is_ctor_new:           is_ctor_new
            is_unsafe:             is_unsafe
            is_must_use:           is_must_use
            is_main:               is_main
            is_test:               is_test
            is_keep_alive:         is_keep_alive
            is_method:             false
            is_static_type_method: is_static_type_method
            receiver_type:         if is_static_type_method { rec.typ } else { 0 } // used only if is static type method
            is_file_translated:    p.is_translated
            //
            attrs:          fn_attrs
            is_conditional: conditional_ctdefine_idx != ast.invalid_type_idx
            ctdefine_idx:   conditional_ctdefine_idx
            //
            no_body:  no_body
            mod:      p.mod
            file:     p.file_path
            pos:      start_pos
            name_pos: name_pos
            language: language
            //
            is_expand_simple_interpolation: is_expand_simple_interpolation
        })
    }
    /*
    // Register implicit context var
    p.scope.register(ast.Var{
        name: 'ctx'
        typ: ast.error_type
        pos: p.tok.pos()
        is_used: true
        is_stack_obj: true
    })
    */
    // Body
    keep_fn_name := p.cur_fn_name
    p.cur_fn_name = name
    mut stmts := []ast.Stmt{}
    body_start_pos := p.tok.pos()
    if p.tok.kind == .lcbr {
        if language != .v && !(language == .js && type_sym.info is ast.Interface) {
            p.error_with_pos('interop functions cannot have a body', body_start_pos)
        }
        last_fn_scope := p.scope
        p.inside_fn = true
        p.inside_unsafe_fn = is_unsafe
        p.cur_fn_scope = p.scope
        if p.is_vls_skip_file {
            p.skip_scope()
        } else {
            stmts = p.parse_block_no_scope(true)
        }
        p.cur_fn_scope = last_fn_scope
        p.inside_unsafe_fn = false
        p.inside_fn = false
    }
    p.cur_fn_name = keep_fn_name
    if !no_body && are_params_type_only {
        p.error_with_pos('functions with type only params can not have bodies', body_start_pos)
        return ast.FnDecl{
            scope: unsafe { nil }
        }
    }
    // if no_body && !name.starts_with('C.') {
    //     p.error_with_pos('did you mean C.${name} instead of ${name}', start_pos)
    // }
    fn_decl := ast.FnDecl{
        name:               name
        short_name:         short_fn_name
        mod:                p.mod
        kind:               p.call_kind(name)
        stmts:              stmts
        return_type:        return_type
        return_type_pos:    return_type_pos
        params:             params
        is_noreturn:        is_noreturn
        is_manualfree:      is_manualfree
        is_deprecated:      is_deprecated
        is_exported:        is_exported
        is_direct_arr:      is_direct_arr
        is_pub:             is_pub
        is_variadic:        is_variadic
        is_c_variadic:      is_c_variadic
        is_c_extern:        is_c_extern
        is_main:            is_main
        is_test:            is_test
        is_keep_alive:      is_keep_alive
        is_unsafe:          is_unsafe
        is_must_use:        is_must_use
        is_markused:        is_markused
        is_ignore_overflow: is_ignore_overflow
        is_weak:            is_weak
        is_file_translated: p.is_translated
        //
        attrs:          fn_attrs
        is_conditional: conditional_ctdefine_idx != ast.invalid_type_idx
        ctdefine_idx:   conditional_ctdefine_idx
        //
        receiver:              ast.StructField{
            name:     rec.name
            typ:      rec.typ
            type_pos: rec.type_pos
            pos:      rec.pos
        }
        generic_names:         generic_names
        receiver_pos:          rec.pos
        is_method:             is_method
        is_static_type_method: is_static_type_method
        static_type_pos:       static_type_pos
        method_type_pos:       rec.type_pos
        method_idx:            type_sym_method_idx
        rec_mut:               rec.is_mut
        language:              language
        no_body:               no_body
        pos:                   start_pos.extend_with_last_line(end_pos, p.prev_tok.line_nr)
        end_pos:               p.tok.pos()
        name_pos:              name_pos
        body_pos:              body_start_pos
        file:                  p.file_path
        is_builtin:            p.builtin_mod || p.mod in util.builtin_module_parts
        scope:                 p.scope
        label_names:           p.label_names
        end_comments:          p.eat_comments(same_line: true)
        comments:              comments
        //
        is_expand_simple_interpolation: is_expand_simple_interpolation
    }
    if generic_names.len > 0 {
        p.table.register_fn_generic_types(fn_decl.fkey())
    }
    p.label_names = []
    if p.pref.is_vls {
        type_str := if (is_method || is_static_type_method) && rec.typ != ast.no_type {
            p.table.sym(rec.typ.idx_type()).name.all_after_last('.')
        } else {
            ''
        }
        key := 'fn_${p.mod}[${type_str}]${short_fn_name}'
        val := ast.VlsInfo{
            pos: fn_decl.pos
            doc: p.keyword_comments_to_string(short_fn_name, comments_before_key_fn) +
                p.comments_to_string(fn_decl.end_comments)
        }
        p.table.register_vls_info(key, val)
    }
    return fn_decl
}

fn (mut p Parser) fn_receiver(mut params []ast.Param, mut rec ReceiverParsingInfo) ! {
    p.inside_receiver_param = true
    defer {
        p.inside_receiver_param = false
    }
    lpar_pos := p.tok.pos()
    p.next() // (
    is_shared := p.tok.kind == .key_shared
    is_atomic := p.tok.kind == .key_atomic
    rec.is_mut = p.tok.kind == .key_mut || is_shared || is_atomic
    if rec.is_mut {
        p.next() // `mut`
    }
    if is_shared {
        p.register_auto_import('sync')
    }
    rec_start_pos := p.tok.pos()
    rec.name = p.check_name()
    if !rec.is_mut {
        rec.is_mut = p.tok.kind == .key_mut
        if rec.is_mut {
            ptoken2 := p.peek_token(2) // needed to prevent codegen bug, where .pos() expects &Token
            p.warn_with_pos('use `(mut f Foo)` instead of `(f mut Foo)`',
                lpar_pos.extend(ptoken2.pos()))
        }
    }
    if p.tok.kind == .key_shared {
        ptoken2 := p.peek_token(2) // needed to prevent codegen bug, where .pos() expects &Token
        p.error_with_pos('use `(shared f Foo)` instead of `(f shared Foo)`',
            lpar_pos.extend(ptoken2.pos()))
    }
    rec.pos = rec_start_pos.extend(p.tok.pos())
    is_amp := p.tok.kind == .amp
    if p.tok.kind == .name && p.tok.lit == 'JS' {
        rec.language = ast.Language.js
    }
    // if rec.is_mut {
    // p.check(.key_mut)
    // }
    // TODO: talk to alex, should mut be parsed with the type like this?
    // or should it be a property of the arg, like this ptr/mut becomes indistinguishable
    rec.type_pos = p.tok.pos()
    rec.typ = p.parse_type_with_mut(rec.is_mut)
    if rec.typ.idx() == 0 {
        // error is set in parse_type
        return error('void receiver type')
    }
    rec.type_pos = rec.type_pos.extend(p.prev_tok.pos())
    if is_amp && rec.is_mut {
        p.error_with_pos('use `(mut f Foo)` or `(f &Foo)` instead of `(mut f &Foo)`',
            lpar_pos.extend(p.tok.pos()))
        return error('invalid `mut f &Foo`')
    }
    if is_shared {
        rec.typ = rec.typ.set_flag(.shared_f)
    }
    if is_atomic {
        rec.typ = rec.typ.set_flag(.atomic_f)
    }

    if rec.language != .v {
        p.check_for_impure_v(rec.language, rec.type_pos)
    }

    p.check(.rpar)

    params << ast.Param{
        pos:       rec_start_pos
        name:      rec.name
        is_mut:    rec.is_mut
        is_atomic: is_atomic
        is_shared: is_shared
        typ:       rec.typ
        type_pos:  rec.type_pos
    }
}

fn (mut p Parser) anon_fn() ast.AnonFn {
    pos := p.tok.pos()
    p.check(.key_fn)
    if p.tok.kind == .name {
        if p.disallow_declarations_in_script_mode() {
            return ast.AnonFn{}
        }
    }
    old_inside_defer := p.inside_defer
    p.inside_defer = false
    p.open_scope()
    defer {
        p.close_scope()
    }
    p.scope.detached_from_parent = true
    inherited_vars := if p.tok.kind == .lsbr && !(p.peek_tok.kind == .name
        && p.peek_tok.lit.len == 1 && p.peek_tok.lit[0].is_capital()) {
        p.closure_vars()
    } else {
        []ast.Param{}
    }
    inherited_vars_name := inherited_vars.map(it.name)
    _, generic_names := p.parse_generic_types()
    params, _, is_variadic, _ := p.fn_params()
    for param in params {
        if param.name == '' && p.table.sym(param.typ).kind != .placeholder {
            p.error_with_pos('use `_` to name an unused parameter', param.pos)
        }
        if param.name in inherited_vars_name {
            p.error_with_pos('the parameter name `${param.name}` conflicts with the captured value name',
                param.pos)
        } else if p.scope.known_var(param.name) {
            p.error_with_pos('redefinition of parameter `${param.name}`', param.pos)
        }
        is_stack_obj := !param.typ.has_flag(.shared_f) && (param.is_mut || param.typ.is_ptr())
        p.scope.register(ast.Var{
            name:          param.name
            typ:           param.typ
            generic_typ:   if param.typ.has_flag(.generic) { param.typ } else { ast.Type(0) }
            is_mut:        p.scope_var_is_mut(param.is_mut)
            is_auto_deref: param.is_mut
            pos:           param.pos
            is_used:       true
            is_arg:        true
            is_stack_obj:  is_stack_obj
        })
    }
    mut same_line := p.tok.line_nr == p.prev_tok.line_nr
    mut return_type := ast.void_type
    mut return_type_pos := p.tok.pos()
    // lpar: multiple return types
    if same_line {
        if (p.tok.kind.is_start_of_type() && (same_line || p.tok.kind != .lsbr))
            || (same_line && p.tok.kind == .key_fn) {
            p.inside_fn_return = true
            return_type = p.parse_type()
            p.inside_fn_return = false
            return_type_pos = return_type_pos.extend(p.tok.pos())
        } else if p.tok.kind != .lcbr {
            p.error_with_pos('expected return type, not ${p.tok} for anonymous function',
                p.tok.pos())
        }
    }
    mut stmts := []ast.Stmt{}
    no_body := p.tok.kind != .lcbr
    same_line = p.tok.line_nr == p.prev_tok.line_nr
    if no_body && same_line {
        p.unexpected(got: '${p.tok} after anonymous function signature', expecting: '`{`')
    }
    mut label_names := []string{}
    mut func := ast.Fn{
        params:      params
        is_variadic: is_variadic
        return_type: return_type
        is_method:   false
    }
    name := p.table.get_anon_fn_name(p.unique_prefix, func, p.tok.pos())
    keep_fn_name := p.cur_fn_name
    p.cur_fn_name = name
    if p.tok.kind == .lcbr {
        tmp := p.label_names
        p.label_names = []
        old_assign_rhs := p.inside_assign_rhs
        p.inside_assign_rhs = false
        stmts = p.parse_block_no_scope(false)
        p.inside_assign_rhs = old_assign_rhs
        label_names = p.label_names.clone()
        p.label_names = tmp
    }
    p.cur_fn_name = keep_fn_name
    func.name = name
    idx := p.table.find_or_register_fn_type(func, true, false)
    typ := if generic_names.len > 0 {
        ast.new_type(idx).set_flag(.generic)
    } else {
        ast.new_type(idx)
    }
    p.inside_defer = old_inside_defer
    // name := p.table.get_type_name(typ)
    return ast.AnonFn{
        decl:           ast.FnDecl{
            name:            name
            short_name:      ''
            mod:             p.mod
            stmts:           stmts
            return_type:     return_type
            return_type_pos: return_type_pos
            params:          params
            is_variadic:     is_variadic
            is_closure:      inherited_vars.len > 0
            is_method:       false
            generic_names:   generic_names
            is_anon:         true
            no_body:         no_body
            pos:             pos.extend(p.prev_tok.pos())
            file:            p.file_path
            scope:           p.scope
            label_names:     label_names
        }
        inherited_vars: inherited_vars
        typ:            typ
    }
}

// part of fn declaration
// returns: params, are_params_type_only, mut is_variadic, mut is_c_variadic
fn (mut p Parser) fn_params() ([]ast.Param, bool, bool, bool) {
    p.check(.lpar)
    mut params := []ast.Param{}
    mut is_variadic := false
    mut is_c_variadic := false
    // `int, int, string` (no names, just types)
    param_name := if p.tok.kind == .name && p.tok.lit.len > 0 && p.tok.lit[0].is_capital() {
        p.prepend_mod(p.tok.lit)
    } else {
        p.tok.lit
    }
    is_generic_type := p.tok.kind == .name && p.tok.lit.len == 1 && p.tok.lit[0].is_capital()

    types_only := p.tok.kind in [.question, .not, .amp, .ellipsis, .key_fn, .lsbr]
        || (p.peek_tok.kind == .comma && (p.table.known_type(param_name) || is_generic_type))
        || p.peek_tok.kind == .dot || p.peek_tok.kind == .rpar || p.fn_language == .c
        || (p.tok.kind == .key_mut && (p.peek_tok.kind in [.amp, .ellipsis, .key_fn, .lsbr]
        || (p.peek_token(2).kind == .comma && (p.tok.kind != .key_mut
        || p.peek_tok.lit[0].is_capital())) || p.peek_token(2).kind == .rpar
        || (p.peek_tok.kind == .name && p.peek_token(2).kind == .dot)))
    mut prev_param_newline := p.tok.pos().line_nr
    // TODO: copy paste, merge 2 branches
    if types_only {
        mut param_no := 1
        for p.tok.kind != .rpar {
            if p.tok.kind == .eof {
                p.error_with_pos('expecting `)`', p.tok.pos())
                return []ast.Param{}, false, false, false
            }
            is_shared := p.tok.kind == .key_shared
            is_atomic := p.tok.kind == .key_atomic
            is_mut := p.tok.kind == .key_mut || is_shared || is_atomic
            mut name := ''
            if is_mut {
                p.next()
            }
            if p.fn_language == .c && (is_ident_name(p.tok.lit) || (p.tok.lit.len > 1
                && p.tok.lit[0] == `@` && is_ident_name(p.tok.lit[1..])))
                && p.tok.kind !in [.key_fn, .key_struct]
                && p.peek_tok.kind !in [.comma, .rpar, .dot] {
                name = p.tok.lit
                p.next()
            }
            if p.tok.kind == .ellipsis {
                p.next()
                is_variadic = true
                is_c_variadic = p.tok.kind == .rpar
                if is_c_variadic {
                    p.check(.rpar)
                    return params, types_only, is_variadic, is_c_variadic
                }
            }
            pos := p.tok.pos()
            prev_inside_fn_param := p.inside_fn_param
            p.inside_fn_param = true
            mut param_type := p.parse_type()
            p.inside_fn_param = prev_inside_fn_param
            orig_param_type := param_type
            type_pos := pos.extend(p.prev_tok.pos())
            if param_type == 0 {
                // error is added in parse_type
                return []ast.Param{}, false, false, false
            }
            if param_type == ast.chan_type {
                p.chan_type_error()
                return []ast.Param{}, false, false, false
            }
            if is_mut {
                if !param_type.has_flag(.generic) {
                    if is_variadic {
                        p.error_with_pos('variadic arguments cannot be `mut`, `shared` or `atomic`',
                            pos)
                    }
                    if is_shared {
                        p.check_fn_shared_arguments(param_type, pos)
                    } else if is_atomic {
                        p.check_fn_atomic_arguments(param_type, pos)
                    } else {
                        p.check_fn_mutable_arguments(param_type, pos)
                    }
                } else if is_shared || is_atomic {
                    p.error_with_pos('generic object cannot be `atomic`or `shared`', pos)
                    return []ast.Param{}, false, false, false
                }
                if param_type.is_ptr() && p.table.sym(param_type).kind == .struct {
                    param_type = param_type.ref()
                } else {
                    param_type = param_type.set_nr_muls(1)
                }
                if param_type.has_flag(.option) {
                    param_type = param_type.set_flag(.option_mut_param_t)
                }
                if is_shared {
                    param_type = param_type.set_flag(.shared_f)
                }
                if is_atomic {
                    param_type = param_type.set_flag(.atomic_f)
                }
            }
            if is_variadic {
                param_type =
                    ast.new_type(p.table.find_or_register_array(param_type)).set_flag(.variadic)
            }
            if p.tok.kind == .eof {
                p.error_with_pos('expecting `)`', p.prev_tok.pos())
                return []ast.Param{}, false, false, false
            }

            if p.tok.kind == .comma {
                if is_variadic {
                    p.error_with_pos('cannot use ...(variadic) with non-final parameter no ${param_no}',
                        pos)
                    return []ast.Param{}, false, false, false
                }
                p.next()
            }
            alanguage := p.table.sym(param_type).language
            if alanguage != .v {
                p.check_for_impure_v(alanguage, pos)
            }
            params << ast.Param{
                pos:        pos
                name:       name
                is_mut:     is_mut
                orig_typ:   orig_param_type
                typ:        param_type
                type_pos:   type_pos
                on_newline: prev_param_newline != pos.line_nr
            }
            prev_param_newline = pos.line_nr
            param_no++
            if param_no > 1024 {
                p.error_with_pos('too many parameters', pos)
                return []ast.Param{}, false, false, false
            }
        }
    } else {
        for p.tok.kind != .rpar {
            if p.tok.kind == .eof {
                p.error_with_pos('expecting `)`', p.tok.pos())
                return []ast.Param{}, false, false, false
            }
            is_shared := p.tok.kind == .key_shared
            is_atomic := p.tok.kind == .key_atomic
            mut is_mut := p.tok.kind == .key_mut || is_shared || is_atomic
            if is_mut {
                p.next()
            }
            if p.tok.kind == .ellipsis && p.peek_tok.kind == .rpar {
                p.check(.ellipsis)
                p.check(.rpar)
                return params, types_only, true, true
            }

            mut param_pos := [p.tok.pos()]
            name := p.check_name()
            mut param_names := [name]
            if name != '' && p.fn_language == .v && name[0].is_capital() {
                p.error_with_pos('parameter name must not begin with upper case letter (`${param_names[0]}`)',
                    p.prev_tok.pos())
            }
            mut type_pos := [p.tok.pos()]
            // `a, b, c int`
            for p.tok.kind == .comma {
                if !p.pref.is_fmt {
                    p.error('`fn f(x, y Type)` syntax has been deprecated. ' +
                        'Use `fn f(x Type, y Type)` instead. You can run `v fmt -w "${p.scanner.file_path}"` to automatically fix your code.')
                }
                p.next()
                param_pos << p.tok.pos()
                param_names << p.check_name()
                type_pos << p.tok.pos()
            }
            if p.tok.kind == .key_mut {
                // TODO: remove old syntax
                if !p.pref.is_fmt {
                    p.warn_with_pos('use `mut f Foo` instead of `f mut Foo`', p.tok.pos())
                }
                is_mut = true
            }
            if p.tok.kind == .key_shared {
                p.error_with_pos('use `shared f Foo` instead of `f shared Foo`', p.tok.pos())
            }
            if p.tok.kind == .ellipsis {
                p.next()
                is_variadic = true
                is_c_variadic = p.tok.kind == .rpar
                if is_c_variadic {
                    p.check(.rpar)
                    return params, types_only, is_variadic, is_c_variadic
                }
            }
            pos := p.tok.pos()
            prev_inside_fn_param := p.inside_fn_param
            p.inside_fn_param = true
            mut typ := p.parse_type()
            p.inside_fn_param = prev_inside_fn_param
            orig_typ := typ
            type_pos[0] = pos.extend(p.prev_tok.pos())
            if typ == 0 {
                // error is added in parse_type
                return []ast.Param{}, false, false, false
            }
            if typ == ast.chan_type {
                p.chan_type_error()
                return []ast.Param{}, false, false, false
            }
            if is_mut {
                if !typ.has_flag(.generic) {
                    if is_variadic {
                        p.error_with_pos('variadic arguments cannot be `mut`, `shared` or `atomic`',
                            pos)
                    }
                    if is_shared {
                        p.check_fn_shared_arguments(typ, pos)
                    } else if is_atomic {
                        p.check_fn_atomic_arguments(typ, pos)
                    } else {
                        p.check_fn_mutable_arguments(typ, pos)
                    }
                } else if is_shared || is_atomic {
                    p.error_with_pos('generic object cannot be `atomic` or `shared`', pos)
                    return []ast.Param{}, false, false, false
                }
                if typ.is_ptr() && p.table.sym(typ).kind == .struct {
                    typ = typ.ref()
                } else {
                    typ = typ.set_nr_muls(1)
                }
                if typ.has_flag(.option) {
                    typ = typ.set_flag(.option_mut_param_t)
                }
                if is_shared {
                    typ = typ.set_flag(.shared_f)
                }
                if is_atomic {
                    typ = typ.set_flag(.atomic_f)
                }
            }
            if is_variadic {
                // derive flags, however nr_muls only needs to be set on the array elem type, so clear it on the arg type
                typ =
                    ast.new_type(p.table.find_or_register_array(typ)).derive(typ).set_nr_muls(0).set_flag(.variadic)
            }
            for i, para_name in param_names {
                alanguage := p.table.sym(typ).language
                if alanguage != .v {
                    p.check_for_impure_v(alanguage, type_pos[i])
                }
                can_omit_comma := p.can_omit_comma_between_fn_params()
                params << ast.Param{
                    pos:        param_pos[i]
                    name:       para_name
                    is_mut:     is_mut
                    is_atomic:  is_atomic
                    is_shared:  is_shared
                    orig_typ:   orig_typ
                    typ:        typ
                    type_pos:   type_pos[i]
                    on_newline: prev_param_newline != param_pos[i].line_nr
                }
                prev_param_newline = param_pos[i].line_nr
                if is_variadic && ((p.tok.kind == .comma && p.peek_tok.kind != .rpar)
                    || can_omit_comma) {
                    p.error_with_pos('cannot use ...(variadic) with non-final parameter ${para_name}',
                        param_pos[i])
                    return []ast.Param{}, false, false, false
                }
            }
            if p.tok.kind == .eof {
                p.error_with_pos('expecting `)`', p.prev_tok.pos())
                return []ast.Param{}, false, false, false
            }
            if p.tok.kind == .comma {
                p.next()
            } else if p.tok.kind != .rpar && !p.can_omit_comma_between_fn_params() {
                p.check(.comma)
            }
        }
    }
    p.check(.rpar)
    return params, types_only, is_variadic, is_c_variadic
}

fn (mut p Parser) spawn_expr() ast.SpawnExpr {
    p.next()
    spos := p.tok.pos()
    old_inside_assign_rhs := p.inside_assign_rhs
    p.inside_assign_rhs = false
    expr := p.expr(0)
    p.inside_assign_rhs = old_inside_assign_rhs
    mut call_expr := if expr is ast.CallExpr {
        expr
    } else {
        p.error_with_pos('expression in `spawn` must be a function call', expr.pos())
        ast.CallExpr{
            scope: p.scope
        }
    }
    call_expr.is_return_used = true
    pos := spos.extend(p.prev_tok.pos())
    p.register_auto_import('sync.threads')
    p.table.gostmts++
    return ast.SpawnExpr{
        call_expr: call_expr
        pos:       pos
    }
}

fn (mut p Parser) go_expr() ast.GoExpr {
    p.next()
    spos := p.tok.pos()
    old_inside_assign_rhs := p.inside_assign_rhs
    p.inside_assign_rhs = false
    expr := p.expr(0)
    p.inside_assign_rhs = old_inside_assign_rhs
    mut call_expr := if expr is ast.CallExpr {
        expr
    } else {
        p.error_with_pos('expression in `go` must be a function call', expr.pos())
        ast.CallExpr{
            scope: p.scope
        }
    }
    call_expr.is_return_used = true
    pos := spos.extend(p.prev_tok.pos())
    // p.register_auto_import('coroutines')
    p.table.gostmts++
    return ast.GoExpr{
        call_expr: call_expr
        pos:       pos
    }
}

fn (mut p Parser) closure_vars() []ast.Param {
    p.check(.lsbr)
    mut vars := []ast.Param{cap: 5}
    for {
        is_shared := p.tok.kind == .key_shared
        is_atomic := p.tok.kind == .key_atomic
        is_mut := p.tok.kind == .key_mut || is_shared || is_atomic
        // FIXME: is_shared & is_atomic aren't used further
        if is_mut {
            p.next()
        }
        var_pos := p.tok.pos()
        p.check(.name)
        var_name := p.prev_tok.lit
        mut var := p.scope.parent.find_var(var_name) or {
            if p.table.global_scope.known_global(var_name) {
                p.error_with_pos('no need to capture global variable `${var_name}` in closure',
                    p.prev_tok.pos())
                return []
            }
            p.error_with_pos('undefined ident: `${var_name}`', p.prev_tok.pos())
            return []
        }
        var.is_used = true
        if is_mut {
            var.is_changed = true
        }
        p.scope.register(ast.Var{
            ...(*var)
            pos:           var_pos
            is_inherited:  true
            has_inherited: var.is_inherited
            is_used:       false
            is_changed:    false
            is_mut:        p.scope_var_is_mut(is_mut)
        })
        vars << ast.Param{
            pos:       var_pos
            name:      var_name
            is_mut:    p.scope_var_is_mut(is_mut)
            is_atomic: is_atomic
            is_shared: is_shared
        }
        if p.tok.kind != .comma {
            break
        }
        p.next()
    }
    p.check(.rsbr)
    return vars
}

fn (mut p Parser) check_fn_mutable_arguments(typ ast.Type, pos token.Pos) {
    sym := p.table.sym(typ)
    if sym.kind in [.array, .array_fixed, .interface, .map, .placeholder, .struct, .generic_inst,
        .sum_type] {
        return
    }
    if typ.is_any_kind_of_pointer() {
        return
    }
    if sym.kind == .alias {
        atyp := (sym.info as ast.Alias).parent_type
        p.check_fn_mutable_arguments(atyp, pos)
        return
    }
    if p.fn_language == .c {
        return
    }
    p.error_with_pos(
        'mutable arguments are only allowed for arrays, interfaces, maps, pointers, structs or their aliases\n' +
        'return values instead: `fn foo(mut n ${sym.name}) {` => `fn foo(n ${sym.name}) ${sym.name} {`',
        pos)
}

fn (mut p Parser) check_fn_shared_arguments(typ ast.Type, pos token.Pos) {
    mut sym := p.table.sym(typ)
    if sym.kind == .generic_inst {
        sym = p.table.type_symbols[(sym.info as ast.GenericInst).parent_idx]
    }
    if sym.kind == .function {
        p.error_with_pos('shared arguments are not allowed for function types', pos)
    }
}

fn (mut p Parser) check_fn_atomic_arguments(typ ast.Type, pos token.Pos) {
    sym := p.table.sym(typ)
    if sym.kind !in [.u32, .int, .u64] {
        p.error_with_pos('atomic arguments are only allowed for 32/64 bit integers\n' +
            'use shared arguments instead: `fn foo(atomic n ${sym.name}) {` => `fn foo(shared n ${sym.name}) {`',
            pos)
    }
}

fn have_fn_main(stmts []ast.Stmt) bool {
    for stmt in stmts {
        if stmt is ast.FnDecl {
            if stmt.name == 'main.main' {
                return true
            }
        }
    }
    return false
}