Extract fourmolu plugin into a standalone package

[gustavoavena]

What

Extract fourmolu plugin to a standalone package.
Similar to what was done for stylish-haskell (#1604) and brittany (#1422) plugins.

RFC: Test case in Progress.hs

TL;DR: is it ok to leave the progress tests case from fourmolu plugin where it is?

I'm basing this PR on the ones that did the same for stylish-haskell (#1604) and brittany (#1422). I moved the functional tests from the Format test suite the same way, but unlike stylish-haskell and brittany, fourmolu has a test case in window/workDoneProgress test suite (in test/functional/Progress.hs).

My initial plan was to extract it to the fourmolu test suite, but it depends on some things from utility modules that are not visible to the new fourmolu test suite (e.g. hlsCommand from Test.Hls.Command).

It seems that to extract it, I would need to move some things around to avoid adding a dependency from the new test suite to the functional test suite. Since I wanted to avoid making bigger changes on my first PR, I wanted to double check if extracting that one test case is necessary, if it's passing as is.

[pepeiborra]

My initial plan was to extract it to the fourmolu test suite, but it depends on some things from utility modules that are not visible to the new fourmolu test suite (e.g. hlsCommand from Test.Hls.Command). It seems that to extract it, I would need to move some things around to avoid adding a dependency from the new test suite to the functional test suite. Since I wanted to avoid making bigger changes on my first PR, I wanted to double check if extracting that one test case is necessary, if it's passing as is.

@gustavoavena nothing should be moved and hlsCommand should not be needed, but maybe some tests need to be refactored.
@berberman how difficult is it to extract the tests? I would think it should be pretty easy after your recent changes introducing his-test-utils.

[gustavoavena]

@gustavoavena can you specify what needs to be moved? Maybe some tests need to be refactored instead.

One thing would be hlsCommand (from Test.Hls.Command). formatLspConfig and progressCaps are also used by the test case. There is also expectProgressReports.

I'm not very familiar with the code, but maybe refactoring the runServer* functions in Test.Hls to provide one that we could use for this test case would also work.

[berberman]

The purpose of hls-test-utils is to decouple plugins test suite with HLS executable, and we should never use hlsCommand in plugin packages. hlsCommand will be removed finally when we migrate all HLS tests (run them in the same process, without building server executable first), but it seems to take a bit more work to do (#1752).

Moreover, now there are some test suites in HLS referencing plugins' test data, e.g. Prograss mentioned above:

haskell-language-server/test/functional/Progress.hs

Lines 32 to 53 in bb99905

	, testCase "eval plugin sends progress reports" $
	runSession hlsCommand progressCaps "plugins/hls-eval-plugin/test/testdata" $ do
	doc <- openDoc "T1.hs" "haskell"
	expectProgressReports ["Setting up testdata (for T1.hs)", "Processing", "Indexing"]
	[evalLens] <- getCodeLenses doc
	let cmd = evalLens ^?! L.command . _Just
	_ <- sendRequest SWorkspaceExecuteCommand $ ExecuteCommandParams Nothing (cmd ^. L.command) (decode $ encode $ fromJust $ cmd ^. L.arguments)
	expectProgressReports ["Evaluating"]
	, testCase "ormolu plugin sends progress notifications" $ do
	runSession hlsCommand progressCaps "test/testdata/format" $ do
	sendNotification SWorkspaceDidChangeConfiguration (DidChangeConfigurationParams (formatLspConfig "ormolu"))
	doc <- openDoc "Format.hs" "haskell"
	expectProgressReports ["Setting up testdata (for Format.hs)", "Processing", "Indexing"]
	_ <- sendRequest STextDocumentFormatting $ DocumentFormattingParams Nothing doc (FormattingOptions 2 True Nothing Nothing Nothing)
	expectProgressReports ["Formatting Format.hs"]
	, testCase "fourmolu plugin sends progress notifications" $ do
	runSession hlsCommand progressCaps "test/testdata/format" $ do
	sendNotification SWorkspaceDidChangeConfiguration (DidChangeConfigurationParams (formatLspConfig "fourmolu"))
	doc <- openDoc "Format.hs" "haskell"
	expectProgressReports ["Setting up testdata (for Format.hs)", "Processing", "Indexing"]
	_ <- sendRequest STextDocumentFormatting $ DocumentFormattingParams Nothing doc (FormattingOptions 2 True Nothing Nothing Nothing)
	expectProgressReports ["Formatting Format.hs"]

Which is a bit hacky but works. Unfortunately, I don't have a good idea so far.

@gustavoavena Could you try changing the path "test/testdata/format" to your extracted test data, like eval plugin, and leaving other things in Prograss unchanged? P.S. There might be other HLS test suites like Prograss which reference fourmolu test data, and you'll need change them as well.

[berberman]

LGTM, thank you!

[Ailrun]

LGTM :)