gh-104374: Remove access to class scopes for inlined comprehensions (#104528)

Co-authored-by: Carl Meyer <carl@oddbird.net>

3 files changed, 125 insertions, 9 deletions

diff --git a/Lib/test/test_listcomps.py b/Lib/test/test_listcomps.py
index 23e1b8c..985274d 100644
--- a/Lib/test/test_listcomps.py
+++ b/Lib/test/test_listcomps.py
@@ -200,7 +200,8 @@ class ListComprehensionTest(unittest.TestCase):
             y = [g for x in [1]]
         """
         outputs = {"y": [2]}
-        self._check_in_scopes(code, outputs)
+        self._check_in_scopes(code, outputs, scopes=["module", "function"])
+        self._check_in_scopes(code, scopes=["class"], raises=NameError)
 
     def test_inner_cell_shadows_outer_redefined(self):
         code = """
@@ -328,7 +329,8 @@ class ListComprehensionTest(unittest.TestCase):
             y = [x for [x ** x for x in range(x)][x - 1] in l]
         """
         outputs = {"y": [3, 3, 3]}
-        self._check_in_scopes(code, outputs)
+        self._check_in_scopes(code, outputs, scopes=["module", "function"])
+        self._check_in_scopes(code, scopes=["class"], raises=NameError)
 
     def test_nested_3(self):
         code = """
@@ -379,6 +381,109 @@ class ListComprehensionTest(unittest.TestCase):
         with self.assertRaises(UnboundLocalError):
             f()
 
+    def test_name_error_in_class_scope(self):
+        code = """
+            y = 1
+            [x + y for x in range(2)]
+        """
+        self._check_in_scopes(code, raises=NameError, scopes=["class"])
+
+    def test_global_in_class_scope(self):
+        code = """
+            y = 2
+            vals = [(x, y) for x in range(2)]
+        """
+        outputs = {"vals": [(0, 1), (1, 1)]}
+        self._check_in_scopes(code, outputs, ns={"y": 1}, scopes=["class"])
+
+    def test_in_class_scope_inside_function_1(self):
+        code = """
+            class C:
+                y = 2
+                vals = [(x, y) for x in range(2)]
+            vals = C.vals
+        """
+        outputs = {"vals": [(0, 1), (1, 1)]}
+        self._check_in_scopes(code, outputs, ns={"y": 1}, scopes=["function"])
+
+    def test_in_class_scope_inside_function_2(self):
+        code = """
+            y = 1
+            class C:
+                y = 2
+                vals = [(x, y) for x in range(2)]
+            vals = C.vals
+        """
+        outputs = {"vals": [(0, 1), (1, 1)]}
+        self._check_in_scopes(code, outputs, scopes=["function"])
+
+    def test_in_class_scope_with_global(self):
+        code = """
+            y = 1
+            class C:
+                global y
+                y = 2
+                # Ensure the listcomp uses the global, not the value in the
+                # class namespace
+                locals()['y'] = 3
+                vals = [(x, y) for x in range(2)]
+            vals = C.vals
+        """
+        outputs = {"vals": [(0, 2), (1, 2)]}
+        self._check_in_scopes(code, outputs, scopes=["module", "class"])
+        outputs = {"vals": [(0, 1), (1, 1)]}
+        self._check_in_scopes(code, outputs, scopes=["function"])
+
+    def test_in_class_scope_with_nonlocal(self):
+        code = """
+            y = 1
+            class C:
+                nonlocal y
+                y = 2
+                # Ensure the listcomp uses the global, not the value in the
+                # class namespace
+                locals()['y'] = 3
+                vals = [(x, y) for x in range(2)]
+            vals = C.vals
+        """
+        outputs = {"vals": [(0, 2), (1, 2)]}
+        self._check_in_scopes(code, outputs, scopes=["function"])
+
+    def test_nested_has_free_var(self):
+        code = """
+            items = [a for a in [1] if [a for _ in [0]]]
+        """
+        outputs = {"items": [1]}
+        self._check_in_scopes(code, outputs, scopes=["class"])
+
+    def test_nested_free_var_not_bound_in_outer_comp(self):
+        code = """
+            z = 1
+            items = [a for a in [1] if [x for x in [1] if z]]
+        """
+        self._check_in_scopes(code, {"items": [1]}, scopes=["module", "function"])
+        self._check_in_scopes(code, {"items": []}, ns={"z": 0}, scopes=["class"])
+
+    def test_nested_free_var_in_iter(self):
+        code = """
+            items = [_C for _C in [1] for [0, 1][[x for x in [1] if _C][0]] in [2]]
+        """
+        self._check_in_scopes(code, {"items": [1]})
+
+    def test_nested_free_var_in_expr(self):
+        code = """
+            items = [(_C, [x for x in [1] if _C]) for _C in [0, 1]]
+        """
+        self._check_in_scopes(code, {"items": [(0, []), (1, [1])]})
+
+    def test_nested_listcomp_in_lambda(self):
+        code = """
+            f = [(z, lambda y: [(x, y, z) for x in [3]]) for z in [1]]
+            (z, func), = f
+            out = func(2)
+        """
+        self._check_in_scopes(code, {"z": 1, "out": [(3, 2, 1)]})
+
 
 __test__ = {'doctests' : doctests}
 
diff --git a/Python/compile.c b/Python/compile.c
index 60c845a..07f8d66 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -388,6 +388,8 @@ struct compiler_unit {
     instr_sequence u_instr_sequence; /* codegen output */
 
     int u_nfblocks;
+    int u_in_inlined_comp;
+
     struct fblockinfo u_fblock[CO_MAXBLOCKS];
 
     _PyCompile_CodeUnitMetadata u_metadata;
@@ -1290,6 +1292,7 @@ compiler_enter_scope(struct compiler *c, identifier name,
     }
 
     u->u_nfblocks = 0;
+    u->u_in_inlined_comp = 0;
     u->u_metadata.u_firstlineno = lineno;
     u->u_metadata.u_consts = PyDict_New();
     if (!u->u_metadata.u_consts) {
@@ -4137,7 +4140,7 @@ compiler_nameop(struct compiler *c, location loc,
     case OP_DEREF:
         switch (ctx) {
         case Load:
-            if (c->u->u_ste->ste_type == ClassBlock) {
+            if (c->u->u_ste->ste_type == ClassBlock && !c->u->u_in_inlined_comp) {
                 op = LOAD_FROM_DICT_OR_DEREF;
                 // First load the locals
                 if (codegen_addop_noarg(INSTR_SEQUENCE(c), LOAD_LOCALS, loc) < 0) {
@@ -4188,7 +4191,12 @@ compiler_nameop(struct compiler *c, location loc,
         break;
     case OP_NAME:
         switch (ctx) {
-        case Load: op = LOAD_NAME; break;
+        case Load:
+            op = (c->u->u_ste->ste_type == ClassBlock
+                    && c->u->u_in_inlined_comp)
+                ? LOAD_GLOBAL
+                : LOAD_NAME;
+            break;
         case Store: op = STORE_NAME; break;
         case Del: op = DELETE_NAME; break;
         }
@@ -5415,6 +5423,8 @@ push_inlined_comprehension_state(struct compiler *c, location loc,
                                  PySTEntryObject *entry,
                                  inlined_comprehension_state *state)
 {
+    int in_class_block = (c->u->u_ste->ste_type == ClassBlock) && !c->u->u_in_inlined_comp;
+    c->u->u_in_inlined_comp++;
     // iterate over names bound in the comprehension and ensure we isolate
     // them from the outer scope as needed
     PyObject *k, *v;
@@ -5426,7 +5436,7 @@ push_inlined_comprehension_state(struct compiler *c, location loc,
         // at all; DEF_LOCAL | DEF_NONLOCAL can occur in the case of an
         // assignment expression to a nonlocal in the comprehension, these don't
         // need handling here since they shouldn't be isolated
-        if (symbol & DEF_LOCAL && !(symbol & DEF_NONLOCAL)) {
+        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);
@@ -5448,8 +5458,7 @@ push_inlined_comprehension_state(struct compiler *c, location loc,
             long scope = (symbol >> SCOPE_OFFSET) & SCOPE_MASK;
             PyObject *outv = PyDict_GetItemWithError(c->u->u_ste->ste_symbols, k);
             if (outv == NULL) {
-                assert(PyErr_Occurred());
-                return ERROR;
+                outv = _PyLong_GetZero();
             }
             assert(PyLong_Check(outv));
             long outsc = (PyLong_AS_LONG(outv) >> SCOPE_OFFSET) & SCOPE_MASK;
@@ -5523,6 +5532,7 @@ static int
 pop_inlined_comprehension_state(struct compiler *c, location loc,
                                 inlined_comprehension_state state)
 {
+    c->u->u_in_inlined_comp--;
     PyObject *k, *v;
     Py_ssize_t pos = 0;
     if (state.temp_symbols) {
diff --git a/Python/symtable.c b/Python/symtable.c
index f896f7c..a319c23 100644
--- a/Python/symtable.c
+++ b/Python/symtable.c
@@ -674,8 +674,9 @@ inline_comprehension(PySTEntryObject *ste, PySTEntryObject *comp,
                 }
 
                 // free vars in comprehension that are locals in outer scope can
-                // now simply be locals, unless they are free in comp children
-                if (!is_free_in_any_child(comp, k)) {
+                // now simply be locals, unless they are free in comp children,
+                // or if the outer scope is a class block
+                if (!is_free_in_any_child(comp, k) && ste->ste_type != ClassBlock) {
                     if (PySet_Discard(comp_free, k) < 0) {
                         return 0;
                     }