1508927 - (Wbitfield-enum-conversion) Enable clang's -Wbitfield-enum-conversion warnings

Status: RESOLVED FIXED

(Developer Infrastructure :: Source Code Analysis, enhancement, P3)

Description

[Chris Peterson [:cpeterson]]

clang's -Wbitfield-enum-conversion warning reports when an enum value is assigned to a bit field that is not wide enough to store all the enum values:

https://clang.llvm.org/docs/DiagnosticsReference.html#wbitfield-enum-conversion

This warning found some real layout style bugs where a 4-bit enum was implicitly truncated to a 3-bit bit field:

layout/tables/nsTableFrame.cpp:5318:14 [-Wbitfield-enum-conversion] bit-field 'ownerElem' is not wide enough to store all enumerators of 'BCBorderOwner'
layout/tables/nsTableFrame.cpp:5358:16 [-Wbitfield-enum-conversion] bit-field 'ownerElem' is not wide enough to store all enumerators of 'BCBorderOwner'
layout/tables/nsTableFrame.cpp:5374:18 [-Wbitfield-enum-conversion] bit-field 'subElem' is not wide enough to store all enumerators of 'BCBorderOwner'
layout/tables/nsTableFrame.cpp:5385:18 [-Wbitfield-enum-conversion] bit-field 'subElem' is not wide enough to store all enumerators of 'BCBorderOwner'

I fixed the bit fields (bug 1485179), which unfortunately revealed some underlying layout bugs (bug 1508921) that depended on the buggy behavior.

Comment 1

[Chris Peterson [:cpeterson]]

Attachment: Bug 1508927 - Enable clang's -Wbitfield-enum-conversion warnings. r?glandium

https://clang.llvm.org/docs/DiagnosticsReference.html#wbitfield-enum-conversion

This clang warning caught a real layout bug related to implicitly truncated enums in the table border style code (bug 1485179):

layout/tables/nsTableFrame.cpp:5318:14 [-Wbitfield-enum-conversion] bit-field 'ownerElem' is not wide enough to store all enumerators of 'BCBorderOwner'
layout/tables/nsTableFrame.cpp:5358:16 [-Wbitfield-enum-conversion] bit-field 'ownerElem' is not wide enough to store all enumerators of 'BCBorderOwner'
layout/tables/nsTableFrame.cpp:5374:18 [-Wbitfield-enum-conversion] bit-field 'subElem' is not wide enough to store all enumerators of 'BCBorderOwner'
layout/tables/nsTableFrame.cpp:5385:18 [-Wbitfield-enum-conversion] bit-field 'subElem' is not wide enough to store all enumerators of 'BCBorderOwner'

Also update the comment linking to clang and gcc's warning documentation.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6feb94524b7e
Enable clang's -Wbitfield-enum-conversion warnings. r=glandium

Comment 3

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/6feb94524b7e