parser: fix sumtype with multi fntype (fix #15557) (#15583)

vlib/v/parser/parse_type.v

@@ -526,7 +526,7 @@ pub fn (mut p Parser) parse_any_type(language ast.Language, is_ptr bool, check_d
 			return p.parse_array_type(p.tok.kind)
 		}
 		else {
-			if p.tok.kind == .lpar && !p.inside_sum_type {
+			if p.tok.kind == .lpar {
 				// multiple return
 				if is_ptr {
 					p.unexpected(prepend_msg: 'parse_type:', got: '`&` before multiple returns')

vlib/v/parser/parser.v

@@ -486,6 +486,33 @@ fn (p &Parser) peek_token_after_var_list() token.Token {
 	return tok
 }
 
+// peek token `type Fn = fn () int`
+fn (p &Parser) is_fn_type_decl() bool {
+	mut n := 1
+	mut tok := p.tok
+	mut prev_tok := p.tok
+	cur_ln := p.tok.line_nr
+	for {
+		tok = p.scanner.peek_token(n)
+		if tok.kind in [.lpar, .rpar] {
+			n++
+			prev_tok = tok
+			continue
+		}
+		if tok.kind == .pipe {
+			if tok.pos - prev_tok.pos > prev_tok.len {
+				return false
+			}
+		}
+		if tok.line_nr > cur_ln {
+			break
+		}
+		prev_tok = tok
+		n++
+	}
+	return true
+}
+
 fn (p &Parser) is_array_type() bool {
 	mut i := 1
 	mut tok := p.tok
@@ -3742,7 +3769,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 	p.check(.assign)
 	mut type_pos := p.tok.pos()
 	mut comments := []ast.Comment{}
-	if p.tok.kind == .key_fn {
+	if p.tok.kind == .key_fn && p.is_fn_type_decl() {
 		// function type: `type mycallback = fn(string, int)`
 		fn_name := p.prepend_mod(name)
 		fn_type := p.parse_fn_type(fn_name)
@@ -3762,7 +3789,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		}
 	}
 	sum_variants << p.parse_sum_type_variants()
-	// type SumType = A | B | c
+	// type SumType = Aaa | Bbb | Ccc
 	if sum_variants.len > 1 {
 		for variant in sum_variants {
 			variant_sym := p.table.sym(variant.typ)

vlib/v/tests/inout/sumtype_with_fntype.out

@@ -1 +1,2 @@
-Fns
+Fn
+Fn

vlib/v/tests/inout/sumtype_with_fntype.vv

@@ -1,8 +1,13 @@
-type Fns = bool | fn (int) int
+type Fn = fn () int | fn (int) int
 
 fn main() {
-	f := Fns(fn (a int) int {
+	f1 := Fn(fn (a int) int {
 		return a
 	})
-	println(typeof(f).name)
+	println(typeof(f1).name)
+
+	f2 := Fn(fn () int {
+		return 22
+	})
+	println(typeof(f2).name)
 }