Allow opting in to faster/sloppier `PathRef` signatures using mtime + filesize instead of md5ing the file body.

Used for third-party dependencies (which are large jars but shouldn't change often) this speeds up the no-op `mill run ScalaPlugin.compile` by about a quarter

1 files changed, 20 insertions, 10 deletions

diff --git a/core/src/main/scala/mill/eval/PathRef.scala b/core/src/main/scala/mill/eval/PathRef.scala
index fa373b5a..5d96d8df 100644
--- a/core/src/main/scala/mill/eval/PathRef.scala
+++ b/core/src/main/scala/mill/eval/PathRef.scala
@@ -15,8 +15,8 @@ import mill.util.JsonFormatters
   * on the contents of the filesystem underneath it. Used to ensure filesystem
   * changes can bust caches which are keyed off hashcodes.
   */
-case class PathRef(path: ammonite.ops.Path){
-  val md5Hash = {
+case class PathRef(path: ammonite.ops.Path, quick: Boolean = false){
+  val sig = {
     val digest = MessageDigest.getInstance("MD5")
 
     val buffer = new Array[Byte](16 * 1024)
@@ -30,15 +30,25 @@ case class PathRef(path: ammonite.ops.Path){
 
         def visitFile(file: jnio.Path, attrs: BasicFileAttributes) = {
           digest.update(file.toAbsolutePath.toString.getBytes)
-          val is = jnio.Files.newInputStream(file)
-          def rec(): Unit = {
-            val length = is.read(buffer)
-            if (length != -1){
-              digest.update(buffer, 0, length)
-              rec()
+          if (quick){
+            val value = (path.mtime.toMillis, path.size).hashCode()
+            digest.update((value >>> 24).toByte)
+            digest.update((value >>> 16).toByte)
+            digest.update((value >>> 8).toByte)
+            digest.update(value.toByte)
+          }else {
+            println("Hashing " + file)
+            val is = jnio.Files.newInputStream(file)
+
+            def rec(): Unit = {
+              val length = is.read(buffer)
+              if (length != -1) {
+                digest.update(buffer, 0, length)
+                rec()
+              }
             }
+            rec()
           }
-          rec()
           FileVisitResult.CONTINUE
         }
 
@@ -50,7 +60,7 @@ case class PathRef(path: ammonite.ops.Path){
     java.util.Arrays.hashCode(digest.digest())
 
   }
-  override def hashCode() = md5Hash
+  override def hashCode() = sig
 }
 
 object PathRef{