checker: fix sum type operator check (#6815)

vlib/v/checker/checker.v

@@ -861,6 +861,12 @@ pub fn (mut c Checker) infix_expr(mut infix_expr ast.InfixExpr) table.Type {
 		c.error('string types only have the following operators defined: `==`, `!=`, `<`, `>`, `<=`, `>=`, and `+`',
 			infix_expr.pos)
 	}
+	// sum types can't have any infix operation except of "is", is is checked before and doesn't reach this
+	if c.table.type_kind(left_type) == .union_sum_type {
+		c.error('cannot use operator `$infix_expr.op` with `$left.name`', infix_expr.pos)
+	} else if c.table.type_kind(right_type) == .union_sum_type {
+		c.error('cannot use operator `$infix_expr.op` with `$right.name`', infix_expr.pos)
+	}
 	// Dual sides check (compatibility check)
 	if !c.symmetric_check(right_type, left_type) && !c.pref.translated {
 		// for type-unresolved consts

vlib/v/checker/tests/sum_type_infix_err.out

@@ -0,0 +1,14 @@
+vlib/v/checker/tests/sum_type_infix_err.vv:5:9: error: cannot use operator `+` with `Abc`
+    3 | fn main() {
+    4 |     x := Abc(0)
+    5 |     _ := x + Abc(5)
+      |            ^
+    6 |     _ := 'test' + x
+    7 |     _ = unsafe{&x + 5}
+vlib/v/checker/tests/sum_type_infix_err.vv:6:14: error: cannot use operator `+` with `Abc`
+    4 |     x := Abc(0)
+    5 |     _ := x + Abc(5)
+    6 |     _ := 'test' + x
+      |                 ^
+    7 |     _ = unsafe{&x + 5}
+    8 | }

vlib/v/checker/tests/sum_type_infix_err.vv

@@ -0,0 +1,8 @@
+__type Abc = int | string
+
+fn main() {
+	x := Abc(0)
+	_ := x + Abc(5)
+	_ := 'test' + x
+	_ = unsafe{&x + 5}
+}

vlib/v/checker/tests/sum_type_mutable_cast_err.out

@@ -1,18 +1,18 @@
-vlib/v/checker/tests/sum_type_mutable_cast_err.vv:23:10: error: infix expr: cannot use `any_int` (right expression) as `Abc`
+vlib/v/checker/tests/sum_type_mutable_cast_err.vv:23:10: error: cannot use operator `+` with `Abc`
    21 |     mut x := Abc(0)
    22 |     if x is int {
    23 |         _ := x + 5
       |                ^
    24 |     }
    25 |     f := Foo{Bar{Abc(0)}}
-vlib/v/checker/tests/sum_type_mutable_cast_err.vv:27:14: error: infix expr: cannot use `any_int` (right expression) as `Abc`
+vlib/v/checker/tests/sum_type_mutable_cast_err.vv:27:14: error: cannot use operator `+` with `Abc`
    25 |     f := Foo{Bar{Abc(0)}}
    26 |     if f.b.a is int {
    27 |         _ := f.b.a + 5
       |                    ^
    28 |     }
    29 |     mut f2 := Foo2{Bar2{Abc(0)}}
-vlib/v/checker/tests/sum_type_mutable_cast_err.vv:31:14: error: infix expr: cannot use `any_int` (right expression) as `Abc`
+vlib/v/checker/tests/sum_type_mutable_cast_err.vv:31:14: error: cannot use operator `+` with `Abc`
    29 |     mut f2 := Foo2{Bar2{Abc(0)}}
    30 |     if f2.b.a is int {
    31 |         _ := f.b.a + 5

vlib/v/table/atypes.v

@@ -26,7 +26,9 @@ pub enum Language {
 
 // Represents a type that only needs an identifier, e.g. int, array_int.
 // A pointer type `&T` would have a TypeSymbol `T`.
-// Note: For a Type, use Table.type_to_str(typ) not TypeSymbol.name.
+// Note: For a Type, use:
+// * Table.type_to_str(typ) not TypeSymbol.name.
+// * Table.type_kind(typ) not TypeSymbol.kind.
 // Each TypeSymbol is entered into `Table.types`.
 // See also: Table.get_type_symbol.
 pub struct TypeSymbol {
@@ -363,6 +365,14 @@ pub:
 	func     Fn
 }
 
+// returns TypeSymbol kind only if there are no type modifiers
+pub fn (table &Table) type_kind(typ Type) Kind {
+	if typ.nr_muls() > 0 || typ.has_flag(.optional) {
+		return Kind.placeholder
+	}
+	return table.get_type_symbol(typ).kind
+}
+
 pub enum Kind {
 	placeholder
 	void