Fix false positive for named args (and other)

- Fix the non-miniphase traverser
- Update test cases

Author: PaulCoral

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -197,12 +197,15 @@ class CheckUnused extends MiniPhase:
         case t:tpd.ValDef =>
           prepareForValDef(t)
           traverseChildren(tree)(using newCtx)
+          transformValDef(t)
         case t:tpd.DefDef =>
           prepareForDefDef(t)
           traverseChildren(tree)(using newCtx)
+          transformDefDef(t)
         case t:tpd.TypeDef =>
           prepareForTypeDef(t)
           traverseChildren(tree)(using newCtx)
+          transformTypeDef(t)
         case t: tpd.Bind =>
           prepareForBind(t)
           traverseChildren(tree)(using newCtx)
@@ -325,7 +328,7 @@ object CheckUnused:
      * The optional name will be used to target the right import
      * as the same element can be imported with different renaming
      */
-    def registerUsed(sym: Symbol, name: Option[Name])(using Context): Unit =
+    def registerUsed(sym: Symbol, name: Option[Name])(using Context): Unit =      
       if !isConstructorOfSynth(sym) && !doNotRegister(sym) then
         if sym.isConstructor && sym.exists then
           registerUsed(sym.owner, None) // constructor are "implicitly" imported with the class
@@ -365,7 +368,7 @@ object CheckUnused:
             implicitParamInScope += memDef
           else
             explicitParamInScope += memDef
-        else if currScopeType.top == ScopeType.Local then
+        else if currScopeType.top == ScopeType.Local then 
           localDefInScope += memDef
         else if currScopeType.top == ScopeType.Template && memDef.symbol.is(Private, butNot = SelfName) then
           privateDefInScope += memDef

tests/neg-custom-args/fatal-warnings/i15503i.scala

@@ -73,4 +73,14 @@ package foo.test.companionprivate:
 
   object A:
     private def b = c // OK
-    def c = List(1,2,3) // OK
+    def c = List(1,2,3) // OK
+
+package foo.test.i16678:
+  def foo(func: Int => String, value: Int): String = func(value) // OK
+
+  def run = 
+    println(foo(number => number.toString, value = 5)) // OK
+    println(foo(number => "<number>", value = 5)) // error
+    println(foo(func = number => "<number>", value = 5)) // error
+    println(foo(func = number => number.toString, value = 5)) // OK
+    println(foo(func = _.toString, value = 5)) // OK