From bd2e02aeaa156acea5138df219e29eb9d53a9151 Mon Sep 17 00:00:00 2001
From: Eugene Yokota <eed3si9n@gmail.com>
Date: Wed, 8 Jun 2016 00:39:04 -0400
Subject: [PATCH] Inform the build user about macro recompilation

---
 .../src/main/scala/sbt/inc/Incremental.scala  |  6 ++++-
 .../scala/sbt/inc/MemberRefInvalidator.scala  | 25 ++++++++++++++-----
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/compile/inc/src/main/scala/sbt/inc/Incremental.scala b/compile/inc/src/main/scala/sbt/inc/Incremental.scala
index db2cff86e..83aca50f6 100644
--- a/compile/inc/src/main/scala/sbt/inc/Incremental.scala
+++ b/compile/inc/src/main/scala/sbt/inc/Incremental.scala
@@ -23,7 +23,11 @@ object Incremental {
   class PrefixingLogger(val prefix: String)(orig: Logger) extends Logger {
     def trace(t: => Throwable): Unit = orig.trace(t)
     def success(message: => String): Unit = orig.success(message)
-    def log(level: sbt.Level.Value, message: => String): Unit = orig.log(level, message.replaceAll("(?m)^", prefix))
+    def log(level: sbt.Level.Value, message: => String): Unit =
+      level match {
+        case Level.Debug => orig.log(level, message.replaceAll("(?m)^", prefix))
+        case _           => orig.log(level, message)
+      }
   }
 
   /**
diff --git a/compile/inc/src/main/scala/sbt/inc/MemberRefInvalidator.scala b/compile/inc/src/main/scala/sbt/inc/MemberRefInvalidator.scala
index 28ac92515..30d5e056b 100644
--- a/compile/inc/src/main/scala/sbt/inc/MemberRefInvalidator.scala
+++ b/compile/inc/src/main/scala/sbt/inc/MemberRefInvalidator.scala
@@ -53,7 +53,7 @@ import xsbt.api.APIUtil
 private[inc] class MemberRefInvalidator(log: Logger) {
   def get[T](memberRef: Relation[File, T], usedNames: Relation[File, String], apiChange: APIChange[_]): T => Set[File] = apiChange match {
     case _: APIChangeDueToMacroDefinition[_] =>
-      new InvalidateUnconditionally(memberRef)
+      new InvalidateDueToMacroDefinition(memberRef)
     case NamesChange(_, modifiedNames) if modifiedNames.implicitNames.nonEmpty =>
       new InvalidateUnconditionally(memberRef)
     case NamesChange(modifiedSrcFile, modifiedNames) =>
@@ -79,18 +79,31 @@ private[inc] class MemberRefInvalidator(log: Logger) {
     "MemberReferenceInvalidator.get should be called when name hashing is enabled " +
       "and in that case we shouldn't have SourceAPIChange as an api change."
 
+  private class InvalidateDueToMacroDefinition[T](memberRef: Relation[File, T]) extends (T => Set[File]) {
+    def apply(from: T): Set[File] = {
+      val invalidated = memberRef.reverse(from)
+      if (invalidated.nonEmpty) {
+        log.info(s"Because $from contains a macro definition, the following dependencies are invalidated unconditionally:\n" +
+          formatInvalidated(invalidated))
+      }
+      invalidated
+    }
+  }
+
   private class InvalidateUnconditionally[T](memberRef: Relation[File, T]) extends (T => Set[File]) {
     def apply(from: T): Set[File] = {
       val invalidated = memberRef.reverse(from)
-      if (invalidated.nonEmpty)
+      if (invalidated.nonEmpty) {
         log.debug(s"The following member ref dependencies of $from are invalidated:\n" +
           formatInvalidated(invalidated))
+      }
       invalidated
     }
-    private def formatInvalidated(invalidated: Set[File]): String = {
-      val sortedFiles = invalidated.toSeq.sortBy(_.getAbsolutePath)
-      sortedFiles.map(file => "\t" + file).mkString("\n")
-    }
+  }
+
+  private def formatInvalidated(invalidated: Set[File]): String = {
+    val sortedFiles = invalidated.toSeq.sortBy(_.getAbsolutePath)
+    sortedFiles.map(file => "\t" + file).mkString("\n")
   }
 
   private class NameHashFilteredInvalidator[T](