Improve symbol order in completions provided by the presentation compiler

Extension methods that are not in the same file are placed after all Product methods and even after extension methods like "ensuring". This PR penalizes the following methods, so that they are no longer at the top of the suggestions:
- scala.Product.*
- scala.Equals.*
- scala.Predef.ArrowAssoc.*
- scala.Predef.Ensuring.*
- scala.Predef.StringFormat.*
- scala.Predef.nn
- scala.Predef.runtimeChecked

Resolves scalameta/metals#7642

Author: Perl99

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

@@ -766,6 +766,13 @@ class Completions(
     ).flatMap(_.alternatives.map(_.symbol)).toSet
   )
 
+  private lazy val EqualsClass: ClassSymbol = requiredClass("scala.Equals")
+  private lazy val ArrowAssocClass: ClassSymbol = requiredClass("scala.Predef.ArrowAssoc")
+  private lazy val EnsuringClass: ClassSymbol = requiredClass("scala.Predef.Ensuring")
+  private lazy val StringFormatClass: ClassSymbol = requiredClass("scala.Predef.StringFormat")
+  private lazy val nnMethod: Symbol = defn.ScalaPredefModule.requiredMethod("nn")
+  private lazy val runtimeCheckedMethod: Symbol = defn.ScalaPredefModule.requiredMethod("runtimeChecked")
+
   private def isNotLocalForwardReference(sym: Symbol)(using Context): Boolean =
     !sym.isLocalToBlock ||
       !sym.srcPos.isAfter(completionPos.originalCursorPosition) ||
@@ -784,6 +791,17 @@ class Completions(
       (sym.isField && !isJavaClass && !isModuleOrClass) || sym.getter != NoSymbol
     catch case _ => false
 
+    def isInheritedFromScalaLibrary(sym: Symbol) =
+      sym.owner == defn.AnyClass || 
+        sym.owner == defn.ObjectClass ||
+        sym.owner == defn.ProductClass ||
+        sym.owner == EqualsClass ||
+        sym.owner == ArrowAssocClass ||
+        sym.owner == EnsuringClass ||
+        sym.owner == StringFormatClass ||
+        sym == nnMethod ||
+        sym == runtimeCheckedMethod
+
     def symbolRelevance(sym: Symbol): Int =
       var relevance = 0
       // symbols defined in this file are more relevant
@@ -801,7 +819,7 @@ class Completions(
         case _ =>
 
       // symbols whose owner is a base class are less relevant
-      if sym.owner == defn.AnyClass || sym.owner == defn.ObjectClass
+      if isInheritedFromScalaLibrary(sym)
       then relevance |= IsInheritedBaseMethod
       // symbols not provided via an implicit are more relevant
       if sym.is(Implicit) ||
@@ -813,7 +831,7 @@ class Completions(
       // accessors of case class members are more relevant
       if !sym.is(CaseAccessor) then relevance |= IsNotCaseAccessor
       // public symbols are more relevant
-      if !sym.isPublic then relevance |= IsNotCaseAccessor
+      if !sym.isPublic then relevance |= IsNotPublic
       // synthetic symbols are less relevant (e.g. `copy` on case classes)
       if sym.is(Synthetic) && !sym.isAllOf(EnumCase) then
         relevance |= IsSynthetic

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

@@ -437,3 +437,44 @@ class CompletionExtensionSuite extends BaseCompletionSuite:
          |""".stripMargin,
       assertSingleItem = false
     )
+
+  @Test def `extension-for-case-class` =
+    check(
+      """|case class Bar():
+         |  def baz(): Unit = ???
+         |
+         |object Bar:
+         |  extension (f: Bar)
+         |    def qux: Unit = ???
+         |
+         |object Main:
+         |  val _ = Bar().@@
+         |""".stripMargin,
+      """|baz(): Unit
+         |copy(): Bar
+         |qux: Unit
+         |asInstanceOf[X0]: X0
+         |canEqual(that: Any): Boolean
+         |equals(x$0: Any): Boolean
+         |getClass[X0 >: Bar](): Class[? <: X0]
+         |hashCode(): Int
+         |isInstanceOf[X0]: Boolean
+         |productArity: Int
+         |productElement(n: Int): Any
+         |productElementName(n: Int): String
+         |productElementNames: Iterator[String]
+         |productIterator: Iterator[Any]
+         |productPrefix: String
+         |synchronized[X0](x$0: X0): X0
+         |toString(): String
+         |->[B](y: B): (Bar, B)
+         |ensuring(cond: Boolean): Bar
+         |ensuring(cond: Bar => Boolean): Bar
+         |ensuring(cond: Boolean, msg: => Any): Bar
+         |ensuring(cond: Bar => Boolean, msg: => Any): Bar
+         |nn: `?1`.type
+         |runtimeChecked: `?2`.type
+         |formatted(fmtstr: String): String
+         |→[B](y: B): (Bar, B)
+         | """.stripMargin
+    )

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

@@ -109,18 +109,9 @@ class CompletionSuite extends BaseCompletionSuite:
          |tabulate[A](n: Int)(f: Int => A): List[A]
          |unapplySeq[A](x: List[A] @uncheckedVariance): UnapplySeqWrapper[A]
          |unfold[A, S](init: S)(f: S => Option[(A, S)]): List[A]
-         |->[B](y: B): (List.type, B)
-         |ensuring(cond: Boolean): List.type
-         |ensuring(cond: List.type => Boolean): List.type
-         |ensuring(cond: Boolean, msg: => Any): List.type
-         |ensuring(cond: List.type => Boolean, msg: => Any): List.type
          |fromSpecific(from: Any)(it: IterableOnce[Nothing]): List[Nothing]
          |fromSpecific(it: IterableOnce[Nothing]): List[Nothing]
-         |nn: List.type
-         |runtimeChecked scala.collection.immutable
          |toFactory(from: Any): Factory[Nothing, List[Nothing]]
-         |formatted(fmtstr: String): String
-         |→[B](y: B): (List.type, B)
          |iterableFactory[A]: Factory[A, List[A]]
          |asInstanceOf[X0]: X0
          |equals(x$0: Any): Boolean
@@ -129,6 +120,15 @@ class CompletionSuite extends BaseCompletionSuite:
          |isInstanceOf[X0]: Boolean
          |synchronized[X0](x$0: X0): X0
          |toString(): String
+         |->[B](y: B): (List.type, B)
+         |ensuring(cond: Boolean): List.type
+         |ensuring(cond: List.type => Boolean): List.type
+         |ensuring(cond: Boolean, msg: => Any): List.type
+         |ensuring(cond: List.type => Boolean, msg: => Any): List.type
+         |nn: List.type
+         |runtimeChecked scala.collection.immutable
+         |formatted(fmtstr: String): String
+         |→[B](y: B): (List.type, B)
          |""".stripMargin
     )