Improve performance of `find-buffer-visiting' (bug#66117)

* src/buffer.c (Fget_truename_buffer): Expose `get_truename_buffer' to
Elisp.
(Ffind_buffer): New subr searching for a live buffer with a given
value of buffer-local variable.
(syms_of_buffer): Register the new added subroutines.
* src/filelock.c (lock_file): Use the new `Fget_truename_buffer' name.
* src/lisp.h:
* test/manual/etags/c-src/emacs/src/lisp.h: Remove no-longer-necessary
extern declarations for `get_truename_buffer'.
* lisp/files.el (find-buffer-visiting): Refactor, using subroutines to
search for buffers instead of slow manual Elisp iterations.

3 files changed, 24 insertions, 4 deletions

diff --git a/src/buffer.c b/src/buffer.c
index ea0c23192b7..73e9839f883 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -519,8 +519,11 @@ See also `find-buffer-visiting'.  */)
   return Qnil;
 }
 
-Lisp_Object
-get_truename_buffer (register Lisp_Object filename)
+DEFUN ("get-truename-buffer", Fget_truename_buffer, Sget_truename_buffer, 1, 1, 0,
+       doc: /* Return the buffer with `file-truename' equal to FILENAME (a string).
+If there is no such live buffer, return nil.
+See also `find-buffer-visiting'.  */)
+  (register Lisp_Object filename)
 {
   register Lisp_Object tail, buf;
 
@@ -533,6 +536,22 @@ get_truename_buffer (register Lisp_Object filename)
   return Qnil;
 }
 
+DEFUN ("find-buffer", Ffind_buffer, Sfind_buffer, 2, 2, 0,
+       doc: /* Return the buffer with buffer-local VARIABLE equal to VALUE.
+               If there is no such live buffer, return nil.
+See also `find-buffer-visiting'.  */)
+  (Lisp_Object variable, Lisp_Object value)
+{
+  register Lisp_Object tail, buf;
+
+  FOR_EACH_LIVE_BUFFER (tail, buf)
+    {
+      if (!NILP (Fequal (value, Fbuffer_local_value(variable, buf))))
+        return buf;
+    }
+  return Qnil;
+}
+
 /* Run buffer-list-update-hook if Vrun_hooks is non-nil and BUF does
    not have buffer hooks inhibited.  */
 
@@ -6010,6 +6029,8 @@ There is no reason to change that value except for debugging purposes.  */);
   defsubr (&Sbuffer_list);
   defsubr (&Sget_buffer);
   defsubr (&Sget_file_buffer);
+  defsubr (&Sget_truename_buffer);
+  defsubr (&Sfind_buffer);
   defsubr (&Sget_buffer_create);
   defsubr (&Smake_indirect_buffer);
   defsubr (&Sgenerate_new_buffer_name);
diff --git a/src/filelock.c b/src/filelock.c
index c2b306ab47d..9ce51c724b1 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -563,7 +563,7 @@ lock_file (Lisp_Object fn)
 
   /* See if this file is visited and has changed on disk since it was
      visited.  */
-  Lisp_Object subject_buf = get_truename_buffer (fn);
+  Lisp_Object subject_buf = Fget_truename_buffer (fn);
   if (!NILP (subject_buf)
       && NILP (Fverify_visited_file_modtime (subject_buf))
       && !NILP (Ffile_exists_p (fn))
diff --git a/src/lisp.h b/src/lisp.h
index ed1b007d4c5..efd36465e62 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4664,7 +4664,6 @@ extern void report_overlay_modification (Lisp_Object, Lisp_Object, bool,
                                          Lisp_Object, Lisp_Object, Lisp_Object);
 extern bool overlay_touches_p (ptrdiff_t);
 extern Lisp_Object other_buffer_safely (Lisp_Object);
-extern Lisp_Object get_truename_buffer (Lisp_Object);
 extern void init_buffer_once (void);
 extern void init_buffer (void);
 extern void syms_of_buffer (void);