Subject: 28.0.50; 'M-x compile' misbehaves if 'process-environment' is buffer-local

From: Augusto Stoffel <[email-masked]>
Date: Wed, 15 Sep 2021 20:08:07 +0200

This has already been discussed on email-devel but didn't come to a
conclusion.  I don't want to linger on it, but I would like the problem
to get assigned a bug number, so it has a chance of being addressed in
the future.

A summary of the problem: suppose buffer A has a buffer-local value of
'process-environment' containing an extra directory in the PATH, and
that a given 'program' is only available on that directory.  Then 'M-x
compile RET program RET' will not find 'program', because the
*compilation* buffer will not "inherit" the PATH from A.

For the reasons why one would want/need such a setup, see
https://lists.gnu.org/archive/html/emacs-devel/2021-08/msg01380.html
and other messages in that thread.

Finally, I attach my proposed patch.

>From a104e1eae100f01585587df30f49866f3b038785 Mon Sep 17 00:00:00 2001
From: Augusto Stoffel <[email-masked]>
Date: Thu, 29 Apr 2021 12:45:04 +0200
Subject: [PATCH] Make 'compile' respect buffer-local process environment

* lisp/progmodes/compile.el (compilation-start): Use
`process-environment' from original buffer in the compilation process.
---
 lisp/progmodes/compile.el | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lisp/progmodes/compile.el b/lisp/progmodes/compile.el
index af7b8292b7..bdf20a3f51 100644
--- a/lisp/progmodes/compile.el
+++ b/lisp/progmodes/compile.el
@@ -1783,6 +1783,8 @@ compilation-start
 	    (replace-regexp-in-string "-mode\\'" "" (symbol-name mode))))
 	 (thisdir default-directory)
 	 (thisenv compilation-environment)
+         (bufferpath (when (local-variable-p 'exec-path) exec-path))
+         (bufferenv (when (local-variable-p 'process-environment) process-environment))
 	 outwin outbuf)
     (with-current-buffer
 	(setq outbuf
@@ -1850,6 +1852,12 @@ compilation-start
         ;; NB: must be done after (funcall mode) as that resets local variables
         (setq-local compilation-directory thisdir)
         (setq-local compilation-environment thisenv)
+        (if bufferpath
+            (setq-local exec-path bufferpath)
+          (kill-local-variable 'exec-path))
+        (if bufferenv
+            (setq-local process-environment bufferenv)
+          (kill-local-variable 'process-environment))
 	(if highlight-regexp
             (setq-local compilation-highlight-regexp highlight-regexp))
         (if (or compilation-auto-jump-to-first-error
-- 
2.31.1