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[CLJS-968] Metadata on function literal inside of a let produces invalid Javascript Created: 07/Jan/15  Updated: 23/Jan/15

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

Type: Defect Priority: Major
Reporter: Bobby Eickhoff Assignee: Nicola Mometto
Resolution: Unresolved Votes: 1
Labels: bug

Originally found with [org.clojure/clojurescript "0.0-2496"]
Still reproducible with the latest cljsc (b5e9a5116259fc9f201bee4b9c6564f35306f9a5)


Here is a minimal test case that produces the invalid Javascript:

(defn f []
  (let [a 0]
    ^{"meta" "data"}
    (fn [] true)))

The compiled Javascript includes the invalid token sequence "return return". (Per Chrome: Uncaught SyntaxError: Unexpected token return)

The problem does not occur if the metadata applies to a map literal instead of a function literal.
The problem only occurs when the function and metadata are inside of a let.

Comment by Bobby Eickhoff [ 07/Jan/15 9:45 PM ]

I forgot to try with-meta. Using with-meta does not produce this syntax error, so it's only a problem with the reader macro for metadata.

Comment by David Nolen [ 08/Jan/15 7:41 AM ]

Any quick thoughts about this one Nicola? Quite possibly a compiler issue on the CLJS side.

Comment by Nicola Mometto [ 08/Jan/15 8:07 AM ]

David, I understand why this happens but I don't know enough about how cljs's js emission to propose a fix.
The issue is that with this commit: https://github.com/clojure/clojurescript/commit/d54defd32d6c5ffcf6b0698072184fe8ccecc93a the following scenario is possible:

{:op :meta
 :env {:context :return}
 :expr {:op :fn
        :env {:context :expr}
        :methods [{:op :fn-method 
                   :env {:context :return} ..}]

i.e. analyze-wrap-meta changes the context of the :fn node to :expr but keeps the context of the :fn-methods to :return.

This causes both
https://github.com/clojure/clojurescript/blob/master/src/clj/cljs/compiler.clj#L488 (https://github.com/clojure/clojurescript/blob/master/src/clj/cljs/compiler.clj#L233)

to be true and emit a "return".

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