[clangd] Show FileStatus in vscode-clangd.

[hokein]

Summary

The file status will be shown in the status bar.
Depends on D55363.

A quick demo: https://reviews.llvm.org/file/data/muv5qgpfjkue4457nz43/PHID-FILE-lma2zbe7adntmzxwgtbv/vscode.gif

[hokein]

Update the patch to reflect LSP file status latest change.

[hokein]

The patch is ready for review now.

[ilya-biryukov]

LGTM

clangd/clients/clangd-vscode/src/extension.ts

 }
 
 namespace SwitchSourceHeaderRequest {
 export const type =
     new vscodelc.RequestType<vscodelc.TextDocumentIdentifier, string|undefined,
                              void, void>('textDocument/switchSourceHeader');
 }
 
+class FileStatus {
+    private statuses = new Map<string, any>();
+    private readonly statusBarItem =
+        vscode.window.createStatusBarItem(vscode.StatusBarAlignment.Left, 10);
+
+    onFileUpdated(fileStatus: any) {
+      const filePath = vscode.Uri.parse(fileStatus.uri);
+      this.statuses.set(filePath.fsPath, fileStatus);
+      this.updateStatus();
+    }
+
+    updateStatus() {
+        const path = vscode.window.activeTextEditor.document.fileName;
+        const status = this.statuses.get(path);
+        if (!status) {
+          this.statusBarItem.hide();
+          return;
+        }
+        this.statusBarItem.text = `clangd: ` + status.state;
+        // FIXME: find a way to show the details in a nicer way.
+        if (status.details.length > 0)
+            this.statusBarItem.tooltip = status.details.map(
+                (detail: any) => detail.message).join('; ');
+        this.statusBarItem.show()
+    }
+
+    dispose() {
+        this.statusBarItem.dispose();
+    }
+}
+
 /**
  *  this method is called when your extension is activate
  *  your extension is activated the very first time the command is executed
  */
 export function activate(context: vscode.ExtensionContext) {
     const syncFileEvents = getConfig<boolean>('syncFileEvents', true);
 
     const clangd: vscodelc.Executable = {
context.subscriptions.push(vscode.commands.registerCommand(
             SwitchSourceHeaderRequest.type, docIdentifier);
         if (!sourceUri) {
           return;
         }
         const doc = await vscode.workspace.openTextDocument(
             vscode.Uri.parse(sourceUri));
         vscode.window.showTextDocument(doc);
       }));
+  const status = new FileStatus();
+  context.subscriptions.push(vscode.window.onDidChangeActiveTextEditor(() => {
+      status.updateStatus();
+  }))
+  clangdClient.onReady().then(() => {
+      clangdClient.onNotification('textDocument/fileStatus', (fileStatus) => {
+          status.onFileUpdated(fileStatus)
+      });
+  })
 }