https://chromium.googlesource.com/chromium/src/+/master/docs/clang.md says to implement all new clang plugins behind a flag for at least one clang roll.

The flag check-enum-unsigned-bitfields enables a check for enums used in bitfields. Enum bitfields should use unsigned as the underlying type to prevent strange behavior in MSVC (see design doc: https://docs.google.com/document/d/1BfjMEXIzvY1WZEn_nESBxyqkazkfa0sBSEvm-F89YwM/edit and discussion on style-dev: https://www.google.com/url?hl=en&q=https://groups.google.com/a/chromium.org/d/msgid/style-dev/CADAgNurPp47TyFcws6LAyY%253DAxT5RpRb0MkAWJ_G3J2oL0Uj-mg%2540mail.gmail.com?utm_medium%3Demail%26utm_source%3Dfooter&source=gmail&ust=1471065087985000&usg=AFQjCNGjo6xUygkhjxGo90tVmjGrlm6MiA). Allowing enums in bitfields has the advantage of saving space while not having to use static casts when reading from/writing to the bitfield, as well as not having to match the correct underlying type (signed/unsigned) when deciding the field to store.
 

https://chromium.googlesource.com/chromium/src/+/master/docs/clang.md says to implement all new clang plugins behind a flag for at least one clang roll.

The flag check-enum-unsigned-bitfields enables a check for enums used in bitfields. Enum bitfields should use unsigned as the underlying type to prevent strange behavior in MSVC.

Design Doc:
https://docs.google.com/document/d/1BfjMEXIzvY1WZEn_nESBxyqkazkfa0sBSEvm-F89YwM/edit

Discussion on style-dev:
https://www.google.com/url?hl=en&q=https://groups.google.com/a/chromium.org/d/msgid/style-dev/CADAgNurPp47TyFcws6LAyY%253DAxT5RpRb0MkAWJ_G3J2oL0Uj-mg%2540mail.gmail.com?utm_medium%3Demail%26utm_source%3Dfooter&source=gmail&ust=1471065087985000&usg=AFQjCNGjo6xUygkhjxGo90tVmjGrlm6MiA).


Allowing enums in bitfields has the advantage of saving space while not having to use static casts when reading from/writing to the bitfield, as well as not having to match the correct underlying type (signed/unsigned) when deciding the field to store.
 

https://chromium.googlesource.com/chromium/src/+/master/docs/clang.md says to implement all new clang plugins behind a flag for at least one clang roll.

The flag check-enum-unsigned-bitfields enables a check for enums used in bitfields. Enum bitfields should use unsigned as the underlying type to prevent strange behavior in MSVC.

Design Doc (in context of ComputedStyle):
https://docs.google.com/document/d/1BfjMEXIzvY1WZEn_nESBxyqkazkfa0sBSEvm-F89YwM/edit

Discussion on style-dev:
https://www.google.com/url?hl=en&q=https://groups.google.com/a/chromium.org/d/msgid/style-dev/CADAgNurPp47TyFcws6LAyY%253DAxT5RpRb0MkAWJ_G3J2oL0Uj-mg%2540mail.gmail.com?utm_medium%3Demail%26utm_source%3Dfooter&source=gmail&ust=1471065087985000&usg=AFQjCNGjo6xUygkhjxGo90tVmjGrlm6MiA).


Allowing enums in bitfields has the advantage of saving space while not having to use static casts when reading from/writing to the bitfield, as well as not having to match the correct underlying type (signed/unsigned) when deciding the field to store.