RFR: 8366224: Introduce DecimalDigits.appendPair for efficient two-digit formatting and refactor DateTimeHelper [v5]

[Per Minborg]

On Mon, 15 Sep 2025 06:45:25 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update test/jdk/jdk/internal/util/DecimalDigitsTest.java
>>   
>>   Co-authored-by: Chen Liang <liach at openjdk.org>
>
> We have, for long, established that changes like this should be discussed before putting forward any code. Yet, I am unable to find any discussion in the appropriate mailing list. Please send me the link to the mailing list discussion. I must have missed it for some reason.

> @minborg
> 
> The process went like this:
> 
> On August 23rd, I posted an email to the core-libs-dev mailing list titled "Introduce and utilize DecimalDigits.appendPair for efficient two-digit formatting." The message included a link to the pull request (PR) #26911. At the time, the PR was in draft status.
> 
> On August 26th, @jodastephen commented on the PR.
> 
> He's an expert in java.time, and based on his comments, I created an issue and changed the PR status to RFR.

This mail appears to merely point out that there is a PR with code. I am unable to locate any discussion *prior* to any code being presented. E.g., whether we should do this or not. What are the pros and cons, etc. What did I miss?

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PR Comment: https://git.openjdk.org/jdk/pull/26911#issuecomment-3291135881