RFR: 8311939: Excessive allocation of Matcher.groups array [v3]

[Cristian Vat]

On Fri, 28 Jul 2023 09:29:48 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:
> 
>   remove new line

`RegExTest#backRefTest` seems to be pretty extensive but only for `BackRef` not `CIBackRef`

I saw one `CIBackRef` related test added in https://github.com/openjdk/jdk/pull/7501 but it's very simple/specific.

I triggered test failure locally by duplicating `backRefTest` 1-9 loop with `(?i)` in pattern so yes it seems like `CIBackRef` needs same change.

But not sure about the test, duplicating loop seems odd. Maybe entire `RegExTest#backRefTest` needs to be duplicated into a `ciBackRefTest` with all patterns preprended with `(?i)` ? Wouldn't look too clean.

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

PR Comment: https://git.openjdk.org/jdk/pull/14894#issuecomment-1655371709