Deduplicate APEX variants that would build identically
APEX variants that share the same SDK version and updatability almost always use identical command line arguments to build but with different intermediates directories. This causes unnecessary build time and disk space for duplicated work. Deduplicate APEX variants that would build identically. Create aliases from the per-APEX variations to the new shared variations so that the APEX modules can continue to depend on them via the APEX name as the variation. This has one significant change in behavior. Before this change, if an APEX had two libraries in its direct dependencies and one of those libraries depended on the other, and the second library had stubs, then the first library would depend on the implementation of the second library and not the stubs. After this change, if the first library is also present in a second APEX but the second library is not, then the common variant shared between the two APEXes would use the stubs, not the implementation. In a correctly configured set of build rules this change will be irrelevant, because if the compilation worked for the second APEX using stubs then it will work for the common variant using stubs. However, if an incorrect change to the build rules is made this could lead to confusing errors, as a previously-working common variant could suddenly stop building when a module is added to a new APEX without its dependencies that require implementation APIs to compile. This change reduces the number of modules in an AOSP arm64-userdebug build by 3% (52242 to 50586), reduces the number of variants of the libcutils module from 74 to 53, and reduces the number of variants of the massive libart[d] modules from 44 to 32. Bug: 164216768 Test: go test ./build/soong/apex/... Change-Id: I0529837476a253c32b3dfb98dcccf107427c742c
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