IDE: fix signature help for Java and Scala 2 methods

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -355,12 +355,18 @@ class Definitions {
     lazy val Predef_undefinedR: TermRef = ScalaPredefModule.requiredMethodRef(nme.???)
     def Predef_undefined(implicit ctx: Context): Symbol = Predef_undefinedR.symbol
 
-  def SubTypeClass(implicit ctx: Context): Symbol =
+  def SubTypeClass(implicit ctx: Context): ClassSymbol =
     if (isNewCollections)
       ctx.requiredClass("scala.<:<")
     else
       ScalaPredefModule.requiredClass("<:<")
 
+  def DummyImplicitClass(implicit ctx: Context): ClassSymbol =
+    if (isNewCollections)
+      ctx.requiredClass("scala.DummyImplicit")
+    else
+      ScalaPredefModule.requiredClass("DummyImplicit")
+
   lazy val ScalaRuntimeModuleRef: TermRef = ctx.requiredModuleRef("scala.runtime.ScalaRunTime")
   def ScalaRuntimeModule(implicit ctx: Context): Symbol = ScalaRuntimeModuleRef.symbol
   def ScalaRuntimeClass(implicit ctx: Context): ClassSymbol = ScalaRuntimeModule.moduleClass.asClass

compiler/src/dotty/tools/dotc/util/Signatures.scala

@@ -80,27 +80,36 @@ object Signatures {
     val symbol = denot.symbol
     val docComment = ParsedComment.docOf(symbol)
     val classTree = symbol.topLevelClass.asClass.rootTree
-    val isImplicit: TermName => Boolean = tpd.defPath(symbol, classTree).lastOption match {
-      case Some(DefDef(_, _, paramss, _, _)) =>
-        val flatParams = paramss.flatten
-        name => flatParams.find(_.name == name).map(_.symbol.is(Implicit)).getOrElse(false)
-      case _ =>
-        _ => false
+
+    def toParamss(tp: MethodType)(implicit ctx: Context): List[List[Param]] = {
+      val rest = tp.resType match {
+        case res: MethodType =>
+          // Hide parameter lists consisting only of CanBuildFrom or DummyImplicit,
+          // we can remove the CanBuildFrom special-case once we switch to the 2.13 standard library.
+          if (res.resultType.isParameterless &&
+              res.isImplicitMethod &&
+              res.paramInfos.forall(info =>
+                info.classSymbol.fullName.toString == "scala.collection.generic.CanBuildFrom" ||
+                info.classSymbol.derivesFrom(ctx.definitions.DummyImplicitClass)))
+            Nil
+          else
+            toParamss(res)
+        case _ =>
+          Nil
+      }
+      val params = tp.paramNames.zip(tp.paramInfos).map { case (name, info) =>
+        Signatures.Param(name.show,
+          info.widenTermRefExpr.show,
+          docComment.flatMap(_.paramDoc(name)),
+          isImplicit = tp.isImplicitMethod)
+      }
+
+      params :: rest
     }
 
     denot.info.stripPoly match {
       case tpe: MethodType =>
-        val infos = {
-          tpe.paramInfoss.zip(tpe.paramNamess).map { case (infos, names) =>
-            infos.zip(names).map { case (info, name) =>
-              Signatures.Param(name.show,
-                               info.widenTermRefExpr.show,
-                               docComment.flatMap(_.paramDoc(name)),
-                               isImplicit = isImplicit(name))
-            }
-          }
-        }
-
+        val paramss = toParamss(tpe)
         val typeParams = denot.info match {
           case poly: PolyType =>
             poly.paramNames.zip(poly.paramInfos).map { case (x, y) => x.show + y.show }
@@ -115,7 +124,7 @@ object Signatures {
         val signature =
           Signatures.Signature(name,
                                typeParams,
-                               infos,
+                               paramss,
                                returnType,
                                docComment.map(_.mainDoc))
 

language-server/test/dotty/tools/languageserver/SignatureHelpTest.scala

@@ -8,6 +8,56 @@ import dotty.tools.dotc.util.Signatures.{Param => P, Signature => S}
 
 class SignatureHelpTest {
 
+  @Test def fromJava: Unit = {
+    val signature =
+      S("codePointAt", Nil, List(List(P("x$0", "Int"))), Some("Int"))
+    code"""object O {
+             "hello".codePointAt($m1)
+           }""".withSource
+      .signatureHelp(m1, List(signature), Some(0), 0)
+  }
+
+  @Test def fromScala2: Unit = {
+    val applySig =
+      S("apply[A]", Nil, List(List(P("xs", "A*"))), Some("List[A]"))
+    val mapSig =
+      S("map[B, That]", Nil, List(List(P("f", "A => B"))), Some("That"))
+    code"""object O {
+             List($m1)
+             List(1, 2, 3).map($m2)
+           }""".withSource
+      .signatureHelp(m1, List(applySig), Some(0), 0)
+      .signatureHelp(m2, List(mapSig), Some(0), 0)
+  }
+
+  /** Implicit parameter lists consisting solely of DummyImplicits are hidden. */
+  @Test def hiddenDummyParams: Unit = {
+    val foo1Sig =
+      S("foo1", Nil, List(List(P("param0", "Int"))), Some("Int"))
+    val foo2Sig =
+      S("foo2", Nil, List(List(P("param0", "Int"))), Some("Int"))
+    val foo3Sig =
+      S("foo3", Nil, List(List(P("param0", "Int")),
+        List(P("dummy", "DummyImplicit"))), Some("Int"))
+    val foo4Sig =
+      S("foo4", Nil, List(List(P("param0", "Int")),
+        List(P("x", "Int", isImplicit = true), P("dummy", "DummyImplicit", isImplicit = true))), Some("Int"))
+    code"""object O {
+             def foo1(param0: Int)(implicit dummy: DummyImplicit): Int = ???
+             def foo2(param0: Int)(implicit dummy1: DummyImplicit, dummy2: DummyImplicit): Int = ???
+             def foo3(param0: Int)(dummy: DummyImplicit): Int = ???
+             def foo4(param0: Int)(implicit x: Int, dummy: DummyImplicit): Int = ???
+             foo1($m1)
+             foo2($m2)
+             foo3($m3)
+             foo4($m4)
+           }""".withSource
+      .signatureHelp(m1, List(foo1Sig), Some(0), 0)
+      .signatureHelp(m2, List(foo2Sig), Some(0), 0)
+      .signatureHelp(m3, List(foo3Sig), Some(0), 0)
+      .signatureHelp(m4, List(foo4Sig), Some(0), 0)
+  }
+
   @Test def singleParam: Unit = {
     val signature =
       S("foo", Nil, List(List(P("param0", "Int"))), Some("Int"))