Survive bad types in pattern alternatives

Author: odersky

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

@@ -1549,7 +1549,13 @@ class Typer extends Namer
 
   def typedAlternative(tree: untpd.Alternative, pt: Type)(implicit ctx: Context): Alternative = {
     val nestedCtx = ctx.addMode(Mode.InPatternAlternative)
+    def ensureValueTypeOrWildcard(tree: Tree) =
+      if tree.tpe.isValueTypeOrWildcard then tree
+      else
+        assert(ctx.reporter.errorsReported)
+        tree.withType(defn.AnyType)
     val trees1 = tree.trees.mapconserve(typed(_, pt)(nestedCtx))
+      .map(ensureValueTypeOrWildcard)
     assignType(cpy.Alternative(tree)(trees1), trees1)
   }
 

tests/neg/i7817.scala

@@ -0,0 +1,8 @@
+trait Foo[A]
+class A {
+    def F[x : Foo]() = ???
+
+    Int match {
+        case Int | F => ()  // error
+    }
+}