[RFC PATCH] [gdb] Fix std::unique_ptr printing regression (PR 28480)

[Tom Tromey]

>>>>> "Bruno" == Bruno Larsen via Gdb-patches <gdb-patches@sourceware.org> writes:

Thank you for the patch.

Bruno> Or with a valid memory address. This happened because the searching
Bruno> algorithm, when looking for internal members of __uniq_ptr, would stop
Bruno> at the first _M_head_impl, which is of type class Deleter, instead of
Bruno> returning the second finding, which is the managed pointer.

I don't really understand this explanation.
However, see my comments below about the test case.

Bruno> The second is that I'm having trouble with the testing. running with
Bruno> -data-directory gdb/data-directory gives me a very verbose printing that
Bruno> is always correct, but also counter-productive for debugging. How can I
Bruno> make the testsuite have the minimal printing?

Bruno> +  std::unique_ptr<int> uptr(nullptr);

Using a standard library type in the test suite is usually not what you
want, because it means that the gdb feature being tested then depends on
the precise implementation of this type.

Instead, because you're changing gdb to handle some C++ scenario, I
think it would be better to write out exactly what is being tested --
basically, the relevant parts of unique_ptr.  I think it's fine to add
these to the existing test.

However, it sounds like you also are trying to test the pretty-printer
here?  This part wasn't clear to me, but IIRC std::unique_ptr has a
pretty-printer in libstdc++.  In this case, you'd also need to write a
pretty-printer, in which case you'd probably just want a whole new test
in gdb.python.

Integration testing for the unique_ptr pretty-printer would also be
good, but those tests ought to be in libstdc++.

I don't have a comment on the particular change here.  I suspect it
ought to be done some other way, but I don't really understand it.  I
think a more self-contained test would help with this as well.

thanks,
Tom