Clojure

print-dup's handling of metadata typehint is unreadable in some circumstances

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Minor Minor
  • Resolution: Unresolved
  • Affects Version/s: Release 1.5, Release 1.6
  • Fix Version/s: None
  • Component/s: None
  • Labels:
  • 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

Activity

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Alex Coventry added a comment -

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

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Alex Coventry added a comment - Corresponding bug on sleight: https://github.com/ztellman/sleight/issues/5
Alex Miller made changes -
Field Original Value New Value
Labels eval metadata print-dup metadata print
Alex Miller made changes -
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
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.

{code}
  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)
{code}

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.

{code}
  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)
{code}

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

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    Updated: