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, 11 insertions, 2 deletions

diff --git a/editors/code/src/client.ts b/editors/code/src/client.ts
index 62980ca0464..565cb9c6432 100644
--- a/editors/code/src/client.ts
+++ b/editors/code/src/client.ts
@@ -6,7 +6,7 @@ import * as Is from "vscode-languageclient/lib/common/utils/is";
 import { assert } from "./util";
 import * as diagnostics from "./diagnostics";
 import { WorkspaceEdit } from "vscode";
-import { Config, substituteVSCodeVariables } from "./config";
+import { Config, prepareVSCodeConfig } from "./config";
 import { randomUUID } from "crypto";
 
 export interface Env {
@@ -95,7 +95,16 @@ export async function createClient(
                     const resp = await next(params, token);
                     if (resp && Array.isArray(resp)) {
                         return resp.map((val) => {
-                            return substituteVSCodeVariables(val);
+                            return prepareVSCodeConfig(val, (key, cfg) => {
+                                // we only want to set discovered workspaces on the right key
+                                // and if a workspace has been discovered.
+                                if (
+                                    key === "linkedProjects" &&
+                                    config.discoveredWorkspaces.length > 0
+                                ) {
+                                    cfg[key] = config.discoveredWorkspaces;
+                                }
+                            });
                         });
                     } else {
                         return resp;