1215411 - (MOZ_FALLTHROUGH) Define MOZ_FALLTHROUGH annotation to suppress clang's -Wimplicit-fallthrough warnings

Status: RESOLVED FIXED

(Core :: MFBT, defect)

Description

[Chris Peterson [:cpeterson]]

Attachment: MOZ_FALLTHROUGH.patch

clang's optional -Wimplicit-fallthrough compiler warning warns about switch
cases that fall through without a break or return statement. MOZ_FALLTHROUGH is an annotation to suppress these warnings. MOZ_FALLTHROUGH is only needed on cases that have code.

I'd like to start fixing the 670 -Wimplicit-fallthrough warnings in mozilla-central. I have local patches to annotate about 200 cases so far and I have found at least 4 real bugs. :)

  switch (foo) {
    case 1: // These cases have no code. No fallthrough annotations are needed.
    case 2:
    case 3:
      foo = 4; // This case has code, so a fallthrough annotation is needed:
      MOZ_FALLTHROUGH;
    default:
      return foo;
  }

clang's fallthrough annotation is only available starting in C++11 because it uses C++11 annotation syntax. MSVC's __fallthrough annotations are checked by MSVC /analyze (Code Analysis), though I have not tested it. gcc does not have a similar warning or annotation.

Comment 1

[:Ms2ger (he/him; ⌚ UTC+1/+2)]

Comment on attachment 8674690 [details] [diff] [review]
MOZ_FALLTHROUGH.patch

Review of attachment 8674690 [details] [diff] [review]:
-----------------------------------------------------------------

Seems neat.

Comment 2

[Botond Ballo [:botond]]

Comment on attachment 8674690 [details] [diff] [review]
MOZ_FALLTHROUGH.patch

Sorry, I meant to r+!

Comment 3

[Chris Peterson [:cpeterson]]

Thanks!

Comment 4

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/b63d88406a53

Comment 5

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/b63d88406a53