improvement: Replace synthetic decorations with inlay hints

Backports changes from Metals: scalameta/metals#5983

Author: jkciesluk

presentation-compiler/src/main/dotty/tools/pc/PcSyntheticDecorationProvider.scala renamed to presentation-compiler/src/main/dotty/tools/pc/PcInlayHintsProvider.scala

@@ -6,18 +6,18 @@ import java.nio.file.Paths
 import scala.meta.internal.metals.ReportContext
 import dotty.tools.pc.utils.MtagsEnrichments.*
 import dotty.tools.pc.printer.ShortenedTypePrinter
+import scala.meta.internal.pc.InlayHints
+import scala.meta.internal.pc.LabelPart
+import scala.meta.internal.pc.LabelPart.*
+import scala.meta.pc.InlayHintsParams
 import scala.meta.pc.SymbolSearch
-import scala.meta.pc.SyntheticDecoration
-import scala.meta.pc.SyntheticDecorationsParams
-import scala.meta.internal.pc.DecorationKind
-import scala.meta.internal.pc.Decoration
-
 
 import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.ast.tpd.*
 import dotty.tools.dotc.core.Contexts.Context
 import dotty.tools.dotc.core.Flags
 import dotty.tools.dotc.core.StdNames.*
+import dotty.tools.dotc.core.Symbols.*
 import dotty.tools.dotc.core.Types.*
 import dotty.tools.dotc.interactive.Interactive
 import dotty.tools.dotc.interactive.InteractiveDriver
@@ -26,9 +26,13 @@ import dotty.tools.dotc.util.SourcePosition
 import dotty.tools.dotc.util.Spans.Span
 import dotty.tools.pc.IndexedContext
 
-final class PcSyntheticDecorationsProvider(
+import org.eclipse.lsp4j.InlayHint
+import org.eclipse.lsp4j.InlayHintKind
+import org.eclipse.{lsp4j as l}
+
+class PcInlayHintsProvider(
     driver: InteractiveDriver,
-    params: SyntheticDecorationsParams,
+    params: InlayHintsParams,
     symbolSearch: SymbolSearch,
 )(using ReportContext):
 
@@ -43,75 +47,81 @@ final class PcSyntheticDecorationsProvider(
   given InferredType.Text = InferredType.Text(text)
   given ctx: Context = driver.currentCtx
   val unit = driver.currentCtx.run.nn.units.head
+  val pos = driver.sourcePosition(params)
 
-  def tpdTree = unit.tpdTree
+  def provide(): List[InlayHint] =
+    val deepFolder = DeepFolder[InlayHints](collectDecorations)
+    Interactive
+      .pathTo(driver.openedTrees(uri), pos)(using driver.currentCtx)
+      .headOption
+      .getOrElse(unit.tpdTree)
+      .enclosedChildren(pos.span)
+      .flatMap(tpdTree => deepFolder(InlayHints.empty, tpdTree).result())
 
-  def provide(): List[SyntheticDecoration] =
-    val deepFolder = DeepFolder[Synthetics](collectDecorations)
-    deepFolder(Synthetics.empty, tpdTree).result()
+  private def adjustPos(pos: SourcePosition): SourcePosition =
+    pos.adjust(text)._1
 
   def collectDecorations(
-      decorations: Synthetics,
+      inlayHints: InlayHints,
       tree: Tree,
-  ): Synthetics =
+  ): InlayHints =
     tree match
-      case ImplicitConversion(name, range) if params.implicitConversions() =>
-        val adjusted = range.adjust(text)._1
-        decorations
+      case ImplicitConversion(symbol, range) if params.implicitConversions() =>
+        val adjusted = adjustPos(range)
+        inlayHints
           .add(
-            Decoration(
-              adjusted.startPos.toLsp,
-              name + "(",
-              DecorationKind.ImplicitConversion,
-            )
+            adjusted.startPos.toLsp,
+            labelPart(symbol, symbol.decodedName) :: LabelPart("(") :: Nil,
+            InlayHintKind.Parameter,
           )
           .add(
-            Decoration(
-              adjusted.endPos.toLsp,
-              ")",
-              DecorationKind.ImplicitConversion,
-            )
+            adjusted.endPos.toLsp,
+            LabelPart(")") :: Nil,
+            InlayHintKind.Parameter,
           )
-      case ImplicitParameters(names, pos, allImplicit)
+      case ImplicitParameters(symbols, pos, allImplicit)
           if params.implicitParameters() =>
+        val labelParts = symbols.map(s => List(labelPart(s, s.decodedName)))
         val label =
-          if allImplicit then names.mkString("(", ", ", ")")
-          else names.mkString(", ", ", ", "")
-        decorations.add(
-          Decoration(
-            pos.adjust(text)._1.toLsp,
-            label,
-            DecorationKind.ImplicitParameter,
-          )
+          if allImplicit then labelParts.separated("(", ", ", ")")
+          else labelParts.separated(", ")
+        inlayHints.add(
+          adjustPos(pos).toLsp,
+          label,
+          InlayHintKind.Parameter,
+        )
+      case ValueOf(label, pos) if params.implicitParameters() =>
+        inlayHints.add(
+          adjustPos(pos).toLsp,
+          LabelPart("(") :: LabelPart(label) :: List(LabelPart(")")),
+          InlayHintKind.Parameter,
         )
       case TypeParameters(tpes, pos, sel)
           if params.typeParameters() && !syntheticTupleApply(sel) =>
-        val label = tpes.map(toLabel(_, pos)).mkString("[", ", ", "]")
-        decorations.add(
-          Decoration(
-            pos.adjust(text)._1.endPos.toLsp,
-            label,
-            DecorationKind.TypeParameter,
-          )
+        val label = tpes.map(toLabelParts(_, pos)).separated("[", ", ", "]")
+        inlayHints.add(
+          adjustPos(pos).endPos.toLsp,
+          label,
+          InlayHintKind.Type,
         )
-      case InferredType(tpe, pos, defTree) if params.inferredTypes() =>
-        val adjustedPos = pos.adjust(text)._1.endPos
-        if decorations.containsDef(adjustedPos.start) then decorations
+      case InferredType(tpe, pos, defTree)
+          if params.inferredTypes() && !isErrorTpe(tpe) =>
+        val adjustedPos = adjustPos(pos).endPos
+        if inlayHints.containsDef(adjustedPos.start) then inlayHints
         else
-          decorations.add(
-            Decoration(
+          inlayHints
+            .add(
               adjustedPos.toLsp,
-              ": " + toLabel(tpe, pos),
-              DecorationKind.InferredType,
-            ),
-            adjustedPos.start,
-          )
-      case _ => decorations
+              LabelPart(": ") :: toLabelParts(tpe, pos),
+              InlayHintKind.Type,
+            )
+            .addDefinition(adjustedPos.start)
+      case _ => inlayHints
 
-  private def toLabel(
+  private def toLabelParts(
       tpe: Type,
       pos: SourcePosition,
-  ): String =
+  ): List[LabelPart] =
     val tpdPath =
       Interactive.pathTo(unit.tpdTree, pos.span)
 
@@ -129,13 +139,15 @@ final class PcSyntheticDecorationsProvider(
           case AppliedType(tycon, args) =>
             isInScope(tycon) && args.forall(isInScope)
           case _ => true
-      if isInScope(tpe)
-      then tpe
+      if isInScope(tpe) then tpe
       else tpe.metalsDealias(using indexedCtx.ctx)
 
     val dealiased = optDealias(tpe)
-    printer.tpe(dealiased)
-  end toLabel
+    val tpeStr = printer.tpe(dealiased)
+    val usedRenames = printer.getUsedRenames
+    val parts = partsFromType(dealiased, usedRenames)
+    InlayHints.makeLabelParts(parts, tpeStr)
+  end toLabelParts
 
   private val definitions = IndexedContext(ctx).ctx.definitions
   private def syntheticTupleApply(tree: Tree): Boolean =
@@ -152,7 +164,32 @@ final class PcSyntheticDecorationsProvider(
             case _ => true
         else false
       case _ => false
-end PcSyntheticDecorationsProvider
+
+  private def labelPart(symbol: Symbol, label: String) =
+    if symbol.source == pos.source then
+      LabelPart(
+        label,
+        pos = Some(symbol.sourcePos.toLsp.getStart().nn),
+      )
+    else
+      LabelPart(
+        label,
+        symbol = SemanticdbSymbols.symbolName(symbol),
+      )
+
+  private def partsFromType(
+      tpe: Type,
+      usedRenames: Map[Symbol, String],
+  ): List[LabelPart] =
+    NamedPartsAccumulator(_ => true)(Nil, tpe)
+      .filter(_.symbol != NoSymbol)
+      .map { t =>
+        val label = usedRenames.get(t.symbol).getOrElse(t.symbol.decodedName)
+        labelPart(t.symbol, label)
+      }
+
+  private def isErrorTpe(tpe: Type): Boolean = tpe.isError
+end PcInlayHintsProvider
 
 object ImplicitConversion:
   def unapply(tree: Tree)(using Context) =
@@ -170,7 +207,7 @@ object ImplicitConversion:
     val lastArgPos =
       args.lastOption.map(_.sourcePos).getOrElse(fun.sourcePos)
     Some(
-      fun.symbol.decodedName,
+      fun.symbol,
       lastArgPos.withStart(fun.sourcePos.start),
     )
 end ImplicitConversion
@@ -183,23 +220,29 @@ object ImplicitParameters:
         val (implicitArgs, providedArgs) = args.partition(isSyntheticArg)
         val allImplicit = providedArgs.isEmpty
         val pos = implicitArgs.head.sourcePos
-        Some(implicitArgs.map(_.symbol.decodedName), pos, allImplicit)
+        Some(implicitArgs.map(_.symbol), pos, allImplicit)
+      case _ => None
+
+  private def isSyntheticArg(tree: Tree)(using Context) = tree match
+    case tree: Ident =>
+      tree.span.isSynthetic && tree.symbol.isOneOf(Flags.GivenOrImplicit)
+    case _ => false
+end ImplicitParameters
+
+object ValueOf:
+  def unapply(tree: Tree)(using Context) =
+    tree match
       case Apply(ta @ TypeApply(fun, _), _)
           if fun.span.isSynthetic && isValueOf(fun) =>
         Some(
-          List("new " + tpnme.valueOf.decoded.capitalize + "(...)"),
+          "new " + tpnme.valueOf.decoded.capitalize + "(...)",
           fun.sourcePos,
-          true,
         )
       case _ => None
   private def isValueOf(tree: Tree)(using Context) =
     val symbol = tree.symbol.maybeOwner
     symbol.name.decoded == tpnme.valueOf.decoded.capitalize
-  private def isSyntheticArg(tree: Tree)(using Context) = tree match
-    case tree: Ident =>
-      tree.span.isSynthetic && tree.symbol.isOneOf(Flags.GivenOrImplicit)
-    case _ => false
-end ImplicitParameters
+end ValueOf
 
 object TypeParameters:
   def unapply(tree: Tree)(using Context) =
@@ -259,35 +302,7 @@ object InferredType:
    */
   def isValDefBind(text: Text, vd: ValDef)(using Context) =
     val afterDef = text.drop(vd.nameSpan.end)
-    val index = afterDef.indexAfterSpacesAndComments
+    val index = indexAfterSpacesAndComments(afterDef)
     index >= 0 && index < afterDef.size && afterDef(index) == '@'
 
 end InferredType
-
-case class Synthetics(
-    decorations: List[Decoration],
-    definitions: Set[Int],
-):
-  def containsDef(offset: Int) = definitions(offset)
-  def add(decoration: Decoration, offset: Int) =
-    copy(
-      decorations = addDecoration(decoration),
-      definitions = definitions + offset,
-    )
-  def add(decoration: Decoration) =
-    copy (
-      decorations = addDecoration(decoration)
-    )
-
-  // If method has both type parameter and implicit parameter, we want the type parameter decoration to be displayed first,
-  // but it's added second. This method adds the decoration to the right position in the list.
-  private def addDecoration(decoration: Decoration): List[Decoration] =
-    val atSamePos =
-      decorations.takeWhile(_.range.getStart() == decoration.range.getStart())
-    (atSamePos :+ decoration) ++ decorations.drop(atSamePos.size)
-
-  def result(): List[Decoration] = decorations.reverse
-end Synthetics
-
-object Synthetics:
-  def empty: Synthetics = Synthetics(Nil, Set.empty)

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

@@ -106,15 +106,15 @@ case class ScalaPresentationCompiler(
       new PcSemanticTokensProvider(driver, params).provide().asJava
     }
 
-  override def syntheticDecorations(
-        params: SyntheticDecorationsParams
-    ): ju.concurrent.CompletableFuture[ju.List[SyntheticDecoration]] =
+  override def inlayHints(
+      params: InlayHintsParams
+  ): ju.concurrent.CompletableFuture[ju.List[l.InlayHint]] =
     compilerAccess.withInterruptableCompiler(Some(params))(
-      new ju.ArrayList[SyntheticDecoration](),
+      new ju.ArrayList[l.InlayHint](),
       params.token(),
     ) { access =>
       val driver = access.compiler()
-      new PcSyntheticDecorationsProvider(driver, params, search)
+      new PcInlayHintsProvider(driver, params, search)
         .provide()
         .asJava
     }

presentation-compiler/src/main/dotty/tools/pc/printer/ShortenedTypePrinter.scala

@@ -66,6 +66,8 @@ class ShortenedTypePrinter(
 
   private val foundRenames = collection.mutable.LinkedHashMap.empty[Symbol, String]
 
+  def getUsedRenames: Map[Symbol, String] = foundRenames.toMap
+
   def getUsedRenamesInfo(using Context): List[String] =
     foundRenames.map { (from, to) =>
       s"type $to = ${from.showName}"

presentation-compiler/src/main/dotty/tools/pc/utils/MtagsEnrichments.scala

@@ -316,6 +316,24 @@ object MtagsEnrichments extends CommonMtagsEnrichments:
             .map(source.apply)
             .contains('.')
         case _ => false
+
+    def children(using Context): List[Tree] =
+      val collector = new TreeAccumulator[List[Tree]]:
+        def apply(x: List[Tree], tree: Tree)(using Context): List[Tree] =
+          tree :: x
+      collector
+        .foldOver(Nil, tree)
+        .reverse
+
+    /**
+     * Returns the children of the tree that overlap with the given span.
+     */
+    def enclosedChildren(span: Span)(using Context): List[Tree] =
+      tree.children
+        .filter(tree =>
+          tree.sourcePos.exists && tree.span.start <= span.end && tree.span.end >= span.start
+        )
+    end enclosedChildren
   end extension
 
   extension (imp: Import)