RFR: 8293499: Provide jmod compression level option

[Aleksey Shipilev]

On Mon, 12 Sep 2022 10:48:53 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> The part about being open-ended about alternate compression algorithms still applies, but since the compression for `jmod` is currently always zip we can defer such wording for if/when that day comes.

Well, we can future-proof it by doing what e.g. ZFS does:


$ zfs set compression
...
	compression     YES      YES   on | off | lzjb | gzip | gzip-[1-9] | zle | lz4 | zstd | zstd-[1-19] | zstd-fast-[1-10,20,30,40,50,60,70,80,90,100,500,1000]
...


Meaning, we allow `--compress=zip-[0..9]` and default to `zip-6`. This has the added benefit of clearly stating that `zip-0` is still ZIP, but without the compression applied. This is a bit ambiguous with `--compression-level=0`.

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PR: https://git.openjdk.org/jdk/pull/10213