linting GHC

[Hécate]

Hi Richard, thanks for your questions! I'll answer them below:

 > […] and I somehow know (though I forget where I learned it)

You can find a summary of the available linting (with HLint) Hadrian 
rules here: 
https://gitlab.haskell.org/ghc/ghc/-/wikis/contributing#working-conventions

 > I introduced one of these errors, in GHC.Tc.Utils.Unify; the other 
errors are in files I have not modified. Will these affect CI?

How old is your latest sync with upstream/master? Maybe these lints have 
been corrected after your last pull?

 > Hadrian crashes at the end. Is that expected? It says "system command 
failed" with a bunch of gobbledegook. Is this an error within Hadrian?

It's Hadrian's way to exit with a non-0 code and give us some info about 
what went wrong

 >  Are these colors configurable?

Not to my knowledge. Until NO_COLOR or more colour schemes are 
implemented in HLint, you can use this (sad) workaround:

```
TERM=dumb hadrian/build -j lint:compiler
```
which remove all the colours from the output.


Hope this helps, sorry for the confusion.

Cheers,

Hécate

Le 30/04/2021 à 22:12, Richard Eisenberg a écrit :
> Hi devs,
>
> I see in CI that we're now linting the GHC source code. In order to 
> avoid CI failure, I would like to lint locally, and I somehow know 
> (though I forget where I learned it) that hadrian/build lint:compiler 
> is the way to do this. After building hlint, I am able to do this. But 
> the output is surprising; here is the tail:
>
> # hlint (for lint:compiler)
> compiler/GHC/Tc/Utils/Unify.hs:2:1-36: Warning: Unused LANGUAGE pragma
> Found:
> {-# LANGUAGE MultiWayIf #-}
> Perhaps you should remove it.
>
> compiler/stage1/build/GHC/Parser.hs:6:1-29: Warning: Unused LANGUAGE 
> pragma
> Found:
> {-# LANGUAGE ViewPatterns #-}
> Perhaps you should remove it.
>
> compiler/stage1/build/GHC/Parser.hs:8:1-27: Warning: Unused LANGUAGE 
> pragma
> Found:
> {-# LANGUAGE LambdaCase #-}
> Perhaps you should remove it.
>
> compiler/stage1/build/GHC/Parser.hs:38:1-54: Warning: Use fewer imports
> Found:
> import Control.Monad ( unless, liftM, when,(<=<))
> import Control.Monad ( ap )
>
> Perhaps:
> import Control.Monad ( unless, liftM, when,(<=<), ap )
>
>
> compiler/stage1/build/GHC/Parser.hs:43:1-18: Warning: Use fewer imports
> Found:
> import GHC.Prelude
> import GHC.Prelude
>
> Perhaps:
> import GHC.Prelude
>
>
> compiler/stage1/build/GHC/Cmm/Parser.hs:17:1-24: Warning: Use fewer 
> imports
> Found:
> import GHC.StgToCmm.Prof
> import GHC.StgToCmm.Prof
>
> Perhaps:
> import GHC.StgToCmm.Prof
>
>
> compiler/stage1/build/GHC/Cmm/Parser.hs:71:1-20: Warning: Use fewer 
> imports
> Found:
> import Control.Monad
> import Control.Monad ( ap )
>
> Perhaps:
> import Control.Monad
>
>
> compiler/stage2/build/GHC/Parser.hs:6:1-29: Warning: Unused LANGUAGE 
> pragma
> Found:
> {-# LANGUAGE ViewPatterns #-}
> Perhaps you should remove it.
>
> compiler/stage2/build/GHC/Parser.hs:8:1-27: Warning: Unused LANGUAGE 
> pragma
> Found:
> {-# LANGUAGE LambdaCase #-}
> Perhaps you should remove it.
>
> compiler/stage2/build/GHC/Parser.hs:38:1-54: Warning: Use fewer imports
> Found:
> import Control.Monad ( unless, liftM, when,(<=<))
> import Control.Monad ( ap )
>
> Perhaps:
> import Control.Monad ( unless, liftM, when,(<=<), ap )
>
>
> compiler/stage2/build/GHC/Parser.hs:43:1-18: Warning: Use fewer imports
> Found:
> import GHC.Prelude
> import GHC.Prelude
>
> Perhaps:
> import GHC.Prelude
>
>
> compiler/stage2/build/GHC/Cmm/Parser.hs:17:1-24: Warning: Use fewer 
> imports
> Found:
> import GHC.StgToCmm.Prof
> import GHC.StgToCmm.Prof
>
> Perhaps:
> import GHC.StgToCmm.Prof
>
>
> compiler/stage2/build/GHC/Cmm/Parser.hs:71:1-20: Warning: Use fewer 
> imports
> Found:
> import Control.Monad
> import Control.Monad ( ap )
>
> Perhaps:
> import Control.Monad
>
>
> 13 hints
> Error when running Shake build system:
>   at want, called at src/Main.hs:104:30 in main:Main
> * Depends on: lint:compiler
>   at cmd_, called at src/Rules/Lint.hs:70:3 in main:Rules.Lint
> * Raised the exception:
> Development.Shake.cmd, system command failed
> Command line: hlint -j --cpp-define x86_64_HOST_ARCH 
> --cpp-include=includes --cpp-include=_build/stage1/lib 
> --cpp-include=compiler --cpp-include=_build/stage1/lib/ghcplatform.h 
> --cpp-include=_build/stage1/compiler/build -h compiler/.hlint.yaml 
> compiler
> Exit code: 1
> Stderr:
>
> There are several curiosities here:
>
> * I introduced one of these errors, in GHC.Tc.Utils.Unify; the other 
> errors are in files I have not modified. Will these affect CI?
> * Hadrian crashes at the end. Is that expected? It says "system 
> command failed" with a bunch of gobbledegook. Is this an error within 
> Hadrian? Or is this just Hadrian's way of saying that it encountered 
> an error when linting? If it's the latter, the current message is hard 
> to read.
> * As you may be able to see, I use a dark-background terminal window. 
> The colors output by the hlint process are nigh impossible to read 
> when describing redundant LANGUAGE pragmas. Are these colors configurable?
>
> Thanks!
> Richard
>
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