Setting version of java_export() jar via command line flag

[caseyduquettesc]

Is there a way to set the version number of the published jar on the command line? If I use an environment variable in the maven_coordinates, it almost works, but it's not substituted in the pom template. I can create my own pom template and do the string replacement via --define= but then I need to set the version in two places. Once by exporting the variable for its use in maven_coordinates and again in a --define=maven_version=0.0.0. Is there a better way to set the version once on the command line and get it applied to the maven_coordinates and the pom file? I've seen a lot of projects using a jenkins build number as part of the published jar version.

java_export(
    name = "export",
    maven_coordinates = "group:pkg:$MAVEN_VERSION",
)

[hisener]

I have a similar use case, where we use the commit sha as the version. I raised the same question on Bazel Slack, and I have a working solution with @shs96c's help. Just posting it as a reference for future readers.

I ended up creating a repository rule and expose some constants. Mostly influenced by https://stackoverflow.com/a/65401963/3528626.

def _maven_configuration_impl(repository_ctx):
    _BUILD_FILE = """
# DO NOT EDIT: automatically generated for _maven_configuration rule
filegroup(
    name = 'files',
    srcs = glob(['**']),
    visibility = ['//visibility:public']
)
"""
    repository_ctx.file("BUILD", _BUILD_FILE, False)

    branch = repository_ctx.os.environ.get("CI_COMMIT_BRANCH")
    repo = "..."

    version = repository_ctx.os.environ.get("CI_COMMIT_SHORT_SHA", "LOCAL")
    if branch != "main":
        version = version + "-SNAPSHOT"

    _MAVEN_CONSTANTS_FILE = """
# DO NOT EDIT: automatically generated for _maven_configuration rule
MAVEN_REPO = \"{repo}\"
MAVEN_VERSION = \"{version}\"
"""

    repository_ctx.file(
        "constants.bzl",
        _MAVEN_CONSTANTS_FILE.format(repo = repo, version = version),
        False
    )

_maven_configuration = repository_rule(
    implementation = _maven_configuration_impl,
    environ = [
        "CI_COMMIT_BRANCH",
        "CI_COMMIT_SHORT_SHA",
    ],
)

def maven_configuration():
    _maven_configuration(name = "maven_configuration")

Loaded the rule in WORKSPACE.

load("//rules/java:maven_configuration.bzl", "maven_configuration")
maven_configuration()

And used the VERSION constant in the BUILD file of the library:

load("@maven_configuration//:constants.bzl", "MAVEN_VERSION")
…
maven_coordinates = "com.datadog.lib:lib:%s" % MAVEN_VERSION,