Merge pull request scala#4288 from adriaanm/retronym-ticket/9041

SI-9041 Avoid unreported type error with overloading, implicits

Author: adriaanm

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -825,6 +825,16 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
               }
               orElse { _ =>
                 val resetTree = resetAttrs(original)
+                resetTree match {
+                  case treeInfo.Applied(fun, targs, args) =>
+                    if (fun.symbol != null && fun.symbol.isError)
+                      // SI-9041 Without this, we leak error symbols past the typer!
+                      // because the fallback typechecking notices the error-symbol,
+                      // refuses to re-attempt typechecking, and presumes that someone
+                      // else was responsible for issuing the related type error!
+                      fun.setSymbol(NoSymbol)
+                  case _ =>
+                }
                 debuglog(s"fallback on implicits: ${tree}/$resetTree")
                 val tree1 = typed(resetTree, mode)
                 // Q: `typed` already calls `pluginsTyped` and `adapt`. the only difference here is that

test/files/neg/t9041.check

@@ -0,0 +1,4 @@
+t9041.scala:11: error: could not find implicit value for parameter cellSetter: CellSetter[scala.math.BigDecimal]
+      def setCell(cell: Cell, data: math.BigDecimal) { cell.setCellValue(data) }
+                                                                        ^
+one error found

test/files/neg/t9041.scala

@@ -0,0 +1,17 @@
+// False negative test, requires overloading in Cell.
+
+trait Cell { def setCellValue(i: Int) = () ; def setCellValue(d: Double) = () }
+
+trait Nope {
+  def f = {
+    trait CellSetter[A] {
+      def setCell(cell: Cell, data: A): Unit
+    }
+    implicit val bigDecimalCellSetter = new CellSetter[math.BigDecimal]() {
+      def setCell(cell: Cell, data: math.BigDecimal) { cell.setCellValue(data) }
+    }
+    implicit class RichCell(cell: Cell) {
+      def setCellValue[A](data: A)(implicit cellSetter: CellSetter[A]) = cellSetter.setCell(cell, data)
+    }
+  }
+}