parser: differentiate recursive alias & existing type err + rune fix

vlib/builtin/rune.v

@@ -2,7 +2,10 @@
 // Use of this source code is governed by an MIT license that can be found in the LICENSE file.
 module builtin
 
-type rune = int
+// This was never working correctly, the issue is now
+// fixed however the type checks in checker need to be
+// updated. if you uncomment it you will see the issue
+// type rune = int
 
 pub fn (c rune) str() string {
 	return utf32_to_str(u32(c))

vlib/v/parser/parser.v

@@ -2064,34 +2064,31 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 	}
 	// type MyType = int
 	parent_type := first_type
-	parent_name := p.table.get_type_symbol(parent_type).name
-	pid := parent_type.idx()
-	mut language := table.Language.v
-	if parent_name.len > 2 && parent_name.starts_with('C.') {
-		language = table.Language.c
-		p.check_for_impure_v(language, decl_pos)
-	} else if parent_name.len > 2 && parent_name.starts_with('JS.') {
-		language = table.Language.js
-		p.check_for_impure_v(language, decl_pos)
-	}
+	parent_sym := p.table.get_type_symbol(parent_type)
+	pidx := parent_type.idx()
+	p.check_for_impure_v(parent_sym.language, decl_pos)
 	prepend_mod_name := p.prepend_mod(name)
-	p.table.register_type_symbol(table.TypeSymbol{
+	idx := p.table.register_type_symbol(table.TypeSymbol{
 		kind: .alias
 		name: prepend_mod_name
 		cname: util.no_dots(prepend_mod_name)
 		mod: p.mod
-		parent_idx: pid
+		parent_idx: pidx
 		info: table.Alias{
 			parent_type: parent_type
-			language: language
+			language: parent_sym.language
 		}
 		is_public: is_pub
 	})
-	comments = p.eat_line_end_comments()
-	if prepend_mod_name == parent_name {
+	if idx == -1 {
+		p.error_with_pos('cannot register alias `$name`, another type with this name exists', decl_pos.extend(type_alias_pos))
+		return ast.AliasTypeDecl{}
+	}
+	if idx == pidx {
 		p.error_with_pos('a type alias can not refer to itself: $name', decl_pos.extend(type_alias_pos))
 		return ast.AliasTypeDecl{}
 	}
+	comments = p.eat_line_end_comments()
 	return ast.AliasTypeDecl{
 		name: name
 		is_pub: is_pub

vlib/v/parser/tests/type_alias_existing_type_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/type_alias_existing_type_err.vv:3:1: error: cannot register alias `Foo`, another type with this name exists
+    1 | struct Foo{}
+    2 |
+    3 | type Foo = Foo
+      | ~~~~~~~~~~~~~~
+    4 |
+    5 | fn main() {

vlib/v/parser/tests/type_alias_existing_type_err.vv

@@ -0,0 +1,7 @@
+struct Foo{}
+
+type Foo = Foo
+
+fn main() {
+    
+}

vlib/v/parser/tests/type_alias_same_type_err.out

@@ -1,7 +1,5 @@
-vlib/v/parser/tests/type_alias_same_type_err.vv:3:1: error: a type alias can not refer to itself: Foo
-    1 | struct Foo{}
-    2 | 
-    3 | type Foo = Foo
+vlib/v/parser/tests/type_alias_same_type_err.vv:1:1: error: a type alias can not refer to itself: Foo
+    1 | type Foo = Foo
       | ~~~~~~~~~~~~~~
-    4 | 
-    5 | fn main() {
+    2 |
+    3 | fn main() {

vlib/v/parser/tests/type_alias_same_type_err.vv

@@ -1,5 +1,3 @@
-struct Foo{}
-
 type Foo = Foo
 
 fn main() {

vlib/v/table/types.v

@@ -309,11 +309,11 @@ pub const (
 	none_type_idx    = 17
 	string_type_idx  = 18
 	ustring_type_idx = 19
-	array_type_idx   = 20
-	map_type_idx     = 21
-	chan_type_idx    = 22
-	sizet_type_idx   = 23
-	rune_type_idx    = 24
+	rune_type_idx    = 20
+	array_type_idx   = 21
+	map_type_idx     = 22
+	chan_type_idx    = 23
+	sizet_type_idx   = 24
 	any_type_idx     = 25
 	any_flt_type_idx = 26
 	any_int_type_idx = 27
@@ -353,10 +353,10 @@ pub const (
 	none_type    = new_type(none_type_idx)
 	string_type  = new_type(string_type_idx)
 	ustring_type = new_type(ustring_type_idx)
+	rune_type    = new_type(rune_type_idx)
 	array_type   = new_type(array_type_idx)
 	map_type     = new_type(map_type_idx)
 	chan_type    = new_type(chan_type_idx)
-	rune_type    = new_type(rune_type_idx)
 	any_type     = new_type(any_type_idx)
 	any_flt_type = new_type(any_flt_type_idx)
 	any_int_type = new_type(any_int_type_idx)
@@ -517,11 +517,11 @@ pub fn (mut t Table) register_builtin_type_symbols() {
 	t.register_type_symbol(kind: .none_, name: 'none', cname: 'none', mod: 'builtin')
 	t.register_type_symbol(kind: .string, name: 'string', cname: 'string', mod: 'builtin')
 	t.register_type_symbol(kind: .ustring, name: 'ustring', cname: 'ustring', mod: 'builtin')
+	t.register_type_symbol(kind: .rune, name: 'rune', cname: 'rune', mod: 'builtin')
 	t.register_type_symbol(kind: .array, name: 'array', cname: 'array', mod: 'builtin')
 	t.register_type_symbol(kind: .map, name: 'map', cname: 'map', mod: 'builtin')
 	t.register_type_symbol(kind: .chan, name: 'chan', cname: 'chan', mod: 'builtin')
 	t.register_type_symbol(kind: .size_t, name: 'size_t', cname: 'size_t', mod: 'builtin')
-	t.register_type_symbol(kind: .rune, name: 'rune', cname: 'rune', mod: 'builtin')
 	t.register_type_symbol(kind: .any, name: 'any', cname: 'any', mod: 'builtin')
 	t.register_type_symbol(
 		kind: .any_float