Separate new-style-hash content in DiskCache

src/main/java/com/google/devtools/build/lib/remote/disk/DiskCacheClient.java

@@ -15,8 +15,10 @@
 
 import build.bazel.remote.execution.v2.ActionResult;
 import build.bazel.remote.execution.v2.Digest;
+import build.bazel.remote.execution.v2.DigestFunction;
 import build.bazel.remote.execution.v2.Directory;
 import build.bazel.remote.execution.v2.Tree;
+import com.google.common.base.Ascii;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.io.ByteStreams;
 import com.google.common.util.concurrent.Futures;
@@ -214,10 +216,25 @@ protected Path toPathNoSplit(String key) {
     return root.getChild(key);
   }
 
+  private static boolean isOldStyleDigestFunction(DigestFunction.Value digestFunction) {
+    // Old-style digest functions (SHA256, etc) are distinguishable by the length
+    // of their hash alone and do not require extra specification, but newer
+    // digest functions (which may have the same length hashes as the older
+    // functions!) must be explicitly specified in the upload resource name.
+    return digestFunction.getNumber() <= 7;
+  }
+
   protected Path toPath(String key, boolean actionResult) {
+    Path rootDir = root;
+    if (!isOldStyleDigestFunction(digestUtil.getDigestFunction())) {
+      rootDir =
+          rootDir.getChild(
+              Ascii.toLowerCase(digestUtil.getDigestFunction().getValueDescriptor().getName()));
+    }
+
     String cacheFolder = actionResult ? AC_DIRECTORY : CAS_DIRECTORY;
     // Create the file in a subfolder to bypass possible folder file count limits
-    return root.getChild(cacheFolder).getChild(key.substring(0, 2)).getChild(key);
+    return rootDir.getChild(cacheFolder).getChild(key.substring(0, 2)).getChild(key);
   }
 
   private void saveFile(String key, InputStream in, boolean actionResult) throws IOException {