parser, checker: move error handling for user defined type duplicates to the checker to resolve parsing issues

vlib/v/checker/checker.v

@@ -499,6 +499,12 @@ fn (mut c Checker) check_valid_pascal_case(name string, identifier string, pos t
 }
 
 fn (mut c Checker) type_decl(node ast.TypeDecl) {
+	if node.typ == ast.invalid_type_idx && (node is ast.AliasTypeDecl || node is ast.SumTypeDecl) {
+		typ_desc := if node is ast.AliasTypeDecl { 'alias' } else { 'sum type' }
+		c.error('cannot register ${typ_desc} `${node.name}`, another type with this name exists',
+			node.pos)
+		return
+	}
 	match node {
 		ast.AliasTypeDecl { c.alias_type_decl(node) }
 		ast.FnTypeDecl { c.fn_type_decl(node) }
@@ -1778,6 +1784,11 @@ fn (mut c Checker) const_decl(mut node ast.ConstDecl) {
 
 fn (mut c Checker) enum_decl(mut node ast.EnumDecl) {
 	c.check_valid_pascal_case(node.name, 'enum name', node.pos)
+	if node.typ == ast.invalid_type_idx {
+		c.error('cannot register enum `${node.name}`, another type with this name exists',
+			node.pos)
+		return
+	}
 	mut useen := []u64{}
 	mut iseen := []i64{}
 	mut seen_enum_field_names := map[string]int{}

vlib/v/checker/tests/alias_type_unkown.out

@@ -0,0 +1,3 @@
+vlib/v/checker/tests/alias_type_unkown.vv:1:15: error: unknown type `Bird`
+    1 | type Pigeon = Bird
+      |               ~~~~

vlib/v/checker/tests/type_exists_err.out

@@ -0,0 +1,28 @@
+vlib/v/checker/tests/type_exists_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 | type Foo = string
+vlib/v/checker/tests/type_exists_err.vv:5:1: error: cannot register alias `Foo`, another type with this name exists
+    3 | type Foo = Foo
+    4 | 
+    5 | type Foo = string
+      | ~~~~~~~~
+    6 | 
+    7 | type Foo = int | string
+vlib/v/checker/tests/type_exists_err.vv:7:1: error: cannot register sum type `Foo`, another type with this name exists
+    5 | type Foo = string
+    6 | 
+    7 | type Foo = int | string
+      | ~~~~~~~~
+    8 | 
+    9 | enum Foo {
+vlib/v/checker/tests/type_exists_err.vv:9:1: error: cannot register enum `Foo`, another type with this name exists
+    7 | type Foo = int | string
+    8 | 
+    9 | enum Foo {
+      | ~~~~~~~~
+   10 |     @none
+   11 | }

vlib/v/checker/tests/type_exists_err.vv

@@ -0,0 +1,11 @@
+struct Foo {}
+
+type Foo = Foo
+
+type Foo = string
+
+type Foo = int | string
+
+enum Foo {
+	@none
+}

vlib/v/fmt/fmt.v

@@ -1009,7 +1009,7 @@ pub fn (mut f Fmt) enum_decl(node ast.EnumDecl) {
 		f.write('pub ')
 	}
 	mut name := node.name.after('.')
-	if node.typ != ast.int_type {
+	if node.typ != ast.int_type && node.typ != ast.invalid_type_idx {
 		senum_type := f.table.type_to_str_using_aliases(node.typ, f.mod2alias)
 		name += ' as ${senum_type}'
 	}

vlib/v/parser/parser.v

@@ -4296,11 +4296,13 @@ fn (mut p Parser) enum_decl() ast.EnumDecl {
 		}
 		is_pub: is_pub
 	})
-	if idx in [ast.invalid_type_idx, ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx,
-		ast.map_type_idx] {
+	if idx in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx] {
 		p.error_with_pos('cannot register enum `${name}`, another type with this name exists',
 			end_pos)
 	}
+	if idx == ast.invalid_type_idx {
+		enum_type = idx
+	}
 
 	enum_decl := ast.EnumDecl{
 		name: name
@@ -4402,8 +4404,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 			}
 			is_pub: is_pub
 		})
-		if typ in [ast.invalid_type_idx, ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx,
-			ast.map_type_idx] {
+		if typ in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx] {
 			p.error_with_pos('cannot register sum type `${name}`, another type with this name exists',
 				name_pos)
 			return ast.SumTypeDecl{}
@@ -4443,8 +4444,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		is_pub: is_pub
 	})
 	type_end_pos := p.prev_tok.pos()
-	if idx in [ast.invalid_type_idx, ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx,
-		ast.map_type_idx] {
+	if idx in [ast.string_type_idx, ast.rune_type_idx, ast.array_type_idx, ast.map_type_idx] {
 		p.error_with_pos('cannot register alias `${name}`, another type with this name exists',
 			name_pos)
 		return ast.AliasTypeDecl{}

vlib/v/parser/tests/sum_type_exists_err.out

@@ -1,3 +1,3 @@
-vlib/v/parser/tests/sum_type_exists_err.vv:1:6: error: cannot register sum type `Option`, another type with this name exists
+vlib/v/parser/tests/sum_type_exists_err.vv:1:1: error: cannot register sum type `Option`, another type with this name exists
     1 | type Option = string | int
-      |      ~~~~~~
+      | ~~~~~~~~~~~