[llvm-dev] [RFC] FileCheck: (dis)allowing unused prefixes

[Johannes Doerfert via llvm-dev]

On 10/29/20 1:40 PM, Chris Lattner via llvm-dev wrote:
> On Oct 29, 2020, at 10:28 AM, Mircea Trofin via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> Hello all,
>>
>> TL;DR; if you used FileCheck --check-prefixes and you missed (misspelled, for instance) one of the prefixes in your test, FileCheck silently ignores that and the test passes.
>>
>> 1579 tests have this property.
> Wow, that is quite a “whoops”.  Thank you for catching this, your plan sounds really great.

It has yet to be seen how many are actual "bugs" or "oversights" vs. 
intentional.
We should try to track that as well ;)

~ Johannes


> -Chris
>
>
>>
>> The details
>> =========
>> Please refer to https://reviews.llvm.org/D90281 <https://reviews.llvm.org/D90281> and the discussion there for more details (make sure you open "older changes" for full context)
>>
>> The problem is covered by the TL;DR;.
>>
>> The proposal is to add an explicit flag to FileCheck, --allow-unused-prefixes, to indicate whether the current behavior is intended (for instance, jdoerfert contributed a scenario where that is the case).
>>
>> We want the default behavior to be 'strict', i.e. --allow-unused-prefixes=false. Doing that right now would lead to 1500 test failures.
>>
>> To get there (thanks, maskray, for suggestion), we propose we:
>> * land D90281 where the flag is introduced, but is flipped to match today's behavior
>> * employ a 'busy beavers' approach, where test maintainers patch their tests:
>>    - either leveraging the flag, to explicitly indicate that unused prefixes is intended (i.e. add --allow-unused-patches=true); or
>>    - fix the test (e.g. maybe there was a misspelling issue/omission/etc).
>>
>> A spreadsheet with the failing tests is available here <https://docs.google.com/spreadsheets/d/1o6q3XH1n3DDyyccnYZ_kVfhFbTDzC_S09e973_cwYuw/edit?usp=sharing> [1].
>>
>> The request to the community members is to please sign up for their respective area in the spreadsheet, and then mark it completed when that's the case (yes/no in the respective column).
>>
>> When all the tests are fixed, we will then flip --allow-unused-prefixes to false by default.
>>
>> Meanwhile, please consider leveraging the flag explicitly when you author new tests that use --check-prefixes. That can be then cleaned up easily after we switch to the 'strict' behavior.
>>
>> Thanks!
>>
>> [1] https://docs.google.com/spreadsheets/d/1o6q3XH1n3DDyyccnYZ_kVfhFbTDzC_S09e973_cwYuw/edit?usp=sharing <https://docs.google.com/spreadsheets/d/1o6q3XH1n3DDyyccnYZ_kVfhFbTDzC_S09e973_cwYuw/edit?usp=sharing>_______________________________________________
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