Indicate language server readiness in the UI

[radeksimko]

Problem Statement

Currently the relationship between the extension (acting as language client) and the language server isn't as transparent as it could be, which can sometimes lead to confusing user experience.

Launching the language server kicks off a number of background operations which user may not necessarily need to know about, but the result of these operations may be interesting when these fail. Currently these errors are only logged (by default to Output pane) and invisible to most users.

Users would benefit from more transparency where they know:

• whether the language server is ready
• what version of the LS is in use (for easy access when they report issues)
• whether there were any significant issues with loading the server / TF module and what these are
• whether there are any background operations running and what state are they in (e.g. how close to completion)

Expected User Experience

User would be able to see an icon, or terraform-ls entry in the status bar which can display:

• progress of any ongoing background operations
• failed operations
• whether the server is ready/running
• version of the launched server

Similar to Java VS Code extension:

IN-PROGRESS

READY

FAILED

Proposal

• We can try to follow the implementation discussed in Discussion: LSP-server readiness indicator microsoft/language-server-protocol#511
• Implement a new client-side command (callable by server as notification)
• Ensure that client announces this as capability somewhere during initialization, so that server knows whether to call it or not
• Server to check relevant client capability and send notification any time status changes
• See also
  • Report progress for indexing operations terraform-ls#5
  • Report progress when obtaining schema terraform-ls#150
  • Raise warnings for unsupported Terraform versions terraform-ls#168

Pending Questions

• TBD: Exact notification request structure
• TBD: Specific icons and text to show in the status bar for each state (in progress, ready, failure)

[jpogran]

While we can use the existing StatusBar API, there is a new proposed API for this kind of status client side for VS Code: microsoft/vscode#129037. We still have to implement something server side to send progress notifications, but there is a UI element for the client being prepared.

A first pass version of this can be seen in https://code.visualstudio.com/updates/v1_61#_new-javascript-and-typescript-language-status-item.

Proposed code: microsoft/vscode#129037 (comment)