Fix missing semantic tokens for named tuple fields

Author: zielinsky

presentation-compiler/src/main/dotty/tools/pc/PcCollector.scala

@@ -14,6 +14,7 @@ import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.ast.untpd
 import dotty.tools.dotc.ast.untpd.ExtMethods
 import dotty.tools.dotc.ast.untpd.ImportSelector
+import dotty.tools.dotc.core.Constants.Constant
 import dotty.tools.dotc.core.Contexts.*
 import dotty.tools.dotc.core.Flags
 import dotty.tools.dotc.core.NameOps.*
@@ -183,6 +184,41 @@ trait PcCollector[T]:
             traverser(set, tree)
           }
 
+        /** Named tuple field access such as:
+         *  ```
+         *  val x: (name: String) = ???
+         *  x.<<name>>
+         *  ```
+         *  Named tuple selections are desugared to `NamedTuple.apply[N, V](qual)(idx)`,
+         */
+        case app @ Apply(
+              Apply(TypeApply(fun, List(t1, t2)), List(qual)),
+              List(Literal(Constant(i: Int)))
+            )
+            if fun.symbol.exists && fun.symbol.name == nme.apply
+              && fun.symbol.owner.exists
+              && fun.symbol.owner == defn.NamedTupleModule.moduleClass
+              && app.span.isCorrect =>
+          def getIndex(t: Tree): Option[Type] =
+            t.tpe.dealias match
+              case AppliedType(_, args) => args.get(i)
+              case _ => None
+          val fieldNameOpt = getIndex(t1) match
+            case Some(c: ConstantType) => Some(termName(c.value.stringValue))
+            case _ => None
+          val fieldType = getIndex(t2).getOrElse(NoType)
+          val fieldOccurrence = fieldNameOpt match
+            case Some(fieldName) =>
+              val fieldSpan = Span(app.span.point, app.span.end, app.span.point)
+              if fieldSpan.isCorrect then
+                val sym = newSymbol(NoSymbol, fieldName: Name, Flags.EmptyFlags, fieldType)
+                Set(collect(app, pos.withSpan(fieldSpan), Some(sym)))
+              else Set.empty
+            case None => Set.empty
+          val traverser =
+            new PcCollector.DeepFolderWithParent[Set[T]](collectNamesWithParent)
+          traverser(occurrences ++ fieldOccurrence, qual)
+
         /* Named parameters don't have symbol so we need to check the owner
          *  ```
          *  foo(<<name>> = "abc")

presentation-compiler/test/dotty/tools/pc/tests/tokens/SemanticTokensSuite.scala

@@ -469,3 +469,19 @@ class SemanticTokensSuite extends BaseSemanticTokensSuite:
          |export <<Test>>/*class*/.<<methodA>>/*method*/
          |""".stripMargin
     )
+
+  @Test def `named-tuple-members` =
+    check(
+      """|object <<A>>/*class*/:
+         |  type <<PersonNN>>/*type,definition*/ = (name: <<String>>/*type*/, age: <<Int>>/*class,abstract*/)
+         |  final case class <<PersonCC>>/*class*/(<<name>>/*variable,declaration,readonly*/: <<String>>/*type*/, <<age>>/*variable,declaration,readonly*/: <<Int>>/*class,abstract*/)
+         |
+         |  val <<pNN>>/*variable,definition,readonly*/: <<PersonNN>>/*type*/ = (name = "John", age = 30)
+         |  val <<pCC>>/*variable,definition,readonly*/: <<PersonCC>>/*class*/ = <<PersonCC>>/*class*/(<<name>>/*parameter,readonly*/ = "John", <<age>>/*parameter,readonly*/ = 30)
+         |
+         |  val <<nn>>/*variable,definition,readonly*/ = <<pNN>>/*variable,readonly*/.<<name>>/*variable,readonly*/
+         |  val <<cc>>/*variable,definition,readonly*/ = <<pCC>>/*variable,readonly*/.<<name>>/*variable,readonly*/
+         |  val <<ccAge>>/*variable,definition,readonly*/ = <<pNN>>/*variable,readonly*/.<<age>>/*variable,readonly*/
+         |  val <<ccAge>>/*variable,definition,readonly*/ = <<pCC>>/*variable,readonly*/.<<age>>/*variable,readonly*/
+         |""".stripMargin
+    )