1 files changed, 79 insertions, 15 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
index 2bba0bfcd5..f949e0a8b1 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
@@ -24,6 +24,7 @@ import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.BuildFileNotFoundException;
 import com.google.devtools.build.lib.packages.NoSuchPackageException;
 import com.google.devtools.build.lib.packages.Package;
+import com.google.devtools.build.lib.packages.PackageSerializer;
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.skyframe.FileSymlinkException;
 import com.google.devtools.build.lib.skyframe.FileValue;
@@ -32,6 +33,7 @@ import com.google.devtools.build.lib.skyframe.PackageValue;
 import com.google.devtools.build.lib.skyframe.RepositoryValue;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.Type;
+import com.google.devtools.build.lib.util.Fingerprint;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -44,6 +46,7 @@ import com.google.devtools.build.skyframe.SkyKey;
 
 import java.io.IOException;
 import java.nio.charset.Charset;
+import java.util.Arrays;
 
 import javax.annotation.Nullable;
 
@@ -51,6 +54,8 @@ import javax.annotation.Nullable;
  * Parent class for repository-related Skyframe functions.
  */
 public abstract class RepositoryFunction implements SkyFunction {
+  protected static final byte[] NO_RULE_SPECIFIC_DATA = new byte[] {};
+
   /**
    * Exception thrown when something goes wrong accessing a remote repository.
    *
@@ -79,6 +84,58 @@ public abstract class RepositoryFunction implements SkyFunction {
 
   private BlazeDirectories directories;
 
+  private byte[] computeRuleKey(Rule rule, byte[] ruleSpecificData) {
+
+    return new Fingerprint()
+        .addBytes(new PackageSerializer().serializeRule(rule).toByteArray())
+        .addBytes(ruleSpecificData)
+        .digestAndReset();
+  }
+
+  private Path getMarkerPath(Rule rule) {
+    return getExternalRepositoryDirectory().getChild("@" + rule.getName() + ".marker");
+  }
+
+  /**
+   * Checks if the state of the repository in the file system is consistent with the rule in the
+   * WORKSPACE file.
+   *
+   * <p>Deletes the marker file if not so that no matter what happens after, the state of the file
+   * system stays consistent.
+   */
+  protected boolean isFilesystemUpToDate(Rule rule, byte[] ruleSpecificData)
+      throws RepositoryFunctionException {
+    try {
+      Path markerPath = getMarkerPath(rule);
+      if (!markerPath.exists()) {
+        return false;
+      }
+
+      boolean result = Arrays.equals(
+          computeRuleKey(rule, ruleSpecificData),
+          FileSystemUtils.readContent(markerPath));
+      if (!result) {
+        // So that we are in a consistent state if something happens while fetching the repository
+        markerPath.delete();
+      }
+
+      return result;
+
+    } catch (IOException e) {
+      throw new RepositoryFunctionException(e, Transience.TRANSIENT);
+    }
+  }
+
+  protected void writeMarkerFile(Rule rule, byte[] ruleSpecificData)
+      throws RepositoryFunctionException {
+    try {
+      FileSystemUtils.writeContent(getMarkerPath(rule), computeRuleKey(rule, ruleSpecificData));
+    } catch (IOException e) {
+      throw new RepositoryFunctionException(e, Transience.TRANSIENT);
+    }
+  }
+
+  
   protected Path prepareLocalRepositorySymlinkTree(Rule rule, Environment env)
       throws RepositoryFunctionException {
     Path repositoryDirectory = getExternalRepositoryDirectory().getRelative(rule.getName());
@@ -117,22 +174,11 @@ public abstract class RepositoryFunction implements SkyFunction {
     return RepositoryValue.create(repositoryDirectory);
   }
 
-  /**
-   * Symlinks a BUILD file from the local filesystem into the external repository's root.
-   * @param rule the rule that declares the build_file path.
-   * @param workspaceDirectory the workspace root for the build.
-   * @param outputDirectory the directory of the remote repository
-   * @param env the Skyframe environment.
-   * @return the file value of the symlink created.
-   * @throws RepositoryFunctionException if the BUILD file specified does not exist or cannot be
-   *         linked.
-   */
-  protected RepositoryValue symlinkBuildFile(
-      Rule rule, Path workspaceDirectory, Path outputDirectory, Environment env)
+  protected FileValue getBuildFileValue(Rule rule, Environment env)
       throws RepositoryFunctionException {
     AggregatingAttributeMapper mapper = AggregatingAttributeMapper.of(rule);
     PathFragment buildFile = new PathFragment(mapper.get("build_file", Type.STRING));
-    Path buildFileTarget = workspaceDirectory.getRelative(buildFile);
+    Path buildFileTarget = directories.getWorkspace().getRelative(buildFile);
     if (!buildFileTarget.exists()) {
       throw new RepositoryFunctionException(
           new EvalException(rule.getLocation(),
@@ -146,7 +192,7 @@ public abstract class RepositoryFunction implements SkyFunction {
       rootedBuild = RootedPath.toRootedPath(
           buildFileTarget.getParentDirectory(), new PathFragment(buildFileTarget.getBaseName()));
     } else {
-      rootedBuild = RootedPath.toRootedPath(workspaceDirectory, buildFile);
+      rootedBuild = RootedPath.toRootedPath(directories.getWorkspace(), buildFile);
     }
     SkyKey buildFileKey = FileValue.key(rootedBuild);
     FileValue buildFileValue;
@@ -162,8 +208,26 @@ public abstract class RepositoryFunction implements SkyFunction {
           Transience.TRANSIENT);
     }
 
+    return buildFileValue;
+  }
+
+  /**
+   * Symlinks a BUILD file from the local filesystem into the external repository's root.
+   * @param rule the rule that declares the build_file path.
+   * @param outputDirectory the directory of the remote repository
+   * @param env the Skyframe environment.
+   * @return the file value of the symlink created.
+   * @throws RepositoryFunctionException if the BUILD file specified does not exist or cannot be
+   *         linked.
+   */
+  protected RepositoryValue symlinkBuildFile(Rule rule, Path outputDirectory, Environment env)
+      throws RepositoryFunctionException {
+    FileValue buildFileValue = getBuildFileValue(rule, env);
+    if (env.valuesMissing()) {
+      return null;
+    }
     Path buildFilePath = outputDirectory.getRelative("BUILD");
-    if (createSymbolicLink(buildFilePath, buildFileTarget, env) == null) {
+    if (createSymbolicLink(buildFilePath, buildFileValue.realRootedPath().asPath(), env) == null) {
       return null;
     }
     return RepositoryValue.createNew(outputDirectory, buildFileValue);