Issue #21591: Handle exec backwards compatibility in the AST builder.

Instead of deferring until runtime. This makes sure we hit the right
conditions in dealing with unqualified exec statements.

Reviewed by Victor Stinner. Test follows in a later commit.

2 files changed, 12 insertions, 9 deletions

diff --git a/Python/ast.c b/Python/ast.c
index 80e6354..ffd5679 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -2679,6 +2679,18 @@ ast_for_exec_stmt(struct compiling *c, const node *n)
     expr1 = ast_for_expr(c, CHILD(n, 1));
     if (!expr1)
         return NULL;
+
+    if (expr1->kind == Tuple_kind && n_children < 4 &&
+        (asdl_seq_LEN(expr1->v.Tuple.elts) == 2 ||
+         asdl_seq_LEN(expr1->v.Tuple.elts) == 3)) {
+        /* Backwards compatibility: pass exec args as a tuple */
+        globals = (expr_ty) asdl_seq_GET(expr1->v.Tuple.elts, 1);
+        if (asdl_seq_LEN(expr1->v.Tuple.elts) == 3) {
+            locals = (expr_ty) asdl_seq_GET(expr1->v.Tuple.elts, 2);
+        }
+        expr1 = (expr_ty) asdl_seq_GET(expr1->v.Tuple.elts, 0);
+    }
+
     if (n_children >= 4) {
         globals = ast_for_expr(c, CHILD(n, 3));
         if (!globals)
diff --git a/Python/ceval.c b/Python/ceval.c
index e008608..38f51fa 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -4673,18 +4673,9 @@ static int
 exec_statement(PyFrameObject *f, PyObject *prog, PyObject *globals,
                PyObject *locals)
 {
-    int n;
     PyObject *v;
     int plain = 0;
 
-    if (PyTuple_Check(prog) && globals == Py_None && locals == Py_None &&
-        ((n = PyTuple_Size(prog)) == 2 || n == 3)) {
-        /* Backward compatibility hack */
-        globals = PyTuple_GetItem(prog, 1);
-        if (n == 3)
-            locals = PyTuple_GetItem(prog, 2);
-        prog = PyTuple_GetItem(prog, 0);
-    }
     if (globals == Py_None) {
         globals = PyEval_GetGlobals();
         if (locals == Py_None) {