parser: fix forwarding vargs & multiple call varg len fix

vlib/compiler/fn.v

@@ -813,8 +813,8 @@ fn (p mut Parser) fn_args(f mut Fn) {
 			f.is_variadic = true
 			t := p.get_type()
 			// register varg struct, incase function is never called
-			if p.first_pass() && !f.is_generic {
-				p.fn_register_vargs_stuct(f, t, []string)
+			if p.first_pass() && !f.is_generic && !f.is_c{
+				p.register_vargs_stuct(t, 0)
 			}
 			typ = '...$t'
 		} else {
@@ -1205,21 +1205,25 @@ fn (p mut Parser) replace_type_params(f &Fn, ti TypeInst) []string {
 	return r
 }
 
-fn (p mut Parser) fn_register_vargs_stuct(f &Fn, typ string, values []string) string {
-	vargs_struct := '_V_FnVargs_$f.name'
+fn (p mut Parser) register_vargs_stuct(typ string, len int) string {
+	vargs_struct := '_V_FnVargs_$typ'
 	varg_type := Type{
 		cat: TypeCategory.struct_,
 		name: vargs_struct,
 		mod: p.mod
 	}
+	mut varg_len := len
 	if !p.table.known_type(vargs_struct) {
 		p.table.register_type2(varg_type)
 		p.cgen.typedefs << 'typedef struct $vargs_struct $vargs_struct;\n'
 	} else {
+		ex_typ := p.table.find_type(vargs_struct)
+		ex_len := ex_typ.fields[1].name[5..ex_typ.fields[1].name.len-1].int()
+		if ex_len > varg_len { varg_len = ex_len }
 		p.table.rewrite_type(varg_type)
 	}
 	p.table.add_field(vargs_struct, 'len', 'int', false, '', .public)
-	p.table.add_field(vargs_struct, 'args[$values.len]', typ, false, '', .public)
+	p.table.add_field(vargs_struct, 'args[$varg_len]', typ, false, '', .public)
 	return vargs_struct
 }
 
@@ -1238,6 +1242,10 @@ fn (p mut Parser) fn_call_vargs(f Fn) (string, []string) {
 		p.cgen.start_tmp()
 		mut varg_type := p.bool_expression()
 		varg_value := p.cgen.end_tmp()
+		if varg_type.starts_with('...') &&
+			(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 {
@@ -1246,7 +1254,6 @@ fn (p mut Parser) fn_call_vargs(f Fn) (string, []string) {
 					p.check_types(varg_type, t)
 				}
 			}
-			varg_def_type = varg_type
 		}
 		ref_deref := if last_arg.typ.ends_with('*') && !varg_type.ends_with('*') { '&' }
 			else if !last_arg.typ.ends_with('*') && varg_type.ends_with('*') { '*' }
@@ -1263,13 +1270,18 @@ fn (p mut Parser) fn_call_vargs(f Fn) (string, []string) {
 	if !f.is_method && f.args.len > 1 {
 		p.cgen.gen(',')
 	}
-	return varg_def_type, values
+	return types[0], values
 }
 
 fn (p mut Parser) fn_gen_caller_vargs(f &Fn, varg_type string, values []string) {
-	vargs_struct := p.fn_register_vargs_stuct(f, varg_type, values)
+	is_varg := varg_type.starts_with('...')
+	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_')
@@ -1450,7 +1462,7 @@ fn (f &Fn) str_args(table &Table) string {
 			}
 		}
 		else if arg.typ.starts_with('...') {
-			s += '_V_FnVargs_$f.name *$arg.name'
+			s += '_V_FnVargs_${arg.typ[3..]} *$arg.name'
 		}
 		else {
 			// s += '$arg.typ $arg.name'

vlib/compiler/tests/fn_variadic_test.v

@@ -2,6 +2,7 @@ struct VaTestGroup {
 	name string
 }
 
+// basic
 fn variadic_test(name string, groups ...VaTestGroup) {
 	assert groups.len == 2
 	assert groups[0].name == 'users' 
@@ -14,6 +15,7 @@ fn test_fn_variadic() {
 	variadic_test('joe', group1, group2)
 }
 
+// generic
 fn variadic_test_generic<T>(a int, b ...T) T {
 	b1 := b[0]
 	b2 := b[1]
@@ -23,3 +25,19 @@ fn variadic_test_generic<T>(a int, b ...T) T {
 fn test_fn_variadic_generic() {
 	assert variadic_test_generic(111, 'hello', 'v') == '111 hello v'
 }
+
+// forwarding
+fn variadic_forward_a(a ...string) string {
+	return variadic_forward_b(a)
+}
+
+fn variadic_forward_b(a ...string) string {
+	a0 := a[0]
+	a1 := a[1]
+	a2 := a[2]
+	return '$a0$a1$a2'
+}
+
+fn test_fn_variadic_forward() {
+	assert variadic_forward_a('a', 'b', 'c') == 'abc'
+}