[llvm-dev] [EXTERNAL] Re: clang-tidy: hard to repro bug in the 'modernize-use-default-member-init' check

[Oleg Smolsky via llvm-dev]

Well, I've just exported the fix with `--export-fixes` and the core data is
identical in both invocations:

Diagnostics:
  - DiagnosticName:  modernize-use-default-member-init
    DiagnosticMessage:
      Message:         'use default member initializer for ''b'''
      FilePath:        'fixed.cpp'
      FileOffset:      63
      Replacements:
        - FilePath:        'fixed.cpp'
          Offset:          44
          Length:          5
          ReplacementText: ''
        - FilePath:        'fixed.cpp'
          Offset:          64
          Length:          0
          ReplacementText: '{0}'

Yet the fix is, apparently, applied in a different way... Hmm... I've never
looked at how/where these insertions/deletions are applied. I'll have to do
some RTFM...

On Mon, Dec 6, 2021 at 5:03 PM David Blaikie <dblaikie at gmail.com> wrote:

> I'd probably start by analyzing the bug, maybe figuring out the root cause
> - then work backwards for the test case to commit along with the test.
> (figuring out the root cause might reveal easier ways to reproduce the bug,
> once it's understood)
>
> To root cause the bug, I'd try parallel debugging sessions - with and
> without a compilation DB, for instance - stepping through each, and seeing
> where the behavior diverges, and why it diverges.
>
> On Mon, Dec 6, 2021 at 3:33 PM Oleg Smolsky via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Folks, I'm trying understand a `clang-tidy` bug where the
>> 'modernize-use-default-member-init' check misbehaves on this (reduced)
>> input:
>>
>> struct Thing {
>>     Thing(int arg) : a(arg), b(0) {}
>>     int a, b;
>> };
>>
>> The check works correctly when running `clang-tidy` without a compilation
>> DB. The tool complains, but works correctly. Things also work correctly in
>> the LIT tests...
>>
>> Yet when running with a compilation DB, I get this output after fixes are
>> applied (notice the trailing comma, which makes the code ill-formed):
>>
>> struct Thing {
>>     Thing(int arg) : a(arg), {}
>>     int a, b{0};
>> };
>>
>> How do I write a unit test for this? I mean how do I create a reliable
>> repro?
>>
>> Thanks,
>> Oleg.
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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