[2.x] perf: Use bytecodeHash for incremental test (#9152)

**Problem**
There's perf issue building ClassStamp for the incremental test.

**Solution**
This reuses the bytecodeHash created during compilation.

build.sbt

@@ -379,6 +379,7 @@ lazy val utilCache = project
     contrabandSettings,
     mimaSettings,
     mimaBinaryIssueFilters ++= Seq(
+      exclude[ReversedMissingMethodProblem]("sbt.util.CacheImplicits.sbt$util*")
     ),
     Test / fork := true,
   )
@@ -742,6 +743,7 @@ lazy val mainProj = (project in file("main"))
     Compile / doc / sources := Nil,
     mimaSettings,
     mimaBinaryIssueFilters ++= Vector(
+      exclude[DirectMissingMethodProblem]("sbt.internal.ClassStamper.stampVf")
     ),
   )
   .dependsOn(lmCore, lmIvy, lmCoursierShadedPublishing)

main/src/main/scala/sbt/internal/IncrementalTest.scala

@@ -19,6 +19,7 @@ import sbt.internal.util.Types.const
 import sbt.io.{ GlobFilter, IO, NameFilter }
 import sbt.protocol.testing.TestResult
 import sbt.util.{ ActionCache, BuildWideCacheConfiguration, CacheLevelTag, Digest, Logger }
+import sbt.util.CacheImplicits
 import sbt.util.CacheImplicits.given
 import scala.collection.concurrent
 import scala.collection.mutable
@@ -151,10 +152,12 @@ class ClassStamper(
     converter: FileConverter,
 ):
   private val stamps = mutable.Map.empty[String, SortedSet[Digest]]
-  private val vfStamps = mutable.Map.empty[VirtualFileRef, Digest]
+  private val internalStamps = mutable.Map.empty[String, SortedSet[Digest]]
   private lazy val analyses = classpath
     .flatMap(a => BuildDef.extractAnalysis(a.metadata, converter))
     .collect { case analysis: Analysis => analysis }
+  private val stampVf: VirtualFileRef => Digest =
+    CacheImplicits.virtualFileRefToDigest(_)(converter)
 
   /**
    * Given a classpath and a class name, this tries to create a SHA-256 digest.
@@ -180,7 +183,7 @@ class ClassStamper(
     import analysis.relations
     // log.debug(s"test: internalStamp($javaClassName)")
     def internalStamp0(className: String): SortedSet[Digest] =
-      // log.debug(s"  internalStamp: relations = $relations")
+      // Zinc doesn't fully track the transitive dependencies
       val internalDeps = relations
         .internalClassDeps(className)
         .flatMap: otherCN =>
@@ -196,17 +199,11 @@ class ClassStamper(
           relations.libraryClassName
             .reverse(libClassName)
             .map(stampVf)
-      val classDigests = relations
-        .definesClass(className)
-        .flatMap: sourceFile =>
-          relations
-            .products(sourceFile)
-            .map(stampVf)
-      // TODO: substitute the above with
-      // val classDigests = analysis.apis.internal
-      //   .get(className)
-      //   .map: analyzed =>
-      //   0L // analyzed.??? we need a hash here
+      val classDigests = analysis.apis.internal
+        .get(className)
+        .toSet
+        .map: analyzed =>
+          Digest.dummy(37 * (17 + analyzed.transitiveBytecodeHash) + analyzed.bytecodeHash)
       val xs =
         (internalDeps union internalJarDeps union externalDeps union classDigests)
           .to(SortedSet)
@@ -221,10 +218,4 @@ class ClassStamper(
           // Note: internalClassDeps uses Scala-encoded class name for companion objects
           val classNames = relations.productClassName.reverse(javaClassName)
           SortedSet(classNames.toSeq*).flatMap(internalStamp0)
-
-  def stampVf(vf: VirtualFileRef): Digest =
-    vf match
-      case h: HashedVirtualFileRef => Digest(h)
-      case _ =>
-        vfStamps.getOrElseUpdate(vf, Digest.sha256Hash(converter.toPath(vf)))
 end ClassStamper

util-cache/src/main/scala/sbt/util/CacheImplicits.scala

@@ -13,7 +13,7 @@ import java.nio.file.{ Files, NoSuchFileException }
 import java.nio.file.attribute.BasicFileAttributes
 import java.util.concurrent.atomic.{ AtomicLong, AtomicReference }
 import sjsonnew.BasicJsonProtocol
-import xsbti.{ HashedVirtualFileRef, PathBasedFile }
+import xsbti.{ FileConverter, HashedVirtualFileRef, PathBasedFile, VirtualFileRef }
 
 object CacheImplicits extends CacheImplicits:
   private[sbt] val defaultLocalDigestCacheByteSize = 1024L * 1024L
@@ -24,6 +24,9 @@ trait CacheImplicits extends BasicCacheImplicits with BasicJsonProtocol:
   private val weigher: Weigher[String, (String, Long, Long)] = { case (k, (v1, _, _)) =>
     k.size + v1.size + 16
   }
+  private val digestWeigher: Weigher[String, (Digest, Long, Long)] = { case (k, (v1, _, _)) =>
+    k.size + v1.digestSize + 16
+  }
 
   private val stampCache: AtomicReference[CCache[String, (String, Long, Long)]] =
     AtomicReference(
@@ -34,6 +37,15 @@ trait CacheImplicits extends BasicCacheImplicits with BasicJsonProtocol:
         .build()
     )
 
+  private val digestCache: AtomicReference[CCache[String, (Digest, Long, Long)]] =
+    AtomicReference(
+      Caffeine
+        .newBuilder()
+        .maximumWeight(localDigestCacheByteSize.get())
+        .weigher(digestWeigher)
+        .build()
+    )
+
   private[sbt] def setCacheSize(size: Long): Unit =
     if localDigestCacheByteSize.get() == size then ()
     else
@@ -46,6 +58,14 @@ trait CacheImplicits extends BasicCacheImplicits with BasicJsonProtocol:
           .weigher(weigher)
           .build()
       )
+      digestCache.get().invalidateAll()
+      digestCache.set(
+        Caffeine
+          .newBuilder()
+          .maximumWeight(localDigestCacheByteSize.get())
+          .weigher(digestWeigher)
+          .build()
+      )
 
   private def getOrElseUpdate(ref: HashedVirtualFileRef, lastModified: Long, sizeBytes: Long)(
       value: => String
@@ -57,6 +77,16 @@ trait CacheImplicits extends BasicCacheImplicits with BasicJsonProtocol:
         stampCache.get().put(ref.id(), (v, lastModified, sizeBytes))
         v
 
+  private def getOrElseUpdate(ref: VirtualFileRef, lastModified: Long, sizeBytes: Long)(
+      value: => Digest
+  ) =
+    Option(digestCache.get().getIfPresent(ref.id())) match
+      case Some((v, mod, i)) if lastModified == mod && sizeBytes == i => v
+      case _ =>
+        val v = value
+        digestCache.get().put(ref.id(), (v, lastModified, sizeBytes))
+        v
+
   /**
    * A string representation of HashedVirtualFileRef, delimited by `>`.
    */
@@ -76,4 +106,21 @@ trait CacheImplicits extends BasicCacheImplicits with BasicJsonProtocol:
               getOrElseUpdate(ref, lastModified, sizeBytes)(fallback)
           catch case e: NoSuchFileException => throw e
         case _ => fallback
+
+  def virtualFileRefToDigest(vf: VirtualFileRef)(converter: FileConverter): Digest =
+    vf match
+      case pbf: PathBasedFile =>
+        val path = pbf.toPath
+        val attrs = Files.readAttributes(path, classOf[BasicFileAttributes])
+        def fallback: Digest = Digest.sha256Hash(path)
+        if attrs.isDirectory then sys.error(s"$vf is a directory")
+        else
+          val lastModified = attrs.lastModifiedTime().toMillis()
+          val sizeBytes = attrs.size()
+          vf match
+            case h: HashedVirtualFileRef =>
+              getOrElseUpdate(vf, lastModified, sizeBytes)(Digest(h))
+            case _ =>
+              getOrElseUpdate(vf, lastModified, sizeBytes)(fallback)
+      case _ => Digest.sha256Hash(converter.toPath(vf))
 end CacheImplicits

util-cache/src/main/scala/sbt/util/Digest.scala

@@ -26,6 +26,7 @@ object Digest:
     def hashHexString: String = parse(d)._2
     def toBytes: Array[Byte] = parse(d)._4
     def sizeBytes: Long = parse(d)._3
+    private[sbt] def digestSize: Int = d.size
 
   given digestOrd(using ord: Ordering[String]): Ordering[Digest] with
     def compare(x: Digest, y: Digest) =