Provide code action in hls-eval-plugin

[jian-lin]

Code action and lens are provided at the same time.

In addition, a file is excluded from stylish-haskell pre-commit hook due to a CPP issue introduced in #4527.

Fix: #496

[jian-lin]

Eval code action works. However, this PR is not complete. As I said below, I need to fix tests and maybe do some refactoring. Since I am still new to HLS (this is my 3rd PR), I think it is better to request some review before doing the rest of the work. cc @fendor @michaelpj

[fendor]

Hi, thanks for the PR!

Personally, I am not in favour of changing the long-standing behaviour of HLS for no real motivation. I quite like the CodeLens for updating the -- >>> and think that CodeAction's are much harder to discover. At most, I would be willing to give it the hls-explicit-imports-plugin treatment and replace CodeLens with InlayHints.

The given issue argues that it should also be possible to use a CodeAction to run the eval. I would be fine with having both available, but I do not think it makes a lot of sense to change default behaviour, unless someone demonstrates a clear advantage.

tl;dr I don't think we should replace the CodeLens with a CodeAction, we can offer both, or by default, only offer a CodeLens and if the CodeLens is disabled, we may fall back to CodeAction.
Inlay Hints may also make a lot of sense.

[fendor]

Also, PR itself looks good :)

[jian-lin]

Thanks for your review @fendor! Now code action and lens are provided at the same time. I also add some code action tests which are a bit tricky because getAllCodeActions cannot get any code action. PTAL.

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Compared with code lens, inlay hint indeed has more functionalities. Some clients such as eglot do not support code lens but do support inlay hint. So providing inlay hint will improve discoverability for some users.

Maybe I will add inlay hint support in a future PR but it is not ranked high in my HLS TODO list because I have already "discovered" this plugin 😄.

[jian-lin]

Windows tests are running and other CI tests are passed. PTAL @fendor

[jian-lin]

• I did a git rebase.
• I updated md docs to mention code action
• All CI tests are passed.

I believe this is a useful feature for users whose LSP client does not support code lens and users who want to trigger eval plugin with a key binding. Hope it can be merged soon.

[fendor]

LGTM, thank you!