bug#66261: Disassembling a regexp's bytecode

[Stefan Monnier]

Tags: patch

I'd like to add a function that lets us see a regexp's bytecode directly
from within Emacs (recompiling with REGEX_EMACS_DEBUG can be quite useful
in many cases, but it's much more invasive and it's often overkill).

The patch below is what I use currently, but clearly it's not ready for
`master`.  Before I try and clean it, I'd like to discuss some issues to
figure out how best to solve them:

- First, in order to easily use the same code between REGEX_EMACS_DEBUG
  and my new `re--describe-compiled`, I need to print sometimes to
  `stderr` and sometimes to a string, which I do using `open_memstream`.
  AFAIK `open_memstream` is not directly available in Windows (and
  maybe under some other Unixes either, tho it's in POSIX-2008, IIUC).
  Could someone help me get an `opem_memstream` emulation working
  (maybe via gnulib)?

- I'm thinking of always providing this function.  Another option would
  be to do it under the control of a compilation flag, tho it doesn't
  seem worth adding a new flag just for that.  I guess we could
  reuse REGEX_EMACS_DEBUG (tho it's too invasive IMO), or
  ENABLE_CHECKING, but I'd rather just always offer the function.
  After all, it might encourage users to look more carefully at their
  regexps and maybe even to help us improve our regexp engine, who knows.


        Stefan


 In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw3d scroll bars) of 2023-09-16 built on pastel
Repository revision: 0954f127b8840bf843a2acfb18d2e18e526166e1
Repository branch: work
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
 'configure -C --enable-checking --enable-check-lisp-object-type --with-modules 
--with-cairo --with-tiff=ifavailable
 'CFLAGS=-Wall -g3 -Og -Wno-pointer-sign'
 PKG_CONFIG_PATH=/home/monnier/lib/pkgconfig'

regexp.patch
Description: Text Data