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[CLJS-891] Defs in "parent" namespaces clash with "child" namespaces with the same name? Created: 28/Nov/14  Updated: 28/Nov/14

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

Type: Defect Priority: Minor
Reporter: Russell Dunphy Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: bug, namespace

Clojurescript 0.0-2371, OSX


This has had me totally flummoxed for a few hours, but I have finally been able to create a minimal project replicating the problem based on the mies template: https://github.com/rsslldnphy/cljs-ns-issue.

The problem seems to happen when a "parent" namespace, for example `my-project.foo`, contains a def with the same name as a "child" namespace, eg if there is a namespace `my-project.foo.bar`, and a def named `bar` in `my-project.foo`, and both those namespaces are required by `my-project.core`, then calling functions in `my-project.foo.bar` ends up with an Uncaught TypeError: Cannot read property 'call' of undefined. Sometimes, depending on which ns requires which, I've also seen an Uncaught Error: Namespace "cljs_ns_issue.foo.bar" already declared.

I don't think I'm doing a particularly good job of explaining this so it might be easier to look at the code. The crux is: comment out this line and the code works, leave it in and you get an error.

Comment by Francis Avila [ 28/Nov/14 2:01 PM ]

Clojurescript implements namespaces with Google Closure compiler's require/provide system. Unfortunately that system does not have a hard distinction between names and namespaces like Clojure does but instead is more like a sloppy java classname. The crux of it is that vars and namespaces occupy the same tree of js objects and thus their names may not overlap.

Compare the cljs on the left with the emitted javascript (This isn't exactly what is happening, but only in essence):

(ns my-project.foo ; goog.provide('my_project.foo') // something like window.my_project = {foo: {}}
  (:require my-project.foo.bar)) //goog.require('my_project.foo.bar')

;; the "require" evaluates the other namespace, which sets
;; // window.my_project.foo = {bar:{}};
;; // my_project.foo.bar.baz = "some var in the bar ns";
;; Now window.my_project.foo.bar = {baz: "some var in the bar ns"};

(defn bar [] 1)         ; my_project.foo.bar = (function bar(){return 1;});
;; Now the js object that was the bar namespace is gone, replaced with this function.

; my_project.foo.bar.baz.call() // Uncaught TypeError: Cannot read property 'call' of undefined.

;; Alternatively, if (ns my-project.foo.bar) got evaluated *after* my-project.foo namespace was
;; evaluated, then my-project.foo/bar is defined, and the emitted goog.provide('my-project.foo.bar')
;; throws "Uncaught Error: Namespace "my_project.foo.bar" already declared".

So basically this is a leaky abstraction. In Clojurescript, you cannot define a var whose ns-qualified name matches that of another namespace: the slash between name and namespace is not real.

I think the only possible things that can be done are either:

  • Warn at compile-time if a var and a namespace object-path clash. Obviously there may still be runtime-created vars.
  • Put namespace vars behind some magic name. E.g. (ns foo.bar)(def baz 1) becomes goog.provide('foo.bar.__NS__'); foo.bar.__NS__.baz = 1; This would significantly uglify cljs names exported to js (and break existing code), and the magic name could never be used as a var name.

[CLJS-890] Incorrect behaviour of (str obj) when obj has valueOf method Created: 24/Nov/14  Updated: 24/Nov/14

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

Type: Defect Priority: Major
Reporter: Nikita Beloglazov Assignee: Unassigned
Resolution: Unresolved Votes: 1
Labels: None



(str #js {"toString" (fn [] "hello") "valueOf" (fn [] 42)}) ; => "42"

The problem in the fact that ClojureScript uses concatenation to convert values to strings and that doesn't work well with objects which have valueOf() method overriden.

Example in js:

var obj = {
    toString: function() { return 'hello'; },
    valueOf: function() { return 42; }
console.log(String(obj)); => 'hello'
console.log(obj.toString()); => 'hello'
console.log('' + obj); => '42'

Potential solution might be to use String() function. Using toString() won't work as described in this issue: http://dev.clojure.org/jira/browse/CLJS-847

Comment by Kevin Neaton [ 24/Nov/14 10:34 AM ]

Is there a valid use case where toString and valueOf are not in sync? E.g.

(not= (.toString x) (js/String (.valueOf x))

If not, is it "incorrect" for the two methods to be out of sync?

Comment by Nikita Beloglazov [ 24/Nov/14 10:40 AM ]

Here is an example of such use case: https://github.com/processing-js/processing-js/blob/master/src/Objects/Char.js
That's how I found this bug.

Comment by Kevin Neaton [ 24/Nov/14 10:49 AM ]

Thanks for the link. I see what you mean.

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