maven_jar migration tool (#217)

* maven_jar migration script WIP

* WIP: Java version of maven_jar migration tool

* Add automatic buildozer feature

* Remove shell script

* remove unused sh_binary

* Fix imports and refactor

* Fixed package

* Generate compat repositories and pin versions by default

* Add a note about maven_install.json

* Revert "Add a note about maven_install.json"

This reverts commit 4703d6e.

* Address laurent's comments

* Add note about buildozer prerequisite.

WORKSPACE

@@ -286,3 +286,6 @@ load("@bazel_toolchains//rules:rbe_repo.bzl", "rbe_autoconfig")
 # Use this as is if you are using the rbe_ubuntu16_04 container,
 # otherwise refer to RBE docs.
 rbe_autoconfig(name = "buildkite_config")
+
+load("//migration:maven_jar_migrator_deps.bzl", "maven_jar_migrator_repositories")
+maven_jar_migrator_repositories()

migration/BUILD

@@ -0,0 +1,13 @@
+licenses(["notice"])
+
+exports_files(["maven_jar_migrator_deps.bzl"])
+
+java_binary(
+    name = "maven_jar",
+    srcs = ["java/rules/jvm/external/MavenJarMigrator.java"],
+    main_class = "rules.jvm.external.MavenJarMigrator",
+    resources = ["java/rules/jvm/external/resources/workspace_template.txt"],
+    deps = [
+        "@maven_jar_migrator//:com_google_guava_guava",
+    ],
+)

migration/README.md

@@ -0,0 +1,49 @@
+# `maven_jar` migration tool
+
+`maven_jar` will be removed from Bazel 2.0 onwards. See [this issue](https://github.com/bazelbuild/bazel/issues/6799) for more information.
+
+This tool helps to automatically migrate your project from `maven_jar` to `maven_install` provided by `rules_jvm_external`.
+
+These PRs were generated using this tool:
+
+* https://github.com/google/copybara/pull/96
+* https://github.com/kythe/kythe/pull/4180
+* https://github.com/bazelbuild/rules_k8s/pull/463
+
+## Prerequisites
+
+* [Buildozer](https://github.com/bazelbuild/buildtools/releases). Ensure that the `buildozer` is available in your `PATH`.
+
+## Usage
+
+First, add the latest version of `rules_jvm_external` to your WORKSPACE by
+following the instructions on the
+[releases](https://github.com/bazelbuild/rules_jvm_external/releases) page.
+
+Then, add the following to your WORKSPACE to load the migrator's
+dependencies:
+
+```python
+load("@rules_jvm_external//:defs.bzl", "maven_install")
+load("@rules_jvm_external//migration:maven_jar_migrator_deps.bzl", "maven_jar_migrator_repositories")
+maven_jar_migrator_repositories()
+```
+
+Next, run this command in root of project workspace to generate the
+`maven_install` WORKSPACE snippet:
+
+```
+$ bazel run @rules_jvm_external//migration:maven_jar
+```
+
+This command will also run the buildozer commands to migrate your project to
+use the new `maven_install` labels.
+
+If the snippet looks good, concatenate it to the end of your WORKSPACE file:
+
+```
+$ bazel run @rules_jvm_external//migration:maven_jar >> WORKSPACE
+```
+
+Finally, if the build continues to succeed, you can remove
+`maven_jar_migrator_repositories` from your WORKSPACE file.

migration/java/rules/jvm/external/MavenJarMigrator.java

@@ -0,0 +1,137 @@
+package rules.jvm.external;
+
+import com.google.common.base.Joiner;
+import com.google.common.collect.ImmutableList;
+import com.google.common.io.ByteStreams;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.util.Iterator;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+/** A migration tool from native.maven_jar to rules_jvm_external's maven_install. */
+public class MavenJarMigrator {
+
+  // Defined by Bazel during a `bazel run`.
+  private static final String BUILD_WORKING_DIRECTORY = System.getenv("BUILD_WORKING_DIRECTORY");
+  // Converts a Maven coordinate to a valid maven_install target label.
+  // e.g. com.google.guava:guava:28.0-jre -> @maven//:com_google_guava_guava
+  private static final Function<String, String> convertCoordinateToNewLabel =
+      (String coordinate) -> {
+        coordinate = coordinate.replace("-", "_").replace(".", "_");
+        String[] parts = coordinate.split(":");
+        return "@maven//:" + Joiner.on("_").join(parts[0], parts[1]);
+      };
+
+  public static void main(String[] args) throws IOException, InterruptedException {
+    checkPrerequisites();
+
+    ImmutableList<String> coordinates = collectMavenJarAttributeValues("artifact");
+    // Phase 1: Run buildozer to convert old maven_jar labels to new maven_install labels.
+    convertLabels(coordinates);
+    // Phase 2: Print maven_install WORKSPACE snippet on stdout.
+    System.out.println(generateWorkspaceSnippet(coordinates));
+  }
+
+  private static void checkPrerequisites() throws InterruptedException, IOException {
+    // Assert that buildozer exists on PATH.
+    if (getProcessBuilder("buildozer", "-version").start().waitFor() != 0) {
+      throw new AssertionError("buildozer is not found on your PATH. Download "
+          + "buildozer for your platform from https://github.com/bazelbuild/buildtools/releases "
+          + "and put the executable in your PATH.");
+    }
+  }
+
+  /**
+   * Converts the old style maven_jar labels to the new style maven_install labels.
+   *
+   * <p>This implementation assumes that the sortedness output of bazel query --output=build is
+   * deterministic.
+   *
+   * @param coordinates A list of coordinates to derive the old and new labels.
+   * @throws IOException
+   * @throws InterruptedException
+   */
+  private static void convertLabels(ImmutableList<String> coordinates)
+      throws IOException, InterruptedException {
+    ImmutableList<String> oldLabels =
+        collectMavenJarAttributeValues("name").stream()
+            .map((String name) -> String.format("@%s//jar", name))
+            .collect(ImmutableList.toImmutableList());
+    ImmutableList<String> newLabels =
+        coordinates.stream()
+            .map(convertCoordinateToNewLabel)
+            .collect(ImmutableList.toImmutableList());
+
+    assert (newLabels.size() == oldLabels.size());
+    Iterator<String> oldLabelIterator = oldLabels.iterator();
+    Iterator<String> newLabelIterator = newLabels.iterator();
+    while (oldLabelIterator.hasNext()) {
+      getProcessBuilder(
+              "buildozer",
+              "substitute * " + oldLabelIterator.next() + " " + newLabelIterator.next(),
+              "//...:*")
+          .start()
+          .waitFor();
+    }
+  }
+
+  private static String generateWorkspaceSnippet(ImmutableList<String> coordinates)
+      throws IOException {
+    InputStream stream =
+        MavenJarMigrator.class.getResourceAsStream("resources/workspace_template.txt");
+    String workspaceTemplate = new String(ByteStreams.toByteArray(stream), UTF_8);
+    return workspaceTemplate.replace(
+        "%maven_artifact_list%",
+        coordinates.stream()
+            .sorted()
+            .map((String line) -> "        \"" + line + "\",")
+            .collect(Collectors.joining("\n")));
+  }
+
+  /**
+   * Aggregate information about an attribute on all maven_jar targets using bazel query.
+   *
+   * <p>The maven_jar declaration does not need to be in the local WORKSPACE. It can be a maven_jar
+   * declaration loaded from a remote repository's deps.bzl.
+   *
+   * @return A list of Maven artifact coordinates used by this workspace.
+   * @throws IOException
+   * @throws InterruptedException
+   */
+  private static ImmutableList<String> collectMavenJarAttributeValues(String attribute)
+      throws IOException, InterruptedException {
+    ProcessBuilder processBuilder =
+        getProcessBuilder(
+            "bazel",
+            "query",
+            "kind(maven_jar, //external:all)",
+            "--output=build",
+            "--noshow_progress");
+
+    return readOutput(processBuilder.start()).stream()
+        .filter((String line) -> line.trim().startsWith(attribute))
+        .map((String line) -> line.split("\"")[1]) // get the value in a string attribute
+        .collect(ImmutableList.toImmutableList());
+  }
+
+  private static ProcessBuilder getProcessBuilder(String... args) {
+    ProcessBuilder processBuilder = new ProcessBuilder();
+    processBuilder.directory(new File(BUILD_WORKING_DIRECTORY));
+    processBuilder.command(args);
+    return processBuilder;
+  }
+
+  private static ImmutableList<String> readOutput(Process p) throws InterruptedException {
+    // ensure that the process is completed before reading the standard output.
+    p.waitFor();
+    BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
+    return br.lines().collect(ImmutableList.toImmutableList());
+  }
+}

migration/java/rules/jvm/external/resources/workspace_template.txt

@@ -0,0 +1,20 @@
+load("@rules_jvm_external//:defs.bzl", "maven_install")
+
+maven_install(
+    name = "maven",
+    artifacts = [
+%maven_artifact_list%
+    ],
+    repositories = [
+        "https://jcenter.bintray.com",
+        "https://maven.google.com",
+        "https://repo1.maven.org/maven2",
+    ],
+    fetch_sources = True,
+    version_conflict_policy = "pinned",
+    # See https://github.com/bazelbuild/rules_jvm_external/#repository-aliases
+    # This can be removed if none of your external dependencies uses `maven_jar`.
+    generate_compat_repositories = True,
+)
+load("@maven//:compat.bzl", "compat_repositories")
+compat_repositories()

migration/maven_jar_migrator_deps.bzl

@@ -0,0 +1,13 @@
+load("@rules_jvm_external//:defs.bzl", "maven_install")
+
+def maven_jar_migrator_repositories():
+    maven_install(
+        name = "maven_jar_migrator",
+        artifacts = [
+            "com.google.guava:guava:28.0-jre",
+        ],
+        repositories = [
+            "https://repo1.maven.org/maven2",
+            "https://jcenter.bintray.com",
+        ],
+    )