Avoid spurious pure expression warning with ErrorTypes

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

@@ -284,8 +284,9 @@ object Types {
     /** Is this type produced as a repair for an error? */
     final def isError(implicit ctx: Context): Boolean = stripTypeVar.isInstanceOf[ErrorType]
 
-    /** Is some part of this type produced as a repair for an error? */
-    def isErroneous(implicit ctx: Context): Boolean = existsPart(_.isError, forceLazy = false)
+    /** Is some part of the widened version of this type produced as a repair for an error? */
+    def isErroneous(implicit ctx: Context): Boolean =
+      widen.existsPart(_.isError, forceLazy = false)
 
     /** Does the type carry an annotation that is an instance of `cls`? */
     @tailrec final def hasAnnotation(cls: ClassSymbol)(implicit ctx: Context): Boolean = stripTypeVar match {

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

@@ -367,7 +367,7 @@ object ProtoTypes {
     def isDropped: Boolean = state.toDrop
 
     override def isErroneous(implicit ctx: Context): Boolean =
-      state.typedArgs.tpes.exists(_.widen.isErroneous)
+      state.typedArgs.tpes.exists(_.isErroneous)
 
     override def toString: String = s"FunProto(${args mkString ","} => $resultType)"
 

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

@@ -735,7 +735,7 @@ class Typer extends Namer
       val ptDefined = isFullyDefined(pt, ForceDegree.none)
       if (ptDefined && !(avoidingType <:< pt)) avoidingType = pt
       val tree1 = ascribeType(tree, avoidingType)
-      assert(ptDefined || noLeaks(tree1) || tree1.tpe.widen.isErroneous,
+      assert(ptDefined || noLeaks(tree1) || tree1.tpe.isErroneous,
           // `ptDefined` needed because of special case of anonymous classes
           i"leak: ${escapingRefs(tree1, localSyms).toList}%, % in $tree1")
       tree1
@@ -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.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
 }