RFR: 8356606: (fs) PosixFileAttributes.permissions() implementations should return an EnumSet

[Chen Liang]

On Fri, 9 May 2025 22:48:11 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

> Drop-in replacement in `sun.nio.fs.UnixFileAttributes::permissions` of `HashSet` with `EnumSet` for hopefully improved efficiency. All tests containing `PosixFileAttributes` passed.

Makes sense. This rejects usages of adding null or invalid objects, but this still abides to the specs, that the returned set can be modified and passed to create new attributes.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25162#pullrequestreview-2829850578