From bf823bc851008491d3b5c06016953a11766c2106 Mon Sep 17 00:00:00 2001
From: Yannick Jadoul <yannick.jadoul@belgacom.net>
Date: Fri, 23 Oct 2020 23:40:15 +0200
Subject: [PATCH 1/2] Add __builtins__ to globals argument of `py::exec` and
 `py::eval` if not present

---
 include/pybind11/eval.h | 15 +++++++++++++++
 tests/test_eval.cpp     |  8 ++++++++
 tests/test_eval.py      |  8 ++++++++
 3 files changed, 31 insertions(+)

diff --git a/include/pybind11/eval.h b/include/pybind11/eval.h
index 05d7bb6140..f9fcce2106 100644
--- a/include/pybind11/eval.h
+++ b/include/pybind11/eval.h
@@ -31,6 +31,15 @@ object eval(str expr, object global = globals(), object local = object()) {
     if (!local)
         local = global;
 
+#if PY_VERSION_HEX < 0x03080000
+    // Running exec and eval on Python 2 and 3 adds `builtins` module under
+    // `__builtins__` key to globals if not yet present.
+    // Python 3.8 made PyRun_String behave similarly. Let's also do that for
+    // older versions, for consistency.
+    if (!global.contains("__builtins__"))
+        global["__builtins__"] = module_::import(PYBIND11_BUILTINS_MODULE);
+#endif
+
     /* PyRun_String does not accept a PyObject / encoding specifier,
        this seems to be the only alternative */
     std::string buffer = "# -*- coding: utf-8 -*-\n" + (std::string) expr;
@@ -85,6 +94,12 @@ object eval_file(str fname, object global = globals(), object local = object())
     if (!local)
         local = global;
 
+#if PY_VERSION_HEX < 0x03080000
+    // See `eval` above.
+    if (!global.contains("__builtins__"))
+        global["__builtins__"] = module_::import(PYBIND11_BUILTINS_MODULE);
+#endif
+
     int start;
     switch (mode) {
         case eval_expr:             start = Py_eval_input;   break;
diff --git a/tests/test_eval.cpp b/tests/test_eval.cpp
index 03d0fb3666..5416c2ec4d 100644
--- a/tests/test_eval.cpp
+++ b/tests/test_eval.cpp
@@ -88,4 +88,12 @@ TEST_SUBMODULE(eval_, m) {
         }
         return false;
     });
+
+    // test_eval_empty_globals
+    m.def("eval_empty_globals", [](py::object global) {
+        if (global.is_none())
+            global = py::dict();
+        auto int_class = py::eval("isinstance(42, int)", global);
+        return global;
+    });
 }
diff --git a/tests/test_eval.py b/tests/test_eval.py
index b6f9d1881d..1bb05af05e 100644
--- a/tests/test_eval.py
+++ b/tests/test_eval.py
@@ -25,3 +25,11 @@ def test_eval_file():
     assert m.test_eval_file(filename)
 
     assert m.test_eval_file_failure()
+
+
+def test_eval_empty_globals():
+    assert "__builtins__" in m.eval_empty_globals(None)
+
+    g = {}
+    assert "__builtins__" in m.eval_empty_globals(g)
+    assert "__builtins__" in g

From 120510bbd58c7c6e6fb7041dba69ba510ac970c6 Mon Sep 17 00:00:00 2001
From: Yannick Jadoul <yannick.jadoul@belgacom.net>
Date: Tue, 27 Oct 2020 19:26:04 +0100
Subject: [PATCH 2/2] Refactor into inline ensure_builtins_in_globals function

---
 include/pybind11/eval.h | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/include/pybind11/eval.h b/include/pybind11/eval.h
index f9fcce2106..fa6b8af479 100644
--- a/include/pybind11/eval.h
+++ b/include/pybind11/eval.h
@@ -14,6 +14,22 @@
 #include "pybind11.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
+PYBIND11_NAMESPACE_BEGIN(detail)
+
+inline void ensure_builtins_in_globals(object &global) {
+    #if PY_VERSION_HEX < 0x03080000
+        // Running exec and eval on Python 2 and 3 adds `builtins` module under
+        // `__builtins__` key to globals if not yet present.
+        // Python 3.8 made PyRun_String behave similarly. Let's also do that for
+        // older versions, for consistency.
+        if (!global.contains("__builtins__"))
+            global["__builtins__"] = module_::import(PYBIND11_BUILTINS_MODULE);
+    #else
+        (void) global;
+    #endif
+}
+
+PYBIND11_NAMESPACE_END(detail)
 
 enum eval_mode {
     /// Evaluate a string containing an isolated expression
@@ -31,14 +47,7 @@ object eval(str expr, object global = globals(), object local = object()) {
     if (!local)
         local = global;
 
-#if PY_VERSION_HEX < 0x03080000
-    // Running exec and eval on Python 2 and 3 adds `builtins` module under
-    // `__builtins__` key to globals if not yet present.
-    // Python 3.8 made PyRun_String behave similarly. Let's also do that for
-    // older versions, for consistency.
-    if (!global.contains("__builtins__"))
-        global["__builtins__"] = module_::import(PYBIND11_BUILTINS_MODULE);
-#endif
+    detail::ensure_builtins_in_globals(global);
 
     /* PyRun_String does not accept a PyObject / encoding specifier,
        this seems to be the only alternative */
@@ -94,11 +103,7 @@ object eval_file(str fname, object global = globals(), object local = object())
     if (!local)
         local = global;
 
-#if PY_VERSION_HEX < 0x03080000
-    // See `eval` above.
-    if (!global.contains("__builtins__"))
-        global["__builtins__"] = module_::import(PYBIND11_BUILTINS_MODULE);
-#endif
+    detail::ensure_builtins_in_globals(global);
 
     int start;
     switch (mode) {