Reset typer state on issueErrors

Author: som-snytt

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

@@ -4406,6 +4406,12 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         /** Reports errors for arguments of `appTree` that have a `SearchFailureType`.
          */
         def issueErrors(fun: Tree, args: List[Tree], failureType: Type): Tree =
+          // If there are several arguments, some arguments might already
+          // have influenced the context, binding variables, but later ones
+          // might fail. In that case the constraint and instantiated variables
+          // need to be reset.
+          ctx.typerState.resetTo(saved)
+
           val errorType = failureType match
             case ai: AmbiguousImplicits => ai.asNested
             case tp => tp
@@ -4426,12 +4432,6 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         val args = implicitArgs(wtp.paramInfos, 0, pt)
         val failureType = propagatedFailure(args)
         if failureType.exists then
-          // If there are several arguments, some arguments might already
-          // have influenced the context, binding variables, but later ones
-          // might fail. In that case the constraint and instantiated variables
-          // need to be reset.
-          ctx.typerState.resetTo(saved)
-
           // If method has default params, fall back to regular application
           // where all inferred implicits are passed as named args.
           if hasDefaultParams && !failureType.isInstanceOf[AmbiguousImplicits] then

tests/pos/i23555.scala

@@ -0,0 +1,19 @@
+trait Behavior[A]
+
+object Behavior:
+  //implicit def mapBehavior[A: Behavior]: Behavior[List[A]] = new Behavior[List[A]] {}
+  given [A: Behavior] => Behavior[List[A]]
+
+object Model:
+  case class Foo(i: Int)
+  object Foo:
+    given Behavior[Foo] = new Behavior[Foo] {}
+    //implicit def dummy[A: Behavior](using s: String = "hello"): Option[A] = None
+    //implicit def dummy[A: Behavior](using s: String = "hello")(using DummyImplicit): Option[A] = None
+    given [A: Behavior] => (s: String = "hello") => Option[A] = None
+
+@main def Test =
+  import Model.Foo
+  //implicitly[Option[List[Foo]]]
+  //Foo.dummy[List[Foo]](using s = "bye")
+  summon[Option[List[Foo]]]