1236322 - Annotate intentional switch fallthroughs to suppress -Wimplicit-fallthrough warnings in parser/

Status: RESOLVED FIXED

(Core :: DOM: HTML Parser, defect)

Description

[Chris Peterson [:cpeterson]]

Attachment: parser_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.

parser/html/nsHtml5Highlighter.cpp:572:9 [-Wimplicit-fallthrough] unannotated fall-through between switch labels

parser/htmlparser/nsScanner.cpp:425:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/htmlparser/nsScanner.cpp:780:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels

Comment 1

[Chris Peterson [:cpeterson]]

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

Part 2: Suppress -Wimplicit-fallthrough warnings in parser/html generated code.

parser/html/nsHtml5Tokenizer.cpp:456:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:463:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:524:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:540:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:563:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:574:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:592:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:611:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:619:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:631:7 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
parser/html/nsHtml5Tokenizer.cpp:647:13 [-Wimplicit-fallthrough] unannotated fall-through between switch labels
...

Comment 2

[Henri Sivonen (:hsivonen)]

Comment on attachment 8703397 [details] [diff] [review]
parser_part-2_Wno-implicit-fallthrough.patch

Review of attachment 8703397 [details] [diff] [review]:
-----------------------------------------------------------------

I've annotated implicit fallthroughs as comments in the Java source, so at some point as a follow-up, I should make the translator translate those into annotations in the C++

Comment 3

[Chris Peterson [:cpeterson]]

(In reply to Henri Sivonen (:hsivonen) from comment #2)
> I've annotated implicit fallthroughs as comments in the Java source, so at
> some point as a follow-up, I should make the translator translate those into
> annotations in the C++

Thanks. I'll look to add the annotations to the Java translator.

Comment 4

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/159e7916ff7d
https://hg.mozilla.org/integration/mozilla-inbound/rev/462d202bc50d

Comment 5

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/159e7916ff7d
https://hg.mozilla.org/mozilla-central/rev/462d202bc50d

Comment 6

[Chris Peterson [:cpeterson]]

Bug 1236322 suppressed clang -Wimplicit-fallthrough warnings in the generated parser code because it did not include MOZ_FALLTHROUGH annotations. I updated the Java translator in bug 1424548.