Add a file hashing utility to the Utilities class.

src/main/scala/org/allenai/plugins/Utilities.scala

@@ -59,8 +59,9 @@ object Utilities {
     */
   def hashFiles(filesToHash: Seq[File], rootDir: File): String = {
     // Resolve the filenames relative to the root directory.
-    val rootDirPath = rootDir.toPath
-    val relativizedNames = filesToHash.map(_.toPath).map(rootDirPath.relativize).map(_.toString)
+    val rootDirPath = rootDir.toPath.normalize
+    val relativizedNames =
+      filesToHash.map(_.toPath.normalize).map(rootDirPath.relativize).map(_.toString)
     // Create a hash of the sorted names, joined by an empty string.
     val nameHash = Hash.toHex(Hash(relativizedNames.sorted.mkString))
 

src/test/scala/org/allenai/plugins/UtilitiesSpec.scala

@@ -61,7 +61,7 @@ class UtilitiesSpec extends FlatSpecLike with Matchers with OneInstancePerTest w
     }
   }
 
-  it should "return the same hash when files have the same relative paths" in {
+  it should "return the same hash when files have the same relative paths w.r.t. the root" in {
     // Use two subdirectories of `tempDirectory`, and hash from both of them. Note that these
     // directories don't currently have to exist, since we're operating only on the paths, but they
     // are created in case this changes.
@@ -76,6 +76,19 @@ class UtilitiesSpec extends FlatSpecLike with Matchers with OneInstancePerTest w
     firstHash shouldBe secondHash
   }
 
+  it should "return the same hash when files have the same normalized path" in {
+    // Create versions of fooFile and barFile which are semantically the same, but have different
+    // paths.
+    val fooRelative = new File("foo.txt")
+    val barRelative = new File(tempDirectory, ".." + File.pathSeparatorChar +
+      tempDirectory.getName + File.pathSeparatorChar + "bar.txt")
+
+    val firstHash = Utilities.hashFiles(Seq(fooFile, barFile), tempDirectory)
+    val secondHash = Utilities.hashFiles(Seq(fooFile, barFile), tempDirectory)
+
+    firstHash shouldBe secondHash
+  }
+
   it should "return a different hash when a file is renamed" in {
     val firstHash = Utilities.hashFiles(Seq(fooFile, barFile), tempDirectory)