Improve session and REPL buffer naming

 - better abbreviation of directory names
 - re-create context buffer on every connect instead of
   `kill-all-local-variables` which could fail

Author: vspinu

cider-connection.el

@@ -451,15 +451,24 @@ The following formats can be used in TEMPLATE string:
 
 In case some values are empty, extra separators (: and -) are automatically
 removed."
-  (let* ((dir (or (plist-get params :project-dir)
-                  (clojure-project-dir (cider-current-dir))
-                  default-directory))
+  (let* ((dir (directory-file-name
+               (abbreviate-file-name
+                (or (plist-get params :project-dir)
+                    (clojure-project-dir (cider-current-dir))
+                    default-directory))))
          (short-proj (file-name-nondirectory (directory-file-name dir)))
          (parent-dir (ignore-errors
-                       (thread-first dir directory-file-name file-name-directory
+                       (thread-first dir file-name-directory
                                      directory-file-name file-name-nondirectory
                                      file-name-as-directory)))
          (long-proj (format "%s%s" (or parent-dir "") short-proj))
+         ;; use `dir` if it is shorter than `long-proj` or `short-proj`
+         (short-proj (if (>= (length short-proj) (length dir))
+                         dir
+                       short-proj))
+         (long-proj (if (>= (length long-proj) (length dir))
+                        dir
+                      long-proj))
          (port (or (plist-get params :port) ""))
          (host (or (plist-get params :host) "localhost"))
          (remote-host (if (member host '("localhost" "127.0.0.1"))
@@ -562,6 +571,7 @@ function with the repl buffer set as current."
       (setq nrepl-err-handler #'cider-default-err-handler
             ;; used as a new-repl marker in cider-set-repl-type
             mode-name nil
+            nrepl-project-dir (plist-get params :project-dir)
             ;; REPLs start with clj and then "upgrade" to a different type
             cider-repl-type "clj"
             ;; ran at the end of cider--connected-handler

cider.el

@@ -1073,19 +1073,23 @@ non-nil, don't start if ClojureScript requirements are not met."
       ;; If proj-dir is not a parent of default-directory, transfer all local
       ;; variables and hack dir-local variables into a temporary buffer and keep
       ;; that buffer within `params` for the later use by other --update-
-      ;; functions.
-      (with-current-buffer (get-buffer-create " *cider-context-buffer*")
-        (kill-all-local-variables)
-        (dolist (pair (buffer-local-variables orig-buffer))
-          (pcase pair
-            (`(,name . ,value)          ;ignore unbound variables
-             (ignore-errors (set (make-local-variable name) value))))
-          (setq-local buffer-file-name nil))
-        (let ((default-directory proj-dir))
-          (hack-dir-local-variables-non-file-buffer)
-          (thread-first params
-            (plist-put :project-dir proj-dir)
-            (plist-put :--context-buffer (current-buffer))))))))
+      ;; functions. The context buffer should not be used outside of the param
+      ;; initialization pipeline. Therefore, we don't bother with making it
+      ;; unique or killing it anywhere.
+      (let ((context-buf-name " *cider-context-buffer*"))
+        (when (get-buffer context-buf-name)
+          (kill-buffer context-buf-name))
+        (with-current-buffer (get-buffer-create context-buf-name)
+          (dolist (pair (buffer-local-variables orig-buffer))
+            (pcase pair
+              (`(,name . ,value)        ;ignore unbound variables
+               (ignore-errors (set (make-local-variable name) value))))
+            (setq-local buffer-file-name nil))
+          (let ((default-directory proj-dir))
+            (hack-dir-local-variables-non-file-buffer)
+            (thread-first params
+              (plist-put :project-dir proj-dir)
+              (plist-put :--context-buffer (current-buffer)))))))))
 
 (defun cider--update-cljs-type (params)
   "Update :cljs-repl-type in PARAMS."

test/cider-connection-tests.el

@@ -307,3 +307,17 @@
          (expect (buffer-live-p b) :not :to-be-truthy)
          (expect (cider-repls) :to-equal (list a))
          (sesman-unregister 'CIDER session))))))
+
+(describe "cider-format-connection-params"
+  (describe "correctly abbreviates short directory names"
+    (expect (cider-format-connection-params "%J" '(:project-dir "~"))
+            :to-equal "~")
+    (expect (cider-format-connection-params "%j" '(:project-dir "~"))
+            :to-equal "~")
+    (expect (cider-format-connection-params "%J" '(:project-dir "~/"))
+            :to-equal "~")
+    (expect (cider-format-connection-params "%J" '(:project-dir "/"))
+            :to-equal "/")
+    (expect (cider-format-connection-params "%J" '(:project-dir "/etc/"))
+            :to-equal "/etc")))
+