emacs-29 50d18bb6ea 1/2: Make tramp-archive autoloads robust for older Emacs versions

[Michael Albinus]

branch: emacs-29
commit 50d18bb6ea7dae575c2b679b63fc6b4b95bdf922
Author: Michael Albinus <michael.albinus@gmx.de>
Commit: Michael Albinus <michael.albinus@gmx.de>

    Make tramp-archive autoloads robust for older Emacs versions
    
    * lisp/net/tramp-archive.el (tramp-archive-file-name-regexp):
    Use `eval-when-compile'.  Set it explicitly for older Emacs versions.
---
 lisp/net/tramp-archive.el | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lisp/net/tramp-archive.el b/lisp/net/tramp-archive.el
index 9c1e78d6b0..49b0c0bb6b 100644
--- a/lisp/net/tramp-archive.el
+++ b/lisp/net/tramp-archive.el
@@ -215,11 +215,18 @@ It must be supported by libarchive(3).")
 ;; In older Emacs (prior 27.1), `tramp-archive-autoload-file-name-regexp'
 ;; is not autoloaded.  So we cannot expect it to be known in
 ;; tramp-loaddefs.el.  But it exists, when tramp-archive.el is loaded.
+;; We must wrap it into `eval-when-compile'.  Otherwise, there could
+;; be an "Eager macro-expansion failure" when unloading/reloading Tramp.
 ;;;###tramp-autoload
 (defconst tramp-archive-file-name-regexp
-  (ignore-errors (tramp-archive-autoload-file-name-regexp))
+  (eval-when-compile (ignore-errors (tramp-archive-autoload-file-name-regexp)))
   "Regular expression matching archive file names.")
 
+;; The value above is nil for Emacs 26.  Set it now.
+(if (<= emacs-major-version 26)
+    (setq tramp-archive-file-name-regexp
+         (ignore-errors (tramp-archive-autoload-file-name-regexp))))
+
 ;;;###tramp-autoload
 (defconst tramp-archive-method "archive"
   "Method name for archives in GVFS.")