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[CLJ-1275] print-dup's handling of metadata typehint is unreadable in some circumstances Created: 02/Oct/13  Updated: 05/Feb/14

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: Release 1.5, Release 1.6
Fix Version/s: None

Type: Defect Priority: Minor
Reporter: Alex Coventry Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: metadata, print

Attachments: Text File 0001-Don-t-use-shorthand-for-typehints-when-print-dup.patch    
Patch: Code and Test

 Description   

With print-dup true, if an object being printed has a metadata map with only a :tag key, the printer renders it as "^value". This can cause an IllegalArgumentException if you try to read the printed string back in, in some circumstances. E.g.

user=> (read-string (let [ge (with-meta (gensym) {:tag Object})] (binding [*print-dup* true] (pr-str ge))))
  IllegalArgumentException Metadata must be Symbol,Keyword,String or Map  clojure.lang.LispReader$MetaReader.invoke (LispReader.java:732)

This is causing problems with sleight/riddley's [1] handling of the (case) macro, which drops a type-hint on a gensym it incorporates in the form it returns. When sleight tries to reserialize a macroexpanded (case) form from riddley, it fails as demonstrated above. E.g.

user=> (read-string (binding [*print-dup* true] (pr-str (macroexpand '(case 1 1 1)))))
  user=> IllegalArgumentException Metadata must be Symbol,Keyword,String or Map  clojure.lang.LispReader$MetaReader.invoke (LispReader.java:732)

The attached patch corrects this by making core_print.clj's print-meta always print out the full metadata map if print-dup is true. The patch also contains a test for this case.

[1] https://github.com/ztellman/sleight https://github.com/ztellman/riddley



 Comments   
Comment by Alex Coventry [ 02/Oct/13 10:28 PM ]

Corresponding bug on sleight: https://github.com/ztellman/sleight/issues/5

Generated at Thu Jul 24 18:09:22 CDT 2014 using JIRA 4.4#649-r158309.