fix new rule - legacy TypeVar not assigned to variable #3755

pyrefly/lib/alt/solve.rs

@@ -4206,6 +4206,33 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
         errors: &ErrorCollector,
     ) -> Type {
         let result = self.expr_check(e, None, errors);
+        match special_export {
+            Some(SpecialExport::TypeVar) => {
+                self.error(
+                    errors,
+                    e.range(),
+                    ErrorKind::InvalidTypeVar,
+                    "TypeVar must be assigned to a variable".to_owned(),
+                );
+            }
+            Some(SpecialExport::ParamSpec) => {
+                self.error(
+                    errors,
+                    e.range(),
+                    ErrorKind::InvalidParamSpec,
+                    "ParamSpec must be assigned to a variable".to_owned(),
+                );
+            }
+            Some(SpecialExport::TypeVarTuple) => {
+                self.error(
+                    errors,
+                    e.range(),
+                    ErrorKind::InvalidTypeVarTuple,
+                    "TypeVarTuple must be assigned to a variable".to_owned(),
+                );
+            }
+            _ => {}
+        }
         if special_export != Some(SpecialExport::AssertType)
             && let Type::ClassType(cls) = &result
             && self.is_coroutine(&result)

pyrefly/lib/test/generic_legacy.rs

@@ -292,6 +292,16 @@ Ts = TypeVarTuple(name = "Ts")
     "#,
 );
 
+testcase!(
+    test_tvar_bare_call,
+    r#"
+from typing import TypeVar, ParamSpec, TypeVarTuple
+TypeVar("T")  # E: TypeVar must be assigned to a variable
+ParamSpec("P")  # E: ParamSpec must be assigned to a variable
+TypeVarTuple("Ts")  # E: TypeVarTuple must be assigned to a variable
+    "#,
+);
+
 testcase!(
     test_tvar_unexpected_keyword,
     r#"

pyrefly/lib/test/simple.rs

@@ -1921,7 +1921,7 @@ testcase!(
     test_crash_on_decorator_assign,
     r#"
 from typing import TypeVar
-@T=TypeVar()  # E: Expected newline, found `=` # E: Missing argument `name`
+@T=TypeVar()  # E: Expected newline, found `=` # E: TypeVar must be assigned to a variable # E: Missing argument `name`
 "#,
 );