Bug 254750 – Return value of LineBoxBuilder::lineContent is not a reference

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[Michael Catanzaro]

The return value of LineBoxBuilder::lineContent looks probably incorrect:

const LineBuilder::LineContent lineContent() const { return m_lineContent; }

If it was intended to return a copy, then it would surely return a non-const LineBuilder::LineContent, so I think this should probably be changed to:

const LineBuilder::LineContent& lineContent() const { return m_lineContent; }

But I have not checked to see if this change would be safe. I noticed due to this false-positive GCC 13 warning:

In file included from /home/mcatanzaro/Projects/WebKit/WebKitBuild/gtk4/WebCore/DerivedSources/unified-sources/UnifiedSource-207b877e-5.cpp:2:
/home/mcatanzaro/Projects/WebKit/Source/WebCore/layout/formattingContexts/inline/InlineLineBoxBuilder.cpp: In member function ‘void WebCore::Layout::LineBoxBuilder::adjustOutsideListMarkersPosition(WebCore::Layout::LineBox&)’:
/home/mcatanzaro/Projects/WebKit/Source/WebCore/layout/formattingContexts/inline/InlineLineBoxBuilder.cpp:714:15: error: possibly dangling reference to a temporary [-Werror=dangling-reference]
  714 |         auto& listMarkerRun = lineContent().runs[listMarkerBoxIndex];
      |               ^~~~~~~~~~~~~
/home/mcatanzaro/Projects/WebKit/Source/WebCore/layout/formattingContexts/inline/InlineLineBoxBuilder.cpp:714:68: note: the temporary was destroyed at the end of the full expression ‘(& WebCore::Layout::LineBoxBuilder::lineContent() const().WebCore::Layout::LineBuilder::LineContent::runs)->WTF::Vector<WebCore::Layout::Line::Run, 10>::operator[](listMarkerBoxIndex)’
  714 |         auto& listMarkerRun = lineContent().runs[listMarkerBoxIndex];
      |                                                                    ^

It looks bad, but I don't think it's a real problem because although lineContent() is itself invalid after this statement, lineContent().runs[listMarkerBoxIndex] should still be valid.

[zalan]

hah, indeed. That's very silly. Thank you! Let me quickly fix that.

[zalan]

Created attachment 465683 [details]
Patch

[zalan]

Created attachment 465691 [details]
[fast-cq]Patch

[EWS]

Committed 262366@main (eff08853244b): <https://commits.webkit.org/262366@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 465691 [details].

[Radar WebKit Bug Importer]

<rdar://problem/107440230>

[zalan]

Thanks again, Michael!