bug#66912: With `require', the byte compiler reports the wrong file for errors.

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> Why not?  We're not in the compilation any more, we're loading a file.
> Some error has prevented that file loading, so we want a backtrace just
> as we would get with M-x load-file foo.elc RET.

Hmm... that's a good point.

>> I think for this specific problem being discussed (which is indeed
>> a fairly common occurrence in my experience), the better solution is to
>> change `load` so it adds the "context" (i.e. filename and ideally also
>> the approximate file position info) to errors.
>> [ This may require something like `handler-bind`.  ]
> Another solution would be to dispense with
> display-byte-compile-warnings, just letting compiler errors generate
> backtraces.
>
> The problem here is that there is no distinction in bytecomp.el between
> "external" errors (such as from require) and errors detected by the
> compiler in the source file being compiled.

These are two fairly "clear" cases, admittedly.

But there are also cases in between where it's less clear, mostly with
errors during macro-expansion where the internal/external distinction is
not always that clear since some macros come from outside but others
come from the very file we're compiling, and where we can't easily tell
if an error is due to a bug in the macro definition or a bug in the use
of the macro.

> The first decidedly want a backtrace, the second probably not.
> All these errors are handled as though they were "internal" errors
> detected by the compiler.  This is suboptimal.

Also there are 2 questions:

- whether to give a backtrace (and/or enter the debugger).
- when we don't show a backtrace, what info do we put in the error message.

For the first, the current "solution" is to set `byte-compile-debug`.
It's not ideal, and we should improve it, but at least we do have
a solution for it.

For the second we currently don't show a good enough info and in my
previous response I focused on that part.

> Perhaps we should report the second type of error (detected by the
> compiler) by calling a warning function, as we do for warnings, and
> removing the damaging condition-case's as suggested two paragraphs back.

If the user is not asking to see backtraces, the current treatment seems
cleaner than without any `condition-case`.  So maybe those
`condition-case` should be turned into `condition-case-unless-debug`?


        Stefan