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Subject: [Bug other/42540] c++ error message [vtable undefined] is unhelpful
Date: Mon, 14 Mar 2022 14:38:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D42540

--- Comment #16 from Eyal Rozenberg <eyalroz1 at gmx dot com> ---
Some comments following my recent dupe...

(In reply to Andrew Pinski from comment #1)
> I don't know if there is anything there could be done here since the link=
er
> is what is producing the error.

The compiler could store information in the compiled object listing the vir=
tual
members for which no implementation was found, due to which reason the vtab=
le
was not defined already. In this specific example, storing the name of "A::=
B()"
somewhere. If that information is available, we could then petition linker
authors to use it and print the missing virtual members in the error messag=
e.

(In reply to  Richard Earnshaw from comment #5)
> As suggested, there's no bug in the compiler here

Not passing sufficient information to the linker is a "bug", or at least - a
missing feature.

(In reply to Zhihao Yuan from comment #11)
> 2. Add extra information to name the key function, and pass it to the lin=
ker, generate an error message to match MSVC's quality.

I'm not quite sure what a key function is, but it sounds like my suggestion=
 is
similar to this one. So, I support your suggestion (2.)

> Calling this a "well-known issue" is irresponsible.  The issue significan=
tly
> increases the bar to learners to consume and accept new paradigms in the
> language.

Not just learners. If you have a large class with many methods, whose
implementation is spread across many files, it can take quite a bit of time=
 to
figure out which method implementation is missing.=