v/vlib/compiler/fn.v

// Copyright (c) 2019-2020 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 compiler

import (
	strings
)

const (
	MaxLocalVars = 50
)

pub struct Fn {
	// addr int
	// pub:
mut:
	name              string
	mod               string
	// local_vars    []Var
	// var_idx       int
	args              []Var
	is_interface      bool
	// called_fns    []string
	// idx           int
	scope_level       int
	typ               string // return type
	receiver_typ      string
	is_c              bool
	is_public         bool
	is_method         bool
	is_decl           bool // type myfn fn(int, int)
	is_unsafe         bool
	is_deprecated     bool
	is_variadic       bool
	is_generic        bool
	returns_error     bool
	defer_text        []string
	type_pars         []string
	type_inst         []TypeInst
	generic_fn_idx    int
	parser_idx        int
	fn_name_token_idx int // used by error reporting
	comptime_define   string
	is_used           bool // so that we can skip unused fns in resulting C code
	// x64_addr i64 // address in the generated x64 binary
}

struct TypeInst {
mut:
// an instantiation of generic params (e.g. ["int","int","double"])
	inst map[string]string
	done bool
}

const (
	EmptyFn = Fn{
	}
	MainFn = Fn{
		name: 'main'
	}
)

pub fn (a []TypeInst) str() string {
	mut r := []string
	for t in a {
		mut s := ' | '
		for k in t.inst.keys() {
			s += k + ' -> ' + t.inst[k] + ' | '
		}
		r << s
	}
	return r.str()
}

fn (p &Parser) find_var_or_const(name string) ?Var {
	if p.known_var(name) {
		return p.find_var(name)
	}
	if p.table.known_const(name) {
		return p.table.find_const(name)
	}
	modname := p.prepend_mod(name)
	if p.table.known_const(modname) {
		return p.table.find_const(modname)
	}
	return none
}

fn (p &Parser) find_var(name string) ?Var {
	for i in 0 .. p.var_idx {
		if p.local_vars[i].name == name {
			return p.local_vars[i]
		}
	}
	return none
}

fn (p &Parser) find_var_check_new_var(name string) ?Var {
	for i in 0 .. p.var_idx {
		if p.local_vars[i].name == name {
			return p.local_vars[i]
		}
	}
	// A hack to allow `newvar := Foo{ field: newvar }`
	// Declare the variable so that it can be used in the initialization
	if name == 'main__' + p.var_decl_name {
		return Var{
			name: p.var_decl_name
			typ: 'voidptr'
			is_mut: true
		}
	}
	return none
}

fn (p mut Parser) open_scope() {
	p.cur_fn.defer_text << ''
	p.cur_fn.scope_level++
}

fn (p mut Parser) mark_var_used(v Var) {
	if v.idx == -1 || v.idx >= p.local_vars.len {
		return
	}
	p.local_vars[v.idx].is_used = true
}

fn (p mut Parser) mark_var_returned(v Var) {
	if v.idx == -1 || v.idx >= p.local_vars.len {
		return
	}
	p.local_vars[v.idx].is_returned = true
}

fn (p mut Parser) mark_var_changed(v Var) {
	if v.idx == -1 || v.idx >= p.local_vars.len {
		return
	}
	p.local_vars[v.idx].is_changed = true
}

fn (p mut Parser) mark_arg_moved(v Var) {
	for i, arg in p.cur_fn.args {
		if arg.name == v.name {
			// println('setting f $p.cur_fn.name arg $arg.name to is_mut')
			p.cur_fn.args[i].is_moved = true
			break
		}
	}
	p.table.fns[p.cur_fn.name] = p.cur_fn
}

fn (p &Parser) known_var(name string) bool {
	_ = p.find_var(name) or {
		return false
	}
	return true
}

fn (p &Parser) known_var_check_new_var(name string) bool {
	_ = p.find_var_check_new_var(name) or {
		return false
	}
	return true
}

fn (p mut Parser) register_var(v Var) {
	mut new_var := {
		v |
		idx:p.var_idx,
		scope_level:p.cur_fn.scope_level
	}
	if v.line_nr == 0 {
		new_var.token_idx = p.cur_tok_index()
		new_var.line_nr = p.cur_tok().line_nr
	}
	// Expand the array
	if p.var_idx >= p.local_vars.len {
		p.local_vars << new_var
	}
	else {
		p.local_vars[p.var_idx] = new_var
	}
	p.var_idx++
}

fn (p mut Parser) clear_vars() {
	// shared a := [1, 2, 3]
	p.var_idx = 0
	if p.local_vars.len > 0 {
		if p.pref.autofree {
			// p.local_vars.free()
		}
		p.local_vars = []
	}
}

// Function signatures are added to the top of the .c file in the first run.
fn (p mut Parser) fn_decl() {
	p.clear_vars() // clear local vars every time a new fn is started
	defer {
		p.fgen_nl()
		p.fgen_nl()
	}
	fn_start_idx := p.cur_tok_index()
	// If we are in the first pass, create a new function.
	// In the second pass fetch the one we created.
	/*
	mut f := if p.first_pass {
		Fn{
			mod: p.mod
			is_public: p.tok == .key_pub
		}
	else {
	}
	*/

	is_pub := p.tok == .key_pub
	mut f := Fn{
		mod: p.mod
		is_public: is_pub || p.is_vh // functions defined in .vh are always public

		is_unsafe: p.attr == 'unsafe_fn'
		is_deprecated: p.attr == 'deprecated'
		comptime_define: if p.attr.starts_with('if ') { p.attr[3..] } else { '' }
	}
	is_live   := p.pref.is_live  && p.attr == 'live'
	is_solive := p.pref.is_solive && p.attr == 'live'
	if is_pub {
		p.next()
		p.fspace()
	}
	p.returns = false
	// p.gen('/* returns $p.returns */')
	p.next()
	p.fspace()
	// Method receiver
	mut receiver_typ := ''
	if p.tok == .lpar {
		f.is_method = true
		p.check(.lpar)
		receiver_name := p.check_name()
		p.fspace()
		is_mut := p.tok == .key_mut
		is_amp := p.tok == .amp
		if is_mut || is_amp {
			p.check(p.tok)
			if !is_amp {
				p.fspace()
			}
		}
		receiver_typ = p.get_type()
		t := p.table.find_type(receiver_typ)
		if (t.name == '' || t.is_placeholder) && !p.first_pass() {
			p.error('unknown receiver type `$receiver_typ`')
		}
		if t.cat == .interface_ {
			p.error('invalid receiver type `$receiver_typ` (`$receiver_typ` is an interface)')
		}
		// Don't allow modifying types from a different module
		if !p.first_pass() && !p.builtin_mod && t.mod != p.mod && !p.is_vgen // let vgen define methods like .str() on types defined in other modules
		{
			// println('T.mod=$T.mod')
			// println('p.mod=$p.mod')
			p.error('cannot define new methods on non-local type `$receiver_typ`')
		}
		// `(f *Foo)` instead of `(f mut Foo)` is a common mistake
		if receiver_typ.ends_with('*') {
			tt := receiver_typ.replace('*', '')
			p.error('use `($receiver_name mut $tt)` instead of `($receiver_name *$tt)`')
		}
		f.receiver_typ = receiver_typ
		if is_mut || is_amp {
			receiver_typ += '*'
		}
		p.check(.rpar)
		p.fspace()
		receiver := Var{
			name: receiver_name
			is_arg: true
			typ: receiver_typ
			is_mut: is_mut
			ref: is_amp
			ptr: is_mut
			line_nr: p.scanner.line_nr
			token_idx: p.cur_tok_index()
		}
		f.args << receiver
		p.register_var(receiver)
	}
	// +-/* methods (operator overloading)
	mut is_op := false
	if p.tok in [.plus, .minus, .mul, .div, .mod] {
		f.name = p.tok.str()
		p.next()
		is_op = true
	}
	else {
		f.name = p.check_name()
	}
	f.fn_name_token_idx = p.cur_tok_index()
	// init fn
	if f.name == 'init' && !f.is_method && f.is_public && !p.is_vh {
		p.error('init function cannot be public')
	}
	// .str() methods
	if f.is_method && f.name == 'str' && !f.is_public {
		p.error('.str() methods must be declared as public')
	}
	// C function header def? (fn C.NSMakeRect(int,int,int,int))
	is_c := f.name == 'C' && p.tok == .dot
	// Just fn signature? only builtin.v + default build mode
	// if p.is_vh {
	// if f.name == 'main' {
	// println('\n\nfn_decl() name=$f.name pass=$p.pass $p.file_name receiver_typ=$receiver_typ nogen=$p.cgen.nogen')
	// }
	if is_c {
		p.check(.dot)
		f.name = p.check_name()
		f.is_c = true
	}
	orig_name := f.name
	// simple_name := f.name
	// user.register() => User_register()
	has_receiver := receiver_typ.len > 0
	if receiver_typ != '' {
		// f.name = '${receiver_typ}_${f.name}'
	}
	// full mod function name
	// `os.exit()` ==> `os__exit()`
	// if !is_c && !p.builtin_mod && receiver_typ.len == 0 {
	if !is_c && !has_receiver && (!p.builtin_mod || (p.builtin_mod && f.name == 'init')) {
		f.name = p.prepend_mod(f.name)
	}
	if p.first_pass() && receiver_typ.len == 0 {
		if existing_fn:=p.table.find_fn(f.name){
			// This existing function could be defined as C decl before
			// (no body), then we don't need to throw an error.
			if !existing_fn.is_decl {
				p.error('redefinition of `$f.name`')
			}
		}
	}
	// Generic?
	if p.tok == .lt {
		// instance (dispatch)
		if p.generic_dispatch.inst.size > 0 {
			rename_generic_fn_instance(mut f, &p.generic_dispatch)
		}
		else {
			f.is_generic = true
		}
		p.next()
		for {
			type_par := p.check_name()
			if type_par.len > 1 || !(type_par in reserved_type_param_names) {
				p.error('type parameters must be single-character, upper-case letters of the following set: $reserved_type_param_names')
			}
			if type_par in f.type_pars {
				p.error('redeclaration of type parameter `$type_par`')
			}
			f.type_pars << type_par
			if p.tok == .gt {
				break
			}
			p.check(.comma)
		}
		p.check(.gt)
		p.set_current_fn(f)
	}
	// Args (...)
	p.fn_args(mut f)
	if is_op {
		if f.args.len != 1 + 1 {
			// +1 is for the receiver
			p.error('operator overloading methods must have only 1 argument')
		}
		if f.args[0].typ != f.args[1].typ {
			p.error('operators must have the same types on both sides')
		}
	}
	// Returns an error?
	if p.tok == .not {
		p.next()
		f.returns_error = true
	}
	// Returns a type?
	mut typ := 'void'
	if p.tok in [.name, .mul, .amp, .lsbr, .question, .lpar] {
		p.fspace()
		typ = p.get_type()
	}
	// V allows empty functions (just definitions)
	is_fn_header := !is_c && !p.is_vh && p.tok != .lcbr
	if is_fn_header {
		f.name = orig_name // don't prepend module to external fn defs
		f.is_decl = true
	}
	// Make sure the name is valid
	if !is_c && !p.pref.translated && !is_fn_header {
		if contains_capital(orig_name) && !p.fileis('view.v') && !p.is_vgen {
			// println(orig_name)
			p.error('function names cannot contain uppercase letters, use snake_case instead')
		}
		if f.name[0] == `_` {
			p.error('function names cannot start with `_`, use snake_case instead')
		}
		if orig_name.contains('__') {
			p.error('function names cannot contain double underscores, use single underscores instead')
		}
	}
	// `{` required only in normal function declarations
	if !is_c && !p.is_vh && !is_fn_header {
		p.fspace()
		p.check(.lcbr)
		// p.fgen_nl()
	}
	// Register ?option type for return value and args
	if typ.starts_with('Option_') {
		p.cgen.typedefs << 'typedef Option $typ;'
		// p.cgen.typedefs << 'typedef struct Option_$typ Option_$typ'
	}
	for arg in f.args {
		if arg.typ.starts_with('Option_') {
			p.cgen.typedefs << 'typedef Option $arg.typ;'
		}
	}
	// Register function
	f.typ = typ
	str_args := f.str_args(p.table)
	// Special case for main() args
	if f.name == 'main__main' && !has_receiver {
		if p.pref.x64 && !p.first_pass() {
			//p.x64.save_main_fn_addr()
		}
		if str_args != '' || typ != 'void' {
			p.error_with_token_index('fn main must have no arguments and no return values', f.fn_name_token_idx)
		}
	}
	dll_export_linkage := p.get_linkage_prefix()
	p.set_current_fn(f)
	// Generate `User_register()` instead of `register()`
	// Internally it's still stored as "register" in type User
	mut fn_name_cgen := p.table.fn_gen_name(f)
	// Start generation of the function body
	skip_main_in_test := false
	if !is_c && !is_live && !p.is_vh && !is_fn_header && !skip_main_in_test {
		if p.pref.obfuscate {
			p.genln('; // $f.name')
		}
		// Generic functions are inserted as needed from the call site
		if f.is_generic && !p.scanner.is_fmt {
			if p.first_pass() {
				if !p.scanner.is_vh {
					gpidx := p.v.get_file_parser_index(p.file_path) or {
						panic('error finding parser for: $p.file_path')
					}
					f.parser_idx = gpidx
				}
				f.generic_fn_idx = fn_start_idx
				if f.is_method {
					rcv := p.table.find_type(receiver_typ)
					if p.first_pass() && rcv.name == '' {
						p.error('cannot currently add generic method to a type declared after it or in another module')
					}
					// println('added generic method r:$rcv.name f:$f.name')
					p.add_method(rcv.name, f)
				}
				else {
					p.table.register_fn(f)
				}
			}
			p.set_current_fn(EmptyFn)
			p.skip_fn_body()
			return
		}
		else {
			p.gen_fn_decl(f, typ, str_args)
		}
	}
	if is_fn_header {
		p.genln('$typ $fn_name_cgen ($str_args);')
		p.fgen_nl()
	}
	if is_c {
		p.fgen_nl()
	}

	// Register the method
	if receiver_typ != '' {
		mut receiver_t := p.table.find_type(receiver_typ)
		// No such type yet? It could be defined later. Create a new type.
		// struct declaration later will modify it instead of creating a new one.
		if p.first_pass() && receiver_t.name == '' {
			// println('fn decl ! registering placeholder $receiver_typ')
			receiver_t = Type{
				name: receiver_typ.replace('*', '')
				mod: p.mod
				is_placeholder: true
			}
			p.table.register_type(receiver_t)
		}
		p.add_method(receiver_t.name, f)
	}
	else if p.first_pass() {
		// println('register_fn $f.name typ=$typ isg=$is_generic pass=$p.pass ' +
		// '$p.file_name')
		p.table.register_fn(f)
	}

	if p.first_pass() && p.attr == 'live' && !(is_live || is_solive) {
		println('INFO: run `v -live $p.v.pref.path `, if you want to use [live] function $f.name .')
	}

	if p.is_vh || p.first_pass() || is_live || is_fn_header || skip_main_in_test {
		// First pass? Skip the body for now
		// Look for generic calls.
		if !p.is_vh && !is_fn_header {
			p.skip_fn_body()
		}
		// Live code reloading? Load all fns from .so
		if is_live && p.first_pass() && p.mod == 'main' {
			// println('ADDING SO FN $fn_name_cgen')
			p.cgen.so_fns << fn_name_cgen
			fn_name_cgen = '(* $fn_name_cgen )'
		}
		// Function definition that goes to the top of the C file.
		mut fn_decl := '$dll_export_linkage$typ $fn_name_cgen ($str_args)'
		if p.pref.obfuscate {
			fn_decl += '; // $f.name'
		}
		// Add function definition to the top
		if !is_c && p.first_pass() {
			p.cgen.fns << fn_decl + ';'
		}
		return
	}

	if is_solive {
		// Live functions are protected by a mutex, because otherwise they
		// can be changed by the live reload thread, *while* they are
		// running, with unpredictable results (usually just crashing).
		// For this purpose, the actual body of the live function,
		// is put under a non publicly accessible function, that is prefixed
		// with 'impl_live_' .
		// The live function just calls its implementation dual, while ensuring
		// that the call is wrapped by the mutex lock & unlock calls.
		// Adding the mutex lock/unlock inside the body of the implementation
		// function is not reliable, because the implementation function can do
		// an early exit, which will leave the mutex locked.
		function_args := f.str_args_without_types(p.table)
		mut live_fncall := 'impl_live_${fn_name_cgen}(${function_args});'
		mut live_fnreturn := ''
		if typ != 'void' {
			live_fncall = '$typ res = $live_fncall'
			live_fnreturn = 'return res;'
		}
		p.genln('  pthread_mutex_lock(&live_fn_mutex);')
		p.genln('  $live_fncall')
		p.genln('  pthread_mutex_unlock(&live_fn_mutex);')
		p.genln('  $live_fnreturn')
		p.genln('}')
		p.genln('$typ impl_live_${fn_name_cgen} ($str_args){')
	}

	if f.name in ['main__main', 'main', 'WinMain'] {
		if p.pref.is_test {
			p.error_with_token_index('tests cannot have function `main`', f.fn_name_token_idx)
		}
	}
	// println('is_c=$is_c name=$f.name')
	if is_c || p.is_vh || is_fn_header {
		return
	}
	// Profiling mode? Start counting at the beginning of the function (save current time).
	if p.pref.is_prof && f.name != 'time__ticks' {
		p.genln('double _PROF_START = time__ticks();//$f.name')
		cgen_name := p.table.fn_gen_name(f)
		if f.defer_text.len > f.scope_level {
			f.defer_text[f.scope_level] = '  ${cgen_name}_time += time__ticks() - _PROF_START;'
		}
	}
	if p.pref.x64 {
		//p.x64.register_function_address(f.name)
	}
	p.statements_no_rcbr()
	// p.cgen.nogen = false
	// Print counting result after all statements in main
	if p.pref.is_prof && f.name == 'main' {
		p.genln(p.print_prof_counters())
	}
	// Counting or not, always need to add defer before the end
	if f.defer_text.len > f.scope_level {
		p.genln(f.defer_text[f.scope_level])
	}
	if typ != 'void' && !p.returns {
		p.error_with_token_index('$f.name must return "$typ"', f.fn_name_token_idx)
	}
	if p.pref.x64 && f.name == 'main__main' && !p.first_pass() {
		//p.x64.gen_exit()
	}
	if p.pref.x64 && !p.first_pass() {
		//p.x64.ret()
	}
	// {} closed correctly? scope_level should be 0
	if p.mod == 'main' {
		// println(p.cur_fn.scope_level)
	}
	if p.cur_fn.scope_level > 2 {
		// p.error('unclosed {')
	}
	// Make sure all vars in this function are used (only in main for now)
	/*
	if p.mod != 'main' {
		p.genln('}')
		return
	}
	*/

	p.genln('}')
	if !p.builtin_mod && p.mod != 'os' {
		p.check_unused_and_mut_vars()
	}
	p.set_current_fn(EmptyFn)
	p.returns = false
}

[inline]
// Skips the entire function's body in the first pass.
fn (p mut Parser) skip_fn_body() {
	mut opened_scopes := 0
	mut closed_scopes := 0
	for {
		if p.tok == .lcbr {
			opened_scopes++
		}
		if p.tok == .rcbr {
			closed_scopes++
		}
		// find `foo<Bar>()` in function bodies and register generic types
		// TODO
		// ...
		// Reached a declaration token? (fn, struct, const etc) Stop.
		if p.tok.is_decl() {
			break
		}
		// fn body ended, and a new fn attribute declaration like [live] is starting?
		if closed_scopes > opened_scopes && p.prev_tok == .rcbr {
			if p.tok == .lsbr {
				break
			}
		}
		p.next()
	}
}

fn (p &Parser) get_linkage_prefix() string {
	return if p.pref.ccompiler == 'msvc' && p.attr == 'live' && p.pref.is_so { '__declspec(dllexport) ' } else if p.attr == 'inline' { 'static inline ' } else { '' }
}

fn (p mut Parser) check_unused_and_mut_vars() {
	for var in p.local_vars {
		if var.name == '' {
			break
		}
		if !var.is_used && !p.pref.is_repl && !var.is_arg && !p.pref.translated &&
			var.name != 'tmpl_res' && p.mod != 'vweb' && var.name != 'it' && !p.cur_fn.is_unsafe {
			p.production_error_with_token_index('`$var.name` declared and not used', var.token_idx)
		}
		if !var.is_changed && var.is_mut && !p.pref.is_repl && !p.pref.translated && var.name != 'it' && var.typ != 'T*' && p.mod != 'ui' && var.typ != 'App*' {
			p.warn_or_error('`$var.name` is declared as mutable, but it was never changed')
		}
	}
}

// user.register() => "User_register(user)"
// method_ph - where to insert "user_register("
// receiver_var - "user" (needed for pthreads)
// receiver_type - "User"
fn (p mut Parser) async_fn_call(f Fn, method_ph int, receiver_var, receiver_type string) {
	p.verify_fn_before_call(f)
	// println('\nfn_call $f.name is_method=$f.is_method receiver_type=$f.receiver_type')
	// p.print_tok()
	mut thread_name := ''
	// Normal function => just its name, method => TYPE_FN.name
	mut fn_name := f.name
	if f.is_method {
		fn_name = receiver_type.replace('*', '') + '_' + f.name
		// fn_name = '${receiver_type}_${f.name}'
	}
	// Generate tmp struct with args
	arg_struct_name := 'thread_arg_$fn_name'
	tmp_struct := p.get_tmp()
	p.genln('$arg_struct_name * $tmp_struct = malloc(sizeof($arg_struct_name));')
	mut arg_struct := 'typedef struct  $arg_struct_name   { '
	p.next()
	p.check(.lpar)
	// str_args contains the args for the wrapper function:
	// wrapper(arg_struct * arg) { fn("arg->a, arg->b"); }
	mut str_args := ''
	mut did_gen_something := false
	for i, arg in f.args {
		arg_struct += '$arg.typ $arg.name ;' // Add another field (arg) to the tmp struct definition
		str_args += 'arg $dot_ptr $arg.name'
		if i == 0 && f.is_method {
			p.genln('$tmp_struct $dot_ptr $arg.name =  $receiver_var ;')
			if i < f.args.len - 1 {
				str_args += ','
			}
			did_gen_something = true
			continue
		}
		// Set the struct values (args)
		p.genln('$tmp_struct $dot_ptr $arg.name =  ')
		p.expression()
		p.genln(';')
		if i < f.args.len - 1 {
			p.check(.comma)
			str_args += ','
		}
		did_gen_something = true
	}
	if !did_gen_something {
		// Msvc doesnt like empty struct
		arg_struct += 'EMPTY_STRUCT_DECLARATION;'
	}
	arg_struct += '} $arg_struct_name ;'
	// Also register the wrapper, so we can use the original function without modifying it
	fn_name = p.table.fn_gen_name(f)
	wrapper_name := '${fn_name}_thread_wrapper'
	mut wrapper_type := 'void*'
	if p.os == .windows {
		wrapper_type = 'DWORD WINAPI'
	}
	wrapper_text := '$wrapper_type $wrapper_name ($arg_struct_name * arg) {$fn_name ( /*f*/$str_args ); return 0; }'
	p.cgen.register_thread_fn(wrapper_name, wrapper_text, arg_struct)
	// Create thread object
	tmp_nr := p.get_tmp_counter()
	thread_name = '_thread$tmp_nr'
	if p.os != .windows {
		p.genln('pthread_t $thread_name;')
	}
	tmp2 := p.get_tmp()
	mut parg := 'NULL'
	if f.args.len > 0 {
		parg = ' $tmp_struct'
	}
	// Call the wrapper
	if p.os == .windows {
		p.genln(' CreateThread(0,0, (LPTHREAD_START_ROUTINE)$wrapper_name, $parg, 0,0);')
	}
	else {
		p.genln('int $tmp2 = pthread_create(& $thread_name, NULL, (void *)$wrapper_name, $parg);')
	}
	p.check(.rpar)
}

fn (p mut Parser) verify_fn_before_call(f &Fn) {
	if f.is_unsafe && !p.builtin_mod && !p.inside_unsafe {
		p.warn('you are calling an unsafe function outside of an unsafe block')
	}
	if f.is_deprecated {
		p.warn('$f.name is deprecated')
	}
	if !f.is_public && !f.is_c && !p.pref.is_test && !f.is_interface && f.mod != p.mod {
		if f.name == 'contains' {
			println('use `value in numbers` instead of `numbers.contains(value)`')
		}
		p.error('function `$f.name` is private')
	}
}

// p.tok == fn_name
fn (p mut Parser) fn_call(f mut Fn, method_ph int, receiver_var, receiver_type string) {
	p.verify_fn_before_call(f)
	is_comptime_define := f.comptime_define != '' && !(f.comptime_define in p.v.pref.compile_defines )
	if is_comptime_define {
		p.cgen.nogen = true
	}
	if p.pref.x64 && !p.first_pass() {
		//p.x64.call_fn(f.name)
	}
	p.calling_c = f.is_c
	if f.is_c && !p.builtin_mod {
		if f.name == 'free' {
			p.error('use `free()` instead of `C.free()`')
		}
		else if f.name == 'malloc' {
			p.error('use `malloc()` instead of `C.malloc()`')
		}
	}
	f.is_used = true
	cgen_name := p.table.fn_gen_name(f)
	p.next() // fn name
	mut generic_param_types := []string
	if p.tok == .lt {
		p.check(.lt)
		for {
			param_type := p.check_name()
			generic_param_types << param_type
			if p.tok != .comma {
				break
			}
			p.check(.comma)
		}
		p.check(.gt)
		// mut i := p.token_idx
		// for {
		// if p.tokens[i].tok == .gt {
		// //p.error('explicit type arguments are not allowed; remove `<...>`')
		// } else if p.tokens[i].tok == .lpar {
		// // probably a typo, do not concern the user with the above error message
		// break
		// }
		// i++
		// }
	}
	// if p.pref.is_prof {
	// p.cur_fn.called_fns << cgen_name
	// }
	// If we have a method placeholder,
	// we need to preappend "method(receiver, ...)"
	if f.is_method {
		receiver := f.args.first()
		mut receiver_is_interface := false
		if receiver.typ.ends_with('er') || receiver.typ[0] == `I` {
			// I absolutely love this syntax
			// `s.speak()` =>
			// `((void (*)())(Speaker_name_table[s._interface_idx][1]))(s._object);
			// where `1` refers to the speak method, since it's the second method
			// of the Speaker interface
			t := p.table.find_type(receiver.typ)
			if t.cat == .interface_ {
				// Find the index of the method
				mut idx := 0
				for i, method in t.methods {
					if method.name == f.name {
						idx = i
					}
				}
				p.cgen.resetln('')
				var := p.expr_var.name
				iname := f.args[0].typ // Speaker
				p.gen('(($f.typ (*)())(${iname}_name_table[${var}._interface_idx][$idx]))(${var}._object')
				receiver_is_interface = true
			}
		}
		// println('r=$receiver.typ RT=$receiver_type')
		if receiver.is_mut && !p.expr_var.is_mut {
			// println('$method_call  recv=$receiver.name recv_mut=$receiver.is_mut')
			if p.expr_var.is_for_var {
				p.error('`$p.expr_var.name` is immutable, `for` variables' + ' always are')
			}
			else {
				p.error('`$p.expr_var.name` is immutable, declare it with `mut`')
			}
		}
		if !p.expr_var.is_changed && receiver.is_mut {
			p.mark_var_changed(p.expr_var)
		}
		if !receiver_is_interface {
			p.gen_method_call(receiver, receiver_type, cgen_name, f.typ, method_ph)
		}
	}
	else {
		// Normal function call
		p.gen('$cgen_name (')
	}
	// `foo<Bar>()`
	// if f is generic, the name is changed to a suitable instance in dispatch_generic_fn_instance()
	// we then replace `cgen_name` with the instance's name
	generic := f.is_generic
	p.fn_call_args(mut f, generic_param_types)
	if generic {
		line := if p.cgen.is_tmp { p.cgen.tmp_line } else { p.cgen.cur_line }
		p.cgen.resetln(line.replace('$cgen_name (', '$f.name ('))
		// println('calling inst $f.name: $p.cgen.cur_line')
	}
	// if !is_interface {
	p.gen(')')
	// }
	p.calling_c = false
	if is_comptime_define {
		p.cgen.nogen = false
		p.cgen.resetln('')
	}
	// println('end of fn call typ=$f.typ')
}
// for declaration
// update the Fn object's args[]
fn (p mut Parser) fn_args(f mut Fn) {
	p.check(.lpar)
	defer {
		p.check(.rpar)
	}
	if f.is_interface {
		interface_arg := Var{
			typ: f.receiver_typ
			token_idx: p.cur_tok_index()
		}
		f.args << interface_arg
	}
	// `(int, string, int)`
	// Just register fn arg types
	types_only := p.tok == .mul || p.tok == .amp || (p.peek() == .comma &&
p.table.known_type(p.lit)) || p.peek() == .rpar // (int, string)
	if types_only {
		for p.tok != .rpar {
			typ := p.get_type()
			if typ == '' {
				// && !f.is_c {
				if p.prev_tok != .ellipsis {
					p.error('bad fn arg type')
				}
			}
			p.check_and_register_used_imported_type(typ)
			v := Var{
				typ: typ
				is_arg: true
				// is_mut: is_mut

				line_nr: p.scanner.line_nr
				token_idx: p.cur_tok_index()
			}
			// f.register_var(v)
			f.args << v
			if p.tok == .comma {
				p.next()
				p.fspace()
			}
		}
	}
	// `(a int, b, c string)` syntax
	for p.tok != .rpar {
		mut names := [p.check_name()]
		// `a,b,c int` syntax
		for p.tok == .comma {
			p.check(.comma)
			p.fspace()
			names << p.check_name()
		}
		p.fspace()
		is_mut := p.tok == .key_mut
		if is_mut {
			p.check(.key_mut)
			p.fspace()
		}
		// variadic arg
		if p.tok == .ellipsis {
			p.check(.ellipsis)
			if p.tok == .rpar {
				p.error('you must provide a type for vargs: eg `...string`. multiple types `...` are not supported yet.')
			}
			f.is_variadic = true
		}
		mut typ := p.get_type()
		if !p.first_pass() && !p.table.known_type(typ) {
			p.error('fn_args: unknown type $typ')
		}
		if f.is_variadic {
			if !f.is_c {
				// register varg struct, incase function is never called
				if p.first_pass() && !f.is_generic {
					p.register_vargs_stuct(typ, 0)
				}
				typ = 'varg_$typ'
			}
			else {
				typ = '...$typ' // TODO: fix, this is invalid in C
			}
		}
		p.check_and_register_used_imported_type(typ)
		if is_mut && is_primitive_type(typ) {
			p.error('mutable arguments are only allowed for arrays, maps, and structs.' + '\nreturn values instead: `fn foo(n mut int) {` => `fn foo(n int) int {`')
		}
		for name in names {
			if is_mut {
				typ += '*'
			}
			v := Var{
				name: name
				typ: typ
				is_arg: true
				is_mut: is_mut
				ptr: is_mut
				line_nr: p.scanner.line_nr
				token_idx: p.cur_tok_index()
			}
			p.register_var(v)
			f.args << v
		}
		if p.tok == .comma {
			p.check(.comma)
			p.fspace()
		}
		// unnamed (C definition)
		if p.tok == .ellipsis {
			if !f.is_c {
				p.error('variadic argument syntax must be `arg_name ...type` eg `argname ...string`.')
			}
			f.args << Var{
				// name: '...'
				typ: '...'
			}
			p.next()
		}
	}
	//if types_only && p.peek() == .lcbr {
		//println('wtf')
	//}
}

// foo *(1, 2, 3, mut bar)*
fn (p mut Parser) fn_call_args(f mut Fn, generic_param_types []string) {
	// println('fn_call_args() name=$f.name args.len=$f.args.len')
	// C func. # of args is not known
	p.check(.lpar)
	if f.is_c {
		for p.tok != .rpar {
			// C.func(var1, var2.method())
			// If the parameter calls a function or method that is not C,
			// the value of p.calling_c is changed
			p.calling_c = true
			ph := p.cgen.add_placeholder()
			typ := p.bool_expression()
			// Cast V byteptr to C char* (byte is unsigned in V, that led to C warnings)
			if typ == 'byte*' {
				p.cgen.set_placeholder(ph, '(char*)')
			}
			if p.tok == .comma {
				p.gen(', ')
				p.check(.comma)
				p.fspace()
			}
		}
		p.check(.rpar)
		return
	}
	// add debug information to panic when -g arg is passed
	if p.v.pref.is_debug && f.name == 'panic' && !p.is_js {
		mod_name := p.mod.replace('_dot_', '.')
		fn_name := p.cur_fn.name.replace('${p.mod}__', '')
		file_path := cescaped_path(p.file_path)
		p.cgen.resetln(p.cgen.cur_line.replace('v_panic (', 'panic_debug ($p.scanner.line_nr, tos3("$file_path"), tos3("$mod_name"), tos2((byte *)"$fn_name"), '))
	}
	// mut saved_args := []string
	mut saved_args := generic_param_types
	for i, arg in f.args {
		// Receiver is the first arg
		// Skip the receiver, because it was already generated in the expression
		if i == 0 && f.is_method {
			if f.args.len > 1 {
				// && !p.is_js {
				p.gen(', ')
			}
			// if f.args[0].typ.ends_with('*') {
			// p.gen('&/*119*/')
			// }
			// pos := p.cgen.cur_line.index('/* ? */')
			// if pos > -1 {
			// expr := p.cgen.cur_line[pos..]
			// // TODO hack
			// // If current expression is a func call, generate the array hack
			// if expr.contains('(') {
			// p.cgen.set_placeholder(pos, '(${arg.typ[..arg.typ.len-1]}[]){')
			// p.gen('}[0] ')
			// }
			// }
			continue
		}
		// Reached the final vararg? Quit
		if i == f.args.len - 1 && arg.typ.starts_with('varg_') {
			break
		}
		ph := p.cgen.add_placeholder()
		// `)` here means that not enough args were provided
		if p.tok == .rpar {
			p.error('not enough arguments in call to `${f.str_for_error()}`')
		}
		// If `arg` is mutable, the caller needs to provide `mut`:
		// `mut numbers := [1,2,3]; reverse(mut numbers);`
		if arg.is_mut {
			if p.tok != .key_mut && p.tok == .name {
				p.mutable_arg_error(i, arg, f)
			}
			if p.peek() != .name {
				p.error('`$arg.name` is a mutable argument, you need to ' + 'provide a variable to modify: `${f.name}(... mut a...)`')
			}
			p.check(.key_mut)
			p.fspace()
			var_name := p.lit
			v := p.find_var(var_name) or {
				p.error('`$arg.name` is a mutable argument, you need to ' + 'provide a variable to modify: `${f.name}(... mut a...)`')
				exit(1)
			}
			if !v.is_changed {
				p.mark_var_changed(v)
			}
		}
		p.expected_type = arg.typ
		clone := p.pref.autofree && p.mod != 'string' && arg.typ == 'string' && !p.builtin_mod // && arg.is_moved
		if clone {
			p.gen('/*YY f=$f.name arg=$arg.name is_moved=$arg.is_moved*/string_clone(')
		}
		// x64 println gen
		if p.pref.x64 && i == 0 && f.name == 'println' && p.tok == .str && p.peek() == .rpar {
			//p.x64.gen_print(p.lit)
		}
		mut typ := p.bool_expression()
		// Register an interface type usage:
		// fn run(r Animal) { ... }
		// `run(dog)` adds `Dog` to the `Animal` interface.
		// This is needed to generate an interface table.
		if arg.typ.ends_with('er') || arg.typ[0] == `I` {
			t := p.table.find_type(arg.typ)
			if t.cat == .interface_ {
				// perform((Speaker) { ._object = &dog,
				// _interface_idx = _Speaker_Dog_index })
				concrete_type_name := typ.replace('*', '_ptr')
				p.cgen.set_placeholder(ph, '($arg.typ) { ._object = &')
				p.gen(', /*OLD*/ ._interface_idx = _${arg.typ}_${concrete_type_name}_index} /* i. arg*/')
				p.table.add_gen_type(arg.typ, typ)
			}
		}
		if clone {
			p.gen(')')
		}
		// Optimize `println`: replace it with `printf` to avoid extra allocations and
		// function calls.
		// `println(777)` => `printf("%d\n", 777)`
		// (If we don't check for void, then V will compile `println(func())`)
		if i == 0 && (f.name == 'println' || f.name == 'print') && typ == 'ustring' {
			if typ == 'ustring' {
				p.gen('.s')
			}
			typ = 'string'
		}
		if i == 0 && (f.name == 'println' || f.name == 'print') && !(typ in ['string', 'ustring', 'void']) {
			//
			tt := p.table.find_type(typ)
			$if !windows {
				$if !js {
					fmt := p.typ_to_fmt(typ, 0)
					if fmt != '' && typ != 'bool' {
						nl := if f.name == 'println' { '\\n' } else { '' }
						p.cgen.resetln(p.cgen.cur_line.replace(f.name + ' (', '/*opt*/printf ("' + fmt + '$nl", '))
						continue
					}
				}
			}
			if typ.ends_with('*') {
				p.cgen.set_placeholder(ph, 'ptr_str(')
				p.gen(')')
				continue
			}
			// Make sure this type has a `str()` method
			$if !js {
				if !tt.has_method('str') {
					// varg
					if tt.name.starts_with('varg_') {
						p.gen_varg_str(tt)
						p.cgen.set_placeholder(ph, '${typ}_str(')
						p.gen(')')
						continue
					}
					// Arrays have automatic `str()` methods
					else if tt.name.starts_with('array_') {
						p.gen_array_str(tt)
						p.cgen.set_placeholder(ph, '${typ}_str(')
						p.gen(')')
						continue
					}
					// struct
					else if tt.cat == .struct_ {
						p.gen_struct_str(tt)
						p.cgen.set_placeholder(ph, '${typ}_str(')
						p.gen(')')
						continue
					}
					else {
						base := p.base_type(tt.name)
						if base != tt.name {
							base_type := p.find_type(base)
							if base_type.has_method('str') {
								p.cgen.set_placeholder(ph, '${base_type.name}_str(')
								p.gen(')')
								continue
							}
						}
					}
					error_msg := ('`$typ` needs to have method `str() string` to be printable')
					p.error(error_msg)
				}
				p.cgen.set_placeholder(ph, '${typ}_str(')
				p.gen(')')
			}
			continue
		}
		got := typ
		expected := arg.typ
		got_ptr := got.ends_with('*')
		exp_ptr := expected.ends_with('*')
		// println('fn arg got="$got" exp="$expected"')
		type_mismatch := !p.check_types_no_throw(got, expected)
		if type_mismatch && f.is_generic {
			// println("argument `$arg.name` is generic")
			saved_args << got
		}
		else if type_mismatch {
			mut j := i
			if f.is_method {
				j--
			}
			mut nr := '${j+1}th'
			if j == 0 {
				nr = 'first'
			}
			else if j == 1 {
				nr = 'second'
			}
			else if j == 2 {
				nr = 'third'
			}
			p.error('cannot use type `$typ` as type `$arg.typ` in $nr ' + 'argument to `${f.name}()`')
		}
		else {
			saved_args << ''
		}
		is_interface := p.table.is_interface(arg.typ)
		// Automatically add `&` or `*` before an argument.
		// V, unlike C and Go, simplifies this aspect:
		// `foo(bar)` is allowed where `foo(&bar)` is expected.
		// The argument is not mutable, so it won't be changed by the function.
		// It doesn't matter whether it's passed by referencee or by value
		// to the end user.
		if !is_interface {
			// Dereference
			if got_ptr && !exp_ptr {
				p.cgen.set_placeholder(ph, '*')
			}
			// Reference
			// TODO ptr hacks. DOOM hacks, fix please.
			if !got_ptr && exp_ptr && got != 'voidptr' {
				// Special case for mutable arrays. We can't `&` function
				// results,
				// have to use `(array[]){ expr }` hack.
				if expected.starts_with('array_') && exp_ptr {
					// && !arg.is_mut{
					p.cgen.set_placeholder(ph, '& /*111*/ (array[]){')
					p.gen('}[0] ')
				}
				else if exp_ptr && expected == got + '*' {
					$if !tinyc {
						expr := p.cgen.cur_line[ph..]
						// TODO hack
						// If current expression is a func call, generate the array hack
						if expr.contains('(') {
							// println('fn hack expr=$expr')
							p.cgen.set_placeholder(ph, '& /*113 e="$expected" g="$got"*/ ($got[]){')
							p.gen('}[0] ')
						}
						else {
							p.cgen.set_placeholder(ph, '& /*114*/')
						}
					} $else {
						p.cgen.set_placeholder(ph, '& /*114*/')
					}
				}
				// println('\ne:"$expected" got:"$got"')
				else if !(expected == 'void*' && got == 'int') && !(expected == 'void*' && got == 'byteptr') && !(expected == 'byte*' && got.contains(']byte')) && !(expected == 'byte*' && got == 'string') &&
				// ! (expected == 'void*' && got == 'array_int') {
				!(expected == 'byte*' && got == 'byteptr') && !p.pref.is_bare {
					p.cgen.set_placeholder(ph, '& /*112 e="$expected" g="$got" */')
				}
			}
		}
		else if is_interface {
			if !got_ptr {
				// p.cgen.set_placeholder(ph, '&')
			}
			// Pass all interface methods
			// interface_type := p.table.find_type(arg.typ)
			// for method in interface_type.methods {
			// p.gen(', ${typ}_${method.name} ')
			// }
		}
		// Check for commas
		if i < f.args.len - 1 {
			// Handle 0 args passed to varargs
			if p.tok != .comma && !f.is_variadic {
				p.error('wrong number of arguments in call to `${f.str_for_error()}`')
			}
			if p.tok == .comma && (!f.is_variadic || (f.is_variadic && i < f.args.len - 2)) {
				p.check(.comma)
				p.fspace()
				p.gen(',')
			}
		}
	}
	// varargs
	varg_type,varg_values := p.fn_call_vargs(f)
	if f.is_variadic {
		saved_args << varg_type
	}
	if p.tok == .comma {
		p.error('wrong number of arguments in call to `${f.str_for_error()}`')
	}
	p.check(.rpar)
	if f.is_generic && !p.scanner.is_fmt {
		type_map := p.extract_type_inst(f, saved_args)
		p.dispatch_generic_fn_instance(mut f, &type_map)
	}
	if f.is_variadic {
		p.fn_gen_caller_vargs(f, varg_type, varg_values)
	}
}

// From a given generic function and an argument list matching its signature,
// create a type instantiation
fn (p mut Parser) extract_type_inst(f &Fn, args_ []string) TypeInst {
	mut r := TypeInst{
	}
	mut i := 0
	mut args := args_
	if f.typ != 'void' {
		args << f.typ
	}
	for e in args {
		if e == '' {
			continue
		}
		tp := f.type_pars[i]
		mut ti := e
		if ti.starts_with('fn (') {
			fn_args := ti[4..].all_before(') ').split(',')
			mut found := false
			for fa_ in fn_args {
				mut fa := fa_
				for fa.starts_with('array_') {
					fa = fa[6..]
				}
				if fa == tp {
					r.inst[tp] = fa
					found = true
					i++
					break
				}
			}
			if found {
				continue
			}
			ti = ti.all_after(') ')
		}
		for ti.starts_with('array_') {
			ti = ti[6..]
		}
		if r.inst[tp] != '' {
			if r.inst[tp] != ti {
				p.error('type parameter `$tp` has type ${r.inst[tp]}, not `$ti`')
			}
			continue
		}
		// println("extracted $tp => $ti")
		r.inst[tp] = ti
		i++
		if i >= f.type_pars.len {
			break
		}
	}
	if r.inst[f.typ] == '' && f.typ in f.type_pars {
		r.inst[f.typ] = '_ANYTYPE_'
	}
	for tp in f.type_pars {
		if r.inst[tp] == '' {
			// p.error_with_token_index('unused type parameter `$tp`', f.body_idx-2)
			p.error('unused type parameter `$tp`')
		}
	}
	return r
}

// replace a generic type using TypeInst
fn replace_generic_type(gen_type string, ti &TypeInst) string {
	mut typ := gen_type.replace('map_', '').replace('varg_', '').trim_right('*').replace('ptr_', '')
	for typ.starts_with('array_') {
		typ = typ[6..]
	}
	if typ in ti.inst {
		typ = gen_type.replace(typ, ti.inst[typ])
		return typ
	}
	typ = gen_type
	if typ.starts_with('fn (') {
		args := typ[4..].all_before_last(')').split(',')
		ret_t := typ.all_after(')').trim_space()
		mut args_r := []string
		for arg in args {
			args_r << replace_generic_type(arg, ti)
		}
		mut t := 'fn (' + args_r.join(',') + ')'
		if ret_t.len > 0 {
			t += ' ' + replace_generic_type(ret_t, ti)
		}
		typ = t
	}
	return typ
}

// replace return type & param types for a given generic function using TypeInst
fn replace_generic_type_params(f mut Fn, ti &TypeInst) {
	mut args := []Var
	for i, _ in f.args {
		mut arg := f.args[i]
		arg.typ = replace_generic_type(arg.typ, ti)
		args << arg
	}
	f.args = args
	f.typ = replace_generic_type(f.typ, ti)
	if f.typ.ends_with('_T') {
		par := ti.inst.keys()[0]
		f.typ = f.typ + '_' + ti.inst[par]
	}
}

fn (p mut Parser) register_vargs_stuct(typ string, len int) string {
	vargs_struct := 'varg_$typ'
	varg_type := Type{
		cat: .struct_
		name: vargs_struct
		mod: p.mod
	}
	mut varg_len := len
	if !p.table.known_type(vargs_struct) {
		p.table.register_type(varg_type)
		p.cgen.typedefs << 'typedef struct $vargs_struct $vargs_struct;\n'
	}
	else {
		ex_typ := p.table.find_type(vargs_struct)
		ex_len := ex_typ.fields[1].name[5..ex_typ.fields[1].name.len - 1].int()
		if ex_len > varg_len {
			varg_len = ex_len
		}
		p.table.rewrite_type(varg_type)
	}
	p.table.add_field(vargs_struct, 'len', 'int', false, '', .public)
	p.table.add_field(vargs_struct, 'args[$varg_len]', typ, false, '', .public)
	return vargs_struct
}

fn (p mut Parser) fn_call_vargs(f Fn) (string,[]string) {
	if !f.is_variadic {
		return '',[]string
	}
	last_arg := f.args.last()
	// varg_def_type := last_arg.typ[3..]
	mut types := []string
	mut values := []string
	for p.tok != .rpar {
		if p.tok == .comma {
			p.check(.comma)
		}
		varg_type,varg_value := p.tmp_expr()
		if varg_type.starts_with('varg_') && (values.len > 0 || p.tok == .comma) {
			p.error('You cannot pass additional vargs when forwarding vargs to another function/method')
		}
		if !f.is_generic {
			p.check_types(last_arg.typ, varg_type)
		}
		else {
			if types.len > 0 {
				for t in types {
					p.check_types(varg_type, t)
				}
			}
		}
		ref_deref := if last_arg.typ.ends_with('*') && !varg_type.ends_with('*') { '&' } else if !last_arg.typ.ends_with('*') && varg_type.ends_with('*') { '*' } else { '' }
		types << varg_type
		values << '$ref_deref$varg_value'
	}
	for va in p.table.varg_access {
		if va.fn_name != f.name {
			continue
		}
		if va.index >= values.len {
			p.error_with_token_index('variadic arg index out of range: $va.index/${values.len-1}, vargs are 0 indexed', va.tok_idx)
		}
	}
	if !f.is_method && f.args.len > 1 {
		p.cgen.gen(',')
	}
	return types[0],values
}

fn (p mut Parser) fn_gen_caller_vargs(f &Fn, varg_type string, values []string) {
	is_varg := varg_type.starts_with('varg_')
	if is_varg {
		// forwarding varg
		p.cgen.gen('${values[0]}')
	}
	else {
		vargs_struct := p.register_vargs_stuct(varg_type, values.len)
		p.cgen.gen('&($vargs_struct){.len=$values.len,.args={' + values.join(',') + '}}')
	}
}

fn (p mut Parser) register_multi_return_stuct(types []string) string {
	typ := '_V_MulRet_' + types.join('_V_').replace('*', '_PTR_')
	if p.table.known_type(typ) {
		return typ
	}
	p.table.register_type(Type{
		cat: .struct_
		name: typ
		mod: p.mod
	})
	for i, t in typ.replace('_V_MulRet_', '').replace('_PTR_', '*').split('_V_') {
		p.table.add_field(typ, 'var_$i', t, false, '', .public)
	}
	p.cgen.typedefs << 'typedef struct $typ $typ;'
	return typ
}

fn rename_generic_fn_instance(f mut Fn, ti &TypeInst) {
	f.name = f.name + '_T'
	for k in ti.inst.keys() {
		f.name = f.name + '_' + type_to_safe_str(ti.inst[k])
	}
}

fn (p mut Parser) dispatch_generic_fn_instance(f mut Fn, ti &TypeInst) {
	mut new_inst := true
	for e in f.type_inst {
		if e.inst.str() == ti.inst.str() {
			new_inst = false
			break
		}
	}
	if !new_inst {
		rename_generic_fn_instance(mut f, ti)
		replace_generic_type_params(mut f, ti)
		_ = p.table.find_fn(f.name) or {
			p.error('function instance `$f.name` not found')
			return
		}
		// println('using existing inst ${p.fn_signature_v(f)}')
		return
	}
	f.type_inst << *ti
	p.table.register_fn(f)
	if f.is_method {
		f.name = f.receiver_typ + '_' + f.name
	}
	rename_generic_fn_instance(mut f, ti)
	replace_generic_type_params(mut f, ti)
	// TODO: Handle case where type not defined yet, see above
	// if f.typ in f.type_pars { f.typ = '_ANYTYPE_' }
	// if f.typ in ti.inst {
	// f.typ = ti.inst[f.typ]
	// }
	if f.is_method {
		// TODO: add_method won't add anything on second pass
		// p.add_method(f.args[0].typ.trim_right('*'), f)
	}
	else {
		p.table.register_fn(f)
	}
	mut gp := p.v.parsers[f.parser_idx]
	gp.is_vgen = true
	saved_state := p.save_state()
	p.clear_state(false, true)
	gp.token_idx = f.generic_fn_idx
	gp.generic_dispatch = *ti
	gp.next()
	gp.fn_decl()
	gp.generic_dispatch = TypeInst{
	}
	p.cgen.lines_extra << p.cgen.lines
	p.restore_state(saved_state, false, true)
	p.cgen.fns << '${p.fn_signature(f)};'
}

// "fn (int, string) int"
fn (f &Fn) typ_str() string {
	mut sb := strings.new_builder(50)
	sb.write('fn (')
	for i, arg in f.args {
		sb.write(arg.typ)
		if i < f.args.len - 1 {
			sb.write(',')
		}
	}
	sb.write(')')
	if f.typ != 'void' {
		sb.write(' $f.typ')
	}
	return sb.str()
}

// f.args => "int a, string b"
fn (f &Fn) str_args(table &Table) string {
	mut s := ''
	for i, arg in f.args {
		// Interfaces are a special case. We need to pass the object + pointers
		// to all methods:
		// fn handle(r Runner) { =>
		// void handle(void *r, void (*Runner_run)(void*)) {
		/*
		if table.is_interface(arg.typ) {
			// First the object (same name as the interface argument)
			s += ' void* $arg.name'
			// Now  all methods
			interface_type := table.find_type(arg.typ)
			for method in interface_type.methods {
				s += ', $method.typ (*${arg.typ}_${method.name})(void*'
				if method.args.len > 1 {
					for a in method.args[1..] {
						s += ', $a.typ'
					}
				}
				s += ')'
			}
		}
		*/
		if arg.typ.starts_with('varg_') {
			s += '$arg.typ *$arg.name'
		}
		else {
			// s += '$arg.typ $arg.name'
			s += table.cgen_name_type_pair(arg.name, arg.typ) // '$arg.typ $arg.name'
		}
		if i < f.args.len - 1 {
			s += ', '
		}
	}
	return s
}


// f.args => "a, b, c"
fn (f &Fn) str_args_without_types(table &Table) string {
	mut res := []string
	for arg in f.args {
		res << arg.name
	}
	return res.join(', ')
}

// find local function variable with closest name to `name`
fn (p &Parser) find_misspelled_local_var(name string, min_match f32) string {
	mut closest := f32(0)
	mut closest_var := ''
	for var in p.local_vars {
		if var.scope_level > p.cur_fn.scope_level {
			continue
		}
		n := name.all_after('.')
		if var.name == '' || (n.len - var.name.len > 2 || var.name.len - n.len > 2) {
			continue
		}
		c := strings.dice_coefficient(var.name, n)
		if c > closest {
			closest = c
			closest_var = var.name
		}
	}
	return if closest >= min_match { closest_var } else { '' }
}

fn (fns []Fn) contains(f Fn) bool {
	for ff in fns {
		if ff.name == f.name {
			return true
		}
	}
	return false
}

fn (p &Parser) fn_signature(f &Fn) string {
	return '$f.typ ${f.name}(${f.str_args(p.table)})'
}

pub fn (f &Fn) v_fn_module() string {
	return f.mod
}

pub fn (f &Fn) v_fn_name() string {
	return f.name.replace('${f.mod}__', '')
}

pub fn (f &Fn) str_for_error() string {
	// Build the args for the error
	mut s := ''
	for i, a in f.args {
		if i == 0 {
			if f.is_method {
				s += a.typ + '.' + f.name + '('
				continue
			}
			s += f.name + '('
		}
		s += a.typ
		if i < f.args.len - 1 {
			s += ', '
		}
	}
	return s + ')'
}