Fix #7808: Weaken an assertion in Typer

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2548,7 +2548,7 @@ class Typer extends Namer
     adapt(tree, pt, ctx.typerState.ownedVars)
 
   private def adapt1(tree: Tree, pt: Type, locked: TypeVars)(implicit ctx: Context): Tree = {
-    assert(pt.exists && !pt.isInstanceOf[ExprType])
+    assert(pt.exists && !pt.isInstanceOf[ExprType] || ctx.reporter.errorsReported)
     def methodStr = err.refStr(methPart(tree).tpe)
 
     def readapt(tree: Tree)(implicit ctx: Context) = adapt(tree, pt, locked)

tests/neg/i7808.scala

@@ -0,0 +1,10 @@
+object A {
+    {
+        val a: Int = 1
+        object a {  // error
+            this match {
+                case _ => ()
+            }
+        }
+    }
+}