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  1. JDK
  2. JDK-8258259

Unicode linebreak matching behavior is incorrect; backout JDK-8235812

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P3
    • Resolution: Fixed
    • Affects Version/s: 15, 16
    • Fix Version/s: 16
    • Component/s: core-libs
    • Labels:
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        Description

        Bug JDK-8235812 changed the behavior of matching of the Unicode linebreak pattern, \R. This change should be reverted.

        The problem stated in that bug report was that the pattern \R{2} did not match the string "\r\n" and the fix changed the behavior so that a match was successful. This *seemed* the correct thing to do, as the Pattern class spec has a definition for \R which is essentially

        -----
        \u000D\u000A|[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]
        -----

        and the behavior after the change conforms to that definition.

        The problem is that this definition of the \R pattern doesn't match the recommendation from TR18, which is

        -----
        (?:\u000D\u000A)|(?!\u000D\u000A)[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]
        -----

        (Based on http://unicode.org/reports/tr18/#Line_Boundaries and corrected and transliterated to Java regex syntax.)

        The salient difference is the appearance of a negative lookahead pattern "?!" which causes the pattern not to match a \r if it's immediately followed by \n. Thus, the TR18 recommendation would have the pattern \R{2} NOT match the string "\r\n". Indeed, PCRE has this behavior.

        This bug covers backing out of the JDK-8235812 change. Follow-on bug JDK-8258119 covers further changes in this area. In particular, the Pattern spec's definition of \R should be revisited to see if it should be adjusted to match TR18 more closely.

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                Assignee:
                smarks Stuart Marks
                Reporter:
                smarks Stuart Marks
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