# Bazel JVM Porting Guide This document explains how to port an existing JVM project (Java or Scala) to Bazel. If you are not intending to port a project to Bazel but rather use Bazel on an already ported project, then please refer to the [Bazel User Guide][bazel_user_guide]. This guide assumes familiarity with Bazel's core concepts and a functioning Bazel setup. If you are not yet familiar with Bazel, need a refresher, or need to setup Bazel, please refer to the [Bazel User Guide][bazel_user_guide]. [bazel_user_guide]: ./BAZEL.md This guide is based on the experience of porting an SBT project to Bazel. If you are not porting an SBT project but a Maven project instead, then you should also have a look at the Maven porting guide in the [official Bazel documentation][bazel_maven_guide]. However, in order to arrive at a homogenous build system and project structure you shuold follow the suggestions in this guide where possible. [bazel_maven_guide]: https://docs.bazel.build/versions/master/migrate-maven.html The structure of this guide is as follows: First, we describe how to define external dependencies to your project in Bazel. This includes additional Bazel rules that you may need to import from external workspaces, Maven JAR dependencies, or other artifacts that need to be fetched from Artifactory. Then, we describe how to build a JVM project with Bazel. This covers the project structure, in particular when coming from SBT, and the details of defining Java and Scala targets in Bazel. In the very end we talk about the Java runtime and toolchain that Bazel uses and provide links to Bazel API documentation. ## External Dependencies External dependencies are targets that your project depends on, but that are not built, or otherwise generated, within the local workspace. Such external dependencies are defined in the `WORKSPACE` file or in Bazel macros that are called from the `WORKSPACE` file. ### Bazel Dependencies Bazel can be extended with custom rules, for example to support languages for which Bazel provides no builtin rules. Extensions that are defined outside the current workspace can be included from an external workspace. Bazel provides the workspace rules `http_archive`, `get_repository`, or `local_repository` in order to define an external workspace. Refer to the [official documentation][bazel_workspace_rules] for details. An example is presented in the Scala section below. [bazel_workspace_rules]: https://docs.bazel.build/versions/master/be/workspace.html#workspace-rules #### Java Bazel has builtin support for Java. No external workspaces need to be imported to support Java projects at the time of writing. #### Scala Bazel does not have builtin Scala support. In this repository we use [`rules_scala`][rules_scala], which defines Bazel rules to build Scala projects. First, we need to import the external workspace: ``` http_archive( name = 'io_bazel_rules_scala', url = 'https://github.com/bazelbuild/rules_scala/...', ... ) ``` This will make `rules_scala` available under the label `@io_bazel_rules_scala//`. Next, we define the exact version of the Scala compiler and core libraries to use: ``` load('@io_bazel_rules_scala//scala:scala.bzl', 'scala_repositories') scala_repositories(("2.12.6", { "scala_compiler": "3023b07cc02f2b0217b2c04f8e636b396130b3a8544a8dfad498a19c3e57a863", "scala_library": "f81d7144f0ce1b8123335b72ba39003c4be2870767aca15dd0888ba3dab65e98", "scala_reflect": "ffa70d522fc9f9deec14358aa674e6dd75c9dfa39d4668ef15bb52f002ce99fa" })) load('@io_bazel_rules_scala//scala:toolchains.bzl', 'scala_register_toolchains') scala_register_toolchains() ``` If you need to update the Scala version, make sure to also update the corresponding SHA-256 hashes in hexadecimal encoding. The hashes can be looked up in the [Artifactory repository browser][artifactory_browser_hash] in the very bottom of the "General" pane. See the [`rules_scala` setup guide][rules_scala_setup] for further details. [rules_scala]: https://github.com/bazelbuild/rules_scala [rules_scala_setup]: https://github.com/bazelbuild/rules_scala#getting-started [artifactory_browser_hash]: https://digitalasset.jfrog.io/digitalasset/webapp/#/artifacts/browse/tree/General/jcenter-cache/org/scala-lang/scala-reflect/2.12.6/scala-reflect-2.12.6.jar ### Maven JAR Dependencies Next, we consider the most common case of Maven JARs which are distributed on Artifactory. We distinguish direct and transitive dependencies. Direct dependencies are explicitly defined on targets in the local workspace. Transitive dependencies are introduced implicitly as dependencies of direct dependencies. It is preferable to only have to define direct dependencies and let a dependency resolver determine all transitive dependencies. The tool [`bazel-deps`][bazel-deps] can read a list of direct Java and Scala JAR dependencies and then use [Coursier][coursier] to perform dependency resolution and generate the whole transitive closure of dependencies. The `dev-env` provides a modified version of `bazel-deps` that supports Artifactory authentication as required at Digital Asset. Please do not execute `bazel-deps` directly. Instead, use the `update-bazel-deps` tool provided in the dev-env. Make sure to check-in the resulting files into revision control. Direct dependencies are manually defined in the file `dependencies.yaml` at the repository root. The generated Bazel definitions are written to the `3rdparty` directory in the repository root. The file `3rdparty/workspace.bzl` lists the individual JAR dependencies and the directory tree under `3rdparty/jvm` defines Bazel targets for them. Only Bazel targets for direct dependencies are publicly visible. The Bazel targets include `exports` attributes to capture indirect dependencies. The file `3rdparty/workspace.bzl` defines Bazel macros that must be called in the `WORKSPACE` file in order to import the external JAR dependencies. ``` load("//3rdparty:workspace.bzl", "maven_servers", "maven_dependencies") maven_servers() maven_dependencies() ``` First, we call `maven_servers` which will define the list of repositories from which to fetch JARs. These are listed in the definition of `list_servers` in `3rdparty/workspace.bzl`. For example: ``` {"name": "central", "url": "https://digitalasset.jfrog.io/digitalasset/libs-release"}, ``` The name of each server must match the id of the corresponding entry in the Maven `settings.xml` file for authentication to work. Second, we call `maven_dependencies` which defines the individual JAR dependencies using the Bazel builtin `maven_jar` rule. The file `dependencies.yaml` consists of three sections `options`, `dependencies`, `replacements`. Their structure is as follows: - `options`: This section configures the dependency resolution process and the generated Bazel definitions. - `buildHeader`: A list of lines of Bazel code to insert at the top of each generated `BUILD` file underneath `3rdparty/jvm`. - `languages`: A list of languages used. Currently supports `java` and `scala`. The `scala` entry can specify the language version e.g. as `"scala:2.12.6"`. - `resolverType`: A string specifying the resolver, either `coursier` or `aether`. Only `coursier` supports authentication at the time of writing. - `resolvers`: A list of repositories to query for dependency resolution. Each entry has the following fields. - `id`: A string that must match the corresponding entry in Maven's `settings.xml`. - `url`: A string describing the repository URL. - `credentials`: An optional string describing the environment variable prefix under which the authentication credentials for this repository are defined. Given a value of `PREF` credentials will be looked up in `PREF_USER` and `PREF_PASSWORD`. Use `DA_JFROG` for a repository under `https://digitalasset.jfrog.io/digitalasset`. The `bazel-deps` wrapper in the dev-env will provide Artifactory credentials in the corresponding environment variables. - `dependencies`: This section configures the direct JAR dependencies. Entries take the following shape: ``` : : lang: version: ``` For example: ``` com.typesafe.scala-logging: scala-logging: lang: scala version: "3.5.0" ``` A group can hold multiple artifacts. In case of Scala dependencies, this will perform the corresponding name mangling to include the Scala version into the Maven coordinate. If you wish to avoid this you can use the language value `scala/unmangled`. For example: ``` org.mongodb: casbah-commons_2.12.0-RC1: lang: scala/unmangled version: "3.1.1" ``` Maven coordinates map to Bazel targets in the following form: ``` //3rdparty/jvm/: ``` Where `` is `` with `.` replaced by `/` and special characters (like `-`) replaced by `_`, and `` is `` with special characters (like `-` or `.`) replaced by `_`. For example ``` com.typesafe.scala-logging:scala-logging -> //3rdparty/jvm/com/typesafe/scala_logging:scala_logging org.mongodb:casbah-commons_2.12.0-RC1 -> //3rdparty/jvm/org/mongodb:casbah_commons_2_12_0_RC1 ``` The above Bazel targets are wrappers that capture indirect dependencies and should be used for regular library dependencies. The naked JAR targets are available under labels of the following form: ``` //external:jar// ``` These are used in cases were individual JAR files need to be provided. For example for Scala compiler plugins. - `replacements`: This section allows to override regular dependency resolution for certain Maven artifacts and instead point to specific Bazel targets. Entries take the following shape: ``` : : lang: target: ``` For example: ``` org.scala-lang: scala-compiler: lang: scala/unmangled target: "@io_bazel_rules_scala_scala_compiler//:io_bazel_rules_scala_scala_compiler" ``` The standard use-case are the Scala core libraries (`scala-compiler`, `scala-library`, `scala-reflect`) which have to match the compiler toolchain. Another use-case are Maven packages that `bazel-deps` does not support, e.g. POM packages. Examples of both can be found in `dependencies.yaml`. Custom replacement targets are defined in `replacements/BUILD.bazel`. For a more detailed explanation of the `dependencies.yaml` file format please refer to the [project README][bazel-deps-readme]. The Bazel code that `bazel-deps` generates uses Bazel's builtin [`maven_jar` workspace rule][maven_jar]. It supports specifying JAR and source SHA1 hashes to ensure reproducibility. By default `bazel-deps` will populate the attributes. The builtin `maven_jar` rule also supports specifying the Maven server that provides the artifact. `bazel-deps` will specify the corresponding `resolvers` entry in `dependencies.yaml` under which it found the artifact. The `server` attribute must match the `id` in the Maven `settings.xml` for authentication to work. A corresponding `maven_server` rule must have been defined before. `bazel-deps` generates calls to Bazel's builtin [`maven_server` workspace rule][maven_server] for every resolver specified in the `dependencies.yaml` file. By default authentication credentials will be looked up in Maven's configuration file `~/.m2/settings.xml`. This default can be overriden by setting the `settings_file` attribute. This is used on Jenkins CI to inject Artifactory credentials. [bazel-deps]: https://github.com/johnynek/bazel-deps [coursier]: https://github.com/coursier/coursier [bazel-deps-readme]: https://github.com/johnynek/bazel-deps#dependencies [maven_jar]: https://docs.bazel.build/versions/master/be/workspace.html#maven_jar [maven_server]: https://docs.bazel.build/versions/master/be/workspace.html#maven_server #### Conflicting Dependencies Following the goal of HEAD based development all projects should strive to share common dependencies in one place, such as `dependencies.yaml` for JAR dependencies. If different projects have conflicting dependencies, then these conflicts should be fixed so that both projects can share the same common dependencies. A valid exception to this rule are external tools that are defined in Bazel and used for build or development. These may have conflicting dependencies with the projects in this repository and changing their code to rectify these conflicts may be out of scope or infeasible. In such a case a separate dedicated `dependencies.yaml` file and `3rdparty` directory tree can be created. See `bazel_tools/scalafmt/dependencies.yaml` for an example. Make sure to adjust `dev-env/bin/update-bazel-deps` accordingly, execute it to perform dependency resolution, and check-in the resoluting files. ## Building a Project with Bazel Recall, that a Bazel workspace consists of packages and targets. A package is a directory that contains a `BUILD.bazel` file. A `BUILD.bazel` file can define rule targets. Additionally, regular files underneath a package are targets as well. ### Project Structure When structuring a Bazel project you should strive for small targets and small packages. Bazel's incremental builds will work best when targets are as small as possible. Additionally, you should make target visibility as tight as possible in favour of a clean dependency graph. If you are porting a JVM component in the `da` repository it is likely that you will be coming from an SBT project structure similar to the following. ``` da ├── WORKSPACE └── my_component ├── build.sbt ├── module1 │ ├── build.sbt │ └── src │ ├── main │ │ └── scala │ │ └── com/digitalasset/module │ │ ├── Main.scala │ │ ⋮ │ └── test │ └── scala │ └── com/digitalasset/module │ ├── SomeSpec.scala │ ⋮ ├── module2 │ ├── build.sbt ⋮ ⋮ └── project ⋮ ``` In this case `da/my_component/build.sbt` defines properties of the whole component and the interdependencies between the modules (subprojects in SBT). The files `da/my_component/moduleX/build.sbt` define properties of a particular module, and its external dependencies. Finally, the folder `da/my_component/project` contains additional files defining further properties of the component, SBT plugins, etc. SBT associates tasks with a project, such as `compile` or `test`. It is then possible to specify dependencies only for certain tasks. E.g. test-only dependencies. Furthermore, if `module2` depends on `module1`, then `module2`'s tests can depend on test classes defined in `module1`. In Bazel things are structured differently. A library, a test-only library, or a test-suite are all separate Bazel targets. Dependencies are defined at each individual target. Repetition can be reduced by transitive dependencies or by giving a name to a list of targets and assigning that list as a dependency Bazel is not extended by a plugin mechanism like SBT plugins. Instead Bazel is extended by user defined rules or macros. It is not often the case that one has to define custom rules or macros. In most cases existing ones can be reused. #### Fine Grained Bazel Project Structure As mentioned before one should strive for as small Bazel targets as possible. Translated to Bazel the above project might take the following form: ``` da ├── WORKSPACE └── my_component ├── BUILD.bazel ├── module1 │ ├── BUILD.bazel │ └── src │ ├── main │ │ └── scala │ │ └── com/digitalasset/module │ │ ├── BUILD.bazel │ │ ├── Main.scala │ │ ⋮ │ └── test │ └── scala │ └── com/digitalasset/module │ ├── BUILD.bazel │ ├── SomeSpec.scala │ ⋮ └── module2 ├── BUILD.bazel ⋮ ``` Here `da/my_component/moduleX/src/.../BUILD.bazel` would define small library, test, and executable targets. `da/my_component/moduleX/BUILD.bazel` would bundle these small targets into larger ones to make module interdependencies easier to manage. Finally, `da/my_component/BUILD.bazel` would bundle the module targets to ease management of component interdependencies or component release. #### Coarse Grained Intermediate Bazel Project Structure However, coming from SBT such a fine grained structure may not immediately be possible without change in the corresponding Java or Scala code. For example due to cyclic dependencies between larger sets of source files. In this case the following structure can be used as an intermediate step: ``` da ├── WORKSPACE └── my_component ├── BUILD.bazel ├── module1 │ ├── BUILD.bazel │ └── src │ ├── main │ │ └── scala │ │ └── com/digitalasset/module │ │ ├── Main.scala │ │ ⋮ │ └── test │ └── scala │ └── com/digitalasset/module │ ├── SomeSpec.scala │ ⋮ └── module2 ├── BUILD.bazel ⋮ ``` Here, `da/my_component/moduleX/BUILD.bazel` defines targets for what was previously an SBT subproject. Note, that a single SBT project will already separate into multiple Bazel targets at this step. Notably, regular library targets and test-only library targets will be separate. Test-cases should be made as small targets as possible at this stage already. Bazel test-suite macros (see below) should be used to reduce boilerplate. ### Java Targets This section will outline how to define common Java targets. Please refer to the [Bazel API documentation][bazel-api-documentation] for further details. #### Libraries Java libraries can be defined using the builtin `java_library` rule. It will generate a JAR file containing the compiled Java classes and a source JAR containing the input Java sources. For example: ``` java_library( name = "example", # JAR dependencies for compiletime and runtime classpath deps = [ "//some/package:some_target", ":some_local_target", ... ], # JAR dependencies for runtime class path only runtime_deps = [ ... ], # JAR dependencies that should be forwarded to anything that depends on this target. exports = [ ... ], # Java source files srcs = glob(["src/main/java/.../my_component/**/*.java"]), # Resource files resources = glob(["src/.../resources/**"]), # Keep target visibility tight. visibility = ["//current_component:__pkg__"], ) ``` #### Tests Java tests can be defined using the builtin `java_test` rule. It will generate an executable wrapper around the given test code that executes the test runner's main method. Test targets can be executed using the `bazel test` command. Bazel can cache test results, which can greatly reduce test-suite execution time. For maximum benefit test targets should be made as small as possible, ideally a single Java source file. Use the `java_test_suite` macro to automatically define one test target for every given source file and bundle them in one test-suite target. If test-cases depend on utility classes defined in other Java sources, then you should define a Java library target for these utility classes and let the test targets depend on this library. For example: ``` load('//bazel_tools/java_testing:java_test_suite.bzl', 'java_test_suite') test_utils = glob(["src/test/java/.../utils/**/*.java"]) java_library( name = "test-utils", srcs = test_utils, ... ) java_test_suite( name = "tests", srcs = glob( ["src/test/java/**/*.java"], exclude = test_utils, ), # Expected runtime and resource requirements. size = "small", ... ) ``` The `size` attribute is used to determine the default timeout and resource requirements. Refer to the [official documentation][bazel_test_size] for details about test size and other common test attributes. [bazel_test_size]: https://docs.bazel.build/versions/master/be/common-definitions.html#common-attributes-tests #### Executables Java executables can be defined using the builtin `java_binary` rule. It will generate a JAR and executable wrapper script that defines the classpath and executes the Java runtime. Executable targets can be executed using the `bazel run` command. For example: ``` java_binary( name = "example", # The srcs attribute is optional. srcs = [ ... ], # The deps attribute is only allowed if srcs are specified. deps = [ ... ], # Name of the class that contains the entrypoint `main()`. # The main class can originate from srcs, deps, or runtime_deps. # A missing main class causes runtime failure. main_class = ..., # A list of flags to pass to the Java runtime. jvm_flags = [ ... ], # A list of files that should be present in the runtime path at runtime. data = [ ... ], ... ) ``` ### Scala Targets This section will outline how to define common Scala targets. Please refer to the [Bazel API documentation][bazel-api-documentation] for further details. This repository uses `rules_scala` to build Scala code in Bazel, which provides rules such as `scala_library`, or `scala_test_suite`. Additionally, wrapper macros are provided in `bazel_tools/scala.bzl`, such as `da_scala_library`, or `da_scala_test_suite`. These apply common compiler flags, plugins, and linter configuration. Please prefer the wrapper macros over the underlying `rules_scala` rules. If the project you are porting uses a different set of default flags, plugins, etc., then see if these could be merged with the common defaults. The goal is to converge on one shared set of common compiler flags. #### Libraries Scala libraries can be defined using the `da_scala_library` rule. It will generate a JAR file containing the compiled Scala classes and a source JAR containing the input Scala sources. For example: ``` load("//bazel_tools:scala.bzl", "da_scala_library") da_scala_library( name = "example", # JAR dependencies for compiletime and runtime classpath deps = [ "//some/package:some_target", ":some_local_target", ... ], # JAR dependencies for runtime class path only runtime_deps = [ ... ], # JAR dependencies that should be forwarded to anything that depends on this target. exports = [ ... ], # Scala source files srcs = glob(["src/main/java/.../my_component/**/*.scala"]), # Resource files resources = glob(["src/.../resources/**"]), # Keep target visibility tight. visibility = ["//current_component:__pkg__"], # Unused dependencies cause an error at build time. unused_dependency_checker_mode = "error", # If the library uses Scala macros you need to add the following attributes. scalacopts = ['-Xplugin-require:macroparadise'], plugins = [ # Plugins have to be specified as JAR targets. '//external:jar/org/scalameta/paradise_2_12_6', ], ) ``` Strive to make library targets as small as possible. In a situation where multiple Scala sources have no interdependencies you can use the `da_scala_library_suite` macro to automatically generate one library target per Scala source file, and bundle them in one target. This rule takes the same attributes as `da_scala_library` with the exception of `unused_dependency_checker_mode` which will always be disabled. If a Scala library defines macros then you must use the `da_scala_macro_library` rule instead of the above. Otherwise, you will encounter compiler errors of the following form (formatted for readability): ``` error: macro annotation could not be expanded (the most common reason for that is that you need to enable the macro paradise plugin; another possibility is that you try to use macro annotation in the same compilation run that defines it) ``` #### Tests Scala tests can be defined using the `da_scala_test` rule. It will generate an executable wrapper around the given test code that executes the test runner's main method. Test targets can be executed using the `bazel test` command. Bazel can cache test results, which can greatly reduce test-suite execution time. For maximum benefit test targets should be made as small as possible, ideally a single Scala source file. Use the `da_scala_test_suite` macro to automatically define one test target for every given source file and bundle them in one test-suite target. If test-cases depend on utility classes defined in other Scala sources, then you should define a Scala library target for these utility classes and let the test targets depend on this library. For example: ``` load("//bazel_tools:scala.bzl", "da_scala_library", "da_scala_test_suite") test_utils = glob(["src/test/scala/.../utils/**/*.scala"]) da_scala_library( name = "test-utils", srcs = test_utils, ... ) da_scala_test_suite( name = "tests", srcs = glob( ["src/test/scala/**/*.scala"], exclude = test_utils, ), # Expected runtime and resource requirements. size = "small", ... ) ``` The `size` attribute is used to determine the default timeout and resource requirements. Refer to the [official documentation][bazel_test_size] for details about test size and other common test attributes. #### Executables Scala executables can be defined using the `da_scala_binary` rule. It will generate a JAR and executable wrapper script that defines the classpath and executes the Java runtime. Executable targets can be executed using the `bazel run` command. For example: ``` load("//bazel_tools:scala.bzl", "da_scala_binary") da_scala_binary( name = "example", # The srcs attribute is optional. srcs = [ ... ], # The deps attribute is only allowed if srcs are specified. deps = [ ... ], # Name of the class that contains the entrypoint `main()`. # The main class can originate from srcs, deps, or runtime_deps. # A missing main class causes runtime failure. main_class = ..., # A list of flags to pass to the Java runtime. jvm_flags = [ ... ], # A list of files that should be present in the runtime path at runtime. data = [ ... ], ... ) ``` ## SBT Plugins If you are porting an SBT project to Bazel then you may encounter SBT plugins that the project's build depends on, or that are important for developer workflow, or project release. SBT's plugin mechanism is very flexible, and it is not possible to describe a general procedure on how to port dependence on any SBT plugin to Bazel. In the following we list examples of SBT plugins that have been encountered and ported to Bazel so far. If the SBT plugin you require has already been ported to Bazel then you should be able to use the ported version in your project as well. Otherwise, you should check if the plugin is similar to one of the previously encountered plugins and port it in an analogous way. ### Built-In Bazel Features It is worth checking whether the functionality provided by an SBT plugin is already built into Bazel or a particular Bazel rule set. For instance, Bazel has built-in support for generating dependency graphs, and `rules_scala` has built-in support for generating deplyment JARs. Refer to the [user guide][bazel_user_guide] for details. ### Compiler Plugins Various SBT plugins make use of compiler plugins, or of components that can be used as compiler plugins. `rules_scala` allows to define compiler plugins on Scala targets. Therefore, such SBT plugins can be ported to Bazel by activating the corresponding compiler plugin. One example is the [wartremover plugin][wartremover_plugin], which provides linting for Scala code. In the Bazel build the wartremover compiler plugin is activated on all Scala targets by default. It is configured in the [Scala rule wrappers][wartremover_config] used in the daml repository. [wartremover_plugin]: https://github.com/wartremover/wartremover [wartremover_config]: https://github.com/DACH-NY/da/blob/f0fe4b65e6cfca4e354d0f6138d04c98107d771c/bazel_tools/scala.bzl#L56 ### Command-Line Tools If an SBT plugin relies on a tool that can be called as a standalone command-line application, then it can be ported to Bazel by defining a custom rule that calls that command-line application. For example, the [`scalafmt` Scala formatting checker][scalafmt] can be invoked as a command-line tool. A custom Bazel rule [`scala_format_test`][scala_format_test] is defined in the daml repository, that generates a test-case that will run `scalafmt` on the specified Scala source files. [scalafmt]: https://github.com/scalameta/scalafmt [scala_format_test]: https://github.com/DACH-NY/da/blob/e904c8eac1427633ef20b6106906a59f590de5a6/bazel_tools/scalafmt/scalafmt.bzl#L31 ### DAML The SBT build of the `ledger-client` component defines a custom SBT plugin for handling DAML code. It covers compilation to LF, packaging to DAR, Scala code generation, and executing the DAML sandbox. This plugin was ported to Bazel as a set of custom Bazel rules defined in [`rules_daml`][rules_daml]. Refer to the [user guide][bazel_user_guide] or the [API docs][bazel-api-documentation] for details. [rules_daml]: https://github.com/DACH-NY/da/tree/f0fe4b65e6cfca4e354d0f6138d04c98107d771c/rules_daml ## Java Runtime and Toolchain Bazel is itself written in Java. By default Bazel will use its own Java runtime and toolchain to build and execute JVM targets. At the time of writing the Bazel executable provided in the dev-env uses the same Oracle JDK version 8 as the rest of the dev-env. Bazel supports specifying a different Java runtime and toolchain for JVM targets via the rules `java_runtime` and `java_toolchain`. Refer to the [official documentation][bazel_java_rules] for further information. Note, at the time of writing the documentation does not display these rules, see [issue 6619][bazel_issue_6619]. They can be viewed on the [web archive][bazel_java_rules_webarchive] instead. [bazel_java_rules]: https://docs.bazel.build/versions/master/be/java.html#java-rules [bazel_issue_6619]: https://github.com/bazelbuild/bazel/issues/6619 [bazel_java_rules_webarchive]: https://web.archive.org/web/20181021162843/https://docs.bazel.build/versions/master/be/java.html ## Bazel API Documentation [bazel-api-documentation]: #bazel-api-documentation - The Bazel API documentation to Bazel rules defined in this repository can be viewed by executing the following command: ``` $ bazel-api-docs ``` And browsing to http://localhost:8000. See `bazel-api-docs -h` for further instructions. - External Bazel rules API documentation is listed in the [official Bazel documentation][bazel_encyclopedia]. [bazel_encyclopedia]: https://docs.bazel.build/versions/master/be/overview.html