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

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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