Substitutions and Java library lifecycle - bazel

Question

I've got a Java project I'm converting to Bazel.
As is typical with Java projects, there are property files with placeholders that need to be resolved/substituted at build time.
Some of the values can be hardcoded in a BUILD or BZL file:
BUILD_PROPERTIES = { "pom.version": "1.0.0", "pom.group.id": "com.mygroup"}
Some of the variables are "stamps" (e.g. BUILD_TIMESTAMP, GIT_REVISION, etc): The source for these variables are volatile-status.txt and stable-status.txt
I must generate a POM for publish, so I use #bazel_common//tools/maven:pom_file in BUILD
(assume that I need ALL the values described above for my pom template):
_local_build_properties = {}
_local_build_properties.update(BUILD_PROPERTIES)
# somehow add workspace status properties?
# add / override
_local_build_properties.update({
"pom.project.name": "my-submodule",
"pom.project.description": "My submodule description",
"pom.artifact.id": "my-submodule",
})
# Variable placeholders in the pom template are wrapped with {}
_pom_substitutions = { '{'+k+'}':v for (k,v) in _local_build_properties.items()}
pom_file(
name = "my_submodule_pom",
targets = [
"//my-submodule",
],
template_file = "//:pom_template.xml",
substitutions = _pom_substitutions,
)
So, my questions are:
How do I get key-value pairs from volatile/stable -status.txt into the
dictionary I need for pom_file.substitutions?
pom_file depends on java_library so that it can write its dependencies
into the POM. How do I update the jar generated by java_library with the
pom?
Once I have the pom and the updated jar containing the pom, how do I publish to a Maven repo?
When I look at existing code, for example rules_docker, it seems that the implementation always bails to a local executable (shell | python | go) to do the real work of substitution, jar manipulation and image publication. Am I trying to do too much in BUILD and BZL files? Should I be thinking, "Ultimately, what do I need to pass to local shell/python/go scripts to get real build work done?

Answer 1

(Answered on bazel-discuss group)
Hi,
You can't get these values from Starlark. You need a genrule to read the stable/volatile files and do the substitutions using an
external tool like 'sed'.
A file cannot be both an input and output of an action, i.e. you can't update the .jar from which you generate the pom. The action has
to produce a new .jar file.
I don't know -- how would you publish outside of Bazel, is there a tool to do so? Can you write a genrule / Starlark rule to wrap this
tool?
Cheers, László