gh-108308: Replace PyDict_GetItem() with PyDict_GetItemRef()

Replace PyDict_GetItem() calls with PyDict_GetItemRef() to handle
errors.

pycore_init_builtins() now checks for _PyType_Lookup() failure.

Python/assemble.c

@@ -466,7 +466,7 @@ dict_keys_inorder(PyObject *dict, Py_ssize_t offset)
 extern void _Py_set_localsplus_info(int, PyObject *, unsigned char,
                                    PyObject *, PyObject *);
 
-static void
+static int
 compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
                         PyObject *names, PyObject *kinds)
 {
@@ -481,7 +481,11 @@ compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
         if (PyDict_Contains(umd->u_fasthidden, k)) {
             kind |= CO_FAST_HIDDEN;
         }
-        if (PyDict_GetItem(umd->u_cellvars, k) != NULL) {
+        int has_cell = PyDict_Contains(umd->u_cellvars, k);
+        if (has_cell < 0) {
+            return -1;
+        }
+        if (has_cell) {
             kind |= CO_FAST_CELL;
         }
         _Py_set_localsplus_info(offset, k, kind, names, kinds);
@@ -492,7 +496,11 @@ compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
     int numdropped = 0;
     pos = 0;
     while (PyDict_Next(umd->u_cellvars, &pos, &k, &v)) {
-        if (PyDict_GetItem(umd->u_varnames, k) != NULL) {
+        int has_name = PyDict_Contains(umd->u_varnames, k);
+        if (has_name < 0) {
+            return -1;
+        }
+        if (has_name) {
             // Skip cells that are already covered by locals.
             numdropped += 1;
             continue;
@@ -512,6 +520,7 @@ compute_localsplus_info(_PyCompile_CodeUnitMetadata *umd, int nlocalsplus,
         assert(offset < nlocalsplus);
         _Py_set_localsplus_info(offset, k, CO_FAST_FREE, names, kinds);
     }
+    return 0;
 }
 
 static PyCodeObject *
@@ -556,7 +565,10 @@ makecode(_PyCompile_CodeUnitMetadata *umd, struct assembler *a, PyObject *const_
     if (localspluskinds == NULL) {
         goto error;
     }
-    compute_localsplus_info(umd, nlocalsplus, localsplusnames, localspluskinds);
+    if (compute_localsplus_info(umd, nlocalsplus,
+                                localsplusnames, localspluskinds) < 0) {
+        goto error;
+    }
 
     struct _PyCodeConstructor con = {
         .filename = filename,

Python/compile.c

@@ -4194,9 +4194,20 @@ compiler_nameop(struct compiler *c, location loc,
         optype = OP_DEREF;
         break;
     case LOCAL:
-        if (_PyST_IsFunctionLike(c->u->u_ste) ||
-                (PyDict_GetItem(c->u->u_metadata.u_fasthidden, mangled) == Py_True))
+        if (_PyST_IsFunctionLike(c->u->u_ste)) {
             optype = OP_FAST;
+        }
+        else {
+            PyObject *item;
+            if (PyDict_GetItemRef(c->u->u_metadata.u_fasthidden, mangled,
+                                  &item) < 0) {
+                return ERROR;
+            }
+            if (item == Py_True) {
+                optype = OP_FAST;
+            }
+            Py_XDECREF(item);
+        }
         break;
     case GLOBAL_IMPLICIT:
         if (_PyST_IsFunctionLike(c->u->u_ste))
@@ -5518,8 +5529,13 @@ push_inlined_comprehension_state(struct compiler *c, location loc,
         if ((symbol & DEF_LOCAL && !(symbol & DEF_NONLOCAL)) || in_class_block) {
             if (!_PyST_IsFunctionLike(c->u->u_ste)) {
                 // non-function scope: override this name to use fast locals
-                PyObject *orig = PyDict_GetItem(c->u->u_metadata.u_fasthidden, k);
-                if (orig != Py_True) {
+                PyObject *orig;
+                if (PyDict_GetItemRef(c->u->u_metadata.u_fasthidden, k, &orig) < 0) {
+                    return ERROR;
+                }
+                int orig_is_true = (orig == Py_True);
+                Py_XDECREF(orig);
+                if (!orig_is_true) {
                     if (PyDict_SetItem(c->u->u_metadata.u_fasthidden, k, Py_True) < 0) {
                         return ERROR;
                     }

Python/flowgraph.c

@@ -2404,12 +2404,16 @@ build_cellfixedoffsets(_PyCompile_CodeUnitMetadata *umd)
     PyObject *varname, *cellindex;
     Py_ssize_t pos = 0;
     while (PyDict_Next(umd->u_cellvars, &pos, &varname, &cellindex)) {
-        PyObject *varindex = PyDict_GetItem(umd->u_varnames, varname);
+        PyObject *varindex;
+        if (PyDict_GetItemRef(umd->u_varnames, varname, &varindex) < 0) {
+            return NULL;
+        }
         if (varindex != NULL) {
             assert(PyLong_AS_LONG(cellindex) < INT_MAX);
             assert(PyLong_AS_LONG(varindex) < INT_MAX);
             int oldindex = (int)PyLong_AS_LONG(cellindex);
             int argoffset = (int)PyLong_AS_LONG(varindex);
+            Py_DECREF(varindex);
             fixed[oldindex] = argoffset;
         }
     }

Python/pylifecycle.c

@@ -762,18 +762,32 @@ pycore_init_builtins(PyThreadState *tstate)
     }
     interp->builtins = Py_NewRef(builtins_dict);
 
-    PyObject *isinstance = PyDict_GetItem(builtins_dict, &_Py_ID(isinstance));
-    assert(isinstance);
+    PyObject *isinstance;
+    if (PyDict_GetItemRef(builtins_dict, &_Py_ID(isinstance), &isinstance) != 1) {
+        goto error;
+    }
     interp->callable_cache.isinstance = isinstance;
-    PyObject *len = PyDict_GetItem(builtins_dict, &_Py_ID(len));
-    assert(len);
+    Py_DECREF(isinstance);
+
+    PyObject *len;
+    if (PyDict_GetItemRef(builtins_dict, &_Py_ID(len), &len) != 1) {
+        goto error;
+    }
     interp->callable_cache.len = len;
+    Py_DECREF(len);
+
     PyObject *list_append = _PyType_Lookup(&PyList_Type, &_Py_ID(append));
-    assert(list_append);
+    if (list_append == NULL) {
+        goto error;
+    }
     interp->callable_cache.list_append = list_append;
+
     PyObject *object__getattribute__ = _PyType_Lookup(&PyBaseObject_Type, &_Py_ID(__getattribute__));
-    assert(object__getattribute__);
+    if (object__getattribute__ == NULL) {
+        goto error;
+    }
     interp->callable_cache.object__getattribute__ = object__getattribute__;
+
     if (_PyBuiltins_AddExceptions(bimod) < 0) {
         return _PyStatus_ERR("failed to add exceptions to builtins");
     }