Backport "Draft: additional completions for using clause" to 3.7.4 (#24027)

Backports #23647 to the 3.7.4.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

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

@@ -201,7 +201,7 @@ class Completions(
     )
   end isAbstractType
 
-  private def findSuffix(symbol: Symbol): CompletionAffix =
+  private def findSuffix(symbol: Symbol, adjustedPath: List[untpd.Tree]): CompletionAffix =
     CompletionAffix.empty
       .chain { suffix => // for [] suffix
         if shouldAddSuffix && symbol.info.typeParams.nonEmpty then
@@ -217,7 +217,6 @@ class Completions(
                   suffix.withNewPrefix(Affix(PrefixKind.Using))
                 case _ => suffix
             case _ => suffix
-
       }
       .chain { suffix => // for () suffix
         if shouldAddSuffix && symbol.is(Flags.Method) then
@@ -290,7 +289,7 @@ class Completions(
       val existsApply = extraMethodDenots.exists(_.symbol.name == nme.apply)
 
       extraMethodDenots.map { methodDenot =>
-        val suffix = findSuffix(methodDenot.symbol)
+        val suffix = findSuffix(methodDenot.symbol, adjustedPath)
         val affix = if methodDenot.symbol.isConstructor && existsApply then
           adjustedPath match
             case (select @ Select(qual, _)) :: _ =>
@@ -312,7 +311,7 @@ class Completions(
 
     if skipOriginalDenot then extraCompletionValues
     else
-      val suffix = findSuffix(denot.symbol)
+      val suffix = findSuffix(denot.symbol, adjustedPath)
       val name = undoBacktick(label)
       val denotCompletionValue = toCompletionValue(name, denot, suffix)
       denotCompletionValue :: extraCompletionValues

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

@@ -238,6 +238,65 @@ class CompletionArgSuite extends BaseCompletionSuite:
       ""
     )
 
+  @Test def `using` =
+    checkEdit(
+      s"""|def hello(using String): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  hello(st@@)
+          |""".stripMargin,
+          s"""|def hello(using String): Unit = ???
+              |@main def main1(): Unit =
+              |  val str = "hello"
+              |  hello(using str)
+              |""".stripMargin,
+          assertSingleItem = false)
+
+  @Test def `using2` =
+    checkEdit(
+      s"""|def hello(using String): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  hello(using st@@)
+          |""".stripMargin,
+      s"""|def hello(using String): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  hello(using str)
+          |""".stripMargin,
+          assertSingleItem = false)
+
+  @Test def `using3` =
+    checkEdit(
+      s"""|def hello(using String, Int): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  val int = 4
+          |  hello(str, in@@)
+          |""".stripMargin,
+      s"""|def hello(using String, Int): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  val int = 4
+          |  hello(str, int)
+          |""".stripMargin,
+          assertSingleItem = false)
+
+  @Test def `using4` =
+    checkEdit(
+      s"""|def hello(name: String)(using String): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  hello("name")(str@@)
+          |""".stripMargin,
+      s"""|def hello(name: String)(using String): Unit = ???
+          |@main def main1(): Unit =
+          |  val str = "hello"
+          |  hello("name")(using str)
+          |""".stripMargin,
+          assertSingleItem = false
+          )
+
   @Test def `default-args` =
     check(
       s"""|object Main {