Bazel aspects: allow sharing source jars and allow empty sourcejars

[antonsviridov-src]

Closes GRAPH-948
Closes GRAPH-949

Test plan

• Reproducers added to existing cases

[antonsviridov-src]

Inexplicably, unzip returns a 1 exit code if there are any warnings (see Diagnostics on https://linux.die.net/man/1/unzip) with no way to turn it off.

So we just literally count the number of files..

[antonsviridov-src]

@JohnnyMorganz would you like to build this PR from source and try on your repos?
Alternatively if you know of any sizeable public bazel repo that uses srcjars, I could use it for testing instead.

[kritzcreek]

If it works, it works. As discussed yesterday :)

Ideally we'd wait with merging until getting positive feedback that it fixes the issue for the customer.

[JohnnyMorganz]

Thanks for checking in!

Looking good from our side, but I am seeing one issue with test targets. You can repro this by changing the java_library to a java_test:

java_test(
    name = "testing",
    srcs = [
        "Foo.java",
        ":generated-srcjar",
    ],
    test_class = "Foo",
)

Running the indexing gives the following error:

$ /home/code/scip-java/out/bin/scip-java index --build-tool=bazel --bazel-scip-java-binary="/home/code/scip-java/out/bin/scip-java" --output=index-java.scip -- -- //test/
ERROR: One of the output paths 'bazel-out/k8-dbg--cd/bin/test/testing' (belonging to //test:testing) and 'bazel-out/k8-dbg--cd/bin/test/testing/extracted_srcjar/test/sources.srcjar' (belonging to //test:testing) is a prefix of the other. These actions cannot be simultaneously present; please rename one of the output files or build just one of them
ERROR: com.google.devtools.build.lib.actions.ArtifactPrefixConflictException: One of the output paths 'bazel-out/k8-dbg--cd/bin/test/testing' (belonging to //test:testing) and 'bazel-out/k8-dbg--cd/bin/test/testing/extracted_srcjar/test/sources.srcjar' (belonging to //test:testing) is a prefix of the other. These actions cannot be simultaneously present; please rename one of the output files or build just one of them

Sorry, unfortunately I do not know of any good public repo using srcjars to test with

[antonsviridov-src]

Thanks @JohnnyMorganz, I'll try to address in a separate PR.

Will rely on your reproductions then :)