feat: provide LSP API support

[angelozerr]

This PR provide LSP API support for:

• diagnostic (done)
• completion (initialized)
• formatting (in progress)
• TODO other features....

Please read docs/LSPApi.md for a sample.

[angelozerr]

@CppCXY @FalsePattern this PR should start working but please give me feedback about the LSP API which should fix #424 and #388

[angelozerr]

@InSyncWithFoo please follow this PR which provides diagnostic support. Any feedback are welcome about the name, how to the configuration is done, etc

[FalsePattern]

The API draft seems alright to me so far.
LSPCustomizedFormattingSupport will resolve the proxy workaround i'm doing in zigbrains, I don't really have a use case for the other two at the moment so I cannot comment on those.

[angelozerr]

Thanks for your feedback.

Please note the Api will change à lot since we have some discussion this morning with @fbricon

[InSyncWithFoo]

I would also like to customize code actions and hover, since these two, along with the original trio of diagnostics, completion and formatting, are the most commonly used.

For reference, the native client uses a boolean to configure hover support, whereas that of code actions allows for separate customizations of quick fixes and intentions, as well as whether the server should be asked to provide such actions.

It would be nice to be able to tweak the textDocument/hover response before displaying it; for example:

class MyServerHoverFeature : LSPHoverFeature {

    // Better name needed (`beforePopupDisplay`? `getPopupContent`?)
    fun modifyContent(content: String): String? {
        if (somethingIsWrong) {
            return null  // No popup should be shown
        }

        return frobnicate(content)
    }

}

[angelozerr]

It would be nice to be able to tweak the textDocument/hover response before displaying it; for example:

Can you do that with LSP JetBrains? Have you implemented this customization?

[InSyncWithFoo]

Can you do that with LSP JetBrains? Have you implemented this customization?

No and no. It is sometimes necessary, though. See this issue for an example of how the default might look wrong (not necessarily in that specific manner).

To give another example: currently, if the returned Markdown snippet has a code block at the very start, it will be rendered with an aesthetically unpleasing dark background.

[InSyncWithFoo]

Features might be enabled or disabled for one project but not another, so this method should be passed the current project.

[angelozerr]

I agree with you.

In short answer, it exists LSPClientFeature#getProject()

LSPClientFeatures is set with the LanguageServerWrapper which have the project. We need LanguageServerWrapper to support server capability see LSPFormattingFeature.

The LanguageServerWrapper set her instance when LSPClientFeatures is created (I did that because I don't want to expose LanguageServerWrapper in the API)

The LanguageServerWrapper hosts the Project, so LSPClientFeatures know the Project.

[InSyncWithFoo]

The native LspFormattingSupport has a similar method:

fun shouldFormatThisFileExclusivelyByServer(
    file: VirtualFile,
    ideCanFormatThisFileItself: Boolean,
    serverExplicitlyWantsToFormatThisFile: Boolean
): Boolean

According to the doc comments, ideCanFormatThisFileItself means whether LanguageFormatting.forContext returns a non-null value, whereas serverExplicitlyWantsToFormatThisFile means whether the file matches the registered DocumentSelectors.

[angelozerr]

We have dicussed with @fbricon and we decide to have an isEnabled method for each LSP*Feature with a custom context instead of having isEnabled with several parameters to be sure that API will not broken if we need new fields.

According to the doc comments, ideCanFormatThisFileItself means whether LanguageFormatting.forContext return a non-null value

Thanks for your feedback. I removed this canFormatEvenIfExistingFormatter and now you have now:

    /**
     * Returns true if existing formatter are overrideable and false (default value) otherwise.
     *
     * @return true if existing formatter are overrideable and false (default value) otherwise.
     */
    protected boolean isExistingFormatterOverrideable(@NotNull PsiFile file) {
        return false;
    }

In this case LanguageFormatting.INSTANCE.forContext(file) != null i sdone.

If you override isExistingFormatterOverrideable to returns true, it will skip the test with LanguageFormatting.INSTANCE.forContext(file) != null`

@InSyncWithFoo @FalsePattern @CppCXY do you like this idea?

[angelozerr]

means whether the file matches the registered DocumentSelectors.

Today we check server capability, but not DocumentSelectors. Once LSP API will be merged,I will work on #517

[InSyncWithFoo]

Note to self: Replace the 4-star review with a new 5-star one when this PR is merged.

[fbricon]

Returns the LSP4J language server, guaranteed to be initialized at that point.

[fbricon]

keepServerRunning() or keepServerAlive()