Clojure

Clojure reader (incorrectly) accepts keywords starting with a number

Details

  • Type: Defect Defect
  • Status: Closed Closed
  • Priority: Minor Minor
  • Resolution: Declined
  • Affects Version/s: Release 1.5
  • Fix Version/s: Release 1.6
  • Component/s: None
  • Labels:
  • Patch:
    Code and Test
  • Approval:
    Screened

Description

The reader page at http://clojure.org/reader states that symbols (and keywords) cannot start with a number and the regex used in LispReader (and EdnReader) also has this intention. But:

user> :5
:5
user> (class *1)
clojure.lang.Keyword

Cause: The pattern for keywords is: "[:]?([\D&&[^/]].*/)?(/|[\D&&[^/]][^/]*)". The intention of the [\D&&[^/]] is to accept all non-digits except /. However, if the : matches and 5 does not, the regex will backtrack and unmatch the :, instead matching it in the non-digit charset. The whole match is sent on in the code and the : is stripped later.

Solution: Prevent back-tracking for the first : match by using the possessive quantifier ?+ instead of ?. Once the first : is matched, it will not backtrack to it. (This is also faster.) The patch makes this change in LispReader and EdnReader, updates a couple tests that were using number keywords, and adds a new negative test to check that :5 isn't read.

Patch: numkeyword.patch

Screened by: Alex Miller

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    Updated:
    Resolved: