checker: fix sumtype comparison and sumtype in itself (#9917)

vlib/v/ast/ast.v

@@ -29,7 +29,7 @@ pub type ScopeObject = AsmRegister | ConstField | GlobalField | Var
 // TODO: replace Param
 pub type Node = CallArg | ConstField | EmptyNode | EnumField | Expr | File | GlobalField |
 	IfBranch | MatchBranch | NodeError | Param | ScopeObject | SelectBranch | Stmt | StructField |
-	StructInitField | SumTypeVariant
+	StructInitField
 
 pub struct TypeNode {
 pub:
@@ -952,13 +952,7 @@ pub:
 	comments []Comment
 	typ      Type
 pub mut:
-	variants []SumTypeVariant
-}
-
-pub struct SumTypeVariant {
-pub:
-	typ Type
-	pos token.Position
+	variants []TypeNode
 }
 
 pub struct FnTypeDecl {
@@ -1661,8 +1655,7 @@ pub fn (node Node) position() token.Position {
 		StructField {
 			return node.pos.extend(node.type_pos)
 		}
-		MatchBranch, SelectBranch, EnumField, ConstField, StructInitField, GlobalField, CallArg,
-		SumTypeVariant {
+		MatchBranch, SelectBranch, EnumField, ConstField, StructInitField, GlobalField, CallArg {
 			return node.pos
 		}
 		Param {
@@ -1810,7 +1803,7 @@ pub fn (node Node) children() []Node {
 			}
 			TypeDecl {
 				if node is SumTypeDecl {
-					children << node.variants.map(Node(it))
+					children << node.variants.map(Node(Expr(it)))
 				}
 			}
 			else {}

vlib/v/checker/checker.v

@@ -350,6 +350,9 @@ pub fn (mut c Checker) sum_type_decl(node ast.SumTypeDecl) {
 		} else if sym.kind == .interface_ {
 			c.error('sum type cannot hold an interface', variant.pos)
 		}
+		if sym.name.trim_prefix(sym.mod + '.') == node.name {
+			c.error('sum type cannot hold itself', variant.pos)
+		}
 		names_used << sym.name
 	}
 }
@@ -1109,7 +1112,8 @@ pub fn (mut c Checker) infix_expr(mut infix_expr ast.InfixExpr) ast.Type {
 		c.error('unwrapped optional cannot be used in an infix expression', left_right_pos)
 	}
 	// Dual sides check (compatibility check)
-	if !c.symmetric_check(right_type, left_type) && !c.pref.translated {
+	if !(c.symmetric_check(left_type, right_type) && c.symmetric_check(right_type, left_type))
+		&& !c.pref.translated {
 		// for type-unresolved consts
 		if left_type == ast.void_type || right_type == ast.void_type {
 			return ast.void_type

vlib/v/checker/tests/sumtype_in_sumtype_err.out

@@ -0,0 +1,3 @@
+vlib/v/checker/tests/sumtype_in_sumtype_err.vv:1:11: error: sum type cannot hold itself
+    1 | type AA = AA | int
+      |           ~~

vlib/v/checker/tests/sumtype_in_sumtype_err.vv

@@ -0,0 +1 @@
+type AA = AA | int

vlib/v/checker/tests/sumtype_mismatched_type.out

@@ -0,0 +1,5 @@
+vlib/v/checker/tests/sumtype_mismatched_type.vv:4:8: error: infix expr: cannot use `int literal` (right expression) as `AA`
+    2 | 
+    3 | a := AA(3)
+    4 | assert a == 3
+      |        ~~~~~~

vlib/v/checker/tests/sumtype_mismatched_type.vv

@@ -0,0 +1,4 @@
+type AA = int | string
+
+a := AA(3)
+assert a == 3

vlib/v/parser/parser.v

@@ -2987,7 +2987,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 			decl_pos)
 		return ast.FnTypeDecl{}
 	}
-	mut sum_variants := []ast.SumTypeVariant{}
+	mut sum_variants := []ast.TypeNode{}
 	p.check(.assign)
 	mut type_pos := p.tok.position()
 	mut comments := []ast.Comment{}
@@ -3012,7 +3012,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		mut type_end_pos := p.prev_tok.position()
 		type_pos = type_pos.extend(type_end_pos)
 		p.next()
-		sum_variants << ast.SumTypeVariant{
+		sum_variants << {
 			typ: first_type
 			pos: type_pos
 		}
@@ -3024,7 +3024,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 			prev_tok := p.prev_tok
 			type_end_pos = prev_tok.position()
 			type_pos = type_pos.extend(type_end_pos)
-			sum_variants << ast.SumTypeVariant{
+			sum_variants << {
 				typ: variant_type
 				pos: type_pos
 			}