Bug 1798373 Part 4 - Remove nsFrameList::SetFrames() that takes nsFrameList. r=emilio

SetFrame() is equivalent to `operator=`, so external callers can use `operator=`
instead. For the two callers wanting to set `nsFrameList` to `AbsoluteFrameList`
in `nsCSSFrameConstructor`, removing SetFrame() disallows it. However, we can
easily change the declaration from `nsFrameList` to a `AbsoluteFrameList` to
resolve the problem.

Differential Revision: https://phabricator.services.mozilla.com/D160840

layout/base/nsCSSFrameConstructor.cpp

@@ -996,7 +996,7 @@ void nsFrameConstructorState::ReparentAbsoluteItems(
   MOZ_ASSERT(aNewParent->HasAnyStateBits(NS_FRAME_HAS_MULTI_COLUMN_ANCESTOR),
              "Restrict the usage under column hierarchy.");
 
-  nsFrameList newAbsoluteItems;
+  AbsoluteFrameList newAbsoluteItems(aNewParent);
 
   nsIFrame* current = mAbsoluteList.FirstChild();
   while (current) {
@@ -1020,7 +1020,7 @@ void nsFrameConstructorState::ReparentAbsoluteItems(
     // It doesn't matter whether aNewParent has position style or not. Caller
     // won't call us if we can't have absolute children.
     PushAbsoluteContainingBlock(aNewParent, aNewParent, absoluteSaveState);
-    mAbsoluteList.SetFrames(newAbsoluteItems);
+    mAbsoluteList = std::move(newAbsoluteItems);
   }
 }
 
@@ -1032,7 +1032,7 @@ void nsFrameConstructorState::ReparentFloats(nsContainerFrame* aNewParent) {
       "Why calling this method if aNewParent is not a float containing block?");
 
   // Gather floats that should reparent under aNewParent.
-  nsFrameList floats;
+  AbsoluteFrameList floats(aNewParent);
   nsIFrame* current = mFloatedList.FirstChild();
   while (current) {
     nsIFrame* placeholder = current->GetPlaceholderFrame();
@@ -1049,7 +1049,7 @@ void nsFrameConstructorState::ReparentFloats(nsContainerFrame* aNewParent) {
     // ~nsFrameConstructorSaveState() when destructing floatSaveState.
     nsFrameConstructorSaveState floatSaveState;
     PushFloatContainingBlock(aNewParent, floatSaveState);
-    mFloatedList.SetFrames(floats);
+    mFloatedList = std::move(floats);
   }
 }
 

layout/generic/nsAbsoluteContainingBlock.cpp

@@ -54,7 +54,7 @@ void nsAbsoluteContainingBlock::SetInitialChildList(nsIFrame* aDelegatingFrame,
     MOZ_ASSERT(f->GetParent() == aDelegatingFrame, "Unexpected parent");
   }
 #endif
-  mAbsoluteFrames.SetFrames(aChildList);
+  mAbsoluteFrames = std::move(aChildList);
 }
 
 void nsAbsoluteContainingBlock::AppendFrames(nsIFrame* aDelegatingFrame,

layout/generic/nsBlockFrame.cpp

@@ -7482,7 +7482,7 @@ void nsBlockFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
 void nsBlockFrame::SetInitialChildList(ChildListID aListID,
                                        nsFrameList& aChildList) {
   if (kFloatList == aListID) {
-    mFloats.SetFrames(aChildList);
+    mFloats = std::move(aChildList);
   } else if (kPrincipalList == aListID) {
 #ifdef DEBUG
     // The only times a block that is an anonymous box is allowed to have a

layout/generic/nsContainerFrame.cpp

@@ -85,7 +85,7 @@ void nsContainerFrame::SetInitialChildList(ChildListID aListID,
   if (aListID == kPrincipalList) {
     MOZ_ASSERT(mFrames.IsEmpty(),
                "unexpected second call to SetInitialChildList");
-    mFrames.SetFrames(aChildList);
+    mFrames = std::move(aChildList);
   } else if (aListID == kBackdropList) {
     MOZ_ASSERT(StyleDisplay()->mTopLayer != StyleTopLayer::None,
                "Only top layer frames should have backdrop");

layout/generic/nsFirstLetterFrame.cpp

@@ -78,7 +78,7 @@ void nsFirstLetterFrame::SetInitialChildList(ChildListID aListID,
     nsLayoutUtils::MarkDescendantsDirty(f);  // Drops cached textruns
   }
 
-  mFrames.SetFrames(aChildList);
+  mFrames = std::move(aChildList);
 }
 
 nsresult nsFirstLetterFrame::GetChildFrameContainingOffset(

layout/generic/nsFrameList.h

@@ -115,7 +115,10 @@ class nsFrameList {
   }
   nsFrameList& operator=(nsFrameList&& aOther) {
     if (this != &aOther) {
-      SetFrames(aOther);
+      MOZ_ASSERT(IsEmpty(), "Assigning to a non-empty list will lose frames!");
+      mFirstChild = aOther.FirstChild();
+      mLastChild = aOther.LastChild();
+      aOther.Clear();
     }
     return *this;
   }
@@ -147,14 +150,6 @@ class nsFrameList {
 
   void Clear() { mFirstChild = mLastChild = nullptr; }
 
-  void SetFrames(nsFrameList& aFrameList) {
-    MOZ_ASSERT(!mFirstChild, "Losing frames");
-
-    mFirstChild = aFrameList.FirstChild();
-    mLastChild = aFrameList.LastChild();
-    aFrameList.Clear();
-  }
-
   /**
    * Append aFrameList to this list.  If aParent is not null,
    * reparents the newly added frames.  Clears out aFrameList and

layout/generic/nsInlineFrame.cpp

@@ -308,7 +308,7 @@ void nsInlineFrame::Reflow(nsPresContext* aPresContext, ReflowOutput& aMetrics,
         // wait to do this until we actually reflow the frame. If the overflow
         // list contains thousands of frames this is a big performance issue
         // (see bug #5588)
-        mFrames.SetFrames(*prevOverflowFrames);
+        mFrames = std::move(*prevOverflowFrames);
         lazilySetParentPointer = true;
       } else {
         // Insert the new frames at the beginning of the child list

layout/tables/nsTableWrapperFrame.cpp

@@ -94,7 +94,7 @@ void nsTableWrapperFrame::SetInitialChildList(ChildListID aListID,
     // the frame constructor already checked for table-caption display type
     MOZ_ASSERT(mCaptionFrames.IsEmpty(),
                "already have child frames in CaptionList");
-    mCaptionFrames.SetFrames(aChildList);
+    mCaptionFrames = std::move(aChildList);
   } else {
     MOZ_ASSERT(kPrincipalList != aListID ||
                    (aChildList.FirstChild() &&