gh-119180: Improvements to ForwardRef.evaluate (#122210)

Noticed some issues while writing documentation for this method.

1 files changed, 41 insertions, 1 deletions

diff --git a/Lib/test/test_annotationlib.py b/Lib/test/test_annotationlib.py
index e4dcdb6b58d..db8350c2746 100644
--- a/Lib/test/test_annotationlib.py
+++ b/Lib/test/test_annotationlib.py
@@ -5,7 +5,7 @@ import functools
 import itertools
 import pickle
 import unittest
-from annotationlib import Format, get_annotations, get_annotate_function
+from annotationlib import Format, ForwardRef, get_annotations, get_annotate_function
 from typing import Unpack
 
 from test.test_inspect import inspect_stock_annotations
@@ -250,6 +250,46 @@ class TestForwardRefClass(unittest.TestCase):
             with self.assertRaises(TypeError):
                 pickle.dumps(fr, proto)
 
+    def test_evaluate_with_type_params(self):
+        class Gen[T]:
+            alias = int
+
+        with self.assertRaises(NameError):
+            ForwardRef("T").evaluate()
+        with self.assertRaises(NameError):
+            ForwardRef("T").evaluate(type_params=())
+        with self.assertRaises(NameError):
+            ForwardRef("T").evaluate(owner=int)
+
+        T, = Gen.__type_params__
+        self.assertIs(ForwardRef("T").evaluate(type_params=Gen.__type_params__), T)
+        self.assertIs(ForwardRef("T").evaluate(owner=Gen), T)
+
+        with self.assertRaises(NameError):
+            ForwardRef("alias").evaluate(type_params=Gen.__type_params__)
+        self.assertIs(ForwardRef("alias").evaluate(owner=Gen), int)
+        # If you pass custom locals, we don't look at the owner's locals
+        with self.assertRaises(NameError):
+            ForwardRef("alias").evaluate(owner=Gen, locals={})
+        # But if the name exists in the locals, it works
+        self.assertIs(
+            ForwardRef("alias").evaluate(owner=Gen, locals={"alias": str}), str
+        )
+
+    def test_fwdref_with_module(self):
+        self.assertIs(ForwardRef("Format", module=annotationlib).evaluate(), Format)
+
+        with self.assertRaises(NameError):
+            # If globals are passed explicitly, we don't look at the module dict
+            ForwardRef("Format", module=annotationlib).evaluate(globals={})
+
+    def test_fwdref_value_is_cached(self):
+        fr = ForwardRef("hello")
+        with self.assertRaises(NameError):
+            fr.evaluate()
+        self.assertIs(fr.evaluate(globals={"hello": str}), str)
+        self.assertIs(fr.evaluate(), str)
+
 
 class TestGetAnnotations(unittest.TestCase):
     def test_builtin_type(self):