Use FileInfo.hash as caching style

* Switch from lastModified to hash caching style in order to produce
a machine-independent file stamping once sbt/sbt#6298 is solved.
* Add a system property "sbt-scalafix.uselastmodified" to force the
utilisation of the lastModified caching style. (Used in scripted
tests)

Author: github-sebastien-boulet

.gitignore

@@ -11,6 +11,7 @@ lib_managed/
 src_managed/
 project/boot/
 project/plugins/project/
+.bsp
 
 # Scala-IDE specific
 .scala_dependencies

build.sbt

@@ -92,5 +92,6 @@ sbtPlugin := true
 scriptedBufferLog := false
 scriptedLaunchOpts ++= Seq(
   "-Xmx2048M",
-  s"-Dplugin.version=${version.value}"
+  s"-Dplugin.version=${version.value}",
+  "-Dsbt-scalafix.uselastmodified=true" // the caching scripted relies on sbt-scalafix only checking file attributes, not content
 )

src/main/scala-sbt-0.13/sbt/internal/sbtscalafix/Caching.scala

@@ -11,6 +11,7 @@ import scala.util.DynamicVariable
 object Caching {
 
   val lastModifiedStyle = FilesInfo.lastModified
+  val hashStyle = FilesInfo.hash
 
   trait CacheKeysStamper
       extends InputCache[Seq[Arg.CacheKey]]

src/main/scala-sbt-1.0/sbt/internal/sbtscalafix/Caching.scala

@@ -9,6 +9,7 @@ import scala.util.DynamicVariable
 object Caching {
 
   val lastModifiedStyle = FileInfo.lastModified
+  val hashStyle = FileInfo.hash
 
   trait CacheKeysStamper
       extends JsonFormat[Seq[Arg.CacheKey]]

src/main/scala/scalafix/sbt/ScalafixPlugin.scala

@@ -170,6 +170,13 @@ object ScalafixPlugin extends AutoPlugin {
       Invisible
     )
 
+  private lazy val cachingStyle = {
+    val useLastModifiedCachingStyle =
+      sys.props.get("sbt-scalafix.uselastmodified") == Some("true")
+    if (useLastModifiedCachingStyle) lastModifiedStyle
+    else hashStyle
+  }
+
   override lazy val projectConfigurations: Seq[Configuration] =
     Seq(ScalafixConfig)
 
@@ -485,7 +492,8 @@ object ScalafixPlugin extends AutoPlugin {
                 case jar =>
                   Seq(jar)
               }
-            write(files.map(FileInfo.lastModified.apply))
+              .filter(_.isFile)
+            write(files.map(stampFile))
             write(customDependencies.map(_.toString))
           case Arg.Rules(rules) =>
             rules.foreach {
@@ -502,10 +510,10 @@ object ScalafixPlugin extends AutoPlugin {
           case Arg.Config(maybeFile) =>
             maybeFile match {
               case Some(path) =>
-                write(FileInfo.lastModified(path.toFile))
+                write(stampFile(path.toFile))
               case None =>
                 val defaultConfigFile = file(".scalafix.conf")
-                write(FileInfo.lastModified(defaultConfigFile))
+                write(stampFile(defaultConfigFile))
             }
           case Arg.ParsedArgs(args) =>
             val cacheKeys = args.filter {
@@ -528,6 +536,13 @@ object ScalafixPlugin extends AutoPlugin {
           case Arg.NoCache =>
             throw StampingImpossible
         }
+        def stampFile(file: File): Array[Byte] = {
+          // ensure the file exists and is not a directory
+          if (file.isFile)
+            Hash(file)
+          else
+            Array.empty[Byte]
+        }
       }
 
       def diffWithPreviousRuns[T](f: (Boolean, Set[File]) => T): T = {
@@ -542,7 +557,7 @@ object ScalafixPlugin extends AutoPlugin {
             )(doForStaleTargets: Set[File] => T): T =
               Tracked.diffInputs(
                 streams.cacheDirectory / "targets-by-rule" / rule,
-                lastModifiedStyle
+                cachingStyle
               )(targets) { changeReport: ChangeReport[File] =>
                 doForStaleTargets(changeReport.modified -- changeReport.removed)
               }
@@ -576,7 +591,9 @@ object ScalafixPlugin extends AutoPlugin {
           // in sbt 1.x, this is not necessary as any exception thrown during stamping is already silently ignored,
           // but having this here helps keeping code as common as possible
           // https://github.com/sbt/util/blob/v1.0.0/util-tracking/src/main/scala/sbt/util/Tracked.scala#L180
-          case _ @StampingImpossible => f(true, Set.empty)
+          case _ @StampingImpossible =>
+            println("StampingImpossible")
+            f(true, Set.empty)
         }.get
       }