py/compile: Fix async for's stack handling of iterator expression.

Prior to this fix, async for assumed the iterator expression was a simple
identifier, and used that identifier as a local to store the intermediate
iterator object.  This is incorrect behaviour.

This commit fixes the issue by keeping the iterator object on the stack as
an anonymous local variable.

Fixes issue #11511.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 20 insertions, 5 deletions

diff --git a/py/compile.c b/py/compile.c
index bb7c1117f..4f91ca49b 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -1768,18 +1768,21 @@ STATIC void compile_await_object_method(compiler_t *comp, qstr method) {
 }
 
 STATIC void compile_async_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
-    // comp->break_label |= MP_EMIT_BREAK_FROM_FOR;
-
-    qstr context = MP_PARSE_NODE_LEAF_ARG(pns->nodes[1]);
+    // Allocate labels.
     uint while_else_label = comp_next_label(comp);
     uint try_exception_label = comp_next_label(comp);
     uint try_else_label = comp_next_label(comp);
     uint try_finally_label = comp_next_label(comp);
 
+    // Stack: (...)
+
+    // Compile the iterator expression and load and call its __aiter__ method.
     compile_node(comp, pns->nodes[1]); // iterator
+    // Stack: (..., iterator)
     EMIT_ARG(load_method, MP_QSTR___aiter__, false);
+    // Stack: (..., iterator, __aiter__)
     EMIT_ARG(call_method, 0, 0, 0);
-    compile_store_id(comp, context);
+    // Stack: (..., iterable)
 
     START_BREAK_CONTINUE_BLOCK
 
@@ -1787,9 +1790,15 @@ STATIC void compile_async_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns
 
     compile_increase_except_level(comp, try_exception_label, MP_EMIT_SETUP_BLOCK_EXCEPT);
 
-    compile_load_id(comp, context);
+    EMIT(dup_top);
+    // Stack: (..., iterable, iterable)
+
+    // Compile: yield from iterable.__anext__()
     compile_await_object_method(comp, MP_QSTR___anext__);
+    // Stack: (..., iterable, yielded_value)
+
     c_assign(comp, pns->nodes[0], ASSIGN_STORE); // variable
+    // Stack: (..., iterable)
     EMIT_ARG(pop_except_jump, try_else_label, false);
 
     EMIT_ARG(label_assign, try_exception_label);
@@ -1806,6 +1815,8 @@ STATIC void compile_async_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns
     compile_decrease_except_level(comp);
     EMIT(end_except_handler);
 
+    // Stack: (..., iterable)
+
     EMIT_ARG(label_assign, try_else_label);
     compile_node(comp, pns->nodes[2]); // body
 
@@ -1817,6 +1828,10 @@ STATIC void compile_async_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns
     compile_node(comp, pns->nodes[3]); // else
 
     EMIT_ARG(label_assign, break_label);
+    // Stack: (..., iterable)
+
+    EMIT(pop_top);
+    // Stack: (...)
 }
 
 STATIC void compile_async_with_stmt_helper(compiler_t *comp, size_t n, mp_parse_node_t *nodes, mp_parse_node_t body) {