<i18n dev> RFR: 8364365: HKSCS encoder does not properly set the replacement character

[Xueming Shen]

On Tue, 5 Aug 2025 08:20:55 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

>> Fix `HKSCS` encoder to correctly set the replacement character, and add tests to verify the `CodingErrorAction.REPLACE` behavior of all available encoders.
>
> test/jdk/sun/nio/cs/TestEncoderReplaceUTF16.java line 146:
> 
>> 144:             System.err.println("Character set is known to be absent of unmappable non-Latin-1 characters!");
>> 145:             return null;
>> 146:         }
> 
> Without this fast-path, this test take several minutes to complete due to `findUnmappableNonLatin1()` taking ~20 seconds for each character set absent of unmappable Latin-1 characters.

we definitely want to exclude 'some' charsets here. yes, all unicode variants probably should be excluded, as they are expected to have a 'mapping' for every unicode character. Additionally, many charsets have an "internal status", meaning they might shift in and shift out its status based on input. See https://www.rfc-editor.org/rfc/rfc1468.html for an example. The encoder might/should add the shift-in/out escape sequence characters on top of the 'replacement', if the replacement character's target sub-charset does not match the 'existing' sub-charset. i would assume this is really out of the scope of this pr though :-)

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PR Review Comment: https://git.openjdk.org/jdk/pull/26635#discussion_r2255705386