Provide signature help for unapply methods

Related to scalameta/metals#1687

Author: tgodzik

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

@@ -10,6 +10,7 @@ import util.Spans.Span
 import core.Types.{ErrorType, MethodType, PolyType}
 import reporting._
 
+import dotty.tools.dotc.core.Types.Type
 
 object Signatures {
 
@@ -48,31 +49,40 @@ object Signatures {
    */
   def callInfo(path: List[tpd.Tree], span: Span)(using Context): (Int, Int, List[SingleDenotation]) =
     path match {
+      case UnApply(fun, _, patterns) :: _ =>
+        callInfo(span, patterns, fun, 0)
       case Apply(fun, params) :: _ =>
         val alreadyAppliedCount = Signatures.countParams(fun)
-        val paramIndex = params.indexWhere(_.span.contains(span)) match {
-          case -1 => (params.length - 1 max 0) + alreadyAppliedCount
-          case n => n + alreadyAppliedCount
-        }
-
-        val (alternativeIndex, alternatives) = fun.tpe match {
-          case err: ErrorType =>
-            val (alternativeIndex, alternatives) = alternativesFromError(err, params)
-            (alternativeIndex, alternatives)
+        callInfo(span, params, fun, alreadyAppliedCount)
+      case _ =>
+        (0, 0, Nil)
+    }
 
-          case _ =>
-            val funSymbol = fun.symbol
-            val alternatives = funSymbol.owner.info.member(funSymbol.name).alternatives
-            val alternativeIndex = alternatives.map(_.symbol).indexOf(funSymbol) max 0
-            (alternativeIndex, alternatives)
-        }
+  def callInfo(
+    span: Span,
+    params: List[Tree[Type]], 
+    fun: Tree[Type], 
+    alreadyAppliedCount : Int
+  )(using Context): (Int, Int, List[SingleDenotation]) =
+    val paramIndex = params.indexWhere(_.span.contains(span)) match {
+      case -1 => (params.length - 1 max 0) + alreadyAppliedCount
+      case n => n + alreadyAppliedCount
+    }
 
-        (paramIndex, alternativeIndex, alternatives)
+    val (alternativeIndex, alternatives) = fun.tpe match {
+      case err: ErrorType =>
+        val (alternativeIndex, alternatives) = alternativesFromError(err, params)
+        (alternativeIndex, alternatives)
 
       case _ =>
-        (0, 0, Nil)
+        val funSymbol = fun.symbol
+        val alternatives = funSymbol.owner.info.member(funSymbol.name).alternatives
+        val alternativeIndex = alternatives.map(_.symbol).indexOf(funSymbol) max 0
+        (alternativeIndex, alternatives)
     }
 
+    (paramIndex, alternativeIndex, alternatives)
+
   def toSignature(denot: SingleDenotation)(using Context): Option[Signature] = {
     val symbol = denot.symbol
     val docComment = ParsedComment.docOf(symbol)

language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala

@@ -556,8 +556,7 @@ class DottyLanguageServer extends LanguageServer
 
     val pos = sourcePosition(driver, uri, params.getPosition)
     val trees = driver.openedTrees(uri)
-    val path = Interactive.pathTo(trees, pos).dropWhile(!_.isInstanceOf[Apply])
-
+    val path = Interactive.pathTo(trees, pos).dropWhile(t => !t.isInstanceOf[Apply] && !t.isInstanceOf[UnApply])
     val (paramN, callableN, alternatives) = Signatures.callInfo(path, pos.span)
     val signatureInfos = alternatives.flatMap(Signatures.toSignature)
 

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

@@ -361,4 +361,18 @@ class SignatureHelpTest {
           )), Some("Int"), Some("Buzzes a fizz up to bar"))
         ), None, 0)
   }
+  
+  @Test def unapplyMethod: Unit = {
+    code"""|object Main {
+           |  Option(1) match {
+           |    case Some(${m1}) =>
+           |  }
+           |}"""
+      .withSource
+      .signatureHelp(m1, List(
+        S("unapply[A]", Nil, List(List(
+          P("x$0", "Some[A]", None),
+          )), Some("Option[A]"), None)
+        ), None, 0)
+  }
 }