Make sure rust-analyser uses rust-project.json Meson generates

This is very similar case than compile_commands.json, Meson generates a
file in builddir that some extensions should be using. It makes static
analysers work out of the box instead of requiring user to configure
paths themself.

We only need to watch for file creation, it was previously wrongly
watching for file changes for legacy reasons (we used to patch
compile_commands.json).

src/extension.ts

@@ -6,12 +6,12 @@ import {
   extensionConfiguration,
   extensionConfigurationSet,
   genEnvFile,
-  useCompileCommands,
   clearCache,
   checkMesonIsConfigured,
   getOutputChannel,
   getBuildDirectory,
   rootMesonFiles,
+  whenFileExists,
 } from "./utils";
 import { DebugConfigurationProviderCppdbg } from "./debug/cppdbg";
 import { DebugConfigurationProviderLldb } from "./debug/lldb";
@@ -26,7 +26,6 @@ export let extensionPath: string;
 export let workspaceState: vscode.Memento;
 let explorer: MesonProjectExplorer;
 let watcher: vscode.FileSystemWatcher;
-let compileCommandsWatcher: vscode.FileSystemWatcher;
 let mesonWatcher: vscode.FileSystemWatcher;
 let controller: vscode.TestController;
 
@@ -137,19 +136,25 @@ export async function activate(ctx: vscode.ExtensionContext) {
     }),
   );
 
-  const compileCommandsHandler = async () => {
-    await useCompileCommands(buildDir);
-  };
-  compileCommandsWatcher = vscode.workspace.createFileSystemWatcher(
-    `${buildDir}/compile_commands.json`,
-    false,
-    false,
-    true,
-  );
-  compileCommandsWatcher.onDidChange(compileCommandsHandler);
-  compileCommandsWatcher.onDidCreate(compileCommandsHandler);
-  ctx.subscriptions.push(compileCommandsWatcher);
-  await useCompileCommands(buildDir);
+  const compileCommandsFile = `${buildDir}/compile_commands.json`;
+  whenFileExists(ctx, compileCommandsFile, async () => {
+    try {
+      const conf = vscode.workspace.getConfiguration("C_Cpp");
+      conf.update("default.compileCommands", compileCommandsFile, vscode.ConfigurationTarget.Workspace);
+    } catch {
+      // Ignore, C/C++ extension might not be installed
+    }
+  });
+
+  const rustProjectFile = `${buildDir}/rust-project.json`;
+  whenFileExists(ctx, rustProjectFile, async () => {
+    try {
+      const conf = vscode.workspace.getConfiguration("rust-analyzer");
+      conf.update("linkedProjects", [rustProjectFile], vscode.ConfigurationTarget.Workspace);
+    } catch {
+      // Ignore, rust-analyzer extension might not be installed
+    }
+  });
 
   ctx.subscriptions.push(
     vscode.commands.registerCommand("mesonbuild.openBuildFile", async (node: TargetNode) => {

src/utils.ts

@@ -207,3 +207,12 @@ export async function rootMesonFiles(): Promise<vscode.Uri[]> {
 
   return rootFiles;
 }
+
+export function whenFileExists(ctx: vscode.ExtensionContext, file: string, listener: () => void) {
+  const watcher = vscode.workspace.createFileSystemWatcher(file, false, true, true);
+  watcher.onDidCreate(listener);
+  ctx.subscriptions.push(watcher);
+  if (fs.existsSync(file)) {
+    listener();
+  }
+}