bpo-32226: Implementation of PEP 560 (core components) (#4732)

This part of the PEP implementation adds support for
__mro_entries__ and __class_getitem__ by updating
__build_class__ and PyObject_GetItem.

1 files changed, 92 insertions, 3 deletions

diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 23d7aa4..a363211 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -37,6 +37,7 @@ _Py_IDENTIFIER(__builtins__);
 _Py_IDENTIFIER(__dict__);
 _Py_IDENTIFIER(__prepare__);
 _Py_IDENTIFIER(__round__);
+_Py_IDENTIFIER(__mro_entries__);
 _Py_IDENTIFIER(encoding);
 _Py_IDENTIFIER(errors);
 _Py_IDENTIFIER(fileno);
@@ -49,12 +50,86 @@ _Py_IDENTIFIER(stderr);
 
 #include "clinic/bltinmodule.c.h"
 
+static PyObject*
+update_bases(PyObject *bases, PyObject *const *args, int nargs)
+{
+    int i, j;
+    PyObject *base, *meth, *new_base, *result, *new_bases = NULL;
+    PyObject *stack[1] = {bases};
+    assert(PyTuple_Check(bases));
+
+    for (i = 0; i < nargs; i++) {
+        base  = args[i];
+        if (PyType_Check(base)) {
+            if (new_bases) {
+                /* If we already have made a replacement, then we append every normal base,
+                   otherwise just skip it. */
+                if (PyList_Append(new_bases, base) < 0) {
+                    goto error;
+                }
+            }
+            continue;
+        }
+        meth = _PyObject_GetAttrId(base, &PyId___mro_entries__);
+        if (!meth) {
+            if (!PyErr_ExceptionMatches(PyExc_AttributeError)) {
+                goto error;
+            }
+            PyErr_Clear();
+            if (new_bases) {
+                if (PyList_Append(new_bases, base) < 0) {
+                    goto error;
+                }
+            }
+            continue;
+        }
+        new_base = _PyObject_FastCall(meth, stack, 1);
+        Py_DECREF(meth);
+        if (!new_base) {
+            goto error;
+        }
+        if (!PyTuple_Check(new_base)) {
+            PyErr_SetString(PyExc_TypeError,
+                            "__mro_entries__ must return a tuple");
+            Py_DECREF(new_base);
+            goto error;
+        }
+        if (!new_bases) {
+            /* If this is a first successful replacement, create new_bases list and
+               copy previously encountered bases. */
+            if (!(new_bases = PyList_New(i))) {
+                goto error;
+            }
+            for (j = 0; j < i; j++) {
+                base = args[j];
+                PyList_SET_ITEM(new_bases, j, base);
+                Py_INCREF(base);
+            }
+        }
+        j = PyList_GET_SIZE(new_bases);
+        if (PyList_SetSlice(new_bases, j, j, new_base) < 0) {
+            goto error;
+        }
+        Py_DECREF(new_base);
+    }
+    if (!new_bases) {
+        return bases;
+    }
+    result = PyList_AsTuple(new_bases);
+    Py_DECREF(new_bases);
+    return result;
+
+error:
+    Py_XDECREF(new_bases);
+    return NULL;
+}
+
 /* AC: cannot convert yet, waiting for *args support */
 static PyObject *
 builtin___build_class__(PyObject *self, PyObject **args, Py_ssize_t nargs,
                         PyObject *kwnames)
 {
-    PyObject *func, *name, *bases, *mkw, *meta, *winner, *prep, *ns;
+    PyObject *func, *name, *bases, *mkw, *meta, *winner, *prep, *ns, *orig_bases;
     PyObject *cls = NULL, *cell = NULL;
     int isclass = 0;   /* initialize to prevent gcc warning */
 
@@ -75,10 +150,16 @@ builtin___build_class__(PyObject *self, PyObject **args, Py_ssize_t nargs,
                         "__build_class__: name is not a string");
         return NULL;
     }
-    bases = _PyStack_AsTupleSlice(args, nargs, 2, nargs);
-    if (bases == NULL)
+    orig_bases = _PyStack_AsTupleSlice(args, nargs, 2, nargs);
+    if (orig_bases == NULL)
         return NULL;
 
+    bases = update_bases(orig_bases, args + 2, nargs - 2);
+    if (bases == NULL) {
+        Py_DECREF(orig_bases);
+        return NULL;
+    }
+
     if (kwnames == NULL) {
         meta = NULL;
         mkw = NULL;
@@ -171,6 +252,11 @@ builtin___build_class__(PyObject *self, PyObject **args, Py_ssize_t nargs,
                              NULL, 0, NULL, 0, NULL, 0, NULL,
                              PyFunction_GET_CLOSURE(func));
     if (cell != NULL) {
+        if (bases != orig_bases) {
+            if (PyMapping_SetItemString(ns, "__orig_bases__", orig_bases) < 0) {
+                goto error;
+            }
+        }
         PyObject *margs[3] = {name, bases, ns};
         cls = _PyObject_FastCallDict(meta, margs, 3, mkw);
         if (cls != NULL && PyType_Check(cls) && PyCell_Check(cell)) {
@@ -209,6 +295,9 @@ error:
     Py_DECREF(meta);
     Py_XDECREF(mkw);
     Py_DECREF(bases);
+    if (bases != orig_bases) {
+        Py_DECREF(orig_bases);
+    }
     return cls;
 }