Re: [PATCH 2/3] reftable: remove unreachable "return" statements
Am 12.01.22 um 13:47 schrieb Ævar Arnfjörð Bjarmason:
Show 62 quoted lines
>
> On Tue, Jan 11 2022, Taylor Blau wrote:
>
>> On Tue, Jan 11, 2022 at 05:40:22PM +0100, Ævar Arnfjörð Bjarmason wrote:
>>> Remove unreachable return statements added in acb533440fc (reftable:
>>> implement refname validation, 2021-10-07) and f14bd719349 (reftable:
>>> write reftable files, 2021-10-07).
>>>
>>> This avoids the following warnings on SunCC 12.5 on
>>> gcc211.fsffrance.org:
>>>
>>> "reftable/refname.c", line 135: warning: statement not reached
>>> "reftable/refname.c", line 135: warning: statement not reached
>>
>> Interesting. From a cursory reading, I agree with the assessment of
>> at least my compiler that these return statements are both unnecessary,
>> but...
>>
>>> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
>>> ---
>>> reftable/refname.c | 1 -
>>> reftable/writer.c | 1 -
>>> 2 files changed, 2 deletions(-)
>>>
>>> diff --git a/reftable/refname.c b/reftable/refname.c
>>> index 95734969324..136001bc2c7 100644
>>> --- a/reftable/refname.c
>>> +++ b/reftable/refname.c
>>> @@ -132,7 +132,6 @@ static int validate_refname(const char *name)
>>> return REFTABLE_REFNAME_ERROR;
>>> name = next + 1;
>>> }
>>> - return 0;
>>> }
>>
>> In this case the loop inside of validate_refname() should always
>> terminate the function within the loop body. But removing this return
>> statement here relies on the compiler to determine that fact.
>>
>> I could well imagine on the other end of the spectrum there exists a
>> compiler which _doesn't_ make this inference pass, and would complain
>> about the opposite thing as you're reporting from SunCC (i.e., that this
>> function which returns something other than void does not have a return
>> statement outside of the loop).
>>
>> So in that sense, I disagree with the guidance of SunCC's warning. In
>> other words: by quelching this warning under one compiler, are we
>> introducing a new warning under a different/less advanced compiler?
>
> I'd think that any compiler who'd warn about this sort of thing at all
> would be able to spot constructs like this one, which are basically:
>
> while (1) {
> ...
> if (x)
> return;
> ...
> }
> return; /* unreachable */
>
> Where the elided code contains no "break", "goto" or other mechanism for
> exiting the for-loop.Why not just sidestep the problematic case:
diff --git a/reftable/refname.c b/reftable/refname.c
index 9573496932..4f89956187 100644
--- a/reftable/refname.c
+++ b/reftable/refname.c
@@ -120,17 +120,17 @@ static int modification_has_ref_with_prefix(struct modification *mod,
static int validate_refname(const char *name)
{
while (1) {
char *next = strchr(name, '/');
if (!*name) {
return REFTABLE_REFNAME_ERROR;
}
if (!next) {
- return 0;
+ break;
}
if (next - name == 0 || (next - name == 1 && *name == '.') ||
(next - name == 2 && name[0] == '.' && name[1] == '.'))
return REFTABLE_REFNAME_ERROR;
name = next + 1;
}
return 0;
}
Sure, there are returns in the loop, but they are clearly error cases.
The regular exit is now at the end of the function.
-- Hannes
Johannes Sixt <j6t@kdbg.org>