Auto merge of #14307 - davidbarsky:davidbarsky/add-cargo-style-project-discovery-for-buck-and-bazel-sickos, r=Veykril

Add Cargo-style project discovery for Buck and Bazel Users

This feature requires the user to add a command that generates a `rust-project.json` from a set of files. Project discovery can be invoked in two ways:

1. At extension activation time, which includes the generated `rust-project.json` as part of the linkedProjects argument in `InitializeParams`.
2. Through a new command titled "rust-analyzer: Add current file to workspace", which makes use of a new, rust-analyzer-specific LSP request that adds the workspace without erasing any existing workspaces. Note that there is no mechanism to _remove_ workspaces other than "quit the rust-analyzer server".

Few notes:
-  I think that the command-running functionality _could_ merit being placed into its own extension (and expose it via extension contribution points) to provide build-system idiomatic progress reporting and status handling, but I haven't (yet) made an extension that does this nor does Buck expose this sort of functionality.
-  This approach would _just work_ for Bazel. I'll try and get the tool that's responsible for Buck integration open-sourced soon.
- On the testing side of things, I've used this in around my employer's Buck-powered monorepo and it's a nice experience. That being said, I can't think of an open-source repository where this can be tested in public, so you might need to trust me on this one.

I'd love to get feedback on:
- Naming of LSP extensions/new commands. I'm not too pleased with how "rust-analyzer: Add current file to workspace" is named, in that it's creating a _new_ workspace. I think that this command being added should be gated on `rust-analyzer.discoverProjectCommand` on being set, so I can add this in sequent commits.
- My Typescript. It's not particularly good.
- Suggestions on handling folders with _both_ Cargo and non-Cargo build systems and if I make activation a bit better.

(I previously tried to add this functionality entirely within rust-analyzer-the-LSP server itself, but matklad was right—an extension side approach is much, much easier.)

1 files changed, 16 insertions, 0 deletions

diff --git a/editors/code/package.json b/editors/code/package.json
index a3b1a3107d0..c5eb08748bf 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -200,6 +200,11 @@
                 "category": "rust-analyzer"
             },
             {
+                "command": "rust-analyzer.addProject",
+                "title": "Add current file's crate to workspace",
+                "category": "rust-analyzer"
+            },
+            {
                 "command": "rust-analyzer.reload",
                 "title": "Restart server",
                 "category": "rust-analyzer"
@@ -428,6 +433,17 @@
                     "default": false,
                     "type": "boolean"
                 },
+                "rust-analyzer.discoverProjectCommand": {
+                    "markdownDescription": "Sets the command that rust-analyzer uses to generate `rust-project.json` files. This command should only be used\n if a build system like Buck or Bazel is also in use. The command must accept files as arguments and return \n a rust-project.json over stdout.",
+                    "default": null,
+                    "type": [
+                        "null",
+                        "array"
+                    ],
+                    "items": {
+                        "type": "string"
+                    }
+                },
                 "$generated-start": {},
                 "rust-analyzer.assist.emitMustUse": {
                     "markdownDescription": "Whether to insert #[must_use] when generating `as_` methods\nfor enum variants.",