test_eval: Show example of working closure (#2743)

* test_eval: Show example of working closure

* Extend test_eval_closure with weirder examples of closures for py::eval
Co-authored-by: Yannick Jadoul <yannick.jadoul@belgacom.net>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

tests/test_eval.cpp

@@ -98,4 +98,22 @@ TEST_SUBMODULE(eval_, m) {
         auto int_class = py::eval("isinstance(42, int)", global);
         return global;
     });
+
+    // test_eval_closure
+    m.def("test_eval_closure", []() {
+        py::dict global;
+        global["closure_value"] = 42;
+        py::dict local;
+        local["closure_value"] = 0;
+        py::exec(R"(
+            local_value = closure_value
+
+            def func_global():
+                return closure_value
+
+            def func_local():
+                return local_value
+            )", global, local);
+        return std::make_pair(global, local);
+    });
 }

tests/test_eval.py

@@ -33,3 +33,20 @@ def test_eval_empty_globals():
     g = {}
     assert "__builtins__" in m.eval_empty_globals(g)
     assert "__builtins__" in g
+
+
+def test_eval_closure():
+    global_, local = m.test_eval_closure()
+
+    assert global_["closure_value"] == 42
+    assert local["closure_value"] == 0
+
+    assert "local_value" not in global_
+    assert local["local_value"] == 0
+
+    assert "func_global" not in global_
+    assert local["func_global"]() == 42
+
+    assert "func_local" not in global_
+    with pytest.raises(NameError):
+        local["func_local"]()