https://github.com/tfausak/splint

:newspaper_roll: HLint as a GHC source plugin.
https://github.com/tfausak/splint

Last synced: 25 days ago
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:newspaper_roll: HLint as a GHC source plugin.

• Host: GitHub
• URL: https://github.com/tfausak/splint
• Owner: tfausak
• License: isc
• Created: 2020-05-23T02:27:34.000Z (over 4 years ago)
• Default Branch: main
• Last Pushed: 2024-07-08T14:37:39.000Z (4 months ago)
• Last Synced: 2024-07-08T18:14:42.486Z (4 months ago)
• Language: Haskell
• Homepage: https://hackage.haskell.org/package/splint
• Size: 76.2 KB
• Stars: 31
• Watchers: 3
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.markdown
  • License: LICENSE.markdown

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README

        
# Splint

[![CI](https://github.com/tfausak/splint/actions/workflows/ci.yml/badge.svg)](https://github.com/tfausak/splint/actions/workflows/ci.yml)

[![Hackage](https://badgen.net/hackage/v/splint)](https://hackage.haskell.org/package/splint)

:warning: This package is not maintained anymore.

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.hs` as:

``` hs

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

running:

``` sh

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

    Suggested fix: 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

`-fplugin-opt=Splint:'--ignore=Use concatMap'`.

## Trade offs

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.

    ``` cabal

    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.

[HLint 3]: https://neilmitchell.blogspot.com/2020/05/hlint-30.html

[GHC source plugin]: https://downloads.haskell.org/~ghc/8.10.1/docs/html/users_guide/extending_ghc.html#source-plugins

[hlint-source-plugin]: https://github.com/ocharles/hlint-source-plugin