Overview
I use Emacs for my Clojure development, and have been using the Emacs front end to the CDT. The CDT and Emacs lib can be found on github at https://github.com/georgejahad/cdt.Setup
The CDT requires that the JVM be started with a debugging socket open. I use the clojure-maven-plugin (https://github.com/talios/clojure-maven-plugin) for my build/dependancy managment, and configure the <clojureoptions> to specify the socket port (in this case 8031).
...
<plugin>
<groupId>com.theoryinpractise</groupId>
<artifactId>clojure-maven-plugin</artifactId>
<version>1.3.6</version>
<configuration>
<sourceDirectories>
<sourceDirectory>src/main/clojure</sourceDirectory>
</sourceDirectories>
<clojureOptions>-Xmx1G -agentlib:jdwp=transport=dt_socket,address=8031,server=y,suspend=n</clojureOptions>
</configuration>
<executions>
<execution>
<id>compile-clojure</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
</plugin>
...
The only quirk that I have noticed configuring it this way is that the the JVM arguments are passed into the compile goal as well as the repl/swank goal, so you will see the debug port open once during compilation, then close and re-open when the repl or swank is running.My clojure sources are located in a standard maven classpath.
...
<build>
<sourceDirectory>src/main/clojure</sourceDirectory>
<testSourceDirectory>src/test/clojure</testSourceDirectory>
<resources>
<resource>
<directory>src/main/clojure</directory>
</resource>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
<testResources>
<testResource>
<directory>src/test/clojure</directory>
</testResource>
</testResource>
...
I set up my debugging classpath to include the ./src/main/clojure directory relative to the current directory where my sourceDirectory in maven is setup. I have placed the clojure and clojure-contrib sources into my classpath as well. When I am ready to debug, I run this elisp function from the root directory of my project to set the source paths prior to running M-x cdt.(defun cdt-set-source-path ()
(interactive)
(setq cdt-source-path
(reduce (lambda (acc f)
(concat (expand-file-name acc) ":" (expand-file-name f)))
'("./src/main/clojure"
"~/.emacs.d/site-lisp/cdt/clojure/clojure-1.2.0/src/jvm"
"~/.emacs.d/site-lisp/cdt/clojure/clojure-1.2.0/src/clj"
"~/.emacs.d/site-lisp/cdt/clojure/clojure-contrib-1.2.0/src/main/clojure")
You can also set the cdt-sourch-path via the REPL attached to the debug port via the clojure function:(set-source-path path)Where path is the string representation of the classpath.
Usage
Below is a list of CDT functions and their Emacs front end keybindings if applicable.
;; set breakpoints
(line-bp fname line) ; C-x C-a C-b set Breakpoint, on the current line
(set-catch Exception :all) ; break on any exception
;; delete breakpoints
(delete-all-breakpoints)
;; stepping
(stepi) ; C-x C-a C-i step the smallest possible Increment
(step) ; C-x C-a C-s Step
(step-over) ; C-x C-a C-n Next
(finish) ; C-x C-a C-f Runs to the end of the current function
; C-x C-a C-g Go/continue
;; evaluation
(print-bps)
(print-frame)
(print-frames)
;; evaluate an expression in the context of the stackframe
(reval sexpr)
Example
I have found myself using the debugger mostly when troubleshooting web/compojure applications. In these situations, I am able to reproduce the conditions that cause the application bug, and then set a break point to examine the state of my running application. I have created a simple compojure application that can be found at http://github.com/ffailla/cdt-example that I will use to demostrate how I use the CDT to evaluate a running web application.cdt-example.clj
(ns ffailla.cdtexample
(:use compojure.core, ring.adapter.jetty)
(:require [compojure.route :as route]))
(defn make-map [arg]
(apply array-map (range (Integer. arg))))
(defn test-fn [arg1 arg2]
(let [a (str arg1 " abcdefg")
b (make-map arg2)]
[a b]))
(defroutes main-routes
(GET "/" {params :params}
(let [arg1 (or (params "arg1") "test string arg")
arg2 (or (params "arg2") 10)]
(apply str (interpose "\n" (test-fn arg1 arg2)))))
(route/not-found "Page not found"))
(defn start []
(run-jetty main-routes {:port 8081 :join? false}))
I first run M-x cdt-set-source-path from the project root directory. This will set the classpath for the cdt to my project sources as well as the clojure sources. Then run M-x cdt to start the debugger, entering the debug port that I specified in my pom.xml file. I now have a buffer called *gud-clojure.main* that I can use.
Current directory is /Users/ffailla/dev/cdt-example/ Clojure 1.2.0 user=> nil user=> "/Users/ffailla/dev/cdt-example/src/main/clojure:/Users/ffailla/.emacs.d/site-lisp/cdt/clojure/clojure-1.2.0/src/jvm:/Users/ffailla/.emacs.d/site-lisp/cdt/clojure/clojure-1.2.0/src/clj:/Users/ffailla/.emacs.d/site-lisp/cdt/clojure/clojure-contrib-1.2.0/src/main/clojure" user=> starting event handler nil
Now I'll set some line break points. This can also be done via C-x C-a C-b.
user=> (line-bp "/Users/ffailla/dev/cdt-example/src/main/clojure/ffailla/cdtexample/clj", 17) bp set on (#<LocationImpl ffailla.cdtexample$fn__1730$fn__1731:17> #<LocationImpl ffailla.cdtexample$fn__1823$fn__1824:17> #<LocationImpl ffailla.cdtexample$fn__1845$fn__1846:17> #<LocationImpl ffailla.cdtexample$fn__1921$fn__1922:17>) nil user=> (line-bp "/Users/ffailla/dev/cdt-example/src/main/clojure/ffailla/cdtexample/clj", 10) bp set on (#<LocationImpl ffailla.cdtexample$test_fn:10> #<LocationImpl ffailla.cdtexample$test_fn:10>) nil user=> (line-bp "/Users/ffailla/dev/cdt-example/src/main/clojure/ffailla/cdtexample/clj", 6) bp set on (#<LocationImpl ffailla.cdtexample$make_map:6> #<LocationImpl ffailla.cdtexample$make_map:6>) nilWhen I make a GET request via curl http://localhost:8081/, the CDT show the following:
user=> Breakpoint #Lets evaluate some variableshit CDT location is /Users/ffailla/dev/cdt-example/src/main/clojure/ffailla/cdtexample.clj:17:0 0 ffailla.cdtexample$fn__1730$fn__1731 invoke [route-params--441--auto--1737 route--439--auto-- map--1732 params temp--3586--auto--1738 request--440--auto-- request--440--auto--1736 arg1 arg2 this] cdtexample.clj:17
user=> (reval params) nil user=> (reval arg1) "test string arg" user=> (reval arg2) 10Lets step to the next breakpoint
user=> (step-over) nil user=> Breakpoint #Here is a situation I do not understand, why is the reval of arg1 nil, yet arg2 is not? They both have non-nil values.hit CDT location is /Users/ffailla/dev/cdt-example/src/main/clojure/ffailla/cdtexample.clj:10:0 0 ffailla.cdtexample$test_fn invoke [this arg1 arg2] cdtexample.clj:10
user=> (reval arg1) nil user=> (reval arg2) 10And local let variables do not appear to be available
user=> (reval a) "remote exception: java.lang.Exception: Unable to resolve symbol: a in this context (NO_SOURCE_FILE:0)"Now I'll step over to the next break point and inspect the argument passed in.
user=> (step-over) nil user=> Breakpoint #<BreakpointEventImpl BreakpointEvent@ffailla.cdtexample$make_map:6 in thread 2115942479@qtp0-0> hit CDT location is /Users/ffailla/dev/cdt-example/src/main/clojure/ffailla/cdtexample.clj:6:0 0 ffailla.cdtexample$make_map invoke [this arg] cdtexample.clj:6 user=> (reval arg) 10I can view my entire stack frame or just my current
user=> (print-frames) 0 ffailla.cdtexample$make_map invoke [this arg] cdtexample.clj:6 1 ffailla.cdtexample$test_fn invoke [this arg1 arg2] cdtexample.clj:10 2 ffailla.cdtexample$fn__1730$fn__1731 invoke [route-params--441--auto--1737 route--439--auto-- map--1732 params temp--3586--auto--1738 request--440--auto-- request--440--auto--1736 arg1 arg2 this] cdtexample.clj:17 3 compojure.core$routes$fn__444$fn__445 invoke [this request p1--443#] core.clj:71 4 clojure.core$some invoke [this coll pred] core.clj:2053 5 compojure.core$routes$fn__444 invoke [this handlers request] core.clj:71 6 ring.middleware.params$wrap_params$fn__163 invoke [this handler opts request encoding] params.clj:76 7 ring.middleware.cookies$wrap_cookies$fn__333 invoke [this handler request] cookies.clj:124 8 ring.adapter.jetty$proxy_handler$fn__531 invoke [this handler target request response dispatch] jetty.clj:17 9 ring.adapter.jetty.proxy$org.mortbay.jetty.handler.AbstractHandler$0 handle [] source not found:-1 10 org.mortbay.jetty.handler.HandlerWrapper handle [this dispatch target response request] HandlerWrapper.java:152 11 org.mortbay.jetty.Server handle [this target connection] Server.java:324 12 org.mortbay.jetty.HttpConnection handleRequest [this threadName info error retrying] HttpConnection.java:534 13 org.mortbay.jetty.HttpConnection$RequestHandler headerComplete [this] HttpConnection.java:864 14 org.mortbay.jetty.HttpParser parseNext [this array total-filled length ch] HttpParser.java:533 15 org.mortbay.jetty.HttpParser parseAvailable [this] HttpParser.java:207 16 org.mortbay.jetty.HttpConnection handle [this more-in-buffer io continuation no-progress] HttpConnection.java:403 17 org.mortbay.jetty.bio.SocketConnector$Connection run [this] SocketConnector.java:228 18 org.mortbay.thread.QueuedThreadPool$PoolThread run [this todo idle job] QueuedThreadPool.java:522 nil user=> (print-frame) 0 ffailla.cdtexample$make_map invoke [this arg] cdtexample.clj:6 nil
