bug#48994: 28.0.50; [PATCH] 28.0.50; Native compilation unnecessarily recompiles .eln (macOS)

[Matthew Bauer]

This is similar to bug#48497, but appears to still happen even after
commit 3f207753a0.

The basic problem is that the installed lisp path does not match either
of the search expressions in comp-el-to-eln-rel-filename, meaning that
native lisp needs to be recompiled needlessly.

The problem seems to come from PATH_REL_LOADSEARCH being set for me (on
macOS) to Contents/Resources/lisp, but the lisp files actually being
installed to
/nix/store/...-emacs-gcc-20210612.0/share/emacs/28.0.50/lisp (path
generated by Nix). As a result, comp-el-to-eln-rel-filename used the
filename comp-034d3699-516ce4bf.eln for comp.el.gz where 516ce4bf is the
md5sum of the contents of comp.el and 034d3699 is the md5sum of the full
path of comp.el, not of //emacs-lisp/comp.el (7672a6ed), which is what
Emacs installs.

To fix this, I propose using PATH_LOADSEARCH in addition to
PATH_REL_LOADSEARCH so that we can catch both types of macOS installs
(.app and unix). I’ve attached a patch which implements this, adding
relative and absolute loadsearch resolution.

- Matthew

>From 32022ee8d977196c72ad42d89d23142a6e59ff8e Mon Sep 17 00:00:00 2001
From: Matthew Bauer <mjbauer95@gmail.com>
Date: Sat, 12 Jun 2021 00:37:28 -0500
Subject: [PATCH] Use PATH_LOADSEARCH to get absolute path of native comp

We need to so that
/usr/local/share/emacs/28.0.50/lisp/emacs-lisp/comp.el

becomes:

//emacs-lisp/comp.el

which is what we install eln files as.
---
 src/comp.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/comp.c b/src/comp.c
index 056d0860d8..8ccd99d583 100644
--- a/src/comp.c
+++ b/src/comp.c
@@ -4049,12 +4049,14 @@ DEFUN ("comp-el-to-eln-rel-filename", 
Fcomp_el_to_eln_rel_filename,
 
      As installing .eln files compiled during the build changes their
      absolute path we need an hashing mechanism that is not sensitive
-     to that.  For this we replace if match PATH_DUMPLOADSEARCH or
-     *PATH_REL_LOADSEARCH with '//' before computing the hash.  */
+     to that.  For this we replace if match PATH_DUMPLOADSEARCH,
+     PATH_REL_LOADSEARCH, or PATH_LOADSEARCH with '//' before
+     computing the hash.  */
 
   if (NILP (loadsearch_re_list))
     {
-      Lisp_Object sys_re =
+      Lisp_Object sys_abs_re = Fregexp_quote (build_string (PATH_LOADSEARCH 
"/"));
+      Lisp_Object sys_rel_re =
        concat2 (build_string ("\\`[[:ascii:]]+"),
                 Fregexp_quote (build_string ("/" PATH_REL_LOADSEARCH "/")));
       Lisp_Object dump_load_search =
@@ -4062,7 +4064,7 @@ DEFUN ("comp-el-to-eln-rel-filename", 
Fcomp_el_to_eln_rel_filename,
 #ifdef WINDOWSNT
       dump_load_search = Fw32_long_file_name (dump_load_search);
 #endif
-      loadsearch_re_list = list2 (sys_re, Fregexp_quote (dump_load_search));
+      loadsearch_re_list = list3 (sys_abs_re, sys_rel_re, Fregexp_quote 
(dump_load_search));
     }
 
   Lisp_Object lds_re_tail = loadsearch_re_list;
-- 
2.29.2