RFR: 8300207: Add a pre-check for the number of canonical equivalent permutations in j.u.r.Pattern [v2]

[Raffaello Giulietti]

On Tue, 17 Jan 2023 14:55:18 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

>> Okay, I see your point and to use apiNote consistently would require "converting" some of the existing text to apiNote too.
>> 
>> I'm still mulling over Pattern.compile throwing OOME. An implNote is probably the right category for this, in which case it can start with "In the the JDK Reference Implementation ...".  I assume the static Pattern.matches needs same, and also Pattern.matcher for the lazy compilation case.
>
> There's no hard limit for the number of combining marks in the Unicode specification, even though in practice it never reaches the implementation limit. A high number of combining marks is thus more akin to a a resource exhaustion condition than to anything else, IMO.
> 
> Even today, compilation of a pattern risks throwing an OOME anyway when trying to generate the permutations. Pre-emptively throwing an OOME just anticipates and extrapolates this behavior beyond the `int` limit of array lengths.
> 
> Alternatively, compilation (greedy or lazy) could throw `PatternSyntaxException`, although there is not really something wrong with syntax.
> 
> I'll add `@implNote` to the other methods you mention.

The CSR will be updated once this PR stabilizes.

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PR: https://git.openjdk.org/jdk/pull/12027