gopls: support a setting to control the frequency of diagnostics

[stamblerre]

It's possible that some users might like to see diagnostics only when they save a file, rather than seeing them as they type.
It is also possible that some users may want to use gopls without seeing any diagnostics at all.

Depending on the popularity of these use cases, we should consider supporting these two configurations.

Please react with a 🚀 if you would like to see diagnostics only when you save a file, not as you type.
Please react with a ❤️ if you would like to disable diagnostics from gopls completely.

Original discussion on microsoft/vscode-go#2907.

[gopherbot]

Change https://golang.org/cl/280601 mentions this issue: src/goLanguageServer: remove languageServerExperimentalFeatures

[tamayika]

Is there any way to use custom go vet tool with gopls enabled in >= 0.21?
Or is there any way to embed custom analysis to gopls?

Here is my configuration.

{
  "go.vetFlags": [
    "--vettool=${workspaceRoot}/bin/my-vet-tool"
  ],
  "go.languageServerExperimentalFeatures": {
    "diagnostics": false, // deprecated and not work >= 0.21
  },
}

Current workaround is to rollback vscode-go to 0.20.x.

[hyangah]

@tamayika Thanks for the report. Sorry that I didn't know users depend on this feature to use custom vet analysis. Currently gopls doesn't allow custom analysis. @stamblerre This affects the current language server users. I will prepare a partial rollback of cl/280601 that still leaves the diagnostics flag.

Turning completely off gopls's diagnostics because of the lack of custom analyzer support in gopls isn't ideal. I think we need a way to allow vet/buildOnSave when the language server is running (so filed #1109 for investigation).

Out of curiosity: @tamayika is there a reason that your analyzer can't run as a linter?

[tamayika]

Thanks for the support.

go.lintTool is already used by other lint tool(revive) in my configuration.
So if go.lintTool supports multiple linters and go vet command with custom vet tool, it may solve the problem.

[gopherbot]

Change https://golang.org/cl/285253 mentions this issue: src/goLanguageServer: partial revert of cl/280601

[gopherbot]

Change https://golang.org/cl/285256 mentions this issue: [release] src/goLanguageServer: partial revert of cl/280601