parser: disallow fns with type only args and a body

vlib/v/parser/fn.v

@@ -201,7 +201,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		p.check(.gt)
 	}
 	// Args
-	args2, is_variadic := p.fn_args()
+	args2, are_args_type_only, is_variadic := p.fn_args()
 	args << args2
 	for arg in args {
 		if p.scope.known_var(arg.name) {
@@ -271,6 +271,9 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		stmts = p.parse_block_no_scope(true)
 	}
 	p.close_scope()
+	if !no_body && are_args_type_only {
+		p.error_with_pos('functions with type only args can not have bodies', body_start_pos)
+	}
 	return ast.FnDecl{
 		name: name
 		mod: p.mod
@@ -303,7 +306,7 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 	p.check(.key_fn)
 	p.open_scope()
 	// TODO generics
-	args, is_variadic := p.fn_args()
+	args, _, is_variadic := p.fn_args()
 	for arg in args {
 		p.scope.register(arg.name, ast.Var{
 			name: arg.name
@@ -359,13 +362,12 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 }
 
 // part of fn declaration
-fn (mut p Parser) fn_args() ([]table.Arg, bool) {
+fn (mut p Parser) fn_args() ([]table.Arg, bool, bool) {
 	p.check(.lpar)
 	mut args := []table.Arg{}
 	mut is_variadic := false
 	// `int, int, string` (no names, just types)
-	types_only := p.tok.kind in [.amp, .ellipsis, .key_fn] || (p.peek_tok.kind == .comma && p.table.known_type(p.tok.lit)) ||
-		p.peek_tok.kind == .rpar
+	types_only := p.tok.kind in [.amp, .ellipsis, .key_fn] || (p.peek_tok.kind in [.comma, .rpar] && p.table.known_type(p.tok.lit))
 	// TODO copy pasta, merge 2 branches
 	if types_only {
 		// p.warn('types only')
@@ -463,7 +465,7 @@ fn (mut p Parser) fn_args() ([]table.Arg, bool) {
 		}
 	}
 	p.check(.rpar)
-	return args, is_variadic
+	return args, types_only, is_variadic
 }
 
 fn (p &Parser) fileis(s string) bool {

vlib/v/parser/parse_type.v

@@ -75,7 +75,7 @@ pub fn (mut p Parser) parse_fn_type(name string) table.Type {
 	// p.warn('parse fn')
 	p.check(.key_fn)
 	line_nr := p.tok.line_nr
-	args, is_variadic := p.fn_args()
+	args, _, is_variadic := p.fn_args()
 	mut return_type := table.void_type
 	if p.tok.line_nr == line_nr && p.tok.kind.is_start_of_type() {
 		return_type = p.parse_type()

vlib/v/parser/struct.v

@@ -345,7 +345,7 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 			p.error('interface methods cannot contain uppercase letters, use snake_case instead')
 		}
 		// field_names << name
-		args2, _ := p.fn_args() // TODO merge table.Arg and ast.Arg to avoid this
+		args2, _, _ := p.fn_args() // TODO merge table.Arg and ast.Arg to avoid this
 		mut args := [table.Arg{
 			name: 'x'
 			typ: typ

vlib/v/parser/tests/fn_type_only_args_no_body.out

@@ -0,0 +1,6 @@
+vlib/v/parser/tests/fn_type_only_args_no_body.v:2:1: error: functions with type only args can not have bodies 
+    1 | fn test(int) {
+    2 | }
+      | ^
+    3 | 
+    4 | fn main() {

vlib/v/parser/tests/fn_type_only_args_no_body.vv

@@ -0,0 +1,6 @@
+fn test(int) {
+}
+
+fn main() {
+	test(0)
+}

vlib/v/parser/tests/fn_type_only_args_unknown_name.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/fn_type_only_args_unknown_name.v:1:16: error: unexpected `{`, expecting `,` 
+    1 | fn test(param) {
+      |                ^
+    2 | }
+    3 | 

vlib/v/parser/tests/fn_type_only_args_unknown_name.vv

@@ -0,0 +1,6 @@
+fn test(param) {
+}
+
+fn main() {
+	test(0)
+}