Introduce ImmutableSnapshot strategy to create snapshots using timestamps

[rpalcolea]

This introduces immutableSnapshot task/strategy to generate snapshot versions that are meant to be immutable and should be unique via UTC timestamp. Ex. 1.2.0-snapshot.20190705210556893+abcdef

Pattern is <major>.<minor>.<patch>-snapshot.<timestamp>+<hash> and timestamp format is YYYYMMddHHmmssSSS

This change doesn't replace devSnapshot and default strategy to prevent breaking changes for consumers.

We should be able to override the default strategy from devSnapshot to immutableSnapshot via ReleasePluginExtension:

release {
                defaultVersionStrategy = nebula.plugin.release.NetflixOssStrategies.IMMUTABLE_SNAPSHOT(project)
            }

[coveralls]

Coverage increased (+0.5%) to 70.03% when pulling 057ec30 on immutable-snapshot-support into 1bf4a5d on master.

[rspieldenner]

if I have 1.2.3-snapshot.2019070511000000+abcdef and 1.2.3-rc.1 which will I get if I ask for 1.+?

[rpalcolea]

if I have 1.2.3-snapshot.2019070511000000+abcdef and 1.2.3-rc.1 which will I get if I ask for 1.+?

@rspieldenner , this is actually a good question. This new immutable snapshot suggests to use the snapshot explicitly instead of relying on things like 1.+. Because in semver identifiers consisting of only digits are compared numerically and identifiers with letters or hyphens are compared lexically in ASCII sort order, 1.2.3-rc.1 would always be first.

I think this should be considered as a breaking change in order to unify versioning with other technologies that are Semver based, like NPM.

I believe snapshots should be always consumed explicitly and not via dynamic versions (1.+) but that's just my opinion.

Also, I think is worth mentioning that generating a snapshot from a branch where latest tag is a RC one, ends up in something like this: 1.2.3-rc.1.dev.0+cd60fe6 which would resolve to 1.2.3-rc.1 if you do 1.+ since 1.2.3-rc.1.dev.0+cd60fe6 < 1.2.3-rc.1 so at the end, it might be the same behavior (unintentionally though)

[rspieldenner]

1.2.3-rc.1.dev.0+cd60fe6 was an accident of how I implemented this if we can fix to always have snapshots be -dev.# or -snapshot.timestamp that would be better

[rspieldenner]

Implementation looks good

[OdysseusLives]

Adding a request to codify the earlier question & discussion around if I have 1.2.3-snapshot.2019070511000000+abcdef and 1.2.3-rc.1 which will I get if I ask for 1.+... with a test to showcase the different semver ordering when using devSnapshot vs immutableSnapshot

[rpalcolea]

Hi @OdysseusLives , let me know if 471dbd4 makes sense to you

[rpalcolea]

Hey @OdysseusLives , based on our conversations and our findings in gradle/gradle#9915

I believe this change is good to go, thoughts?