improvement: Don't fail on hashing, but use a random one

Previously, when hashing would fail the whole compilation would also fail and while this seems incredibly rare let's try to guard ourselves here.

Connected to #2053

backend/src/main/scala/sbt/internal/inc/bloop/BloopZincCompiler.scala

@@ -247,7 +247,7 @@ object BloopZincCompiler {
       skip: Boolean = false,
       incrementalCompilerOptions: IncOptions,
       extra: List[(String, String)]
-  ): Task[CompileConfiguration] = Task.now {
+  )(implicit logger: ObservedLogger[_]): Task[CompileConfiguration] = Task.now {
     // Remove directories from classpath hashes, we're only interested in jars
     val jarClasspathHashes = BloopLookup.filterOutDirsFromHashedClasspath(classpathHashes)
     val compileSetup = MiniSetup.of(
@@ -284,7 +284,7 @@ object BloopZincCompiler {
       earlyOutput = None,
       // deals with pipelining, not supported yet
       earlyAnalysisStore = None,
-      stamper = BloopStamps.initial
+      stamper = BloopStamps.initial(logger)
     )
   }
 }

backend/src/main/scala/sbt/internal/inc/bloop/internal/BloopIncremental.scala

@@ -48,7 +48,7 @@ object BloopIncremental {
       }
     }
 
-    val current = BloopStamps.initial
+    val current = BloopStamps.initial(log)
     val externalAPI = getExternalAPI(lookup)
     val previous = previous0 match { case a: Analysis => a }
     val previousRelations = previous.relations

backend/src/main/scala/sbt/internal/inc/bloop/internal/BloopStamps.scala

@@ -12,17 +12,35 @@ import xsbti.VirtualFileRef
 import xsbti.compile.FileHash
 import xsbti.compile.analysis.ReadStamps
 import xsbti.compile.analysis.Stamp
+import scala.util.control.NonFatal
+import sbt.util.Logger
+import sbt.internal.inc.FarmHash
 
 object BloopStamps {
   private val converter = PlainVirtualFileConverter.converter
 
-  private def underlying = Stamps.initial(
+  private def underlying(logger: Logger) = Stamps.initial(
     BloopStamps.forHash,
     // The hash is for the sources
     BloopStamps.forHash,
-    Stamper.forHashInRootPaths(converter)
+    libraryStamp(logger)
   )
-  def initial: ReadStamps = Stamps.timeWrapBinaryStamps(underlying, converter)
+
+  def libraryStamp(logger: Logger): VirtualFileRef => Stamp = { (file: VirtualFileRef) =>
+    {
+      val baseStamp = Stamper.forHashInRootPaths(converter)
+      try {
+        baseStamp(file)
+      } catch {
+        case NonFatal(e) =>
+          logger.error(s"Could not calculate hash for ${file.id} because of ${e.getMessage}")
+          FarmHash.fromLong(emptyHash.toLong)
+      }
+
+    }
+  }
+
+  def initial(logger: Logger): ReadStamps = Stamps.timeWrapBinaryStamps(underlying(logger), converter)
 
   private final val emptyHash = scala.util.Random.nextInt()
   private final val directoryHash = scala.util.Random.nextInt()