RFR: 8288589: Files.readString ignores encoding errors for UTF-16

[Roger Riggs]

On Thu, 16 Jun 2022 22:21:23 GMT, Naoto Sato <naoto at openjdk.org> wrote:

> This is a regression caused by the fix to [JDK-8286287](https://bugs.openjdk.org/browse/JDK-8286287), which assumed the method `String.decodeWithDecoder()` was only invoked with cs.REPLACE mode based on the comment "should not happen". Possibly this refers to the `String(byte[], int, int, Charset)` constructor, which specifically mentions the `REPLACE` mode. However, the method is invoked with `String.newStringNoRepl()` and it should NOT replace the malformed input (duh!). The fix is to throw an `Error` for the former case as before the regression, and `CharacterCodingException` for the latter via an `IllegalArgumentException`.
> In fact, `Files.readString()` stopped throwing a `MalformedInputException` since JDK17 with the fix to JDK-8259842, which started throwing an `Error`.

LGTM

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Marked as reviewed by rriggs (Reviewer).

PR: https://git.openjdk.org/jdk/pull/9193