Avoid expensive file-truename call when possible

CHANGELOG.md

@@ -42,6 +42,7 @@
 - Improve the presentation of `xref` data.
 - [#3419](https://github.com/clojure-emacs/cider/issues/3419): Also match friendly sessions based on the buffer's ns form.
 - `cider-test`: only show diffs for collections.
+- Avoid expensive `file-truename` call when possible.
 - [#3375](https://github.com/clojure-emacs/cider/pull/3375): `cider-test`: don't render a newline between expected and actual, most times.
 - Improve `nrepl-dict` error reporting.
 - Bump the injected `piggieback` to [0.5.3](https://github.com/nrepl/piggieback/blob/0.5.3/CHANGES.md#053-2021-10-26).

cider-repl.el

@@ -1760,7 +1760,16 @@ The checking is done as follows:
  (setcdr session (seq-filter #'buffer-live-p (cdr session)))
  (when-let* ((repl (cadr session))
  (proc (get-buffer-process repl))
- (file (file-truename (or (buffer-file-name) default-directory))))
+ (file (or
+ ;; favor a built-in buffer-local variable if possible, for performance:
+ (and buffer-file-truename
+ (if (file-remote-p buffer-file-truename)
+ buffer-file-truename
+ ;; buffer-file-truename has symlinks resolved, but can be abbreviated,
+ ;; except in remote files. Expand it:
+ (expand-file-name buffer-file-truename)))
+ ;; else, call file-truename, which is expensive:
+ (file-truename (or (buffer-file-name) default-directory)))))
  ;; With avfs paths look like /path/to/.avfs/path/to/some.jar#uzip/path/to/file.clj
  (when (string-match-p "#uzip" file)
  (let ((avfs-path (directory-file-name (expand-file-name (or (getenv "AVFSBASE") "~/.avfs/")))))