checker: disallow invalid T cast (fix #22346) (#22354)

vlib/v/checker/checker.v

@@ -3191,6 +3191,11 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		return to_type
 	}
 
+	if !c.expected_type.has_flag(.generic) && to_sym.name.len == 1
+		&& to_sym.name.starts_with_capital() {
+		c.error('unknown type `${to_sym.name}`', node.pos)
+	}
+
 	if to_sym.language != .c {
 		c.ensure_type_exists(to_type, node.pos)
 

vlib/v/checker/tests/cast_expr_T_type_err.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/cast_expr_T_type_err.vv:4:9: error: unknown type `A`
+    2 | 
+    3 | fn main() {
+    4 |     _ = A(0)
+      |         ~~~~
+    5 |     _ = &A(0)
+    6 | }
+vlib/v/checker/tests/cast_expr_T_type_err.vv:5:9: error: unknown type `A`
+    3 | fn main() {
+    4 |     _ = A(0)
+    5 |     _ = &A(0)
+      |         ~~~~~
+    6 | }

vlib/v/checker/tests/cast_expr_T_type_err.vv

@@ -0,0 +1,6 @@
+module main
+
+fn main() {
+    _ = A(0)
+    _ = &A(0)
+}

vlib/v/checker/tests/globals/cast_expr_T_type_err.out

@@ -0,0 +1,14 @@
+vlib/v/checker/tests/globals/cast_expr_T_type_err.vv:4:7: error: unknown type `A`
+    2 | 
+    3 | __global (
+    4 |     fo = A(0)
+      |          ~~~~
+    5 |     fo1 = &A(0)
+    6 | )
+vlib/v/checker/tests/globals/cast_expr_T_type_err.vv:5:8: error: unknown type `A`
+    3 | __global (
+    4 |     fo = A(0)
+    5 |     fo1 = &A(0)
+      |           ~~~~~
+    6 | )
+    7 |

vlib/v/checker/tests/globals/cast_expr_T_type_err.vv

@@ -0,0 +1,10 @@
+module main
+
+__global (
+	fo = A(0)
+	fo1 = &A(0)
+)
+
+fn main() {
+
+}