gh-142829: Add test for __hash__ re-entrancy in Context comparison

Author: Abdoulrasheed

Lib/test/test_context.py

@@ -570,6 +570,22 @@ def __eq__(self, other):
         ctx2.run(var.set, object())
         ctx1 == ctx2
 
+    def test_context_eq_reentrant_contextvar_set_in_hash(self):
+        var = contextvars.ContextVar("v")
+        ctx1 = contextvars.Context()
+        ctx2 = contextvars.Context()
+
+        class ReentrantHash:
+            def __hash__(self):
+                ctx1.run(lambda: var.set(object()))
+                return 0
+            def __eq__(self, other):
+                return isinstance(other, ReentrantHash)
+
+        ctx1.run(var.set, ReentrantHash())
+        ctx2.run(var.set, ReentrantHash())
+        ctx1 == ctx2
+
 
 # HAMT Tests