bpo-36052: Raise a SyntaxError when assigning a value to __debug__ with := (GH-11958)

matrixise · pablogsal · commit 3ad91673057d · 2019-02-21T10:11:53.000Z
Trying to assign a value to __debug__ using the assignment operator is supposed to fail, but
a missing check for forbidden names when setting the context in the ast was preventing this behaviour.
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
@@ -51,6 +51,10 @@
 Traceback (most recent call last):
 SyntaxError: cannot assign to __debug__
 
+>>> (__debug__ := 1)
+Traceback (most recent call last):
+SyntaxError: cannot assign to __debug__
+
 >>> f() = 1
 Traceback (most recent call last):
 SyntaxError: cannot assign to function call
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-02-20-17-57-31.bpo-36052.l8lJSi.rst b/Misc/NEWS.d/next/Core and Builtins/2019-02-20-17-57-31.bpo-36052.l8lJSi.rst
@@ -0,0 +1,2 @@
+Raise a :exc:`SyntaxError` when assigning a value to `__debug__` with the
+Assignment Operator. Contributed by Stéphane Wirtel and Pablo Galindo.
diff --git a/Python/ast.c b/Python/ast.c
@@ -1084,7 +1084,7 @@ set_context(struct compiling *c, expr_ty e, expr_context_ty ctx, const node *n)
                 return 0;
             break;
         case Name_kind:
-            if (ctx == Store) {
+            if (ctx == Store || ctx == NamedStore) {
                 if (forbidden_name(c, e->v.Name.id, n, 0))
                     return 0; /* forbidden_name() calls ast_error() */
             }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Raise a :exc:`SyntaxError` when assigning a value to `__debug__` with the
	`2`	`+Assignment Operator. Contributed by Stéphane Wirtel and Pablo Galindo.`
Original file line number	Diff line number	Diff line change
`@@ -1084,7 +1084,7 @@ set_context(struct compiling c, expr_ty e, expr_context_ty ctx, const node n)`
`1084`	`1084`	`return 0;`
`1085`	`1085`	`break;`
`1086`	`1086`	`case Name_kind:`
`1087`		`- if (ctx == Store) {`
	`1087`	`+ if (ctx == Store \|\| ctx == NamedStore) {`
`1088`	`1088`	`if (forbidden_name(c, e->v.Name.id, n, 0))`
`1089`	`1089`	`return 0; /* forbidden_name() calls ast_error() */`
`1090`	`1090`	`}`