Merge pull request #14849 from dotty-staging/fix-14842

Don't issue implicit errors if parameter has default value

Author: odersky

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

@@ -3539,14 +3539,10 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
             val namedArgs = wtp.paramNames.lazyZip(args).flatMap { (pname, arg) =>
               if (arg.tpe.isError) Nil else untpd.NamedArg(pname, untpd.TypedSplice(arg)) :: Nil
             }
-            tryEither {
-              val app = cpy.Apply(tree)(untpd.TypedSplice(tree), namedArgs)
-              if (wtp.isContextualMethod) app.setApplyKind(ApplyKind.Using)
-              typr.println(i"try with default implicit args $app")
-              typed(app, pt, locked)
-            } { (_, _) =>
-              issueErrors()
-            }
+            val app = cpy.Apply(tree)(untpd.TypedSplice(tree), namedArgs)
+            if (wtp.isContextualMethod) app.setApplyKind(ApplyKind.Using)
+            typr.println(i"try with default implicit args $app")
+            typed(app, pt, locked)
           else issueErrors()
         }
         else tree match {

tests/neg/i14772.check

@@ -4,12 +4,3 @@
   |       Overloaded or recursive method impl needs return type
   |
   | longer explanation available when compiling with `-explain`
--- Error: tests/neg/i14772.scala:8:12 ----------------------------------------------------------------------------------
-8 |    Expr(())  // error
-  |            ^
-  |         no given instance of type quoted.ToExpr[Unit] was found for parameter x$2 of method apply in object Expr.
-  |         I found:
-  |
-  |             quoted.ToExpr.ClassToExpr[T]
-  |
-  |         But given instance ClassToExpr in object ToExpr does not match type quoted.ToExpr[Unit].

tests/neg/i14772.scala

@@ -5,6 +5,6 @@ object A {
 
   def impl(a: Expr[Any])(using Quotes)/*: Expr[Any]*/ = {
     foo(a)    // error
-    Expr(())  // error
+    ???
   }
 }

tests/neg/i14842.check

@@ -0,0 +1,7 @@
+-- [E007] Type Mismatch Error: tests/neg/i14842.scala:11:35 ------------------------------------------------------------
+11 |  val x: Either[Int, Any] = node.as[Any] // error
+   |                            ^^^^^^^^^^^^
+   |                            Found:    Either[String, Any]
+   |                            Required: Either[Int, Any]
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg/i14842.scala

@@ -0,0 +1,12 @@
+class Dummy
+object Dummy:
+  val empty = new Dummy
+
+sealed trait Node:
+  def as[T](using d: Dummy = Dummy.empty): Either[String, T] = ???
+
+object Sample extends App {
+  val node: Node = ???
+
+  val x: Either[Int, Any] = node.as[Any] // error
+}