Remove the library() macro and _lib targets

[jin]

The original motivation for adding _lib targets for every artifact was to ensure that you don't need to specify transitive dependencies on top of the top level artifact in deps in order to use the top level artifact. This is already fully wired up in the versionless aliases and the java_import and aar_import targets.

For example, if you want to use junit:junit which itself depends on org.hamcrest:hamcrest-core, you do not need to specify artifact("org.hamcrest:hamcrest-core") alongside artifact("junit:junit") in deps, because the java_import target for junit:junit already depends on org:hamcrest:hamcrest-core.

The generated _lib targets, as it's implemented currently, re-exports the direct dependencies of an artifact, and itself, in a java_library. This may be useful to reduce the number of specified artifacts in deps, but it can hide unnecessary dependencies in the classpath, causing a large over-specification of available compile-time classes. If a target wishes to use an indirect dependency, the target should specify the versionless alias of the indirect dependency in its deps, and not rely on the overspecification of _lib/library() targets.

[jin]

cc @davidsantiago

[davidsantiago]

FWIW, LGTM. 🙈

[dkelmer]

I want to make sure I understand: let's assume maven jar-A depends on maven jar-B. Before this change, projects could depend on the _lib target and then use symbols from both jar-A and jar-B? And what you're saying is that with this change, users would need to explicitly depend on jar-B if they wanted to use symbols from it? That definitely sounds like a step in the right direction. I eventually want to ban usage of jar-B entirely unless it's explicitly added to the artifacts list in the repository rule.

[jin]

@dkelmer that is exactly right.