parser: fix required function members in struct (#10299)

vlib/v/checker/tests/struct_required_fn_field.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/struct_required_fn_field.vv:12:6: error: field `Abc.f3` must be initialized
+   10 |         f3: fn () {}
+   11 |     }
+   12 |     _ = Abc{
+      |         ~~~~
+   13 |         f1: 123
+   14 |         f2: 789

vlib/v/checker/tests/struct_required_fn_field.vv

@@ -0,0 +1,16 @@
+struct Abc {
+	f1 int [required]
+	f2 int
+	f3 fn () [attr1; required; attr2]
+}
+
+fn main() {
+	_ = Abc{
+		f1: 123
+		f3: fn () {}
+	}
+	_ = Abc{
+		f1: 123
+		f2: 789
+	}
+}

vlib/v/parser/parse_type.v

@@ -212,7 +212,7 @@ pub fn (mut p Parser) parse_fn_type(name string) ast.Type {
 	}
 	mut return_type := ast.void_type
 	mut return_type_pos := token.Position{}
-	if p.tok.line_nr == line_nr && p.tok.kind.is_start_of_type() {
+	if p.tok.line_nr == line_nr && p.tok.kind.is_start_of_type() && !p.is_attributes() {
 		return_type_pos = p.tok.position()
 		return_type = p.parse_type()
 		if return_type.has_flag(.generic) {

vlib/v/parser/parser.v

@@ -1460,6 +1460,28 @@ fn (mut p Parser) expr_list() ([]ast.Expr, []ast.Comment) {
 	return exprs, comments
 }
 
+fn (mut p Parser) is_attributes() bool {
+	if p.tok.kind != .lsbr {
+		return false
+	}
+	mut i := 0
+	for {
+		tok := p.peek_token(i)
+		if tok.kind == .eof || tok.line_nr != p.tok.line_nr {
+			return false
+		}
+		if tok.kind == .rsbr {
+			break
+		}
+		i++
+	}
+	peek_rsbr_tok := p.peek_token(i + 1)
+	if peek_rsbr_tok.line_nr == p.tok.line_nr && peek_rsbr_tok.kind != .rcbr {
+		return false
+	}
+	return true
+}
+
 // when is_top_stmt is true attrs are added to p.attrs
 fn (mut p Parser) attributes() {
 	p.check(.lsbr)

vlib/v/tests/struct_fields_storing_required_functions_test.v

@@ -0,0 +1,17 @@
+struct Struct {
+	f1 fn () [required]
+	f2 fn () [attr1; required]
+}
+
+fn func() {
+}
+
+fn test_struct_fields_storing_required_functions() {
+	s := Struct{
+		f1: func
+		f2: func
+	}
+
+	assert s.f1 == func
+	assert s.f2 == func
+}