1 files changed, 90 insertions, 0 deletions
diff --git a/layout/base/nsAutoLayoutPhase.cpp b/layout/base/nsAutoLayoutPhase.cpp
new file mode 100644
index 0000000000..94258f943e
--- /dev/null
+++ b/layout/base/nsAutoLayoutPhase.cpp
@@ -0,0 +1,90 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DEBUG
+static_assert(false, "This should not be compiled in !DEBUG");
+#endif  // DEBUG
+
+#include "nsAutoLayoutPhase.h"
+#include "nsPresContext.h"
+#include "nsContentUtils.h"
+
+nsAutoLayoutPhase::nsAutoLayoutPhase(nsPresContext* aPresContext,
+                                     nsLayoutPhase aPhase)
+    : mPresContext(aPresContext), mPhase(aPhase), mCount(0) {
+  Enter();
+}
+
+nsAutoLayoutPhase::~nsAutoLayoutPhase() {
+  Exit();
+  MOZ_ASSERT(mCount == 0, "imbalanced");
+}
+
+void nsAutoLayoutPhase::Enter() {
+  switch (mPhase) {
+    case nsLayoutPhase::Paint:
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Paint] == 0,
+                 "recurring into paint");
+      MOZ_ASSERT(
+          mPresContext->mLayoutPhaseCount[nsLayoutPhase::DisplayListBuilding] ==
+              0,
+          "recurring into paint from display list building");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Reflow] == 0,
+                 "painting in the middle of reflow");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::FrameC] == 0,
+                 "painting in the middle of frame construction");
+      break;
+    case nsLayoutPhase::DisplayListBuilding:
+      // It's fine and expected to be in a paint here.
+      MOZ_ASSERT(
+          mPresContext->mLayoutPhaseCount[nsLayoutPhase::DisplayListBuilding] ==
+              0,
+          "recurring into display list building");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Reflow] == 0,
+                 "display list building in the middle of reflow");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::FrameC] == 0,
+                 "display list building in the middle of frame construction");
+      break;
+    case nsLayoutPhase::Reflow:
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Paint] == 0,
+                 "reflowing in the middle of a paint");
+      MOZ_ASSERT(
+          mPresContext->mLayoutPhaseCount[nsLayoutPhase::DisplayListBuilding] ==
+              0,
+          "reflowing in the middle of a display list building");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Reflow] == 0,
+                 "recurring into reflow");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::FrameC] == 0,
+                 "reflowing in the middle of frame construction");
+      break;
+    case nsLayoutPhase::FrameC:
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Paint] == 0,
+                 "constructing frames in the middle of a paint");
+      MOZ_ASSERT(
+          mPresContext->mLayoutPhaseCount[nsLayoutPhase::DisplayListBuilding] ==
+              0,
+          "constructing frames in the middle of a display list building");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::Reflow] == 0,
+                 "constructing frames in the middle of reflow");
+      MOZ_ASSERT(mPresContext->mLayoutPhaseCount[nsLayoutPhase::FrameC] == 0,
+                 "recurring into frame construction");
+      MOZ_ASSERT(!nsContentUtils::IsSafeToRunScript(),
+                 "constructing frames and scripts are not blocked");
+      break;
+    case nsLayoutPhase::COUNT:
+      break;
+  }
+
+  ++(mPresContext->mLayoutPhaseCount[mPhase]);
+  ++mCount;
+}
+
+void nsAutoLayoutPhase::Exit() {
+  MOZ_ASSERT(mCount > 0 && mPresContext->mLayoutPhaseCount[mPhase] > 0,
+             "imbalanced");
+  --(mPresContext->mLayoutPhaseCount[mPhase]);
+  --mCount;
+}