Disable pattern matching in val syntax in sbt 0.13.7.

Fixes #1661 or at least works around it for now.

main/src/main/scala/sbt/internals/parser/SbtParser.scala

@@ -92,6 +92,21 @@ private[sbt] case class SbtParser(file: File, lines: Seq[String]) extends Parsed
         Seq(t)
     }
 
+    // Check No val (a,b) = foo *or* val a,b = foo as these are problematic to range positions and the WHOLE architecture.
+    def isBadValDef(t: Tree): Boolean =
+      t match {
+        case (x @ (toolbox.u.ValDef(_, _, _, _) | toolbox.u.DefDef(_, _, _, _, _, _))) =>
+          val content = modifiedContent.substring(x.pos.start, x.pos.end)
+          val prettyPrint = x.toString
+          (!(content contains "=") && (prettyPrint contains "="))
+        case _ => false
+      }
+    parsedTrees.filter(isBadValDef).foreach { badTree =>
+      // Issue errors
+      val positionLine = badTree.pos.line
+      throw new MessageOnlyException(s"""[$fileName]:$positionLine: Pattern matching in val statements is not supported""".stripMargin)
+    }
+
     val (imports, statements) = parsedTrees partition {
       case _: Import => true
       case _         => false

main/src/test/resources/error-format/4.sbt.txt

@@ -0,0 +1 @@
+val a,b = project

main/src/test/resources/old-format/21.sbt.txt

@@ -0,0 +1,5 @@
+val x = bar
+
+{
+  val a,b = project
+}

main/src/test/scala/sbt/internals/parser/SplitExpressionsFilesTest.scala

@@ -134,6 +134,7 @@ abstract class AbstractSplitExpressionsFilesTest(pathName: String) extends Speci
           println(s"In file: $fileName, old splitter failed. ${ex.toString}")
         case SplitterComparison(_, util.Failure(ex)) =>
           println(s"In file: $fileName, new splitter failed. ${ex.toString}")
+          ex.printStackTrace()
         case SplitterComparison(util.Success(resultOld), util.Success(resultNew)) =>
           if (resultOld == resultNew) {
             println(s"In file: $fileName, same results (imports, settings): $resultOld")

sbt/src/sbt-test/project/defs/build.sbt

@@ -1,3 +1,5 @@
+lazy val a,b = project
+
 def now = System.currentTimeMillis
 
 lazy val v = "1.0-" +
@@ -10,3 +12,5 @@ val descr = "Description"
 name := n
 
 version := v
+
+