Re: [PATCH] gdb: don't treat empty enums as flag enums

[Andreas Schwab <schwab@suse.de>]

On Feb 20 2023, Andrew Burgess via Gdb-patches wrote:

> In C++ it is possible to use an empty enum as a strong typedef.  For
> example, a user could write:
>
>   enum class my_type : unsigned char {};
>
> Now my_type can be used like 'unsigned char' except the compiler will
> not allow implicit conversion too and from the native 'unsigned char'
> type.
>
> This is used in the standard library for things like std::byte.
>
> Currently, when GDB prints a value of type my_type, it looks like
> this:
>
>   (gdb) print my_var
>   $1 = (unknown: 0x4)
>
> Which isn't great.  This gets worse when we consider something like:
>
>   std::vector<my_type> vec;
>
> When using a pretty-printer, this could look like this:
>
>   std::vector of length 2, capacity 2 = {(unknown: 0x2), (unknown: 0x4)}
>
> Clearly not great.  This is described in PR gdb/30148.
>
> The problem here is in dwarf2/read.c, we assume all enums are flag
> enums unless we find an enumerator with a non-flag like value.
> Clearly an empty enum contains no non-flag values, so we assume the
> enum is a flag enum.
>
> I propose adding an extra check here; that is, an empty enum should
> never be a flag enum.
>
> With this the above cases look more like:
>
>   (gdb) print my_var
>   $1 = (unknown: 0x4)

I guess this should look different from the output above?

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
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