bug#71522: 29.2.50; Allow associating module symbols with defining files

bug#71522: 29.2.50; Allow associating module symbols with defining files

[Spencer Baugh]

It's currently impossible to associate a symbol defined by a module with
the source file which actually defined that symbol.

1. Make any native module whatsoever, defining any Lisp symbols at all
2. emacs -Q -l ./your-native-module.so
3. (symbol-file your-native-module-symbol) yields "your-native-module.so"
4. If it's a function:
   C-h f your-native-module-symbol RET
5. Observe that it says "your-native-module.so" defines this function,
   and that jumping to the source via the link or "s" drops you in
   your-native-module.so.

It should instead be possible for a module to express which files
defines a symbol, so that it's possible to jump to the source for that
symbol, if it's around.


In GNU Emacs 29.2.50 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2024-06-01 built on
 igm-qws-u22796a
Repository revision: fcef787a846f0c51f7443dfab6af6e18b476b166
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Rocky Linux 8.9 (Green Obsidian)

bug#71522: 29.2.50; Allow associating module symbols with defining files

[Eli Zaretskii]

> From: Spencer Baugh <sbaugh@janestreet.com>
> Date: Wed, 12 Jun 2024 11:12:30 -0400
> 
> 
> It's currently impossible to associate a symbol defined by a module with
> the source file which actually defined that symbol.
> 
> 1. Make any native module whatsoever, defining any Lisp symbols at all
> 2. emacs -Q -l ./your-native-module.so
> 3. (symbol-file your-native-module-symbol) yields "your-native-module.so"
> 4. If it's a function:
>    C-h f your-native-module-symbol RET
> 5. Observe that it says "your-native-module.so" defines this function,
>    and that jumping to the source via the link or "s" drops you in
>    your-native-module.so.

I'm guessing that what Emacs knows is the directory and the file name
from which it loaded the module.  If we want to be able to find the
source file, that information needs to be recorded somewhere inside
the module, otherwise there's no way Emacs could reliably find the
sources, since the module could be stripped of all the symbolic debug
info.  Suggestions for how to implement that are welcome.