bugfix: Named args completions with default values (#18633)

connected to scalameta/metals#5657

Author: tgodzik

presentation-compiler/src/main/dotty/tools/pc/completions/NamedArgCompletions.scala

@@ -237,15 +237,24 @@ object NamedArgCompletions:
         .getOrElse(baseArgs)
         .filterNot(isUselessLiteral)
 
+      @tailrec
+      def isDefaultArg(t: Tree): Boolean = t match
+        // default args
+        case Ident(name) => name.is(DefaultGetterName)
+        // default args for methods defined in object
+        case Select(_, name) =>
+          name.is(DefaultGetterName)
+        // default args in not-first parameter list
+        // eg. def m(fst: Int)(snd: Int)(arg1: Int, arg2: Int = 123) = ???
+        case Apply(fun, _) => isDefaultArg(fun)
+        case _ => false
+
       val isNamed: Set[Name] = args.iterator
         .zip(baseParams.iterator)
         // filter out synthesized args and default arg getters
         .filterNot {
           case (arg, _) if arg.symbol.denot.is(Flags.Synthetic) => true
-          case (Ident(name), _) => name.is(DefaultGetterName) // default args
-          case (Select(Ident(_), name), _) =>
-            name.is(DefaultGetterName) // default args for apply method
-          case _ => false
+          case (arg, _) => isDefaultArg(arg)
         }
         .map {
           case (NamedArg(name, _), _) => name

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionArgSuite.scala

@@ -238,6 +238,111 @@ class CompletionArgSuite extends BaseCompletionSuite:
       ""
     )
 
+  @Test def `default-args` =
+    check(
+      s"""|object Main {
+          |  def foo() = {
+          |    def deployment(
+          |      fst: Option[String],
+          |      snd: Int = 1,
+          |    ): Option[Int] = ???
+          |    val abc = deployment(@@)
+          |  }
+          |}
+          |""".stripMargin,
+      """|fst = : Option[String]
+         |snd = : Int
+         |""".stripMargin,
+      topLines = Some(2),
+    )
+  @Test def `default-args2` =
+    check(
+      s"""|object Main {
+          |  def deployment(
+          |    fst: Option[String],
+          |    snd: Int = 1,
+          |  ): Option[Int] = ???
+          |  val abc = deployment(@@)
+          |}
+          |""".stripMargin,
+      """|fst = : Option[String]
+         |snd = : Int
+         |""".stripMargin,
+      topLines = Some(2),
+    )
+
+  @Test def `default-args3` =
+    check(
+      s"""|object Main {
+          |  def deployment(str: String)(
+          |    fst: Option[String],
+          |    snd: Int = 1,
+          |  ): Option[Int] = ???
+          |  val abc = deployment("str")(
+          |    @@
+          |  )
+          |}
+          |""".stripMargin,
+      """|fst = : Option[String]
+         |snd = : Int
+         |""".stripMargin,
+      topLines = Some(2),
+    )
+
+  @Test def `default-args4` =
+    check(
+      s"""|object Main {
+          |  def deployment(str: String)(opt: Option[Int])(
+          |    fst: Option[String],
+          |    snd: Int = 1,
+          |  ): Option[Int] = ???
+          |  val abc = deployment("str")(None)(
+          |    @@
+          |  )
+          |}
+          |""".stripMargin,
+      """|fst = : Option[String]
+         |snd = : Int
+         |""".stripMargin,
+      topLines = Some(2),
+    )
+
+  @Test def `default-args5` =
+    check(
+      s"""|object Main {
+          |  def deployment(str: String)(opt: Option[Int] = None)(
+          |    fst: Option[String],
+          |    snd: Int = 1,
+          |  ): Option[Int] = ???
+          |  val abc = deployment("str")(
+          |    @@
+          |  )
+          |}
+          |""".stripMargin,
+      """|opt = : Option[Int]
+         |""".stripMargin,
+      topLines = Some(1),
+    )
+
+  @Test def `default-args6` =
+    check(
+      s"""|object Main {
+          |  def deployment(using str: String)(
+          |    fst: Option[String],
+          |    snd: Int = 1,
+          |  ): Option[Int] = ???
+          |  val abc = deployment(using "str")(
+          |    @@
+          |  )
+          |}
+          |""".stripMargin,
+      """|fst = : Option[String]
+         |snd = : Int
+         |""".stripMargin,
+      topLines = Some(2),
+    )
+
+
   // @Test def `explicit-dollar` =
   // checkSnippet( // see: https://github.com/scalameta/metals/issues/2400
   //   """