Add a doc listing the LSP protocol status/supported features

Change-Id: If37d0333b4a59eca7f02ec371ac8f12719470f46
Reviewed-on: https://dart-review.googlesource.com/c/87040
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Danny Tuppeny <[email protected]>

Author: DanTup

pkg/analysis_server/tool/lsp_spec/README.md

@@ -0,0 +1,75 @@
+# Language Server Protocol
+
+## LSP Support Status
+
+Support for [the Language Server Protocol](https://microsoft.github.io/language-server-protocol/) (LSP) is **not production ready** but available as a preview to allow testing/integration work.
+
+## Running the Server
+
+Run the server from source to ensure you're running code that matches the status shown below. If you don't have a locally built SDK then a recent nightly should do. Pass the `--lsp` flag to start the server in LSP mode:
+
+```
+dart pkg/analysis_server/bin/server.dart --lsp
+```
+
+Note: In LSP the client makes the first request so there is no obvious confirmation that the server is working correctly until the client sends an `initialize` request. Unlike standard JSON RPC, [LSP requires that headers are sent](https://microsoft.github.io/language-server-protocol/specification).
+
+## Message Status
+
+Below is a list of LSP methods and their implementation status.
+
+- Method: The LSP method name
+- Basic Impl: This method has a basic implementation but may not support all capabilities
+- Capabilities: All client capabilities (in the spec at time of writing) are supported/handled correctly
+- Tests: Has automated tests
+- Tested Client: Has been manually tested in at least one LSP client editor
+
+| Method | Basic Impl | Capabilities | Tests | Tested Client | Notes |
+| - | - | - | - | - | - |
+| initialize | ✅ | | ✅ | ✅ | trace and other options NYI
+| initialized | ✅ | ✅ | ✅ | ✅ |
+| shutdown | ✅ | ✅ | ✅ | ✅ | supported but does nothing |
+| exit | | | | | |
+| $/cancelRequest | | | | | ignored (unsupported) |
+| window/showMessage | ✅ | | | |
+| window/showMessageRequest | | | | |
+| window/logMessage | ✅ | | | |
+| telemetry/event | | | | |
+| client/registerCapability | | | | | unused, but should be used for DocumentSelector at least
+| client/unregisterCapability | | | | |
+| workspace/didChangeWatchedFiles | | | | | unused, server does own watching |
+| workspace/symbol | | | | |
+| workspace/executeCommand | ✅ | ✅ | ✅ | ✅ |
+| workspace/applyEdit | ✅ | ✅ | ✅ | ✅ |
+| textDocument/didOpen | ✅ | ✅ | ✅ | ✅ |
+| textDocument/didChange | ✅ | ✅ | ✅ | ✅ |
+| textDocument/willSave | | | | |
+| textDocument/willSaveWaitUntil | | | | |
+| textDocument/didClose | ✅ | ✅ | ✅ | ✅ |
+| textDocument/publishDiagnostics | ✅ | ✅ | ✅ | ✅ |
+| textDocument/completion | ✅ | | ✅ | |
+| completionItem/resolve | | | | | not required |
+| textDocument/hover | ✅ | | ✅ | |
+| textDocument/signatureHelp | ✅ | | ✅ | | correct trigger character handling outstanding
+| textDocument/definition | ✅ | | ✅ | |
+| textDocument/typeDefinition | | | | |
+| textDocument/implementation | | | | |
+| textDocument/references | ✅ | | ✅ | |
+| textDocument/documentHighlight | | | | |
+| textDocument/documentSymbol | ✅ | | ✅ | |
+| textDocument/codeAction (sortMembers) | ✅ | ✅ | ✅ | ✅ |
+| textDocument/codeAction (organiseImports) | ✅ | ✅ | ✅ | ✅ |
+| textDocument/codeAction (refactors) | | | | |
+| textDocument/codeAction (assists) | | | | |
+| textDocument/codeAction (fixes) | | | | |
+| textDocument/codeLens | | | | |
+| codeLens/resolve | | | | |
+| textDocument/documentLink | | | | |
+| documentLink/resolve | | | | |
+| textDocument/formatting | ✅ | ✅ | ✅ | ✅ |
+| textDocument/rangeFormatting | | | | | requires support from dart_style?
+| textDocument/onTypeFormatting | ✅ | ✅ | ✅ | ✅ |
+| textDocument/rename | | | | |
+| textDocument/prepareRename | | | | |
+| textDocument/foldingRange | | | | |
+