bug#31636: 27.0.50; lockfile syntax searchable from info manual

[Robert Pluim]

Eli Zaretskii <eliz@gnu.org> writes:

>> > As I said above, I think if we are describing this in more detail, why
>> > not describe also the information recorded in the lockfile?  If
>> > someone looked up the lockfile name, someone else may wish to look up
>> > the data it records and understand what that is, no?
>> 
>> Didnʼt you make the point just now that this kind of detail could
>> change and weʼd forget to update the documentation? Or did you want
>> this in the elisp manual?
>
> The latter.

So what I currently have is below. create-lockfiles references the
user manual (and 'lock-buffer') which in turn references the lisp
reference manual.

Do we want a '.#' index entry in the lispref as well?
Do I need to explain that USER will be replaced by the current user,
etc?

Let the wordsmithing begin!

2018-05-31  Robert Pluim  <rpluim@gmail.com>

        * src/filelock.c (create-lockfiles): Add cross reference to
        file locking in user manual and to 'lock-buffer'.  Add string
        '.#' to help users find the doc string.

        * doc/emacs/files.texi (Interlocking): Point user at detailed
        file locking description in lisp reference manual.  Add index
        entry for '.#' to improve disoverability of information about locking.

        * doc/lispref/files.texi (File Locks): Describe in detail what
        the form of the lock file is.

diff --git i/doc/emacs/files.texi w/doc/emacs/files.texi
index 1ced7ca07c..406e7d980c 100644
--- i/doc/emacs/files.texi
+++ w/doc/emacs/files.texi
@@ -766,13 +766,16 @@ Interlocking
 
 @findex ask-user-about-lock
 @cindex locking files
+@cindex .#, lock file names
+@cindex file locking
   When you make the first modification in an Emacs buffer that is
 visiting a file, Emacs records that the file is @dfn{locked} by you.
 (It does this by creating a specially-named symbolic link@footnote{If
 your file system does not support symbolic links, a regular file is
-used.} with special contents in the same directory.)  Emacs removes the lock
-when you save the changes.  The idea is that the file is locked
-whenever an Emacs buffer visiting it has unsaved changes.
+used.} with special contents in the same directory. @xref{File
+Locks,,, elisp} for more details.)  Emacs removes the lock when you
+save the changes.  The idea is that the file is locked whenever an
+Emacs buffer visiting it has unsaved changes.
 
 @vindex create-lockfiles
   You can prevent the creation of lock files by setting the variable
diff --git i/doc/lispref/files.texi w/doc/lispref/files.texi
index f62b670f47..89a98bd588 100644
--- i/doc/lispref/files.texi
+++ w/doc/lispref/files.texi
@@ -720,8 +720,13 @@ File Locks
 Emacs can then detect the first attempt to modify a buffer visiting a
 file that is locked by another Emacs job, and ask the user what to do.
 The file lock is really a file, a symbolic link with a special name,
-stored in the same directory as the file you are editing.  (On file
-systems that do not support symbolic links, a regular file is used.)
+stored in the same directory as the file you are editing.  The name is
+constructed by prepending @file{.#} to the filename of the buffer.
+The target of the symbolic link will be of the form
+@code{USER@@HOST.PID:BOOT}.  @code{:BOOT} is omitted if the boot time
+is unavailable.  (On file systems that do not support symbolic links,
+a regular file is used instead, with contents of the form
+@code{USER@@HOST.PID:BOOT}.)
 
   When you access files using NFS, there may be a small probability that
 you and another user will both lock the same file simultaneously.
diff --git i/src/filelock.c w/src/filelock.c
index f2dc723407..4f7ec414f5 100644
--- i/src/filelock.c
+++ w/src/filelock.c
@@ -849,7 +849,9 @@ syms_of_filelock (void)
   Vtemporary_file_directory = Qnil;
 
   DEFVAR_BOOL ("create-lockfiles", create_lockfiles,
-              doc: /* Non-nil means use lockfiles to avoid editing collisions. 
 */);
+              doc: /* Non-nil means use lockfiles to avoid editing collisions.
+The names of the lockfiles will start with `.#'.  See also
+`lock-buffer' and Info node `(emacs)Interlocking'.  */);
   create_lockfiles = 1;
 
   defsubr (&Sunlock_buffer);