bpo-42990: Introduce 'frame constructor' struct to simplify API for PyEval_CodeEval and friends (GH-24298)

* Introduce 'frame constructor' to simplify API for frame creation

* Embed struct using a macro to conform to PEP 7

Include/funcobject.h

@@ -7,6 +7,21 @@
 extern "C" {
 #endif
 
+
+#define COMMON_FIELDS(PREFIX) \
+    PyObject *PREFIX ## globals; \
+    PyObject *PREFIX ## builtins; \
+    PyObject *PREFIX ## name; \
+    PyObject *PREFIX ## qualname; \
+    PyObject *PREFIX ## code;        /* A code object, the __code__ attribute */ \
+    PyObject *PREFIX ## defaults;    /* NULL or a tuple */ \
+    PyObject *PREFIX ## kwdefaults;  /* NULL or a dict */ \
+    PyObject *PREFIX ## closure;     /* NULL or a tuple of cell objects */
+
+typedef struct {
+    COMMON_FIELDS(fc_)
+} PyFrameConstructor;
+
 /* Function objects and code objects should not be confused with each other:
  *
  * Function objects are created by the execution of the 'def' statement.
@@ -20,18 +35,12 @@ extern "C" {
 
 typedef struct {
     PyObject_HEAD
-    PyObject *func_code;        /* A code object, the __code__ attribute */
-    PyObject *func_globals;     /* A dictionary (other mappings won't do) */
-    PyObject *func_defaults;    /* NULL or a tuple */
-    PyObject *func_kwdefaults;  /* NULL or a dict */
-    PyObject *func_closure;     /* NULL or a tuple of cell objects */
+    COMMON_FIELDS(func_)
     PyObject *func_doc;         /* The __doc__ attribute, can be anything */
-    PyObject *func_name;        /* The __name__ attribute, a string object */
     PyObject *func_dict;        /* The __dict__ attribute, a dict or NULL */
     PyObject *func_weakreflist; /* List of weak references */
     PyObject *func_module;      /* The __module__ attribute, can be anything */
     PyObject *func_annotations; /* Annotations, a dict or NULL */
-    PyObject *func_qualname;    /* The qualified name */
     vectorcallfunc vectorcall;
 
     /* Invariant:
@@ -84,6 +93,9 @@ PyAPI_FUNC(PyObject *) _PyFunction_Vectorcall(
 #define PyFunction_GET_ANNOTATIONS(func) \
         (((PyFunctionObject *)func) -> func_annotations)
 
+#define PyFunction_AS_FRAME_CONSTRUCTOR(func) \
+        ((PyFrameConstructor *)&((PyFunctionObject *)(func))->func_globals)
+
 /* The classmethod and staticmethod types lives here, too */
 PyAPI_DATA(PyTypeObject) PyClassMethod_Type;
 PyAPI_DATA(PyTypeObject) PyStaticMethod_Type;