Merge pull request #3705 from dotty-staging/fix-#3703

Fix #3703: Various fixes to make printing more robust in face of errors

Author: odersky

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -113,7 +113,11 @@ object Trees {
      */
     def withType(tpe: Type)(implicit ctx: Context): ThisTree[Type] = {
       if (tpe.isInstanceOf[ErrorType])
-        assert(!Config.checkUnreportedErrors || ctx.reporter.errorsReported)
+        assert(!Config.checkUnreportedErrors ||
+               ctx.reporter.errorsReported ||
+               ctx.settings.YshowPrintErrors.value
+                 // under -Yshow-print-errors, errors might arise during printing, but they do not count as reported
+              )
       else if (Config.checkTreesConsistent)
         checkChildrenTyped(productIterator)
       withTypeUnchecked(tpe)

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -34,7 +34,7 @@ object Formatting {
           case NonFatal(ex)
           if !ctx.mode.is(Mode.PrintShowExceptions) &&
              !ctx.settings.YshowPrintErrors.value =>
-            s"[cannot display due to $ex, raw string = $toString]"
+            s"[cannot display due to $ex, raw string = ${arg.toString}]"
         }
       case _ => arg.toString
     }

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -196,7 +196,12 @@ class PlainPrinter(_ctx: Context) extends Printer {
           else toText(tp.origin)
         }
       case tp: LazyRef =>
-        "LazyRef(" ~ toTextGlobal(tp.ref) ~ ")" // TODO: only print this during debug mode?
+        def refTxt =
+          try toTextGlobal(tp.ref)
+          catch {
+            case ex: Throwable => Str("...")
+          }
+        "LazyRef(" ~ refTxt ~ ")"
       case _ =>
         tp.fallbackToText(this)
     }
@@ -217,7 +222,10 @@ class PlainPrinter(_ctx: Context) extends Printer {
 
   /** If -uniqid is set, the hashcode of the lambda type, after a # */
   protected def lambdaHash(pt: LambdaType): Text =
-    if (ctx.settings.uniqid.value) "#" + pt.hashCode else ""
+    if (ctx.settings.uniqid.value)
+      try "#" + pt.hashCode
+      catch { case ex: NullPointerException => "" }
+    else ""
 
   /** If -uniqid is set, the unique id of symbol, after a # */
   protected def idString(sym: Symbol): String =

tests/pos/i3703.scala

@@ -0,0 +1,11 @@
+package bar {
+  trait M[F[_]]
+  class S[XS[_] <: M[XS], A](val x: XS[A])
+  object S {
+    def apply[X[_] <: M[X], A](x: X[A]): S[X, A] = S[X, A](x)
+    def unapply[X[_] <: M[X], A](p: S[X, A]): S[X, A] = S(p.x)
+  }
+}
+
+
+