JDK-8258259 : Unicode linebreak matching behavior is incorrect; backout JDK-8235812
- Type: Bug
- Component: core-libs
- Sub-Component: java.util.regex
- Affected Version: 15,16
- Priority: P3
- Status: Resolved
- Resolution: Fixed
- Submitted: 2020-12-14
- Updated: 2021-01-20
- Resolved: 2020-12-18
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| JDK 16 | JDK 17 |
|---|---|
16 b30Fixed  |
17Fixed |
Related Reports
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Sub Tasks
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JDK-8258456 :
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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
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\u000D\u000A|[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]
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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
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(?:\u000D\u000A)|(?!\u000D\u000A)[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]
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(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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