Support rust-analyzer as alternate LSP engine

package.json

@@ -50,13 +50,15 @@
         "installDevExtension": "npm install && ./node_modules/.bin/vsce package -o ./out/rls-vscode-dev.vsix && code --install-extension ./out/rls-vscode-dev.vsix"
     },
     "dependencies": {
+        "node-fetch": "^2.6.0",
         "vscode-languageclient": "^6.0.0"
     },
     "devDependencies": {
         "@types/chai": "^4.2.11",
         "@types/glob": "^7.1.1",
         "@types/mocha": "^5.2.6",
         "@types/node": "^12.8.1",
+        "@types/node-fetch": "^2.5.7",
         "@types/vscode": "^1.43.0",
         "chai": "^4.2.0",
         "glob": "^7.1.4",
@@ -160,6 +162,20 @@
             "type": "object",
             "title": "Rust configuration",
             "properties": {
+                "rust-client.engine": {
+                    "type": "string",
+                    "enum": [
+                        "rls",
+                        "rust-analyzer"
+                    ],
+                    "enumDescriptions": [
+                        "Use the Rust Language Server (RLS)",
+                        "EXPERIMENTAL: Use the rust-analyzer language server"
+                    ],
+                    "default": "rls",
+                    "description": "The underlying LSP server used to provide IDE support for Rust projects.",
+                    "scope": "window"
+                },
                 "rust-client.logToFile": {
                     "type": "boolean",
                     "default": false,
@@ -448,6 +464,22 @@
                     "default": true,
                     "description": "Show additional context in hover tooltips when available. This is often the type local variable declaration.",
                     "scope": "resource"
+                },
+                "rust.rust-analyzer": {
+                    "type": "object",
+                    "default": {},
+                    "description": "Settings passed down to rust-analyzer server",
+                    "scope": "resource"
+                },
+                "rust.rust-analyzer.releaseTag": {
+                    "type": "string",
+                    "default": "nightly",
+                    "description": "Which binary release to download and use"
+                },
+                "rust.rust-analyzer.path": {
+                    "type": ["string", "null"],
+                    "default": null,
+                    "description": "When specified, uses the rust-analyzer binary at a given path"
                 }
             }
         }

src/configuration.ts

@@ -50,13 +50,13 @@ export class RLSConfiguration {
    */
   private static readChannel(
     wsPath: string,
-    rustupConfiguration: RustupConfig,
+    rustupPath: string,
     configuration: WorkspaceConfiguration,
   ): string {
     const channel = configuration.get<string>('rust-client.channel');
     if (channel === 'default' || !channel) {
       try {
-        return getActiveChannel(wsPath, rustupConfiguration);
+        return getActiveChannel(wsPath, rustupPath);
       } catch (e) {
         // rustup might not be installed at the time the configuration is
         // initially loaded, so silently ignore the error and return a default value
@@ -83,6 +83,13 @@ export class RLSConfiguration {
     );
   }
 
+  public get rustAnalyzer(): { path?: string; releaseTag: string } {
+    const cfg = this.configuration;
+    const releaseTag = cfg.get('rust.rust-analyzer.releaseTag', 'nightly');
+    const path = cfg.get<string>('rust.rust-analyzer.path');
+    return { releaseTag, ...{ path } };
+  }
+
   public get revealOutputChannelOn(): RevealOutputChannelOn {
     return RLSConfiguration.readRevealOutputChannelOn(this.configuration);
   }
@@ -94,7 +101,7 @@ export class RLSConfiguration {
   public get channel(): string {
     return RLSConfiguration.readChannel(
       this.wsPath,
-      this.rustupConfig(true),
+      this.rustupPath,
       this.configuration,
     );
   }
@@ -106,17 +113,21 @@ export class RLSConfiguration {
     return this.configuration.get<string>('rust-client.rlsPath');
   }
 
+  /** Returns the language analysis engine to be used for the workspace */
+  public get engine(): 'rls' | 'rust-analyzer' {
+    return this.configuration.get('rust-client.engine') || 'rls';
+  }
+
   /**
    * Whether RLS should be automaticallystarted when opening a relevant Rust project.
    */
   public get autoStartRls(): boolean {
     return this.configuration.get<boolean>('rust-client.autoStartRls', true);
   }
 
-  // Added ignoreChannel for readChannel function. Otherwise we end in an infinite loop.
-  public rustupConfig(ignoreChannel: boolean = false): RustupConfig {
+  public rustupConfig(): RustupConfig {
     return {
-      channel: ignoreChannel ? '' : this.channel,
+      channel: this.channel,
       path: this.rustupPath,
     };
   }