Fix v/parser: Failure to parse structs with fields typed as anonymous functions returning having an optional void (?) return type. (#5684)

* Handle optional void return type in function types in struct fields.

* Add more testing for optional return types in struct fields.

* Move language parsing into it's own function

* Fix issue caused by not setting typ.

* Fix test for structs containing anon fn with optional void return types

vlib/v/parser/parse_type.v

@@ -98,25 +98,8 @@ pub fn (mut p Parser) parse_type_with_mut(is_mut bool) table.Type {
 	return typ
 }
 
-pub fn (mut p Parser) parse_type() table.Type {
-	// optional
-	mut is_optional := false
-	if p.tok.kind == .question {
-		p.next()
-		is_optional = true
-	}
-	is_shared := p.tok.kind in [.key_shared, .key_rwshared]
-	is_atomic_or_rw := p.tok.kind in [.key_rwshared, .key_atomic]
-	mut nr_muls := 0
-	if p.tok.kind == .key_mut || is_shared || is_atomic_or_rw {
-		nr_muls++
-		p.next()
-	}
-	// &Type
-	for p.tok.kind == .amp {
-		nr_muls++
-		p.next()
-	}
+// Parses any language indicators on a type.
+pub fn (mut p Parser) parse_language() table.Language {
 
 	language := if p.tok.lit == 'C' {
 		table.Language.c
@@ -130,6 +113,40 @@ pub fn (mut p Parser) parse_type() table.Type {
 		p.next()
 		p.check(.dot)
 	}
+
+	return language
+}
+
+pub fn (mut p Parser) parse_type() table.Type {
+	// optional
+	mut is_optional := false
+	if p.tok.kind == .question {
+		line_nr := p.tok.line_nr
+		p.next()
+		is_optional = true
+
+		if p.tok.line_nr > line_nr {
+			mut typ := table.void_type
+			if is_optional {
+				typ = typ.set_flag(.optional)
+			}
+			return typ
+		}
+	}
+	is_shared := p.tok.kind in [.key_shared, .key_rwshared]
+	is_atomic_or_rw := p.tok.kind in [.key_rwshared, .key_atomic]
+
+	mut nr_muls := 0
+	if p.tok.kind == .key_mut || is_shared || is_atomic_or_rw {
+		nr_muls++
+		p.next()
+	}
+	// &Type
+	for p.tok.kind == .amp {
+		nr_muls++
+		p.next()
+	}
+	language := p.parse_language()
 	mut typ := table.void_type
 	if p.tok.kind != .lcbr {
 		pos := p.tok.position()

vlib/v/tests/option_test.v

@@ -279,3 +279,40 @@ fn test_optional_val_with_empty_or() {
 	ret_none() or {}
 	assert true
 }
+
+fn test_optional_void_return_types_of_anon_fn() {
+	f := fn(i int) ? {
+		if i == 0 {
+			return error("0")
+		}
+
+		return
+	}
+
+	f(0) or {
+		assert err == "0"
+		return
+	}
+}
+
+struct Foo {
+	f fn(int) ?
+}
+
+fn test_option_void_return_types_of_anon_fn_in_struct() {
+	foo := Foo {
+		f: fn(i int) ? {
+			if i == 0 {
+				return error("0")
+			}
+
+			return
+		}
+	}
+
+	foo.f(0) or {
+		assert err == "0"
+		return
+	}
+}
+

vlib/v/tests/struct_test.v

@@ -313,3 +313,28 @@ fn test_struct_with_default_values_no_init() {
 	assert s2.field_optional == 3
 	assert s3.field_optional == 2
 }
+
+struct FieldsWithOptionalVoidReturnType {
+	f fn() ?
+	g fn() ?
+}
+
+fn test_fields_anon_fn_with_optional_void_return_type() {
+	foo := FieldsWithOptionalVoidReturnType {
+		f: fn() ? {
+			return error("oops")
+		}
+		g: fn() ? {
+			return
+		}
+	}
+
+	foo.f() or {
+		assert err == "oops"
+	}
+
+	foo.g() or {
+		assert false
+	}
+}
+