Mabel

Yet another Maven dependency graph generator for Bazel.

This WORKSPACE will provide mabel_rule rule and artifact macro which will automatically generate a set of targets that can be used as dependencies based on a given list of Maven coordinates. The rule will output the dependencies-graph to a file (similar to Yarn's lock-file).

Features

Transitively resolves all dependencies from a given list of Maven dependencies, and manages version conflicts - ensuring that only one version of each artifact is available in the dependencies graph.
Generates repository-rules for all remote artifacts.
Generates required Java rule (with transitive dependencies).
Allows to mark dependencies as test_only.
Automatically detects which rule-type to create for a given dependency:
- aar_import for Android artifacts.
- java_plugin + java_library for annotation-processors. More about this here.
- jvm_import for anything else.
Allow implementation replacement for jvm_import and aar_import. Those can be replaced with another rule or macro. See examples/android/program/BUILD.bazel for an example.
Support custom Maven repo URLs and locking dependency for a Maven repository.
Adds licenses data to jvm_import rules, if license is declared in the artifact's POM file. Also, adds license metadata to the targets' tags attribute:
- mabel_license_name - The name of the license, as appears in the pom.xml file.
- mabel_license_url - The URL to the license's file, as appears in the pom.xml file.
- mabel_license_detected_type - The type of the license (Apache, MIT, GPL, etc.) as detected by mabel.
Adds srcjar if sources available in the Maven repository.
Handle POM options:
- Profiles and placeholders.
- Version-specification.
- Dependencies that do not have POM.
- Exports the Maven coordinate as a tag in the jvm_import rule. This can help with Bazel's pom_file rule.
Calculates sha256 for each remote artifact.
Produces a lock file that describes the dependency graph. This file should be checked into your repo.

Why

Unlike other build systems, Bazel does not provide a dependency management service as part of the build and does not provide a way to specify a Maven dependency (which will be resolved transitively) and be available during compilation.
There are several attempts to solve this problem (such as sync-deps, gmaven, rules_jvm_external, migration-tooling, maven-rules and bazel-deps), but some do not support Kotlin or Android, some do not support customized Maven repositories, etc.

Example

WORKSPACE file

Add this repository to your WORKSPACE (set mabel_version to the latest release or, if you are adventurous, commit):

# We'll need the java_rules already setup, you probably have that already anyway:
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
    name = "rules_java",
    urls = [
        "https://github.com/bazelbuild/rules_java/releases/download/5.5.0/rules_java-5.5.0.tar.gz",
    ],
    sha256 = "bcfabfb407cb0c8820141310faa102f7fb92cc806b0f0e26a625196101b0b57e",
)
load("@rules_java//java:repositories.bzl", "rules_java_dependencies", "rules_java_toolchains")
rules_java_dependencies()
rules_java_toolchains()

# Actual mabel setup
# Check out the release page for the latest version
mabel_version = "0.30.0"
mabel_sha = "c4487134b386be1d9a4b4f48b1bd6fabd77331188e0ae769cdf08cebc39546d0"
http_archive(
    name = "mabel",
    urls = ["https://github.com/menny/mabel/archive/%s.zip" % mabel_version],
    type = "zip",
    sha256 = mabel_sha,
    strip_prefix = "mabel-%s" % mabel_version
)

load("@mabel//:init_rules.bzl", "init_mabel_rules")
init_mabel_rules()

target definition

In your module's BUILD.bazel file (let's say resolver/BUILD.bazel) load the dependencies rule and artifact macro:

load("@mabel//rules/maven_deps:maven_deps_workspace_generator.bzl", "mabel_rule", "artifact")

And define a target for resolving dependencies:

mabel_rule(name = 'main_deps',
    maven_deps = [
        artifact("com.google.guava:guava:20.0"),
        artifact("org.apache.commons:commons-lang3:jar:3.8.1"),
        artifact("com.google.code.findbugs:jsr305:3.0.2"),
        artifact("com.google.auto.value:auto-value:1.6.3")
    ],
    generated_targets_prefix = "main_deps___")

In this example above we defined the target //resolver:main_deps with 4 maven dependencies:

com.google.guava:guava:20.0
org.apache.commons:commons-lang3:jar:3.8.1 - here we are specifically asking for jar classifier. In most cases we don't need to do that.
com.google.code.findbugs:jsr305:3.0.2
com.google.auto.value:auto-value:1.6.3 - which is an annotation-processor.

Resolving the dependency graph

To generate the transitive rules for the required maven_deps, you'll run the target:

bazel run //resolver:main_deps

This will retrieve all the transitive dependencies and resolve conflicts. We will store the resolved dependencies graph (Bazel rules) in the file resolver/main_deps/dependencies.bzl, and will create a folder-structure matching all the deps:

resolver/
    main_deps/
        BUILD.bazel
        dependencies.bzl
        com\
            google\
                guava\
                    guave\
                        BUILD.bazel (with alias guava -> //resolver:main_deps___com_google_guava__guave)
                code\
                    findbugs\
                        jsr305\
                            BUILD.bazel (with alias jsr305 -> //resolver:main_deps___com_google_code_findbugs__jsr305)
                auto\
                    value\
                        auto-value\
                            BUILD.bazel (with alias auto-value -> //resolver:main_deps___com_google_auto_value__auto_value)
        org\
            apache\
                commons\
                    commons-lang3\
                        BUILD.bazel (with alias commons-lang3 -> //resolver:main_deps___org_apache_commons__commons_lang3)

You'll noticed that there's a prefix main_deps___ to all targets, this prefix allows you to generate several graphs for different cases (for example, compile vs annotation-processor stages). It was added because we specified generated_targets_prefix = "main_deps___" in the target definition.
This file will need to be checked into your repository, same as Yarn's lock file.
NOTE: If you do not wish the rule to generate the sub-folders, you can add generate_deps_sub_folder = False to your artifact target definition.

Using the generated Maven dependencies

First, you'll need to register all the repository rules for the remote maven artifacts. In your WORKSPACE file, add:

load("//resolver/main_deps:dependencies.bzl", main_mabel_deps_rules = "generate_workspace_rules")
main_mabel_deps_rules()

And, in the same module you declared mabel_rule (in our example //resolver) add to the BUILD.bazel file:

load("//resolver/main_deps:dependencies.bzl", main_generate_transitive_dependency_targets = "generate_transitive_dependency_targets")
main_generate_transitive_dependency_targets()

This will make the rules available in any target defined in that BUILD.bazel file as //resolver:mvn_main___XXX:

com.google.guava:guava:20.0 as //resolver:main_deps___com_google_guava__guava
org.apache.commons:commons-lang3:jar:3.8.1 as //resolver:main_deps___org_apache_commons__commons_lang3
com.google.code.findbugs:jsr305:3.0.2 as //resolver:main_deps___com_google_code_findbugs__jsr305

Or, you can use the sub-folder structure (IDEs find this easier to auto-complete):

com.google.guava:guava:20.0 as //resolver/main_deps/com/google/guava/guava
org.apache.commons:commons-lang3:jar:3.8.1 as //resolver/main_deps/org/apache/commons/commons_lang3
com.google.code.findbugs:jsr305:3.0.2 as //resolver/main_deps/com/google/code/findbugs/jsr305

Rule configuration

`mabel_rule`

This rule will merge the dependencies into one, version-conflict-resolved, dependencies graph ensuring you do not have conflicting versions of an artifact in your classpath.
Attributes:

maven_deps: List of artifact targets representing a Maven coordinate.
generate_deps_sub_folder: Default True. Will create sub-folders with BUILD.bazel file for each dependency.
keep_output_folder: Default False. Will delete the output folder prior to generating the outputs.
public_targets_category: Default all. Set public visibility of resolved targets. Can be: requested_deps, recursive_exports, all.
version_conflict_resolver: Default latest_version. Defines the strategy used to resolve version-conflicts. Default is latest_version. Can be: latest_version, breadth_first.
calculate_sha: Default True. Will calculate the sha256 value of each remote artifact.
fetch_srcjar: Default False. Will also try to fetch sources jar for each dependency.
generated_targets_prefix: A prefix to add to all generated targets. Default is an empty string, meaning no-prefix. This might be useful if you want to generate several, unrelated, graphs.
output_graph_to_file: If set to True, will output the graph to dependencies.txt. Default is False.

`artifact`

This rule declares a Maven dependency to be resolved and import into your WORKSPACE.
Attributes:

coordinate: Maven coordinate in the form of group-id:artifact-id:version.
type: What is the type of target(s) to create for this artifact. Default auto. Can be jar, aar, naive, processor, auto. For more details, see here.
test_only: Mark this dependency to be used in tests only.
maven_exclude_deps: List of Maven dependencies which should not be resolved. You can omit the version or both artifact-id:version.
repositories: List of URLs that point to Maven servers. The default list includes Maven-Central.

Real Examples

You can find a few examples under the examples/ folder in this repo. These examples are built as part of the CI process, so they represent a working use-case.

Detected rules

Android AARs

If the resolved artifact is an aar file, we'll create aar_import target.

Annotation-Processors

For dependencies that are detected as annotation-processors we are creating a java_plugin rule for each detected processor_class, and then wrap all of these rules in a java_library rule that exports the plugins.
In the example above we included com.google.auto.value:auto-value:1.6.3, which is a Java annotation-processor, we create the following rules:

//resolver:main_deps___com_google_auto_value__auto_value - which is a java_library without any annotation-processing capabilities.
//resolver:main_deps___com_google_auto_value__auto_value___processor_class_0..4 - which is a java_plugin with annotation-processing capabilities using the first detected processor-class. Four of those, because there are four such classes.
//resolver:main_deps___com_google_auto_value__auto_value___generates_api___processor_class_0..4 - the same as before, but generate API.
//resolver:main_deps___com_google_auto_value__auto_value___processor_class_all - a java_library that groups all the processors that do not generate API.
//resolver:main_deps___com_google_auto_value__auto_value___generates_api___processor_class_all - same as before, but generates API.

Please, read the Bazel docs about which variant you want.
Also, since we are wrapping the java_plugin rules in a java_library rules, you should add them to the deps list of your rule and not to the plugins list, unless you are directly using the X___processor_class_Y variant in which case you should use it in the plugins field.

menny / mabel