From d53f2e156570a75e6d719a04250ee423c60b555a Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Thu, 15 Jul 2021 14:02:29 +1000
Subject: [PATCH] Avoid re-using empty iterator in debug logging

---
 .../internal/inc/MemberRefInvalidator.scala   |  9 +++--
 .../test/scala/sbt/inc/binary/Scratch.scala   | 33 +++++++++++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 internal/zinc-persist/src/test/scala/sbt/inc/binary/Scratch.scala

diff --git a/internal/zinc-core/src/main/scala/sbt/internal/inc/MemberRefInvalidator.scala b/internal/zinc-core/src/main/scala/sbt/internal/inc/MemberRefInvalidator.scala
index 1189bd45fb..4ef2c242a0 100644
--- a/internal/zinc-core/src/main/scala/sbt/internal/inc/MemberRefInvalidator.scala
+++ b/internal/zinc-core/src/main/scala/sbt/internal/inc/MemberRefInvalidator.scala
@@ -135,14 +135,17 @@ private[inc] class MemberRefInvalidator(log: Logger, logRecompileOnMacro: Boolea
     private def filteredDependencies(dependent: Set[String]): Set[String] = {
       dependent.filter {
         case from if isScalaClass(from) =>
-          val affectedNames = usedNames(from).iterator.filter(modifiedNames.isModified)
-          if (affectedNames.isEmpty) {
+          val fromUsedNames = usedNames(from)
+          val affected = fromUsedNames.exists(modifiedNames.isModified)
+          if (!affected) {
             log.debug(
               s"None of the modified names appears in source file of $from. This dependency is not being considered for invalidation."
             )
             false
           } else {
-            log.debug(s"The following modified names cause invalidation of $from: $affectedNames")
+            def showUsedNames: String =
+              fromUsedNames.iterator.filter(modifiedNames.isModified).mkString("[", ", ", "]")
+            log.debug(s"The following modified names cause invalidation of $from: $showUsedNames")
             true
           }
         case from =>
diff --git a/internal/zinc-persist/src/test/scala/sbt/inc/binary/Scratch.scala b/internal/zinc-persist/src/test/scala/sbt/inc/binary/Scratch.scala
new file mode 100644
index 0000000000..35e18d9294
--- /dev/null
+++ b/internal/zinc-persist/src/test/scala/sbt/inc/binary/Scratch.scala
@@ -0,0 +1,33 @@
+package sbt.inc.binary
+
+object Scratch {
+  def timed[T](f: => T) = {
+    val start = System.nanoTime;
+    try f
+    finally {
+      println(((System.nanoTime - start) / 1000 / 1000) + " ms")
+    }
+  }
+  def main(args: Array[String]): Unit = {
+    for (i <- 1 to 32) {
+      println(
+        timed(
+          sbt.internal.inc.FileAnalysisStore
+            .binary(new java.io.File("/Users/jz/code/scala/target/compiler/zinc/inc_compile.zip"))
+            .get
+        )
+      )
+    }
+    timed(
+      for (i <- 1 to 32) {
+        println(
+          timed(
+            sbt.internal.inc.FileAnalysisStore
+              .binary(new java.io.File("/Users/jz/code/scala/target/compiler/zinc/inc_compile.zip"))
+              .get
+          )
+        )
+      }
+    )
+  }
+}