cider--completing-read-port: Default to 7888

Whilst 7888 isn't the official port (see
nrepl/nrepl#6 discussion), it's frequently
used in practice. Set that as the default value in the minibuffer if
we couldn't infer a port.

Most nREPL implementations do create a `.nrepl-port` file but it's
nice to have 7888 suggested to save a few keystrokes.

Author: Wilfred

CHANGELOG.md

@@ -29,6 +29,7 @@
 - [#3909](https://github.com/clojure-emacs/cider/issues/3909): `cider--sesman-friendly-session-p` is more robust at attaching buffers to existing sessions. The classpath and namespace caches are now populated eagerly at connection time instead of lazily on first sesman call (previously a nil/empty result was indistinguishable from "not cached" and was re-fetched on every check). The matcher is now a pure path comparison and never blocks on the REPL. Beyond the caching fix, it also falls back to the connection's `nrepl-project-dir` when classpath matching fails, uses `file-in-directory-p` for classpath-root boundary checks (avoiding spurious prefix matches like `/foo/bar` against `/foo/barber/...`), and short-circuits to the chosen session when `cider-default-session` is set.
 - `nrepl-bencode` no longer crashes when handed a non-string scalar (symbol, float, etc.). The documented fallback ("everything else is encoded as string") used `string-bytes` directly, which errors on non-string input; values are now coerced via `format' before measuring byte length.
 - [#3915](https://github.com/clojure-emacs/cider/issues/3915): Fix `cider-repl-history` failing with "Unmatched bracket or quote" on its second invocation in a session when the user's history contained an entry with unbalanced parens. `cider-repl-history-setup` now erases the reused `*cider-repl-history*` buffer before re-entering `cider-repl-history-mode`, so any user-configured `clojure-mode-hook` (e.g. one that runs `check-parens') runs on an empty buffer instead of stale content from the previous render.
+- `cider--completing-read-port` now defaults to `7888` when no running nREPL port can be inferred.
 
 ### Changes
 

lisp/cider-endpoint.el

@@ -70,6 +70,9 @@ Sub-match 1 must be the project path.")
 (defvar cider-host-history nil
   "Completion history for connection hosts.")
 
+(defconst cider-default-nrepl-port "7888"
+  "Use this port number when we couldn't infer a port.
+See also https://github.com/nrepl/nREPL/issues/6.")
 
 ;;; Endpoint selection
 
@@ -158,7 +161,8 @@ of remote SSH hosts."
   "Interactively select port for HOST from PORTS."
   (let* ((ports (cider-join-into-alist ports))
          (sel-port (completing-read (format "Port for %s: " host) ports
-                                    nil nil nil nil (caar ports)))
+                                    nil nil nil nil (or (caar ports)
+                                                        cider-default-nrepl-port)))
          (port (or (cdr (assoc sel-port ports)) sel-port))
          (port (if (listp port) (cadr port) port)))
     (if (stringp port) (string-to-number port) port)))