Bug 185621 – Fix -Wreturn-std-move warnings in WebKit found by new clang compiler

• Component: WebCore Misc.
• Status: RESOLVED FIXED

[David Kilzer (:ddkilzer)]

Building WebKit with a newer clang compiler enables a -Wreturn-std-move warning that catches cases where a parameter is passed by rvalue reference (T&& t), but then gets copied when returning that reference by value from the function (return t).

For example, this method:

    String PeerConnectionBackend::filterSDP(String&& sdp) const

generates a warning like this:

    In file included from DerivedSources/WebCore/unified-sources/UnifiedSource139.cpp:5:
    ./Modules/mediastream/PeerConnectionBackend.cpp:412:16: error: local variable 'sdp' will be copied despite being returned by name [-Werror,-Wreturn-std-move]
            return sdp;
                   ^~~
    ./Modules/mediastream/PeerConnectionBackend.cpp:412:16: note: call 'std::move' explicitly to avoid copying
            return sdp;
                   ^~~
                   std::move(sdp)
    1 error generated.

[David Kilzer (:ddkilzer)]

Created attachment 340343 [details]
Patch v1

[Radar WebKit Bug Importer]

<rdar://problem/40232133>

[EWS Watchlist]

Comment on attachment 340343 [details]
Patch v1

Attachment 340343 [details] did not pass win-ews (win):
Output: http://webkit-queues.webkit.org/results/7682747

New failing tests:
http/tests/security/canvas-remote-read-remote-video-blocked-no-crossorigin.html

[EWS Watchlist]

Created attachment 340377 [details]
Archive of layout-test-results from ews206 for win-future

The attached test failures were seen while running run-webkit-tests on the win-ews.
Bot: ews206  Port: win-future  Platform: CYGWIN_NT-6.1-2.9.0-0.318-5-3-x86_64-64bit

[WebKit Commit Bot]

Comment on attachment 340343 [details]
Patch v1

Clearing flags on attachment: 340343

Committed r231796: <https://trac.webkit.org/changeset/231796>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.