master 13fdded: Allow preserving symlinks with file-precious-flag set

[Lars Ingebrigtsen]

branch: master
commit 13fdded2c19823d9216b391d0636345029cf3e81
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Allow preserving symlinks with file-precious-flag set
    
    * doc/lispref/files.texi (Saving Buffers): Document it.
    * lisp/files.el (file-preserve-symlinks-on-save): New user option
    (bug#18125).
    (basic-save-buffer-2): Use it.
---
 doc/lispref/files.texi |  7 +++++++
 etc/NEWS               |  5 +++++
 lisp/files.el          | 17 ++++++++++++++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 266501d..12c0611 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -503,6 +503,13 @@ all hard links between the file you save and other file 
names.
 
 Some modes give this variable a non-@code{nil} buffer-local value
 in particular buffers.
+
+@vindex file-preserve-symlinks-on-save
+If this option is non-@code{nil} and you're visiting files via a
+symbolic link, Emacs break the symbolic link and write the buffer to a
+file with the same name as the symbolic link.  To instead write to the
+file the symbolic link points to (and thereby preserving the link),
+set @code{file-preserve-symlinks-on-save} to @code{t}.
 @end defopt
 
 @defopt require-final-newline
diff --git a/etc/NEWS b/etc/NEWS
index 7cd0c5f..cdc70d6 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2461,6 +2461,11 @@ images are marked.
 ** Miscellaneous
 
 +++
+*** New user option 'file-preserve-symlinks-on-save'.
+This controls what Emacs does when saving buffers visited via a
+symbolic link, and 'file-precious-flag' is non-nil.
+
++++
 *** New user option 'copy-directory-create-symlink'.
 If non-nil, will make `copy-directory' (when used on a symbolic
 link) copy the link instead of following the link.
diff --git a/lisp/files.el b/lisp/files.el
index 90de149..6a617fe 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -5446,6 +5446,14 @@ symbolic link and copy the contents instead."
   :version "28.1"
   :group 'files)
 
+(defcustom file-preserve-symlinks-on-save nil
+  "If non-nil, saving a buffer visited via a symlink won't overwrite the 
symlink.
+This is only relevant if `file-precious-flag' is non-nil -- if
+this is nil, Emacs will preserve the symlinks anyway."
+  :type 'boolean
+  :version "28.1"
+  :group 'files)
+
 (defvar-local save-buffer-coding-system nil
   "If non-nil, use this coding system for saving the buffer.
 More precisely, use this coding system in place of the
@@ -5648,7 +5656,14 @@ Before and after saving the buffer, this function runs
                                     buffer-file-name)))
            ;; We succeeded in writing the temp file,
            ;; so rename it.
-           (rename-file tempname buffer-file-name t))
+           (rename-file tempname
+                         (if (and file-preserve-symlinks-on-save
+                                  (file-symlink-p buffer-file-name))
+                             ;; Write to the file that the symlink
+                             ;; points to.
+                             (file-chase-links buffer-file-name)
+                           buffer-file-name)
+                         t))
        ;; If file not writable, see if we can make it writable
        ;; temporarily while we write it.
        ;; But no need to do so if we have just backed it up