Fix {new_,}git_repository after shutdown.

Previously, after a server shutdown they would fail because the
repository already exists. This change fixes that and avoids
re-downloading if the local repository is already the correct version
and unmodified.

An example of the error before:
$ bazel fetch ...
.......
INFO: Loading package: tools/cpp
java.lang.RuntimeException: Unrecoverable error while evaluating node 'GIT_CLONE:file:///tmp/gtest-1.7.0 -> /home/brian/.cache/bazel/_bazel_brian/46af2c6e62e13aca9af015360f8fb1da/external/gtest_repo (091e69312f2c133860e71e6b01118c1f5a8c943d) submodules: false' (requested by nodes 'NEW_GIT_REPOSITORY:@gtest_repo')
	at com.google.devtools.build.skyframe.ParallelEvaluator$Evaluate.run(ParallelEvaluator.java:745)
	at com.google.devtools.build.lib.concurrent.AbstractQueueVisitor$1.run(AbstractQueueVisitor.java:346)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)
Caused by: org.eclipse.jgit.api.errors.JGitInternalException: Destination path "gtest_repo" already exists and is not an empty directory
	at org.eclipse.jgit.api.CloneCommand.init(CloneCommand.java:152)
	at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:132)
	at com.google.devtools.build.lib.bazel.repository.GitCloneFunction.compute(GitCloneFunction.java:68)
	at com.google.devtools.build.skyframe.ParallelEvaluator$Evaluate.run(ParallelEvaluator.java:709)
	... 4 more

--
Change-Id: Ifca46302537248106740941b70bc5bd11fa1eeb1
Reviewed-on: https://bazel-review.googlesource.com/#/c/1650
MOS_MIGRATED_REVID=101045419

1 files changed, 65 insertions, 9 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/GitCloneFunction.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/GitCloneFunction.java
index 2c8e50a684..29c7b729f6 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/GitCloneFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/GitCloneFunction.java
@@ -20,6 +20,7 @@ import com.google.devtools.build.lib.packages.AggregatingAttributeMapper;
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.packages.Type;
 import com.google.devtools.build.lib.syntax.EvalException;
+import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.skyframe.SkyFunction;
 import com.google.devtools.build.skyframe.SkyFunctionException.Transience;
@@ -28,14 +29,19 @@ import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;
 
 import org.eclipse.jgit.api.Git;
+import org.eclipse.jgit.api.Status;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.api.errors.InvalidRefNameException;
 import org.eclipse.jgit.api.errors.InvalidRemoteException;
 import org.eclipse.jgit.api.errors.RefNotFoundException;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.storage.file.FileRepositoryBuilder;
 
-import java.io.File;
 import java.io.IOException;
 import java.util.Objects;
+import java.util.Set;
 
 import javax.annotation.Nullable;
 
@@ -51,21 +57,71 @@ public class GitCloneFunction implements SkyFunction {
     this.reporter = reporter;
   }
 
+  private boolean isUpToDate(GitRepositoryDescriptor descriptor) {
+    // Initializing/checking status of/etc submodules cleanly is hard, so don't try for now.
+    if (descriptor.initSubmodules) {
+      return false;
+    }
+    Repository repository = null;
+    try {
+      repository =
+          new FileRepositoryBuilder()
+              .setGitDir(descriptor.directory.getChild(Constants.DOT_GIT).getPathFile())
+              .setMustExist(true)
+              .build();
+      ObjectId head = repository.resolve(Constants.HEAD);
+      ObjectId checkout = repository.resolve(descriptor.checkout);
+      if (head != null && checkout != null && head.equals(checkout)) {
+        Status status = Git.wrap(repository).status().call();
+        if (!status.hasUncommittedChanges()) {
+          // new_git_repository puts (only) BUILD and WORKSPACE, and
+          // git_repository doesn't add any files.
+          Set<String> untracked = status.getUntracked();
+          if (untracked.isEmpty()
+              || (untracked.size() == 2
+                  && untracked.contains("BUILD")
+                  && untracked.contains("WORKSPACE"))) {
+            return true;
+          }
+        }
+      }
+    } catch (GitAPIException | IOException e) {
+      // Any exceptions here, we'll just blow it away and try cloning fresh.
+      // The fresh clone avoids any weirdness due to what's there and has nicer
+      // error reporting.
+    } finally {
+      if (repository != null) {
+        repository.close();
+      }
+    }
+    return false;
+  }
+
   @Nullable
   @Override
   public SkyValue compute(SkyKey skyKey, Environment env) throws RepositoryFunctionException {
     GitRepositoryDescriptor descriptor = (GitRepositoryDescriptor) skyKey.argument();
-    String outputDirectory = descriptor.directory.toString();
 
     Git git = null;
     try {
-      git = Git.cloneRepository()
-          .setURI(descriptor.remote)
-          .setDirectory(new File(outputDirectory))
-          .setCloneSubmodules(false)
-          .setProgressMonitor(
-              new GitProgressMonitor("Cloning " + descriptor.remote, reporter))
-          .call();
+      if (descriptor.directory.exists()) {
+        if (isUpToDate(descriptor)) {
+          return new HttpDownloadValue(descriptor.directory);
+        }
+        try {
+          FileSystemUtils.deleteTree(descriptor.directory);
+        } catch (IOException e) {
+          throw new RepositoryFunctionException(e, Transience.TRANSIENT);
+        }
+      }
+      git =
+          Git.cloneRepository()
+              .setURI(descriptor.remote)
+              .setDirectory(descriptor.directory.getPathFile())
+              .setCloneSubmodules(false)
+              .setNoCheckout(true)
+              .setProgressMonitor(new GitProgressMonitor("Cloning " + descriptor.remote, reporter))
+              .call();
       git.checkout()
           .setCreateBranch(true)
           .setName("bazel-checkout")