Scaladoc: new heuristic for extension method parameter extraction (#14810)

Before this changes, it wouldn't generate due to incorrect extension
parameters extractor functions.
It also implements new heuristic to distinct extensions and method
parameters based on definition position.
Also fixed type parameter coloring by adding new css rule, to match doc
style.
Based on #14321 , it should be
closed after this PR is merged.

Documentation for test `tests.extensionParams`

![image](https://user-images.githubusercontent.com/48657087/160649612-ac5b1883-0e28-4acb-9886-c9108b376665.png)

Author: Sporarum

Diff for: scaladoc-testcases/src/tests/extensionParams.scala

@@ -1,22 +1,54 @@
 package tests.extensionParams
 
+trait Animal
+
 extension [A](thiz: A)
-  def toTuple2[B](that: B): (A, B) = thiz -> that
+  def toTuple2[B](that: B): (A, B)
+   = thiz -> that
 
 extension [A](a: A)(using Int)
-  def f[B](b: B): (A, B) = ???
+  def f1[B](b: B): (A, B)
+  = ???
 
 extension [A](a: A)(using Int)
-  def ff(b: A): (A, A) = ???
+  def f2(b: A): (A, A)
+  = ???
 
 extension [A](a: A)(using Int)
-  def fff(using String)(b: A): (A, A) = ???
+  def f3(using String)(b: A): (A, A)
+  = ???
 
 extension (a: Char)(using Int)
-  def ffff(using String)(b: Int): Unit = ???
+  def f4(using String)(b: Int): Unit
+  = ???
 
 extension (a: Char)(using Int)
-  def fffff[B](using String)(b: B): Unit = ???
+  def f5[B](using String)(b: B): Unit
+  = ???
+
+extension [A <: List[Char]](a: Int)(using Int)
+  def f6[B](b: B): (A, B)
+  = ???
+
+extension [A <: List[Char]](using String)(using Unit)(a: A)(using Int)(using Number)
+  def f7[B, C](b: B)(c: C): (A, B)
+  = ???
+
+extension [A <: List[Char]](using String)(using Unit)(a: A)(using Int)(using Number)
+  def f8(b: Any)(c: Any): Any
+  = ???
+
+extension [A <: List[Char]](using String)(using Unit)(a: A)(using Int)(using Number)
+  def f9[B, C](using Int)(b: B)(c: C): (A, B)
+  = ???
+
+extension [A <: List[Char]](using String)(using Unit)(a: A)(using Int)(using Number)
+  def f10(using Int)(b: Any)(c: Any): Any
+   = ???
+
+  def f12(using Int)(b: A)(c: String): Number
+   = ???
 
-extension [A <: List[Char]](a: A)(using Int)
-  def ffffff[B](b: B): (A, B) = ???
+extension (using String)(using Unit)(a: Animal)(using Int)(using Number)
+  def f11(b: Any)(c: Any): Any
+  = ???

Diff for: scaladoc/resources/dotty_res/styles/scalastyle.css

@@ -962,8 +962,7 @@ footer .socials {
   color: var(--type);
 }
 
-.signature *[t="t"] {
-  /* Types with links */
+.signature *[t="t"] { /* Types with links */
   color: var(--type-link);
 }
 

Diff for: scaladoc/src/dotty/tools/scaladoc/renderers/MemberRenderer.scala

@@ -415,8 +415,8 @@ class MemberRenderer(signatureRenderer: SignatureRenderer)(using DocContext) ext
             .functionParameters(on.argsLists)
             .content
           val sig = typeSig ++ Signature(Plain(s"(${on.name}: ")) ++ on.signature ++ Signature(Plain(")")) ++ argsSig
-          MGroup(span(cls := "groupHeader")(sig.map(renderElement(_))), members.sortBy(_.name).toSeq, on.name)
-      }.toSeq
+          MGroup(span(cls := "groupHeader")(sig.map(renderElement(_))), members.sortBy(_.name).toSeq, on.name) -> on.position
+      }.toSeq.sortBy(_._2).map(_._1)
 
     div(cls := "membersList expand")(
     renderTabs(

Diff for: scaladoc/src/dotty/tools/scaladoc/renderers/Resources.scala

@@ -177,7 +177,15 @@ trait Resources(using ctx: DocContext) extends Locations, Writer:
 
     def extensionTarget(member: Member): String =
       member.kind match
-        case Kind.Extension(on, _) => flattenToText(on.signature)
+        case Kind.Extension(on, _) =>
+          val typeSig = SignatureBuilder()
+            .keyword("extension ")
+            .generics(on.typeParams)
+            .content
+          val argsSig = SignatureBuilder()
+            .functionParameters(on.argsLists)
+            .content
+          flattenToText(typeSig ++ argsSig)
         case _ => ""
 
     def docPartRenderPlain(d: DocPart): String =

Diff for: scaladoc/src/dotty/tools/scaladoc/tasty/ClassLikeSupport.scala

@@ -539,14 +539,13 @@ trait ClassLikeSupport:
         // Documenting method slightly different then its definition is withing the 'undefiend behaviour'.
         symbol.paramSymss.flatten.find(_.name == name).exists(_.flags.is(Flags.Implicit))
 
-    def handlePolyType(polyType: PolyType): MemberInfo =
-      MemberInfo(polyType.paramNames.zip(polyType.paramBounds).toMap, List.empty, polyType.resType)
+    def handlePolyType(memberInfo: MemberInfo, polyType: PolyType): MemberInfo =
+      MemberInfo(polyType.paramNames.zip(polyType.paramBounds).toMap, memberInfo.paramLists, polyType.resType)
 
     def handleMethodType(memberInfo: MemberInfo, methodType: MethodType): MemberInfo =
       val rawParams = methodType.paramNames.zip(methodType.paramTypes).toMap
       val (evidences, notEvidences) = rawParams.partition(e => isSyntheticEvidence(e._1))
 
-
       def findParamRefs(t: TypeRepr): Seq[ParamRef] = t match
         case paramRef: ParamRef => Seq(paramRef)
         case AppliedType(_, args) => args.flatMap(findParamRefs)
@@ -583,7 +582,7 @@ trait ClassLikeSupport:
       MemberInfo(memberInfo.genericTypes, memberInfo.paramLists, byNameType.underlying)
 
     def recursivelyCalculateMemberInfo(memberInfo: MemberInfo): MemberInfo = memberInfo.res match
-      case p: PolyType => recursivelyCalculateMemberInfo(handlePolyType(p))
+      case p: PolyType => recursivelyCalculateMemberInfo(handlePolyType(memberInfo, p))
       case m: MethodType => recursivelyCalculateMemberInfo(handleMethodType(memberInfo, m))
       case b: ByNameType => handleByNameType(memberInfo, b)
       case _ => memberInfo

Diff for: scaladoc/src/dotty/tools/scaladoc/tasty/SymOps.scala

@@ -147,28 +147,43 @@ object SymOps:
 
     def extendedSymbol: Option[reflect.ValDef] =
       import reflect.*
-      Option.when(sym.isExtensionMethod){
-        val termParamss = sym.tree.asInstanceOf[DefDef].termParamss
-        if sym.isLeftAssoc || termParamss.size == 1 then termParamss(0).params(0)
-        else termParamss(1).params(0)
+      if sym.isExtensionMethod then
+        sym.extendedTermParamLists.find(param => !param.isImplicit && !param.isGiven).flatMap(_.params.headOption)
+      else None
+
+    def splitExtensionParamList: (List[reflect.ParamClause], List[reflect.ParamClause]) =
+      import reflect.*
+
+      def getPositionStartOption(pos: Option[Position]): Option[Int] = pos.flatMap {
+        case dotty.tools.dotc.util.NoSourcePosition => None
+        case pos: Position => Some(pos.start)
       }
 
+      def comparePositionStarts(posA: Option[Position], posB: Option[Position]): Option[Boolean] =
+        for {
+          startA <- getPositionStartOption(posA)
+          startB <- getPositionStartOption(posB)
+        } yield startA < startB
+
+      sym.tree match
+        case tree: DefDef =>
+          tree.paramss.partition(_.params.headOption.flatMap(param =>
+            comparePositionStarts(param.symbol.pos, tree.symbol.pos)).getOrElse(false)
+          )
+        case _ => Nil -> Nil
+
     def extendedTypeParams: List[reflect.TypeDef] =
       import reflect.*
-      val method = sym.tree.asInstanceOf[DefDef]
-      method.leadingTypeParams
+      sym.tree match
+        case tree: DefDef =>
+          tree.leadingTypeParams
+        case _ => Nil
 
     def extendedTermParamLists: List[reflect.TermParamClause] =
       import reflect.*
-      if sym.nonExtensionLeadingTypeParams.nonEmpty then
-        sym.nonExtensionParamLists.takeWhile {
-          case _: TypeParamClause => false
-          case _ => true
-        }.collect {
-          case tpc: TermParamClause => tpc
-        }
-      else
-        List.empty
+      sym.splitExtensionParamList._1.collect {
+        case tpc: TermParamClause => tpc
+      }
 
     def nonExtensionTermParamLists: List[reflect.TermParamClause] =
       import reflect.*
@@ -185,14 +200,7 @@ object SymOps:
         }
 
     def nonExtensionParamLists: List[reflect.ParamClause] =
-      import reflect.*
-      val method = sym.tree.asInstanceOf[DefDef]
-      if sym.isExtensionMethod then
-        val params = method.paramss
-        val toDrop = if method.leadingTypeParams.nonEmpty then 2 else 1
-        if sym.isLeftAssoc || params.size == 1 then params.drop(toDrop)
-        else params.head :: params.tail.drop(toDrop)
-      else method.paramss
+      sym.splitExtensionParamList._2
 
     def nonExtensionLeadingTypeParams: List[reflect.TypeDef] =
       import reflect.*

Diff for: scaladoc/test/dotty/tools/scaladoc/signatures/TranslatableSignaturesTestCases.scala

@@ -41,6 +41,8 @@ class MergedPackageSignatures extends SignatureTest("mergedPackage", SignatureTe
 
 class ExtensionMethodSignature extends SignatureTest("extensionMethodSignatures", SignatureTest.all)
 
+class ExtensionMethodParamsSignature extends SignatureTest("extensionParams", SignatureTest.all)
+
 class ClassModifiers extends SignatureTest("classModifiers", SignatureTest.classlikeKinds)
 
 class EnumSignatures extends SignatureTest("enumSignatures", SignatureTest.all)