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bpo-34850: Emit a warning for "is" and "is not" with a literal. (GH-9642)

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Serhiy Storchaka 2019-01-18 07:47:48 +02:00 • committed by GitHub
parent e55cf024ca
commit 3bcbedc9f1
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5 changed files with 95 additions and 11 deletions
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47
Python/compile.c
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@ -2284,6 +2284,47 @@ compiler_class(struct compiler *c, stmt_ty s)
return 1;
}
/* Return 0 if the expression is a constant value except named singletons.
Return 1 otherwise. */
static int
check_is_arg(expr_ty e)
{
if (e->kind != Constant_kind) {
return 1;
}
PyObject *value = e->v.Constant.value;
return (value == Py_None
|| value == Py_False
|| value == Py_True
|| value == Py_Ellipsis);
}
/* Check operands of identity chacks ("is" and "is not").
Emit a warning if any operand is a constant except named singletons.
Return 0 on error.
*/
static int
check_compare(struct compiler *c, expr_ty e)
{
Py_ssize_t i, n;
int left = check_is_arg(e->v.Compare.left);
n = asdl_seq_LEN(e->v.Compare.ops);
for (i = 0; i < n; i++) {
cmpop_ty op = (cmpop_ty)asdl_seq_GET(e->v.Compare.ops, i);
int right = check_is_arg((expr_ty)asdl_seq_GET(e->v.Compare.comparators, i));
if (op == Is || op == IsNot) {
if (!right || !left) {
const char *msg = (op == Is)
? "\"is\" with a literal. Did you mean \"==\"?"
: "\"is not\" with a literal. Did you mean \"!=\"?";
return compiler_warn(c, msg);
}
}
left = right;
}
return 1;
}
static int
cmpop(cmpop_ty op)
{
@ -2363,6 +2404,9 @@ compiler_jump_if(struct compiler *c, expr_ty e, basicblock *next, int cond)
return 1;
}
case Compare_kind: {
if (!check_compare(c, e)) {
return 0;
}
Py_ssize_t i, n = asdl_seq_LEN(e->v.Compare.ops) - 1;
if (n > 0) {
basicblock *cleanup = compiler_new_block(c);
@ -3670,6 +3714,9 @@ compiler_compare(struct compiler *c, expr_ty e)
{
Py_ssize_t i, n;
if (!check_compare(c, e)) {
return 0;
}
VISIT(c, expr, e->v.Compare.left);
assert(asdl_seq_LEN(e->v.Compare.ops) > 0);
n = asdl_seq_LEN(e->v.Compare.ops) - 1;