1236393 - Annotate intentional switch fallthrough to suppress -Wimplicit-fallthrough warning in tools/power/rapl.cpp

Status: RESOLVED FIXED

(Core :: General, defect)

Description

[Chris Peterson [:cpeterson]]

Attachment: annotate-rapl-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 where the fallthrough is intentional.

rapl.cpp deliberately uses only standard libraries and avoids Mozilla-specific code, to make it easy to compile and test on different machines. MOZ_FALLTHROUGH is defined in MFBT's Attributes.h, which we can't #include in rapl.cpp so I copied the MOZ_FALLTHROUGH definition. Should I add a comment saying this definition was copied from Attributes.h?

Alternately, if you don't like the duplicate MOZ_FALLTHROUGH definitions in multiple files, I could instead suppress the warning with -Wno-implicit-fallthrough in tools/power/moz.build.

tools/power/rapl.cpp:331:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels

Comment 1

[Nicholas Nethercote [inactive]]

Comment on attachment 8703473 [details] [diff] [review]
annotate-rapl-fallthrough.patch

Review of attachment 8703473 [details] [diff] [review]:
-----------------------------------------------------------------

::: tools/power/rapl.cpp
@@ +53,5 @@
>  //---------------------------------------------------------------------------
>  
> +// MOZ_FALLTHROUGH is an annotation to suppress compiler warnings about switch
> +// cases that fall through without a break or return statement. MOZ_FALLTHROUGH
> +// is only needed on cases that have code.

I suggest changing this comment to something like "This is identical to the definition in mfbt/Attributes.h, which we don't use here because this file avoids depending on Mozilla headers."

Comment 2

[Chris Peterson [:cpeterson]]

(In reply to Nicholas Nethercote [:njn] from comment #1)
> I suggest changing this comment to something like "This is identical to the
> definition in mfbt/Attributes.h, which we don't use here because this file
> avoids depending on Mozilla headers."

Thanks. I'll add this comment before landing.

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/c1b0bb0c1201

Comment 4

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/c1b0bb0c1201