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[CLJS-985] ex-info loses stack information Created: 20/Jan/15  Updated: 02/Jul/15  Resolved: 23/Jan/15

Status: Closed
Project: ClojureScript
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Defect Priority: Major
Reporter: Nikita Prokopov Assignee: Unassigned
Resolution: Completed Votes: 1
Labels: None

Attachments: Text File cljs-985-ex-info-stack.patch    

 Description   

Native js Error keeps stacktrace:

(js/console.log (.-stack (js/Error. "message")))

Error: message
    at eval (/Users/prokopov/Dropbox/ws/datascript/test/test/datascript.cljs[eval5]:10:14)
    at eval (native)
    at SocketNamespace.<anonymous> (http://localhost:65000/socket.io/lighttable/ws.js:118:26)
    at SocketNamespace.EventEmitter.emit [as $emit] (http://localhost:65000/socket.io/socket.io.js:633:15)
    at SocketNamespace.onPacket (http://localhost:65000/socket.io/socket.io.js:2248:20)
    at Socket.onPacket (http://localhost:65000/socket.io/socket.io.js:1930:30)
    at Transport.onPacket (http://localhost:65000/socket.io/socket.io.js:1332:17)
    at Transport.onData (http://localhost:65000/socket.io/socket.io.js:1303:16)
    at WebSocket.websocket.onmessage (http://localhost:65000/socket.io/socket.io.js:2378:12)

But ex-info does not:

(js/console.log (.-stack (ex-info "message")))

Error
    at file:///Users/prokopov/Dropbox/ws/datascript/web/target-cljs/cljs/core.js:32066:38

Problem is that ex-info inherits stack property from prototype which is instantiated at script load time here:

(deftype ExceptionInfo [message data cause])

(set! (.-prototype ExceptionInfo) (js/Error.))
(set! (.. ExceptionInfo -prototype -constructor) ExceptionInfo)

The possible solution is to create new instance of js/Error at (ex-info) and manually copy stack property to ExceptionInfo object. Related SO: http://stackoverflow.com/questions/783818/how-do-i-create-a-custom-error-in-javascript

Problem is that Chrome has setter on stack property, and it only allows for this property to be set inside a constructor functions.

Proposed fix creates new Error each time ex-info is called and sets ExceptionInfo.prototype to newly created error. This way new ExceptionInfo instance will inherit stack from newly created Error with correct stack.

This patch has been tested in Chrome 39 Mac, Safari 8 Mac, Firefox 35 Mac and IE 10 Win. Here's test code I used:

(defn -ex-info
  ([msg data]
    (set! (.-prototype ExceptionInfo) (js/Error msg))
    (set! (.. ExceptionInfo -prototype -name) "ExceptionInfo")
    (set! (.. ExceptionInfo -prototype -constructor) ExceptionInfo)
    (ExceptionInfo. msg data nil))
  ([msg data cause]
    (set! (.-prototype ExceptionInfo) (js/Error msg))
    (set! (.. ExceptionInfo -prototype -name) "ExceptionInfo")
    (set! (.. ExceptionInfo -prototype -constructor) ExceptionInfo)
    (ExceptionInfo. msg data cause)))

(try
  (throw (ex-info "[ -- Current ex-info message -- ]" 123))
  (catch ExceptionInfo e
    (js/console.log "Current ex-info::" (.-stack e))))

(try
  (throw (js/Error "[ -- Native message -- ]"))
  (catch js/Error e
    (js/console.log "Native error::" (.-stack e))))

(try
  (throw (-ex-info "[ -- Patched ex-info message -- ]" 123))
  (catch ExceptionInfo e
    (js/console.log "Patched ex-info::" (.-stack e))))

Test results:

Chrome, Firefox, IE, Safari

Note that current implementation reports line number and overall stacktrace from cljs.core file where Error prototype is created in current implementation.
Note that patched version reports correct line number (it should be close to native error stack), stack, message and exception name.
Also note that IE is fine even without patch — that's because in IE stack is capturead at throw place, not at new Error() call site.



 Comments   
Comment by Nikita Prokopov [ 20/Jan/15 2:48 PM ]

Ok, this is crazy, but this seems to solve the issue:

(defn ex-info [msg data cause]
  (set! (.-prototype ExceptionInfo) (js/Error msg))
  (set! (.. ExceptionInfo -prototype -name) "cljs.core.ExceptionInfo")
  (set! (.. ExceptionInfo -prototype -constructor) ExceptionInfo)
  (ExceptionInfo. msg data cause))

Basically we change prototype before creating each object.

(taken from http://stackoverflow.com/questions/783818/how-do-i-create-a-custom-error-in-javascript#answer-12030032)

I guess high performance is not needed from ex-info, so this solution is somewhat okay-ish? Should I make a patch from it?

Comment by David Nolen [ 20/Jan/15 2:55 PM ]

It would be nice to get confirmation from others that this works under the major browser - Safari, Firefox, Chrome, and modern IE.

Comment by Nikita Prokopov [ 20/Jan/15 3:12 PM ]

I can confirm Firefox 34, Firefox 35, Safari 8.0.2 and Chrome 39 (all Mac) for now

Comment by Nikita Prokopov [ 22/Jan/15 3:50 AM ]

David, I updated issue, added patch, test code and test results (including IE). There’s no unit test on this because stack traces are very engine-specific. Please take a look

Comment by David Nolen [ 22/Jan/15 2:24 PM ]

Nikita, thanks for the update will check it out.

Comment by David Nolen [ 23/Jan/15 6:13 PM ]

fixed https://github.com/clojure/clojurescript/commit/93dce672e1af8f698cfc2a61e293cb48aeeddc2c

Comment by Aleksey Kladov [ 01/Jul/15 7:19 PM ]

Looks like it should be reopened because of this commit
https://github.com/clojure/clojurescript/commit/de130a335bd761d580d04dadb8a5a43d3c0a35b4

js/Error is constructed with empty message on this line https://github.com/clojure/clojurescript/commit/de130a335bd761d580d04dadb8a5a43d3c0a35b4#diff-a98a037c6c098dd3707e861df3c2f5acR9197

So, when stack is assigned here
https://github.com/clojure/clojurescript/commit/de130a335bd761d580d04dadb8a5a43d3c0a35b4#diff-a98a037c6c098dd3707e861df3c2f5acR9210
it does not have a message.

I guess that the fix will be to change `(let [e (js/Error.)]` to `(let [e (js/Error. message)]`

Comment by David Nolen [ 02/Jul/15 5:59 PM ]

fixed in master

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