Use alias instead of override destination.

[samshadwell]

Resolves https://github.com/bazelbuild/rules_jvm_external/issues/582

Problem

That issue is caused by overrides to fully-qualified labels being duplicative with their non-overridden counterparts. For example, consider ndbench-core, which takes a dependency on both com.codahale.metrics:metrics-core and io.dropwizard.metrics:metrics-core. Those two libraries expose many of the same fully-qualified classes, and we'd like to only have one version of each class on the classpath.

To accomplish this, we could use an override like:

override_targets = {
    "com.codahale.metrics:metrics-core": "@regression_testing//:io_dropwizard_metrics_metrics_core",
},

so that the "old" codahale metrics-core is replaced with the "new" dropwizard one.

Currently, this results in generated deps like:

...
jvm_import(
...
	deps = [
                ...
		"@regression_testing//:io_dropwizard_metrics_metrics_core",
		...
		":io_dropwizard_metrics_metrics_core",
		...
	],
...

Analysis of this fails with errors like:

ERROR: /private/var/tmp/_bazel_sam_shadwell/7db21a72dc367049bac9ba2882a68834/external/regression_testing/BUILD:2469:11: Label '@regression_testing//:io_dropwizard_metrics_metrics_core' is duplicated in the 'deps' attribute of rule 'com_netflix_ndbench_ndbench_core'

Solution

As suggested by @jdai8, the solution is to instead reference the generated alias in deps (instead of eagerly resolving the alias as is done now).

So now we generate deps like:

alias(
	name = "com_codahale_metrics_metrics_core",
	actual = "@regression_testing//:io_dropwizard_metrics_metrics_core",
	visibility = ["//visibility:public"],)
...
jvm_import(
...
	deps = [
                ...
		":com_codahale_metrics_metrics_core",
		...
		":io_dropwizard_metrics_metrics_core",
		...
	],
...

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[alexeagle]

Ping @shs96c - it looks reasonable to me. (I'm working with Sam)

[samshadwell]

Welp, we're going on 2 years now and no word from anyone.

While I still think this would be a positive change, I'm no longer working on Bazel-related things. Closing this PR to clean up my personal PR dashboard.