RFR: 8311939: Excessive allocation of Matcher.groups array [v4]

[Cristian Vat]

On Fri, 28 Jul 2023 12:15:21 GMT, Cristian Vat <duke at openjdk.org> wrote:

>> Reduces excessive allocation of Matcher.groups array when the original Pattern has no groups or less than 9 groups.
>> 
>> Original clamping to 10 possibly due to documented behavior from javadoc: 
>> "In this class, \1 through \9 are always interpreted as back references, "
>> 
>> Only with Matcher changes RegExTest.backRefTest fails when backreferences to non-existing groups are present.
>> Added a match failure condition in Pattern that fixes failing tests.
>> 
>> As per existing `java.util.regex.Pattern.BackRef#match`: "// If the referenced group didn't match, neither can this"
>> 
>> A group that does not exist in the original Pattern can never match so neither can a backref to that group.
>> If the group existed in the original Pattern then it would have had space allocated in Matcher.groups for that group index.
>> So a group index outside groups array length must never match.
>
> Cristian Vat has updated the pull request incrementally with one additional commit since the last revision:
> 
>   changes and test for CIBackRef

Made changes also in `CIBackRef` and copied/changed test into new `ciBackRefTest`

Not pretty since changes to one could miss the other, but all patterns are different. (for what it's worth tests pass...)

There's also a special case with supplementary character tests since `toSupplementaries` given `(?i)` generates invalid pattern, so I had to change those like:
``
pattern = Pattern.compile("(?i)" + toSupplementaries("(a*)bc\\1"));
``

Definitely needs a close look by a regex expert.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/14894#issuecomment-1655581689