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

[Chris Lattner via llvm-dev]

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.

-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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