[cfe-users] clang-tidy bug?

[Aaron Ballman via cfe-users]

On Wed, Oct 30, 2019 at 9:23 PM David Blaikie <dblaikie at gmail.com> wrote:
>
> Two separate issues here
>
> 1) the fixit hint, as one of a set of alternatives, isn't likely to be removed/changed - the (albeit quirky) convention of using extra () to indicate an intentional assignment in a condition has been around for a while. So if you use the extra parens without writing an assignment, the compiler's going to suggest you resolve this "conflict" with the style - either you didn't intend the extra (), or you intended to use assignment. Those are the two alternative suggestions being made.
>
> 2) automatically applying one fixit hint of several ambiguous ones seems like a bug to me - Aaron - do you know anything about this? Is this accurate/intended/etc?

I also think that's a bug. It looks like it's coming from
Sema::DiagnoseEqualityWithExtraParens(). It looks like it presents
both fixits, which strikes me as a bad thing to do when automatically
applying fixits.

~Aaron

>
> On Tue, Oct 29, 2019 at 10:13 AM Robert Ankeney <rrankene at gmail.com> wrote:
>>
>> This was just a example of what I ran into when I used run-clang-tidy.py across a compilation database with a -export-fixes=fix.yaml and then ra
>>  clang-apply-replacements. Mainly I object to the suggestion+fixit to switch to an assignment. Most coding standards would disallow assignments
>> in if conditionals. If anything, I would think a suggestion of "if (true == isValid)" would be more appropriate.
>>
>> Thanks for the feedback!
>> Robert
>>
>> On Mon, Oct 28, 2019 at 2:17 PM David Blaikie <dblaikie at gmail.com> wrote:
>>>
>>> clang-tidy in the command line you gave didn't seem to modify the file for me, did it modify the file for you?
>>>
>>> Are you objecting to the suggestion, or that it was automatically applied? I would think it'd be a bug to apply any fixit/hint if there are multiple possible suggestions.
>>>
>>> But the existence of the suggestion (without the application of it) to the user seems right to me. The use of extra () to suppress the assignment-in-conditional warning (-Wparentheses) has been around for quite a while, so it's possible that the user intended assignment rather than comparison when they added the extra parentheses.
>>>
>>> - Dave
>>>
>>> On Sun, Oct 27, 2019 at 11:32 AM Robert Ankeney via cfe-users <cfe-users at lists.llvm.org> wrote:
>>>>
>>>> For the following code (wrong.cpp):
>>>>
>>>> bool check(bool isValid)
>>>> {
>>>>     bool retVal = false;
>>>>
>>>>     if (( isValid == true ))
>>>>     {
>>>>         retVal = true;
>>>>     }
>>>>
>>>>     return retVal;
>>>> }
>>>>
>>>> when I run:
>>>>     clang-tidy -checks=modernize-use-default-member-init wrong.cpp
>>>>
>>>> I get:
>>>> 4 warnings and 1 error generated.
>>>> Error while processing /llvm/match/ctBad/wrong.cpp.
>>>> /llvm/match/ctBad/wrong.cpp:5:19: error: equality comparison with extraneous parentheses [clang-diagnostic-parentheses-equality]
>>>>     if (( isValid == true ))
>>>>         ~         ^~      ~
>>>>                   =
>>>> /llvm/match/ctBad/wrong.cpp:5:19: note: remove extraneous parentheses around the comparison to silence this warning
>>>> /llvm/match/ctBad/wrong.cpp:5:19: note: use '=' to turn this equality comparison into an assignment
>>>>
>>>> Note it turns the if into:
>>>>     if ( isValid = true )
>>>>
>>>> Seems like a very bad idea. Removing the redundant parentheses seems fine, but changing the comparison to an assignment does not. Is this a bug?
>>>>
>>>> Thanks,
>>>> Robert
>>>>
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