Backport of 26012,26013.

Author: Antonio Cunei

src/compiler/scala/tools/nsc/symtab/classfile/UnPickler.scala

@@ -50,15 +50,25 @@ abstract class UnPickler extends reflect.generic.UnPickler {
     def newLazyTypeRef(i: Int): LazyType = new LazyTypeRef(i)
     def newLazyTypeRefAndAlias(i: Int, j: Int): LazyType = new LazyTypeRefAndAlias(i, j)
 
+    /** Convert to a type error, that is printed gracefully instead of crashing.
+     *
+     *  Similar in intent to what SymbolLoader does (but here we don't have access to
+     *  error reporting, so we rely on the typechecker to report the error).
+     */
+    def toTypeError(e: MissingRequirementError) =
+      new TypeError(e.msg)
+
     /** A lazy type which when completed returns type at index `i`. */
     private class LazyTypeRef(i: Int) extends LazyType {
       private val definedAtRunId = currentRunId
       private val p = phase
-      override def complete(sym: Symbol) : Unit = {
+      override def complete(sym: Symbol) : Unit = try {
         val tp = at(i, readType)
         if (p != phase) atPhase(p) (sym setInfo tp)
         else sym setInfo tp
         if (currentRunId != definedAtRunId) sym.setInfo(adaptToNewRunMap(tp))
+      } catch {
+        case e: MissingRequirementError => throw toTypeError(e)
       }
       override def load(sym: Symbol) { complete(sym) }
     }
@@ -67,7 +77,7 @@ abstract class UnPickler extends reflect.generic.UnPickler {
      *  of completed symbol to symbol at index `j`.
      */
     private class LazyTypeRefAndAlias(i: Int, j: Int) extends LazyTypeRef(i) {
-      override def complete(sym: Symbol) {
+      override def complete(sym: Symbol) = try {
         super.complete(sym)
         var alias = at(j, readSymbol)
         if (alias hasFlag OVERLOADED) {
@@ -76,6 +86,8 @@ abstract class UnPickler extends reflect.generic.UnPickler {
           }
         }
         sym.asInstanceOf[TermSymbol].setAlias(alias)
+      } catch {
+        case e: MissingRequirementError => throw toTypeError(e)
       }
     }
   }