Avoid spurious pure expression warning with ErrorTypes

Author: smarter

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

@@ -2897,7 +2897,8 @@ class Typer extends Namer
   }
 
   private def checkStatementPurity(tree: tpd.Tree)(original: untpd.Tree, exprOwner: Symbol)(implicit ctx: Context): Unit = {
-    if (!ctx.isAfterTyper && isPureExpr(tree) && !tree.tpe.isRef(defn.UnitClass) && !isSelfOrSuperConstrCall(tree))
+    if (!tree.tpe.widen.isErroneous && !ctx.isAfterTyper && isPureExpr(tree) &&
+        !tree.tpe.isRef(defn.UnitClass) && !isSelfOrSuperConstrCall(tree))
       ctx.warning(PureExpressionInStatementPosition(original, exprOwner), original.sourcePos)
   }
 }

tests/neg-custom-args/fatal-warnings/pureStatement.scala

@@ -25,4 +25,8 @@ object Test {
   2 // error: pure expression does nothing in statement position
 
   doSideEffects(1) // error: pure expression does nothing in statement position
+
+  val broken = new IDontExist("") // error // error
+  broken.foo // no extra error, and no pure expression warning
+  broken.foo() // same
 }