Merge #6932

6932: Added a warning if conflicting rust-lang.rust is enabled. r=lnicola a=extremegf

Added a warning if conflicting rust-lang.rust plugin is enabled.

Resolves #6463

![Screenshot from 2020-12-18 18-33-02](https://user-images.githubusercontent.com/1788593/102644202-b2f50500-4160-11eb-8fb0-76aeebd80aea.png)


Co-authored-by: Przemyslaw Horban <[email protected]>

Author: bors[bot]

editors/code/src/main.ts

@@ -132,6 +132,7 @@ async function tryActivate(context: vscode.ExtensionContext) {
     ctx.pushCleanup(activateTaskProvider(workspaceFolder, ctx.config));
 
     activateInlayHints(ctx);
+    warnAboutRustLangExtensionConflict();
 
     vscode.workspace.onDidChangeConfiguration(
         _ => ctx?.client?.sendNotification('workspace/didChangeConfiguration', { settings: "" }),
@@ -399,3 +400,13 @@ async function queryForGithubToken(state: PersistentState): Promise<void> {
         await state.updateGithubToken(newToken);
     }
 }
+
+function warnAboutRustLangExtensionConflict() {
+    const rustLangExt = vscode.extensions.getExtension("rust-lang.rust");
+    if (rustLangExt !== undefined) {
+        vscode.window.showWarningMessage(
+            "You have both rust-analyzer (matklad.rust-analyzer) and Rust (rust-lang.rust) " +
+            "plugins enabled. These are known to conflict and cause various functions of " +
+            "both plugins to not work correctly. You should disable one of them.", "Got it");
+    };
+}