Allow FileInfo for non-existent files with the new timestamps

FileInfo is used to wrap information like last modified time on
files that may or may not exist. Arguably, that does not make
much sense: the non-existent files should not lead to modification
file information, hashes, and a persistent serialized version of
the resulting meaningless information. However, considering that
the FileInfo information is serialized and saved, it is necessary
to preserve compatibility at this stage. Therefore the modification
time is explicitly set to zero for those files that do not exist
when each FileInfo is built.

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

@@ -4,6 +4,7 @@
 package sbt.util
 
 import java.io.File
+import java.io.FileNotFoundException
 import scala.util.control.NonFatal
 import sbt.io.Hash
 import sjsonnew.{ Builder, JsonFormat, Unbuilder, deserializationError }
@@ -50,6 +51,15 @@ object FilesInfo {
 }
 
 object FileInfo {
+
+  def getModifiedTimeOrZero(file: File) = { // returns 0L if file does not exist
+    try {
+      getModifiedTime(file)
+    } catch {
+      case _: FileNotFoundException => 0L
+    }
+  }
+
   sealed trait Style {
     type F <: FileInfo
 
@@ -89,7 +99,7 @@ object FileInfo {
     }
 
     implicit def apply(file: File): HashModifiedFileInfo =
-      FileHashModified(file.getAbsoluteFile, Hash(file).toList, getModifiedTime(file))
+      FileHashModified(file.getAbsoluteFile, Hash(file).toList, getModifiedTimeOrZero(file))
   }
 
   object hash extends Style {
@@ -146,7 +156,7 @@ object FileInfo {
     }
 
     implicit def apply(file: File): ModifiedFileInfo =
-      FileModified(file.getAbsoluteFile, getModifiedTime(file))
+      FileModified(file.getAbsoluteFile, getModifiedTimeOrZero(file))
   }
 
   object exists extends Style {