Simulate crash

Author: vmoroz

.ado/jobs/e2e-test.yml

@@ -8,6 +8,18 @@ parameters:
       - Continuous
   - name: AgentPool
     type: object
+  - name: simulateCrashForTesting
+    # !!! TEMPORARY DEFAULT: true !!!
+    # This branch (PR/0.84-fix-e2e-test-flakiness) flips the default to true so
+    # that PR validation actually exercises the crash-dump-collection path end
+    # to end. MUST be flipped back to false before merging anywhere — with it
+    # enabled the E2E app crashes on startup and no real tests run.
+    type: boolean
+    default: true
+    # When true, drops a sentinel file that RNTesterApp-Fabric reads on startup
+    # and uses to trigger a deliberate access violation. Used to validate that
+    # the crash-dump collection path (WER LocalDumps + artifact publish)
+    # actually produces a usable .dmp in CI.
   - name: buildMatrix
     type: object
     default:
@@ -76,12 +88,33 @@ jobs:
                 echo ##vso[task.setvariable variable=StartedFabricTests]true
               displayName: Set StartedFabricTests
 
+            # Test-only: arm the crash-simulation sentinel so RNTesterApp-Fabric
+            # crashes on startup. Validates the WER LocalDumps artifact path.
+            - ${{ if eq(parameters.simulateCrashForTesting, true) }}:
+              - pwsh: |
+                  $flagPath = Join-Path $env:ProgramData 'rnw-e2e-simulate-crash.flag'
+                  New-Item -Path $flagPath -ItemType File -Force | Out-Null
+                  Write-Host "Crash-simulation sentinel created at $flagPath"
+                displayName: Arm crash-simulation sentinel (TEST ONLY)
+
             - script: |
                 yarn e2etest
               displayName: yarn e2etest
               workingDirectory: packages/e2e-test-app-fabric
               timeoutInMinutes: 10 # Time to wait for this task to complete before the server kills it.
 
+            # Always disarm the crash sentinel so it cannot leak to a rerun on
+            # the same agent.
+            - ${{ if eq(parameters.simulateCrashForTesting, true) }}:
+              - pwsh: |
+                  $flagPath = Join-Path $env:ProgramData 'rnw-e2e-simulate-crash.flag'
+                  if (Test-Path $flagPath) {
+                    Remove-Item $flagPath -Force
+                    Write-Host "Removed crash-simulation sentinel at $flagPath"
+                  }
+                displayName: Disarm crash-simulation sentinel (TEST ONLY)
+                condition: always()
+
             # On test failure, snapshot any lingering RNTesterApp-Fabric / node
             # processes before subsequent steps (or the agent) tear them down.
             # WER LocalDumps only fires on actual crashes; this catches hangs

packages/e2e-test-app-fabric/windows/RNTesterApp-Fabric/RNTesterApp-Fabric.cpp

@@ -99,8 +99,33 @@ winrt::Microsoft::ReactNative::ReactNativeHost CreateReactNativeHost(
   return host;
 }
 
+// Test-only: if the sentinel file exists, deliberately crash the app on startup.
+// Used by the E2E pipeline (see .ado/jobs/e2e-test.yml `simulateCrashForTesting`
+// parameter) to validate that the WER LocalDumps path produces a usable crash
+// dump artifact. File-based trigger is used because environment variables do
+// not reliably propagate through the packaged-app activation flow used by the
+// automation test driver.
+static void MaybeSimulateCrashForTesting() {
+  wchar_t flagPath[MAX_PATH];
+  DWORD len = GetEnvironmentVariableW(L"ProgramData", flagPath, MAX_PATH);
+  if (len == 0 || len >= MAX_PATH) {
+    return;
+  }
+  if (FAILED(PathCchAppend(flagPath, MAX_PATH, L"rnw-e2e-simulate-crash.flag"))) {
+    return;
+  }
+  if (GetFileAttributesW(flagPath) == INVALID_FILE_ATTRIBUTES) {
+    return;
+  }
+  // Deliberate null-pointer write to trigger an access violation. Volatile so
+  // the optimizer keeps it.
+  *reinterpret_cast<volatile int *>(nullptr) = 0xC0FFEE;
+}
+
 _Use_decl_annotations_ int CALLBACK
 WinMain(HINSTANCE /* instance */, HINSTANCE, PSTR /* commandLine */, int /* showCmd */) {
+  MaybeSimulateCrashForTesting();
+
   // Initialize WinRT.
   winrt::init_apartment(winrt::apartment_type::single_threaded);