Fix possible race condition for new and changed scripts

src/chrome/chromeDebugAdapter.ts

@@ -857,6 +857,8 @@ export abstract class ChromeDebugAdapter implements IDebugAdapter {
     }
 
     protected async sendLoadedSourceEvent(script: Crdp.Debugger.ScriptParsedEvent, loadedSourceEventReason: LoadedSourceEventReason = 'new'): Promise<void> {
+        const source = await this.scriptToSource(script);
+
         // This is a workaround for an edge bug, see https://github.com/Microsoft/vscode-chrome-debug-core/pull/329
         switch (loadedSourceEventReason) {
             case 'new':
@@ -878,7 +880,7 @@ export abstract class ChromeDebugAdapter implements IDebugAdapter {
                 telemetry.reportEvent('LoadedSourceEventError', { issue: 'Unknown reason', reason: loadedSourceEventReason });
         }
 
-        const scriptEvent = await this.scriptToLoadedSourceEvent(loadedSourceEventReason, script);
+        const scriptEvent = new LoadedSourceEvent(loadedSourceEventReason, source as any);
 
         this._session.sendEvent(scriptEvent);
     }
@@ -1944,11 +1946,6 @@ export abstract class ChromeDebugAdapter implements IDebugAdapter {
         };
     }
 
-    private async scriptToLoadedSourceEvent(reason: LoadedSourceEventReason, script: Crdp.Debugger.ScriptParsedEvent): Promise<LoadedSourceEvent> {
-        const source = await this.scriptToSource(script);
-        return new LoadedSourceEvent(reason, source as any);
-    }
-
     private async scriptToSource(script: Crdp.Debugger.ScriptParsedEvent): Promise<DebugProtocol.Source> {
         const sourceReference = this.getSourceReferenceForScriptId(script.scriptId);
         const origin = this.getReadonlyOrigin(script.url);

test/chrome/chromeDebugAdapter.test.ts

@@ -22,6 +22,7 @@ import { Protocol as Crdp } from 'devtools-protocol';
 
 import * as testUtils from '../testUtils';
 import * as utils from '../../src/utils';
+import * as fs from 'fs';
 
 /** Not mocked - use for type only */
 import {ChromeDebugAdapter as _ChromeDebugAdapter } from '../../src/chrome/chromeDebugAdapter';
@@ -603,6 +604,78 @@ suite('ChromeDebugAdapter', () => {
             });
         });
 
+        // This is needed for Edge debug adapter, please keep the logic of sendLoadedSourceEvent()
+        test('tests that sendLoadedSourceEvent will set the `reason` parameter based on our internal view of the events we sent to the client even if fs.access takes unexpected times while blocking async', async () => {
+            let eventIndex = 0;
+            sendEventHandler = (event) => {
+                switch (eventIndex) {
+                    case 0:
+                        assert.equal('loadedSource', event.event);
+                        assert.notEqual(null, event.body);
+                        assert.equal('new', event.body.reason);
+                        break;
+                    case 1:
+                        assert.equal('loadedSource', event.event);
+                        assert.notEqual(null, event.body);
+                        assert.equal('changed', event.body.reason);
+                        break;
+                    default:
+                        throw new RangeError('Unexpected event index');
+                }
+                ++eventIndex;
+            };
+
+            await chromeDebugAdapter.attach(ATTACH_ARGS);
+
+            const originalFSAccess = fs.access;
+            let callIndex = 0;
+            let callbackForFirstEvent = null;
+
+            /* Mock fs.access so the first call will block until the second call is finished */
+            (fs as any).access = (path, callback) => {
+                if (callIndex === 0) {
+                    callbackForFirstEvent = callback;
+                    console.log("Blocking first fs.access until second call is finished");
+                    ++callIndex;
+                } else {
+                    callback();
+
+                    if (callbackForFirstEvent !== null) {
+                        console.log("Second call when thorugh. Unblocking first call");
+                        setTimeout(callbackForFirstEvent, 50);
+                        callbackForFirstEvent = null;
+                    }
+                }
+            };
+
+            try {
+                const firstEvent = (<any>chromeDebugAdapter).sendLoadedSourceEvent({
+                    scriptId: 1,
+                    url: '',
+                    startLine: 0,
+                    startColumn: 0,
+                    endLine: 0,
+                    endColumn: 0,
+                    executionContextId: 0,
+                    hash: ''
+                });
+                const secondEvent =  (<any>chromeDebugAdapter).sendLoadedSourceEvent({
+                    scriptId: 1,
+                    url: '',
+                    startLine: 0,
+                    startColumn: 0,
+                    endLine: 0,
+                    endColumn: 0,
+                    executionContextId: 0,
+                    hash: ''
+                });
+
+                await Promise.all([firstEvent, secondEvent]);
+            } finally {
+                (fs as any).access = originalFSAccess;
+            }
+        });
+
         function createSource(name: string, path?: string, sourceReference?: number, origin?: string): Source {
             return <Source>{
                 name: name,