HLint as a GHC source plugin.
|Version on this page:||18.104.22.168|
|LTS Haskell 19.33:||22.214.171.124|
|Stackage Nightly 2022-09-21:||126.96.36.199|
|Latest on Hackage:||188.8.131.52|
Module documentation for 184.108.40.206
Splint makes HLint 3 available as a GHC source plugin. It is similar to hlint-source-plugin by Ollie Charles, except that it doesn’t have to re-parse the module in order to lint it.
To use Splint, pass
-fplugin=Splint to GHC. Any ideas suggested by HLint will
be reported as warnings by GHC. For example, if you define
main = print . concat $ map pure [ 'a' .. 'z' ]
You would expect HLint to tell you to use
concatMap. Normally you would need
to both compile your module with GHC and lint it with HLint. However with
Splint you can compile it and get suggestions from HLint all at once by
ghc -fplugin=Splint Main.hs
Among all the usual output from GHC, you should see this new warning:
Main.hs:1:8: warning: Use concatMap Perhaps: print (concatMap pure ['a' .. 'z']) | 1 | main = print . concat $ map pure [ 'a' .. 'z' ] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
And that’s all there is to it! HLint suggestions as part of your normal build process. What a time to be alive.
If you want to pass arguments through to HLint, you can use
-fplugin-opt=Splint:arg. For example you can ignore the warning above with
Running HLint as a GHC source plugin has some upsides:
Modules are only linted when they’re compiled, so if they haven’t changed they won’t be linted again.
HLint’s suggestions are reported just like GHC’s warnings. They’re formatted the same way and they’re reported at the same time.
Each module is only parsed once.
Parsing is done by GHC instead of something like
haskell-src-exts. HLint already works like this, but by using a plugin you can be sure that all of the versions and options line up correctly.
However it’s also got some downsides:
Using Splint means adding it as a dependency to the targets you want to lint. Normally HLint is either a test dependency or just installed on the system.
You may be able to lessen the impact of this by providing a flag to control linting. That way you can enable it locally and in CI, but not require everything downstream of you to depend on HLint.
flag lint default: False manual: True library if flag(lint) build-depends: splint ghc-options: -fplugin=Splint
It’s slower. I’ve found that it adds about a tenth of a second per module.
You can’t use the automated refactorings that HLint provides.
Using plugins marks every module as unsafe.