[Python-checkins] bpo-38640: Allow break and continue in always false while loops (GH-16992)

Wed Oct 30 08:11:44 EDT 2019

https://github.com/python/cpython/commit/dcb338ea1b8f14e21dde3564658b9040df996349
commit: dcb338ea1b8f14e21dde3564658b9040df996349
branch: 3.8
author: Miss Skeleton (bot) <31488909+miss-islington at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2019年10月30日T05:11:41-07:00
summary:
bpo-38640: Allow break and continue in always false while loops (GH-16992)
(cherry picked from commit 6c3e66a34b95fff07df0ad5086104dd637a091ce)
Co-authored-by: Pablo Galindo <Pablogsal at gmail.com>
files:
A Misc/NEWS.d/next/Core and Builtins/2019-10-30-11-25-25.bpo-38640.4sAFh5.rst
M Lib/test/test_compile.py
M Python/compile.c

diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py
index 9d77f7af05d6f..566ca27fca893 100644
--- a/Lib/test/test_compile.py
+++ b/Lib/test/test_compile.py
@@ -731,6 +731,24 @@ def unused_block_while_else():
 self.assertEqual(None, opcodes[0].argval)
 self.assertEqual('RETURN_VALUE', opcodes[1].opname)
 
+ def test_false_while_loop(self):
+ def break_in_while():
+ while False:
+ break
+
+ def continue_in_while():
+ while False:
+ continue
+
+ funcs = [break_in_while, continue_in_while]
+
+ # Check that we did not raise but we also don't generate bytecode
+ for func in funcs:
+ opcodes = list(dis.get_instructions(func))
+ self.assertEqual(2, len(opcodes))
+ self.assertEqual('LOAD_CONST', opcodes[0].opname)
+ self.assertEqual(None, opcodes[0].argval)
+ self.assertEqual('RETURN_VALUE', opcodes[1].opname)
 
 class TestExpressionStackSize(unittest.TestCase):
 # These tests check that the computed stack size for a code object
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-10-30-11-25-25.bpo-38640.4sAFh5.rst b/Misc/NEWS.d/next/Core and Builtins/2019-10-30-11-25-25.bpo-38640.4sAFh5.rst
new file mode 100644
index 0000000000000..d99db3cce49a6
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-10-30-11-25-25.bpo-38640.4sAFh5.rst	
@@ -0,0 +1,3 @@
+Fixed a bug in the compiler that was causing to raise in the presence of
+break statements and continue statements inside always false while loops.
+Patch by Pablo Galindo.
diff --git a/Python/compile.c b/Python/compile.c
index a512e9cbd13a1..f09e99fd4a43d 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2736,7 +2736,15 @@ compiler_while(struct compiler *c, stmt_ty s)
 
 if (constant == 0) {
 BEGIN_DO_NOT_EMIT_BYTECODE
+ // Push a dummy block so the VISIT_SEQ knows that we are
+ // inside a while loop so it can correctly evaluate syntax
+ // errors.
+ if (!compiler_push_fblock(c, WHILE_LOOP, NULL, NULL)) {
+ return 0;
+ }
 VISIT_SEQ(c, stmt, s->v.While.body);
+ // Remove the dummy block now that is not needed.
+ compiler_pop_fblock(c, WHILE_LOOP, NULL);
 END_DO_NOT_EMIT_BYTECODE
 if (s->v.While.orelse) {
 VISIT_SEQ(c, stmt, s->v.While.orelse);
