Re: scratch/accurate-warning-pos: next steps.

[Paul Eggert <eggert@cs.ucla.edu>]

On 12/11/18 11:20 AM, Alan Mackenzie wrote:
>> If so, aren't we limiting builds to platforms that have binutils,
>> which would be a new restriction?
> Well, we use ld, which also belongs to binutils, and that doesn't seem
> to restrict the platforms.  Other platforms surely have equivalents to
> both objdump and ld, and they are/would be used appropriately.


We don't use ld, at least not directly. The makefile uses $(CC), just as 
it uses $(CC) to compile. On GNU/Linux hosts this eventually uses ld (or 
gold or whatever), but those details are largely immaterial.

If we required objdump or similar utilities, that would be yet another 
porting hassle. And we might run into platforms where there is no 
objdump-like utility and we have to write one ourselves. This doesn't 
sound good at all.


> globals.h seems to manage.

globals.h manages because we decorate every symbol it needs to find. If 
we have to decorate every C function that might call EQ (either directly 
or indirectly), that would also work but it would be a lot more 
intrusive than globals.h is. And the proposal to use objdump seems to 
acknowledge this, by proposing a method that wouldn't require such 
decoration but would have significant portability problems.


>
>> It should be easy enough to move shared file-static data into another
>> file, that would be compiled only once.
> Possibly not.  The same would have to be done with file global data,
> too.  But doing it that way would involve a great deal of change to the
> source code (testing for the -D option) which would not be popular.

It'd be less change than having to decorate every function that might 
call EQ.


> It would likely slow down the compilation by a very great deal.

That's OK, if the cost is borne only by people who want accurate 
diagnostics. People who want compilation speed can simply turn off the 
accurate-diagnostics flag.


> You're conflating "tedious" with "tedious in the extreme".

We're estimating how much work would be needed. Even if there would be 
more work in changing the byte compiler, it shouldn't be so much more 
work that we need to contort all the rest of Emacs. It's better to 
localize such changes when possible.


> This would place onerous restrictions on what macros were allowed to do,
> and likely be incompatible with a vast proportion of existing macros.

But under both proposals I mentioned, existing macros would work just 
fine with no new restrictions. So what I think you're saying is that if 
people want to write macros that allow for more-accurate diagnostics, 
they'll find that they can't easily do it for some reason. What reason 
would that be? Can you give an example based on some macro already 
defined in Emacs?