Handle "textDocument/rangeFormatting" and "textDocument/onTypeFormatting"

[MahdiBM]

Description

Now that swift-format has some support for range formatting, sourcekit-lsp can implement handling these requests as well.

This will elevate the VSCode formatting experience since the VSCode extension is calling through to sourcekit-lsp for formatting.

sourcekit-lsp seems to already have some support for these. Just the logic isn't implemented.
For example there are some existing DocumentRangeFormattingRequest and DocumentOnTypeFormattingRequest types.

[ahoppen]

Synced to Apple’s issue tracker as rdar://139287738

[MahdiBM]

@ahoppen How would you like OnTypeFormatting to be implemented?

I quite like the Xcode formatting behavior, so not sure if any of your colleagues working on Xcode can provide some tips about this.
Also not sure that swift-format will have the ability to do those formatting anyway, even if we knew Xcode's algorithm.

What I did for the vknabel formatter extensions was to perform a format of the whole file after hitting "return" on non-empty lines. But that formatted the whole file, not just some certain lines (this was before the selection-formatting PR being merged into swift-format).

I guess we could start with that "perform a format of the whole file after hitting "return" on non-empty lines" although I'd like to leverage the selection-formatting capabilities.

[ahoppen]

What do you think of running swift-format on the line that we receive the textDocument/onTypeFormatting request for if ch is a newline? I am a little doubtful how well this will work though because swift-format can’t format if you have syntax errors and I assume there will likely be syntax errors during typing.

Anyway, I think we would need to get a feel for this, so I’d implement it behind an experimental feature and then use it for a while to see how it feels and if we have improvement ideas.

[MahdiBM]

@ahoppen why the reopen? Curious 🙂

[ahoppen]

Because it’s gated behind the experimental feature and thus not generally available.

[MahdiBM]

@ahoppen friendly ping: I don't think textDocument/onTypeFormatting has made it to the 6.1 toolchains yet. I would have loved to try it out.

[MahdiBM]

@ahoppen any updates on this? 🙂

[ahoppen]

On-type formatting should be available behind the experimental features. Is it not?

[MahdiBM]

Not even on 6.2 nightlies. Does not appear to make any difference to turn it on or not (using config file).

[MahdiBM]

There are no logs related to on-type-formatting so it doesn't even get triggered.
Testing on a dev container using 6.2 nightly images (not the latest image though, but a recent one).

[MahdiBM]

Could this be related to #2124 ?

Another thing; Checking for experimental flags in the logs shows mixed results:

$ tail -F -n 10000 ~/.sourcekit-lsp/logs/* | grep experimentalFeatures -A 10 -B 10 -n
34116-  "backgroundIndexing" : 1,
34117-  "backgroundPreparationMode" : "<private fb9cf75606b4070d>",
34118-  "clangdOptions" : [
34119-
34120-  ],
34121-  "compilationDatabase" : {
34122-    "searchPaths" : [
34123-
34124-    ]
34125-  },
34126:  "experimentalFeatures" : [
34127-
34128-  ],
34129-  "fallbackBuildSystem" : {
34130-    "cCompilerFlags" : [
34131-
34132-    ],
34133-    "cxxCompilerFlags" : [
34134-
34135-    ],
34136-    "swiftCompilerFlags" : [
--
34172-  "backgroundIndexing" : 1,
34173-  "backgroundPreparationMode" : "<private fb9cf75606b4070d>",
34174-  "clangdOptions" : [
34175-
34176-  ],
34177-  "compilationDatabase" : {
34178-    "searchPaths" : [
34179-
34180-    ]
34181-  },
34182:  "experimentalFeatures" : [
34183-    "<private cebebca138850fa6>",
34184-    "<private 66698aa4335cd79b>"
34185-  ],
34186-  "fallbackBuildSystem" : {
34187-    "cCompilerFlags" : [
34188-
34189-    ],
34190-    "cxxCompilerFlags" : [
34191-
34192-    ],

The one above is with logging.privacyLevel set to private in the config, and it shows no experimental features (EDIT: or at least that's what I think based on what I did).
The one below is with the default logging settings and shows 2 experimental features.
This is with me having set experimentalFeatures to ["on-type-formatting", "structured-logs"].

EDIT: interesting that backgroundPreparationMode is always showing up as "<private>" ... maybe my config stuff are not taking effect at all?! They are at project/.sourcekit-lsp/config.json and I'm using the official VSCode extension.