Allow connecting to nbb via connect-clj (clojure-emacs#3061) (clojure-emacs#3272)

This is for nbb, scittle, joyride.
Better support for "pain" repls, support "cljs" without setup.

We want to:

1. connect with a plain nREPL client
2. make any assumptions explicit about the nREPL server/runtime
3. connect cljs buffers with those plain repls

1. Check for cider middleware being present, before using it
(already being done)
2. Check for cider-library-present-p, before relying on anything in
the runtime.
3. Make assumptions about the runtime explicit

My suggestion is to solve these problems is `cider-connection-capabilities`.
Currently, there was an implicit assumption about the compilation
error format.

Changes to `cider-repls`:

Now returns cljs, if the repl capabilities include 'cljs.
This way we can make a "plain" clj client, upgrade on connect with
cljs capability and have it be connected in cljs buffers.

This is more a concession / workaround the current repl-type setup.

Here's the slack discussion that lead to this PR:
https://clojurians.slack.com/archives/C04CAKAGADU

Author: benjamin-asdf

CHANGELOG.md

@@ -17,6 +17,8 @@
 - [#3251](https://github.com/clojure-emacs/cider/pull/3251): Disable undo in `*cider-stacktrace*` buffers.
 - Consecutive overlays will not be spuriously deleted.
 - [#3260](https://github.com/clojure-emacs/cider/pull/3260): Scroll REPL buffer in other frame.
+- [#3061](https://github.com/clojure-emacs/cider/issues/3061): Allow
+  connect-clj for plain cljs repls (nbb etc).
 
 ## 1.5.0 (2022-08-24)
 

cider-connection.el

@@ -343,6 +343,19 @@ buffer."
        (when cider-auto-mode
          (cider-enable-on-existing-clojure-buffers))
 
+       (setf cider-connection-capabilities
+             (append
+              (pcase (cider-runtime)
+                ('clojure '(clojure jvm-compilation-errors))
+                ('babashka '(babashka jvm-compilation-errors))
+                (_ '()))
+              (when
+                  ;; see `cider-sync-tooling-eval', but it is defined on a higher layer
+                  (nrepl-dict-get
+                   (nrepl-sync-request:eval "cljs.core/demunge" (current-buffer) nil 'tooling)
+                   "value")
+                '(cljs))))
+
        (run-hooks 'cider-connected-hook)))))
 
 (defun cider--disconnected-handler ()
@@ -437,6 +450,19 @@ about this buffer (like variable `cider-repl-type')."
               (plist-get nrepl-endpoint :host)
               (plist-get nrepl-endpoint :port))))))
 
+(defvar-local cider-connection-capabilities '()
+  "A list of some of the capabilites of this connection buffer.
+Aka what assumptions we make about the runtime.
+This is more general than
+`cider-nrepl-op-supported-p' and `cider-library-present-p'.
+But does not need to replace them.")
+
+(defun cider-connection-has-capability-p (capability :optional connection-buffer)
+  "Return non nil when the cider connection has CAPABILITY.
+By default it assumes the connection buffer is current."
+  (with-current-buffer (or connection-buffer (current-buffer))
+    (member capability cider-connection-capabilities)))
+
 
 ;;; Connection Management Commands
 
@@ -885,7 +911,13 @@ no linked session or there is no REPL of TYPE within the current session."
     (cond ((null buffer-repl-type) nil)
           ((or (null type) (eq type 'multi) (eq type 'any)) t)
           ((listp type) (member buffer-repl-type type))
-          (t (string= type buffer-repl-type)))))
+          (t
+           (or (string= type buffer-repl-type)
+               (let ((capabilities
+                      (buffer-local-value 'cider-connection-capabilities buffer)))
+                 (cond ((listp type)
+                        (cl-some (lambda (it) (member it capabilities)) type))
+                       (t (member type capabilities)))))))))
 
 (defun cider--get-host-from-session (session)
   "Returns the host associated with SESSION."

cider-eval.el

@@ -462,6 +462,13 @@ Uses the value of the `out' slot in RESPONSE."
    (cider-nrepl-sync-request:eval
     "(clojure.stacktrace/print-cause-trace *e)")))
 
+(defun cider-default-err-eval-print-handler ()
+  "Display the last exception without middleware support.
+When clojure.stracktrace is not present."
+  (cider--handle-err-eval-response
+   (cider-nrepl-sync-request:eval
+    "(println (ex-data *e))")))
+
 (defun cider--render-stacktrace-causes (causes &optional error-types)
   "If CAUSES is non-nil, render its contents into a new error buffer.
 Optional argument ERROR-TYPES contains a list which should determine the
@@ -498,9 +505,10 @@ into a new error buffer."
 (defun cider-default-err-handler ()
   "This function determines how the error buffer is shown.
 It delegates the actual error content to the eval or op handler."
-  (if (cider-nrepl-op-supported-p "stacktrace")
-      (cider-default-err-op-handler)
-    (cider-default-err-eval-handler)))
+  (cond ((cider-nrepl-op-supported-p "stacktrace") (cider-default-err-op-handler))
+        ((cider-library-present-p "clojure.stacktrace") (cider-default-err-eval-handler))
+        (t (cider-default-err-eval-print-handler))))
+
 
 ;; The format of the error messages emitted by Clojure's compiler changed in
 ;; Clojure 1.10.  That's why we're trying to match error messages to both the
@@ -739,7 +747,10 @@ when `cider-auto-inspect-after-eval' is non-nil."
                                    (cider-emit-interactive-eval-output out))
                                  (lambda (_buffer err)
                                    (cider-emit-interactive-eval-err-output err)
-                                   (unless cider-show-error-buffer
+
+                                   (when (or (not cider-show-error-buffer)
+                                             (not (cider-connection-has-capability-p 'jvm-compilation-errors)))
+
                                      ;; Display errors as temporary overlays
                                      (let ((cider-result-use-clojure-font-lock nil))
                                        (cider--display-interactive-eval-result

cider-overlays.el

@@ -303,6 +303,7 @@ focused."
   (let* ((font-value (if cider-result-use-clojure-font-lock
                          (cider-font-lock-as-clojure value)
                        value))
+         (font-value (string-trim-right font-value))
          (used-overlay (when (and point cider-use-overlays)
                          (cider--make-result-overlay font-value
                            :where point

cider-repl.el

@@ -153,7 +153,8 @@ you'd like to use the default Emacs behavior use
 (make-obsolete-variable 'cider-repl-print-level 'cider-print-options "0.21")
 
 (defvar cider-repl-require-repl-utils-code
-  '((clj . "(clojure.core/apply clojure.core/require clojure.main/repl-requires)")
+  '((clj . "(when-let [requires (resolve 'clojure.main/repl-requires)]
+  (clojure.core/apply clojure.core/require @requires))")
     (cljs . "(require '[cljs.repl :refer [apropos dir doc find-doc print-doc pst source]])")))
 
 (defcustom cider-repl-init-code (list (cdr (assoc 'clj cider-repl-require-repl-utils-code)))

cider.el

@@ -778,9 +778,13 @@ Generally you should not disable this unless you run into some faulty check."
   :safe #'booleanp
   :package-version '(cider . "0.17.0"))
 
+(defun cider-clojurescript-present-p ()
+  "Return non nil when ClojureScript is present."
+  (nrepl-dict-get (cider-sync-tooling-eval "cljs.core/demunge") "value"))
+
 (defun cider-verify-clojurescript-is-present ()
   "Check whether ClojureScript is present."
-  (unless (cider-library-present-p "cljs.core")
+  (unless (cider-clojurescript-present-p)
     (user-error "ClojureScript is not available.  See https://docs.cider.mx/cider/basics/clojurescript for details")))
 
 (defun cider-verify-piggieback-is-present ()

doc/modules/ROOT/nav.adoc

@@ -13,6 +13,7 @@
 * Alternative Platforms
 ** xref:platforms/overview.adoc[Overview]
 ** xref:platforms/babashka.adoc[Babashka]
+** xref:platforms/scittle_and_friends.adoc[Scittle and Friends]
 * Using CIDER
 ** xref:usage/interactive_programming.adoc[Interactive Programming]
 ** xref:usage/cider_mode.adoc[Using cider-mode]

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

@@ -0,0 +1,29 @@
+= Scittle, Nbb, Joyride, and future plain repls
+
+The default cider (clj-repl) should be capable of connecting to any
+nrepl server that provides minimal functionality.
+
+As such, all of these work:
+https://github.com/babashka/nbb[nbb],
+https://github.com/babashka/scittle[scittle], https://github.com/BetterThanTomorrow/joyride[joyride]
+
+First start an nrepl server (the project's Readme usually has a section
+on starting a nrepl server).
+
+You can use
+
+kbd:[M-x `cider-connect-clj` <RET>]
+
+to connect to any plain Clojure(Script) nrepl server.
+
+Features:
+
+* Eval, load file etc.
+* Errors as overlays. (The default cider error buffer is not implemented currently).
+* Other nrepl features the server provides; This might be rather minimal.
+
+Nbb, Scittle and Joyride all have quite cool completions already.
+
+== Note
+
+For nbb you can alternatively connect via cljs, see xref:platform/nbb.adoc[Nbb]

test/cider-connection-tests.el

@@ -370,6 +370,26 @@
            (expect (cider-repls) :to-equal (list a b))
            (kill-buffer b)
            (expect (cider-repls) :to-equal (list a))
+           (sesman-unregister 'CIDER session))))))
+
+  (describe "cljs capability"
+    (it "Upgraded clj repl counts as cljs"
+      (let ((default-directory (expand-file-name "/tmp/some-dir")))
+        (cider-test-with-buffers
+         (a b)
+         (let ((session (list "some-session" a b)))
+           (with-current-buffer a
+             (setq cider-repl-type 'clj))
+           (with-current-buffer b
+             (setq cider-repl-type 'cljs))
+           (sesman-register 'CIDER session)
+           (expect (cider-repls 'cljs) :to-equal (list b))
+
+           (with-current-buffer a
+             (setf cider-connection-capabilities
+                   (append cider-connection-capabilities '(cljs))))
+
+           (expect (cider-repls) :to-equal (list a b))
            (sesman-unregister 'CIDER session)))))))
 
 (describe "cider--connection-info"