Debugging in Cider

README.md

@@ -32,6 +32,7 @@ middleware to to `:nrepl-middleware` under `:repl-options`.
                  [cider.nrepl.middleware.apropos/wrap-apropos
                   cider.nrepl.middleware.classpath/wrap-classpath
                   cider.nrepl.middleware.complete/wrap-complete
+                  cider.nrepl.middleware.debug/wrap-debug
                   cider.nrepl.middleware.format/wrap-format
                   cider.nrepl.middleware.info/wrap-info
                   cider.nrepl.middleware.inspect/wrap-inspect
@@ -90,6 +91,7 @@ Middleware        | Op(s)      | Description
 `wrap-apropos`    | `apropos`  | Pattern search for symbols and documentation.
 `wrap-classpath`  | `classpath` | Java classpath.
 `wrap-complete`   | `complete` | Simple completion. Supports both Clojure & ClojureScript.
+`wrap-debug`      | `init-debugger` | Establish a channel for `cider-debug` commands.
 `wrap-format`     | `format-(code/edn)` | Code and data formatting.
 `wrap-info`       | `info/eldoc` | File/line, arglists, docstrings and other metadata for vars.
 `wrap-inspect`    |`inspect-(start/refresh/pop/push/reset)` | Inspect a Clojure expression.

project.clj

@@ -11,6 +11,7 @@
             :url "http://www.eclipse.org/legal/epl-v10.html"}
   :dependencies [[compliment "0.2.1-SNAPSHOT"]
                  [cljs-tooling "0.1.5-SNAPSHOT"]
+                 [debugger "0.1.6"]
                  [cljfmt "0.1.10"]
                  [org.tcrawley/dynapath "0.2.3"]
                  [org.clojure/tools.nrepl "0.2.7"]
@@ -24,6 +25,7 @@
              :dev {:repl-options {:nrepl-middleware [cider.nrepl.middleware.apropos/wrap-apropos
                                                      cider.nrepl.middleware.classpath/wrap-classpath
                                                      cider.nrepl.middleware.complete/wrap-complete
+                                                     cider.nrepl.middleware.debug/wrap-debug
                                                      cider.nrepl.middleware.format/wrap-format
                                                      cider.nrepl.middleware.info/wrap-info
                                                      cider.nrepl.middleware.inspect/wrap-inspect

src/cider/nrepl.clj

@@ -3,6 +3,7 @@
             [cider.nrepl.middleware.apropos]
             [cider.nrepl.middleware.classpath]
             [cider.nrepl.middleware.complete]
+            [cider.nrepl.middleware.debug]
             [cider.nrepl.middleware.format]
             [cider.nrepl.middleware.info]
             [cider.nrepl.middleware.inspect]
@@ -20,6 +21,7 @@
   '[cider.nrepl.middleware.apropos/wrap-apropos
     cider.nrepl.middleware.classpath/wrap-classpath
     cider.nrepl.middleware.complete/wrap-complete
+    cider.nrepl.middleware.debug/wrap-debug
     cider.nrepl.middleware.format/wrap-format
     cider.nrepl.middleware.info/wrap-info
     cider.nrepl.middleware.inspect/wrap-inspect

src/cider/nrepl/middleware/debug.clj

@@ -0,0 +1,59 @@
+(ns cider.nrepl.middleware.debug
+  (:require [clojure.tools.nrepl.transport :as transport]
+            [clojure.tools.nrepl.middleware :refer [set-descriptor!]]
+            [clojure.tools.nrepl.misc :refer [response-for]]
+            [cider.nrepl.middleware.util.instrument :refer [instrument]]
+            [debugger.core :refer [break]]))
+
+;;;; ## Interaction with the client
+;;; `wrap-debug` receives an initial message from the client, stores
+;;; it in `debugger-message`, and `breakpoint` answers it.
+(def debugger-message (atom nil))
+
+(defn wrap-debug [h]
+  (fn [{:keys [op force] :as msg}]
+    (if (= "init-debugger" op)
+      (let [stored-message @debugger-message]
+        (if (and stored-message (not force))
+          (transport/send (:transport msg)
+                          (response-for msg :status :done))
+          (do (when stored-message
+                (transport/send (:transport stored-message)
+                                (response-for stored-message :status :done)))
+              ;; TODO: Redefine this in the session binding map, see inspect.clj.
+              (reset! debugger-message msg))))
+      (h msg))))
+
+(defn breakpoint
+  "Send value and coordinates to the client through the debug channel.
+  Sends a response to the message stored in debugger-message."
+  [value extras]
+  ;; Notify cider that a (break) is incoming, along with the value of
+  ;; the instrumented sexp and instructions on how to find it in the
+  ;; code.
+  (transport/send
+   (:transport @debugger-message)
+   (response-for @debugger-message
+                 (assoc extras
+                        :value (pr-str value)
+                        :breakfunction nil)))
+  ;; Send the actual break.
+  (binding [*out* (new java.io.StringWriter)]
+    (break value)))
+
+(defn instrument-and-eval
+  "Instrument form and evaluate the result.
+  Call cider.nrepl.middleware.util.instrument."
+  [ex form]
+  (eval
+   (instrument (merge {:coor [], :breakfunction breakpoint} ex)
+               form)))
+
+(set-descriptor!
+ #'wrap-debug
+ {:handles
+  {"init-debugger"
+   {:doc "Initialize the debugger so that #'breakpoint works correctly.
+This does not respond immediately. It sends a response when a breakpoint is reached."
+    :requires {"id" "A message id that will be responded to when a breakpoint is reached."}
+    :returns {"status" "debugging"}}}})