Recognize let-go as a known nREPL runtime

let-go (https://github.com/nooga/let-go) is a Clojure dialect
implemented in Go that ships an nREPL server.  Connections work today
via plain `cider-connect-clj`, but `cider-runtime` reported `generic`
for them, so the connection info line was bare (no runtime version).

Add a `cider--let-go-version` helper that reads the `let-go` key from
the `describe` response's `versions` map (let-go reports separate
`major`/`minor` fields rather than a `version-string`, hence the
custom format).  Wire it into `cider-runtime`, the capability table
in `cider--connected-handler`, and the `cider--connection-info`
runtime cond.

Also list let-go on the "Other Platforms" docs page.

Verified end-to-end against a running let-go 2.0.2 nREPL: connection
info reads `CLJ project@localhost:2137 (let-go 1.0)` and a simple
`(+ 1 2)` round-trips as expected.

Author: bbatsov

CHANGELOG.md

@@ -10,6 +10,7 @@
 - Cache the result of `cider--running-nrepl-paths` (used by `cider-locate-running-nrepl-ports`) for `cider-running-nrepl-paths-cache-ttl` seconds (default 5). Repeated `cider-connect` completions no longer re-spawn a fresh round of `ps`/`lsof` subprocesses each time. `cider-clear-running-nrepl-paths-cache` discards the cache on demand.
 - New `nrepl-make-eval-handler` with a keyword-arg API (`:on-value`, `:on-stdout`, `:on-stderr`, `:on-done`, `:on-eval-error`, `:on-content-type`, `:on-truncated`). Sub-handlers no longer take a buffer argument -- they close over whatever they need. `nrepl-make-response-handler`, the legacy 7-positional-arg form, is preserved as an obsolete shim that adapts the old (buffer x) lambdas to the new (x) lambdas, so existing extensions keep working.
 - New `cider-repl-history-doctor` command: walks `cider-repl-input-history` looking for entries whose parens don't balance under Clojure syntax, shows each in a side buffer, and asks whether to delete it.  When done, rewrites `cider-repl-history-file` if one is configured.  Useful for cleaning up history after a typo got committed that breaks `cider-repl-history` rendering (see [#3915](https://github.com/clojure-emacs/cider/issues/3915)).
+- Recognize [let-go](https://github.com/nooga/let-go) (a Clojure dialect implemented in Go) as a known nREPL runtime.  `cider-runtime` returns `let-go` for these connections and the connection info line shows the runtime version, e.g. `CLJ project@localhost:2137 (let-go 1.0)`.
 - Decouple the nREPL transport layer from CIDER's UI layer (closes [#1099](https://github.com/clojure-emacs/cider/issues/1099)). `nrepl-make-eval-handler` is now CIDER-agnostic: it no longer references `nrepl-namespace-handler-function`, `nrepl-err-handler-function`, `nrepl-need-input-handler-function`, or any hardcoded UI strings. New `:on-ns` and `:on-status` keyword slots let any consumer wire up their own namespace tracking and status handling. The editor-level `cider-make-eval-handler` wraps it with CIDER's UI behavior (ns tracking, default error handler, need-input prompt, "Evaluation interrupted." / "Namespace not found." messages); in-tree callers all use it.
 
 ### Bugs fixed

doc/modules/ROOT/pages/platforms/other_platforms.adoc

@@ -29,6 +29,7 @@ Here's an incomplete list of Clojure platforms that you can use as described abo
 * https://github.com/babashka/nbb[nbb]
 * https://github.com/babashka/scittle[scittle]
 * https://github.com/BetterThanTomorrow/joyride[joyride]
+* https://github.com/nooga/let-go[let-go] (a Clojure dialect implemented in Go)
 
 NOTE: For `nbb` you can alternatively connect via `cider-connect-cljs`, see xref:platforms/nbb.adoc[nbb].
 

lisp/cider-connection.el

@@ -254,6 +254,7 @@ See `cider-connection-capabilities'."
              ('babashka '(babashka jvm-compilation-errors))
              ('nbb '(cljs))
              ('scittle '(cljs))
+             ('let-go '(let-go))
              (_ '()))
            (when
                (eq cider-repl-type 'cljs)
@@ -347,6 +348,13 @@ about this buffer (like variable `cider-repl-type')."
                           (plist-get nrepl-endpoint :port)
                           (cider--babashka-version)
                           (cider--babashka-nrepl-version)))
+                 ((cider--let-go-version)
+                  (format "%s%s@%s:%s (let-go %s)"
+                          (if genericp "" (upcase (concat (symbol-name cider-repl-type) " ")))
+                          (or (cider--project-name nrepl-project-dir) "<no project>")
+                          (plist-get nrepl-endpoint :host)
+                          (plist-get nrepl-endpoint :port)
+                          (cider--let-go-version)))
                  (t
                   (format "%s%s@%s:%s"
                           (if genericp "" (upcase (concat (symbol-name cider-repl-type) " ")))

lisp/cider-session.el

@@ -203,13 +203,25 @@ But helps us know if this is a nbb repl, or not."
     (when nrepl-versions
       (nrepl-dict-get nrepl-versions "scittle-nrepl"))))
 
+(defun cider--let-go-version ()
+  "Retrieve the underlying connection's let-go version.
+Formatted as \"MAJOR.MINOR\" since let-go's nREPL `describe` response
+splits the version into separate fields rather than a `version-string`."
+  (with-current-buffer (cider-current-repl)
+    (when-let* ((versions nrepl-versions)
+                (lg (nrepl-dict-get versions "let-go")))
+      (format "%s.%s"
+              (or (nrepl-dict-get lg "major") "?")
+              (or (nrepl-dict-get lg "minor") "?")))))
+
 (defun cider-runtime ()
   "Return the runtime of the nREPl server."
   (cond
    ((cider--clojure-version) 'clojure)
    ((cider--babashka-version) 'babashka)
    ((cider--nbb-nrepl-version) 'nbb)
    ((cider--scittle-nrepl-version) 'scittle)
+   ((cider--let-go-version) 'let-go)
    (t 'generic)))
 
 (defun cider-runtime-clojure-p ()