Add support for custom java install with coursier

[cristi-]

We are using this to avoid java versions mismatch between environments (where some machines may have jdk1.8 or jdk14 instead of jdk11), which causes pinning to generate different results.

A rough example of how we use this with a repository_rule

JAVA_EXEC_TEMPLATE = """
#!/usr/bin/env bash
exec %s "$@"
"""

BUILD_FILE_CONTENTS = """
exports_files(["java"])
"""

def _jdkenv(repository_ctx):
    cwd = repository_ctx.execute(["pwd"]).stdout.strip()
    java_bin = check_path_or_download_jdk11()
    repository_ctx.file(
        "java",
        content = JAVA_EXEC_TEMPLATE % java_bin,
        executable = True,
    )

    repository_ctx.file("BUILD", content = BUILD_FILE_CONTENTS)
jdkenv = repository_rule(
    implementation = _jdkenv,
    environ = ["JAVA_HOME"],
    doc = """Repository rule for detecting jdk11:
@repo//:java -- Java binary
""",

And in maven_install:

load("@rules_jvm_external//:defs.bzl", "maven_install")
load("//tools/build:jdk.bzl", "jdkenv")

jdkenv(
    name = "jdk11",
)
maven_install(
        name = "jdk_deps",
        ....
        java_binary = "@jdk11//:java",
)   

[shs96c]

Is there any reason not to use the JAVA_BASE environment variable? That should mean your build and coursier would share the same JDK.... https://docs.bazel.build/versions/master/be/make-variables.html#custom_variables

[cristi-]

Is there any reason not to use the JAVA_BASE environment variable? That should mean your build and coursier would share the same JDK.... https://docs.bazel.build/versions/master/be/make-variables.html#custom_variables

I was looking at #445 (comment) and I thought it would be impossible to access the path as provided by JAVA_BASE. Do you think there is a way to get to provide the path to coursier ?