Fix git_repository rule to support fetching a commit on a tag

- specified commit may only be present on a tag, not on any branch
- use the verbose references specification in git fetch command
- add black box test
- initially implemented by https://github.com/jamiesnape in bazelbuild#8933, but the suggested solution with --tags flag does not work for CentOS Bazel CI configuration

Closes bazelbuild#9059.

PiperOrigin-RevId: 261316448

src/test/java/com/google/devtools/build/lib/blackbox/tests/workspace/GitRepositoryBlackBoxTest.java

@@ -51,7 +51,6 @@
  * "out.txt" file.
  */
 public class GitRepositoryBlackBoxTest extends AbstractBlackBoxTest {
-
   private static final String HELLO_FROM_EXTERNAL_REPOSITORY = "Hello from GIT repository!";
   private static final String HELLO_FROM_BRANCH = "Hello from branch!";
 
@@ -192,6 +191,56 @@ public void testCheckoutOfCommitFromBranch() throws Exception {
     WorkspaceTestUtils.assertLinesExactly(outPath, HELLO_FROM_BRANCH);
   }
 
+  /**
+   * Tests usage of git_repository workspace rule in the particular use case, when only the commit
+   * hash is specified, and the commit is not in the HEAD-reachable subtree, on a separate tag and
+   * not on any branch.
+   */
+  @Test
+  public void testCheckoutOfCommitFromTag() throws Exception {
+    Path repo = context().getTmpDir().resolve("tag_repo");
+    GitRepositoryHelper gitRepository = initGitRepository(context(), repo);
+
+    context().write(repo.resolve("master.marker").toString());
+    gitRepository.addAll();
+    gitRepository.commit("Initial commit");
+
+    gitRepository.createNewBranch("demonstrate_branch");
+
+    RepoWithRuleWritingTextGenerator generator = new RepoWithRuleWritingTextGenerator(repo);
+    generator.withOutputText(HELLO_FROM_BRANCH).setupRepository();
+
+    gitRepository.addAll();
+    gitRepository.commit("Commit in tag1");
+    gitRepository.tag("tag1");
+    String tagCommitHash = gitRepository.getHead();
+
+    gitRepository.checkout("master");
+
+    // delete branch, so that the last commit is not an any branch.
+    gitRepository.deleteBranch("demonstrate_branch");
+
+    generator.withOutputText(HELLO_FROM_EXTERNAL_REPOSITORY).setupRepository();
+    gitRepository.addAll();
+    gitRepository.commit("Commit in master");
+
+    context()
+        .write(
+            "WORKSPACE",
+            "load(\"@bazel_tools//tools/build_defs/repo:git.bzl\", \"git_repository\")",
+            "git_repository(",
+            "  name='ext',",
+            String.format("  remote='%s',", PathUtils.pathToFileURI(repo.resolve(".git"))),
+            String.format("  commit='%s',", tagCommitHash),
+            ")");
+
+    // This creates Bazel without MSYS, see implementation for details.
+    BuilderRunner bazel = WorkspaceTestUtils.bazel(context());
+    bazel.build("@ext//:write_text");
+    Path outPath = context().resolveBinPath(bazel, "external/ext/out");
+    WorkspaceTestUtils.assertLinesExactly(outPath, HELLO_FROM_BRANCH);
+  }
+
   private static String setupGitRepository(BlackBoxTestContext context, Path repo)
       throws Exception {
     GitRepositoryHelper gitRepository = initGitRepository(context, repo);

src/test/java/com/google/devtools/build/lib/blackbox/tests/workspace/GitRepositoryHelper.java

@@ -97,6 +97,18 @@ void createNewBranch(String branchName) throws Exception {
     runGit("checkout", "-b", branchName);
   }
 
+  /**
+   * Deletes the local branch with the specified name.
+   *
+   * @param branchName branch name
+   * @throws Exception related to the invocation of the external git process (like IOException or
+   *     TimeoutException) or ProcessRunnerException if the process returned not expected return
+   *     code.
+   */
+  void deleteBranch(String branchName) throws Exception {
+    runGit("branch", "-D", branchName);
+  }
+
   /**
    * Checks out specified revision or reference.
    *

tools/build_defs/repo/git_worker.bzl

@@ -119,9 +119,21 @@ def add_origin(ctx, git_repo, remote):
 
 def fetch(ctx, git_repo):
     if not git_repo.fetch_ref:
-        # We need to explicitly specify to fetch all branches, otherwise only HEAD-reachable
-        # is fetched.
-        _git_maybe_shallow(ctx, git_repo, "fetch", "--all")
+        # We need to explicitly specify to fetch all branches and tags, otherwise only
+        # HEAD-reachable is fetched.
+        # The semantics of --tags flag of git-fetch have changed in Git 1.9, from 1.9 it means
+        # "everything that is already specified and all tags"; before 1.9, it used to mean
+        # "ignore what is specified and fetch all tags".
+        # The arguments below work correctly for both before 1.9 and after 1.9,
+        # as we directly specify the list of references to fetch.
+        _git_maybe_shallow(
+            ctx,
+            git_repo,
+            "fetch",
+            "origin",
+            "refs/heads/*:refs/remotes/origin/*",
+            "refs/tags/*:refs/tags/*",
+        )
     else:
         _git_maybe_shallow(ctx, git_repo, "fetch", "origin", git_repo.fetch_ref)