1236323 - Annotate intentional switch fallthroughs to suppress -Wimplicit-fallthrough warnings in gfx/

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[Chris Peterson [:cpeterson]]

Attachment: gfx_part-1_MOZ_FALLTHROUGH.patch

clang's -Wimplicit-fallthrough warnings (not yet enabled in mozilla-central) warn about switch cases that fall through without a break or return statement. MOZ_FALLTHROUGH (bug 1215411) is an annotation to suppress -Wimplicit-fallthrough warnings about switch cases that intentionally fall through without a break or return statement.  MOZ_FALLTHROUGH is only needed on cases that have code.

MOZ_FALLTHROUGH_ASSERT (bug 1235277) will suppress -Wimplicit-fallthrough warnings about switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in debug builds, but intentionally fall through in release builds.

Why do we need MOZ_FALLTHROUGH_ASSERT in addition to MOZ_FALLTHROUGH? In release builds, the MOZ_ASSERT(false) will expand to `do { } while (0)`, requiring a MOZ_FALLTHROUGH annotation to suppress a -Wimplicit-fallthrough warning. In debug builds, the MOZ_ASSERT(false) will expand to something like `if (true) { MOZ_CRASH(); }` and the MOZ_FALLTHROUGH annotation will cause a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this warning stalemate.

gfx/thebes/gfxFcPlatformFontList.cpp:706:9: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
gfx/thebes/gfxFontconfigFonts.cpp:2183:9: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
gfx/2d/DrawTargetCG.cpp:812:5: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
gfx/2d/DrawTargetCairo.cpp:636:5: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]

Comment 1

[Chris Peterson [:cpeterson]]

Attachment: gfx_part-2_Wno-implicit-fallthrough.patch

Part 2: Suppress -Wimplicit-fallthrough warnings in gfx/ from Skia header files. I will try to submit upstream fixes for these Skia warnings. Then I can remove this -Wno-implicit-fallthrough change from mozilla-central.

gfx/skia/skia/include/gpu/GrTestUtils.h:94:9 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
gfx/skia/skia/include/gpu/GrTypesPriv.h:181:9 [-Wimplicit-fallthrough] unannotated fall-through between switch labels

Comment 2

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/0e3c7d1d3c80
https://hg.mozilla.org/integration/mozilla-inbound/rev/400861eb8c62

Comment 3

[Chris Peterson [:cpeterson]]

I backed out part 2 for introducing -Wunreachable-code warnings-as-errors, which I have a fix waiting for review in bug 1237352.

Comment 4

[Pulsebot]

Backout:
https://hg.mozilla.org/integration/mozilla-inbound/rev/2c86ca757a1e

Comment 5

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/0e3c7d1d3c80

Comment 6

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9f62f4be98b0

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/9f62f4be98b0