bpo-1875: Raise SyntaxError in invalid blocks that will be optimised away (GH-13332)

miss-islington · pablogsal · web-flow · commit 85ed1712e428 · 2019-05-17T03:59:48.000-07:00
Move the check for dead conditionals (if 0) to the peephole optimizer and make sure that the code block is still compiled to report any existing syntax errors within. (cherry picked from commit af8646c) Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
@@ -650,6 +650,20 @@ def error2():
     def test_break_outside_loop(self):
         self._check_error("break", "outside loop")
 
+    def test_yield_outside_function(self):
+        self._check_error("if 0: yield",               "outside function")
+        self._check_error("class C:\n    if 0: yield", "outside function")
+
+    def test_return_outside_function(self):
+        self._check_error("if 0: return",               "outside function")
+        self._check_error("class C:\n    if 0: return", "outside function")
+
+    def test_break_outside_loop(self):
+        self._check_error("if 0: break",                "outside loop")
+
+    def test_continue_outside_loop(self):
+        self._check_error("if 0: continue",     "not properly in loop")
+
     def test_unexpected_indent(self):
         self._check_error("foo()\n bar()\n", "unexpected indent",
                           subclass=IndentationError)
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-05-15-01-29-29.bpo-1875.9oxXFX.rst b/Misc/NEWS.d/next/Core and Builtins/2019-05-15-01-29-29.bpo-1875.9oxXFX.rst
@@ -0,0 +1,3 @@
+A :exc:`SyntaxError` is now raised if a code blocks that will be optimized
+away (e.g. if conditions that are always false) contains syntax errors.
+Patch by Pablo Galindo.
diff --git a/Python/compile.c b/Python/compile.c
@@ -2301,13 +2301,12 @@ compiler_if(struct compiler *c, stmt_ty s)
         return 0;
 
     constant = expr_constant(s->v.If.test);
-    /* constant = 0: "if 0"
+    /* constant = 0: "if 0" Leave the optimizations to
+     * the pephole optimizer to check for syntax errors
+     * in the block.
      * constant = 1: "if 1", "if 2", ...
      * constant = -1: rest */
-    if (constant == 0) {
-        if (s->v.If.orelse)
-            VISIT_SEQ(c, stmt, s->v.If.orelse);
-    } else if (constant == 1) {
+    if (constant == 1) {
         VISIT_SEQ(c, stmt, s->v.If.body);
     } else {
         if (asdl_seq_LEN(s->v.If.orelse)) {
diff --git a/Python/peephole.c b/Python/peephole.c
@@ -304,11 +304,19 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
             case LOAD_CONST:
                 cumlc = lastlc + 1;
                 if (nextop != POP_JUMP_IF_FALSE  ||
-                    !ISBASICBLOCK(blocks, op_start, i + 1)  ||
-                    !PyObject_IsTrue(PyList_GET_ITEM(consts, get_arg(codestr, i))))
+                    !ISBASICBLOCK(blocks, op_start, i + 1)) {
                     break;
-                fill_nops(codestr, op_start, nexti + 1);
-                cumlc = 0;
+                }
+                PyObject* cnt = PyList_GET_ITEM(consts, get_arg(codestr, i));
+                int is_true = PyObject_IsTrue(cnt);
+                if (is_true == 1) {
+                    fill_nops(codestr, op_start, nexti + 1);
+                    cumlc = 0;
+                } else if (is_true == 0) {
+                    h = get_arg(codestr, nexti) / sizeof(_Py_CODEUNIT);
+                    tgt = find_op(codestr, codelen, h);
+                    fill_nops(codestr, op_start, tgt);
+                }
                 break;
 
                 /* Try to fold tuples of constants.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+A :exc:`SyntaxError` is now raised if a code blocks that will be optimized
	`2`	`+away (e.g. if conditions that are always false) contains syntax errors.`
	`3`	`+Patch by Pablo Galindo.`