Merge pull request #2787 from dotty-staging/change-harden-ide

Harden IDE some more

Author: odersky

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

@@ -1305,8 +1305,10 @@ object Trees {
             this(this(x, arg), annot)
           case Thicket(ts) =>
             this(x, ts)
-          case _ if ctx.reporter.errorsReported =>
-            // in case of errors it may be that typed trees point to untyped ones.
+          case _ if ctx.mode.is(Mode.Interactive) =>
+            // In case of errors it may be that typed trees point to untyped ones.
+            // The IDE can still traverse inside such trees, either in the run where errors
+            // are reported, or in subsequent ones.
             x
         }
       }

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1538,7 +1538,9 @@ object Types {
               else recomputeMember(d) // symbol could have been overridden, recompute membership
             else {
               val newd = loadDenot
-              if (newd.exists) newd else d.staleSymbolError
+              if (newd.exists) newd
+              else if (ctx.mode.is(Mode.Interactive)) d
+              else d.staleSymbolError
             }
           case d =>
             if (d.validFor.runId != ctx.period.runId) loadDenot