[PATCH] D114105: [clang-tidy] Ignore narrowing conversions in case of bitfields

[Clement Courbet via Phabricator via cfe-commits]

courbet added a comment.

Thanks for the details, this explains the motivation well. I think the key point is the combination of:

> It turns out doing anything useful with a bitfield will eventually result in an integral promotion, which mandates that the type must be 'int' if it fits
> conv.prom/5: <https://eel.is/c++draft/conv.prom#5>
>
>> A prvalue for an integral bit-field ([class.bit]) can be converted to a prvalue of type **int if int can represent all the values of the bit-field**; otherwise, it can be converted to unsigned int if unsigned int can represent all the values of the bit-field. If the bit-field is larger yet, no integral promotion applies to it. If the bit-field has an enumerated type, it is treated as any other value of that type for promotion purposes.

and

> shift expression is the only one whose return type depends only on the //left// operand

So adding that as a comment above `ShiftingWidenedBitfieldValue` would help.

Maybe also add a note in the comment that we are not interested in whether the shift itself might overflow.


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https://reviews.llvm.org/D114105