Add tests showing two bugs in tuple_infer

Summary: I noticed that tuple_infer skips using vars as hints to avoid premature pinning. Add tests showing some problems this causes.

Reviewed By: grievejia

Differential Revision: D91639156

fbshipit-source-id: 4891d9cb1f2584f5406de95546a68472c4378610

Author: rchen152

pyrefly/lib/alt/expr.rs

@@ -655,7 +655,9 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
             }
             if !nontuples.is_empty() {
                 // The non-tuple options may contain a type like Sequence[T] that provides an additional default hint.
-                // Filter out top-level Vars: they don't provide any hints, and we don't want to pin them.
+                // TODO: we filter out top-level Vars to prevent premature pinning
+                // (https://github.com/facebook/pyrefly/issues/105), but this also prevents us from picking up hints
+                // from Quantified restrictions. See test::contextual::test_sequence_hint_in_typevar_bound.
                 let nontuple_hint = self.unions(
                     nontuples
                         .into_iter()

pyrefly/lib/test/contextual.rs

@@ -660,3 +660,29 @@ x3: tuple[TD1] | tuple[TD2] = ({"y": "a"},)
 x4: tuple[TD1] | tuple[TD2, ...] = ({"x": 0}, {"y": "a"})  # E: `tuple[TD1, TD2]` is not assignable to `tuple[TD1] | tuple[TD2, ...]`
     "#,
 );
+
+testcase!(
+    bug = "`Sequence[TD]` hint should be used when typing `({'x': 0},)`",
+    test_sequence_hint_in_typevar_bound,
+    r#"
+from typing import Sequence, TypedDict
+class TD(TypedDict):
+    x: int
+def f[T: Sequence[TD]](x: T) -> T:
+    return x
+f(({"x": 0},))  # E: `tuple[dict[str, int]]` is not assignable to upper bound `Sequence[TD]`
+    "#,
+);
+
+testcase!(
+    bug = "`TD` should be used as a hint when typing `{'x': 0}`",
+    test_typed_dict_hint_in_typevar_bound,
+    r#"
+from typing import TypedDict
+class TD(TypedDict):
+    x: int
+def f[T: TD](x: tuple[T, ...]) -> T:
+    return x[0]
+f(({"x": 0},))  # E: `dict[str, int]` is not assignable to upper bound `TD`
+    "#,
+);