Use one lstat call instead of calling exists first

extensions/ql-vscode/src/common/vscode/file-path-discovery.ts

@@ -9,8 +9,8 @@ import {
 import { MultiFileSystemWatcher } from "./multi-file-system-watcher";
 import { AppEventEmitter } from "../events";
 import { extLogger } from "..";
-import { lstat, pathExists } from "fs-extra";
-import { containsPath } from "../../pure/files";
+import { lstat } from "fs-extra";
+import { containsPath, isIOError } from "../../pure/files";
 import { getOnDiskWorkspaceFoldersObjects } from "./workspace-folders";
 
 interface PathData {
@@ -140,13 +140,24 @@ export abstract class FilePathDiscovery<T extends PathData> extends Discovery {
   }
 
   private async handledChangedPath(path: string): Promise<boolean> {
-    if (!(await pathExists(path)) || !this.pathIsInWorkspace(path)) {
-      return this.handleRemovedPath(path);
+    try {
+      // If the path is not in the workspace then we don't want to be
+      // tracking or displaying it, so treat it as if it doesn't exist.
+      if (!this.pathIsInWorkspace(path)) {
+        return this.handleRemovedPath(path);
+      }
+
+      if ((await lstat(path)).isDirectory()) {
+        return await this.handleChangedDirectory(path);
+      } else {
+        return this.handleChangedFile(path);
+      }
+    } catch (e) {
+      if (isIOError(e) && e.code === "ENOENT") {
+        return this.handleRemovedPath(path);
+      }
+      throw e;
     }
-    if ((await lstat(path)).isDirectory()) {
-      return await this.handleChangedDirectory(path);
-    }
-    return this.handleChangedFile(path);
   }
 
   private pathIsInWorkspace(path: string): boolean {

extensions/ql-vscode/src/pure/files.ts

@@ -107,3 +107,14 @@ export async function* walkDirectory(
     }
   }
 }
+
+/**
+ * Error thrown from methods from the 'fs' module.
+ */
+export interface IOError {
+  readonly code: string;
+}
+
+export function isIOError(e: any): e is IOError {
+  return e.code !== undefined && typeof e.code === "string";
+}