checker: disallow string(bool) (#6863)

vlib/v/checker/checker.v

@@ -3032,7 +3032,7 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) table.Type {
 				node.pos)
 		}
 	} else if node.typ == table.string_type &&
-		(from_type_sym.kind in [.any_int, .int, .byte, .byteptr] ||
+		(from_type_sym.kind in [.any_int, .int, .byte, .byteptr, .bool] ||
 		(from_type_sym.kind == .array && from_type_sym.name == 'array_byte')) {
 		type_name := c.table.type_to_str(node.expr_type)
 		c.error('cannot cast type `$type_name` to string, use `x.str()` instead', node.pos)

vlib/v/checker/tests/bool_string_cast_err.out

@@ -0,0 +1,12 @@
+vlib/v/checker/tests/bool_string_cast_err.vv:2:13: error: cannot cast type `bool` to string, use `x.str()` instead
+    1 | fn main() {
+    2 |     println(string(true))
+      |             ~~~~~~~~~~~~
+    3 |     println(string(false))
+    4 | }
+vlib/v/checker/tests/bool_string_cast_err.vv:3:13: error: cannot cast type `bool` to string, use `x.str()` instead
+    1 | fn main() {
+    2 |     println(string(true))
+    3 |     println(string(false))
+      |             ~~~~~~~~~~~~~
+    4 | }

vlib/v/checker/tests/bool_string_cast_err.vv

@@ -0,0 +1,4 @@
+fn main() {
+    println(string(true))
+    println(string(false))
+}