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Shared Library Versioning

When the API of a shared library changes in a backwards incompatible way, it is useful to be have both versions of the library installed on the system so that old and new clients can be supported simultaneously.

In order to do this, version information must be added to shared libraries. At link time, the libraries user will record the version that it needs. When installed a few symlinks also need to be setup.

Bob supports creation of versioned libraries. Simply set library_version to the required version string. The expected version format is "MAJOR.MINOR.PATCH(-PRERELEASE)", where MAJOR, MINOR and PATCH are integers, and PRERELEASE is a string. The version must change for every public release.

The "-PRERELEASE" string should only be used to identify early releases, and indicates an unstable release.

The MAJOR number must increase whenever a backwards incompatible API change is made. A backwards incompatible API change will break anything compiled against the older version of the library. A running system can expect to have a library installed for each MAJOR version of the library. MINOR and PATCH are expected to reset to 0.

The MINOR number must increase when new APIs are added to the library, but it is otherwise backwards compatible. In a running system the existing library of the same MAJOR version can be replaced with the MINOR release. PATCH is expected to reset to 0.

The PATCH number must increment on all other releases, which must be backwards compatible. The new library can replace an existing library with the same MAJOR.

Examples:

Version Description
1.0.0 First production release
1.0.1 Bugfix release
1.1.0-alpha New functionality added (compared to 1.0.0), early test
1.1.0-rc3 New functionality added (compared to 1.0.0), 3rd release candidate
1.1.0 Production release, new functionality compared to 1.0.0
2.0.0 Production release, incompatible with 1.x series 
bob_shared_library {
    name: "libdrm",
    srcs: ["libdrm.c"],
    export_local_include_dirs: ["include"],

    library_version: "1.4.2",
}