Fixes to allow Configuration Caching in Gradle 6.6+

[timyates]

We (myself and @britter) believe this PR allows the Shadow Plugin to be used
in a Gradle 6.6+ build with --configuration-cache enabled.

We unfortunately did not get round to fixing the case where minimize() is
used, so it does not work if that is called in the build.

We're basically looking for suggestions on what we can do to improve it,
or whether it is good enough to go in as-is

Cheers

Tim (and Benedikt)

[timyates]

(upcoming configuration cache feature is described here https://docs.gradle.org/release-candidate/userguide/configuration_cache.html)

[eskatos]

@timyates, @britter, any chance you could add a failing test for minimize()? I think this could help moving this forward

[britter]

@eskatos I think you only need to call minimize() in the ShadowJar configuration. Haven't checked it, but this test case should fail:

    def "configuration caching supports minimize"() {
        given:
        buildFile << """
            shadowJar {
               minimize()
            }
        """.stripIndent()

        when:
        runner.withArguments('--configuration-cache', 'shadowJar').build()
        output.delete()
        def result = runner.withArguments('--configuration-cache', 'shadowJar').build()

        then:
        contains(output, ['a.properties', 'b.properties'])

        and:
        doesNotContain(output, ['a2.properties'])
        result.output.contains("Reusing configuration cache.")
    }

[eskatos]

With the latest changes above, the minimize {} use case now works with the configuration cache enabled.

Here are some links about configuration caching in Gradle:

• https://docs.gradle.org/current/userguide/configuration_cache.html
• https://blog.gradle.org/introducing-configuration-caching
• https://medium.com/androiddevelopers/configuration-caching-deep-dive-bcb304698070

@johnrengelman this should be ready for review, could you please take a look?

BTW it looks like the circleci build is broken
https://app.circleci.com/pipelines/github/johnrengelman/shadow/42/workflows/1b019a05-d7a1-47e5-aa42-3a45781b228e/jobs/497

[vlsi]

manifest.attributes support providers: https://twitter.com/VladimirSitnikv/status/1260952932981313544