Add SplicePattern AST to parse and type quote pattern splices (#17396)

Splices in quoted expressions and quoted patterns are fundamentally
different. SplicePattern makes this difference explicit and also handles
HOAS arguments to the pattern splices.

Author: smarter

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -338,9 +338,9 @@ object desugar {
   def quotedPattern(tree: untpd.Tree, expectedTpt: untpd.Tree)(using Context): untpd.Tree = {
     def adaptToExpectedTpt(tree: untpd.Tree): untpd.Tree = tree match {
       // Add the expected type as an ascription
-      case _: untpd.Splice =>
+      case _: untpd.SplicePattern =>
         untpd.Typed(tree, expectedTpt).withSpan(tree.span)
-      case Typed(expr: untpd.Splice, tpt) =>
+      case Typed(expr: untpd.SplicePattern, tpt) =>
         cpy.Typed(tree)(expr, untpd.makeAndType(tpt, expectedTpt).withSpan(tpt.span))
 
       // Propagate down the expected type to the leafs of the expression
@@ -1979,7 +1979,7 @@ object desugar {
       case Quote(body, _) =>
         new UntypedTreeTraverser {
           def traverse(tree: untpd.Tree)(using Context): Unit = tree match {
-            case Splice(expr) => collect(expr)
+            case SplicePattern(body, _) => collect(body)
             case _ => traverseChildren(tree)
           }
         }.traverse(body)

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -737,6 +737,22 @@ object Trees {
     type ThisTree[+T <: Untyped] = Splice[T]
   }
 
+  /** A tree representing a pattern splice `${ pattern }`, `$ident` or `$ident(args*)` in a quote pattern.
+   *
+   *  Parser will only create `${ pattern }` and `$ident`, hence they will not have args.
+   *  While typing, the `$ident(args*)` the args are identified and desugared into a `SplicePattern`
+   *  containing them.
+   *
+   *  SplicePattern are removed after typing the pattern and are not present in TASTy.
+   *
+   *  @param body  The tree that was spliced
+   *  @param args  The arguments of the splice (the HOAS arguments)
+   */
+  case class SplicePattern[+T <: Untyped] private[ast] (body: Tree[T], args: List[Tree[T]])(implicit @constructorOnly src: SourceFile)
+    extends TermTree[T] {
+    type ThisTree[+T <: Untyped] = SplicePattern[T]
+  }
+
   /** A type tree that represents an existing or inferred type */
   case class TypeTree[+T <: Untyped]()(implicit @constructorOnly src: SourceFile)
     extends DenotingTree[T] with TypTree[T] {
@@ -1147,6 +1163,7 @@ object Trees {
     type Inlined = Trees.Inlined[T]
     type Quote = Trees.Quote[T]
     type Splice = Trees.Splice[T]
+    type SplicePattern = Trees.SplicePattern[T]
     type TypeTree = Trees.TypeTree[T]
     type InferredTypeTree = Trees.InferredTypeTree[T]
     type SingletonTypeTree = Trees.SingletonTypeTree[T]
@@ -1325,6 +1342,10 @@ object Trees {
         case tree: Splice if (expr eq tree.expr) => tree
         case _ => finalize(tree, untpd.Splice(expr)(sourceFile(tree)))
       }
+      def SplicePattern(tree: Tree)(body: Tree, args: List[Tree])(using Context): SplicePattern = tree match {
+        case tree: SplicePattern if (body eq tree.body) && (args eq tree.args) => tree
+        case _ => finalize(tree, untpd.SplicePattern(body, args)(sourceFile(tree)))
+      }
       def SingletonTypeTree(tree: Tree)(ref: Tree)(using Context): SingletonTypeTree = tree match {
         case tree: SingletonTypeTree if (ref eq tree.ref) => tree
         case _ => finalize(tree, untpd.SingletonTypeTree(ref)(sourceFile(tree)))
@@ -1566,6 +1587,8 @@ object Trees {
               cpy.Quote(tree)(transform(body)(using quoteContext), transform(tags))
             case tree @ Splice(expr) =>
               cpy.Splice(tree)(transform(expr)(using spliceContext))
+            case tree @ SplicePattern(body, args) =>
+              cpy.SplicePattern(tree)(transform(body)(using spliceContext), transform(args))
             case tree @ Hole(isTerm, idx, args, content) =>
               cpy.Hole(tree)(isTerm, idx, transform(args), transform(content))
             case _ =>
@@ -1711,6 +1734,8 @@ object Trees {
               this(this(x, body)(using quoteContext), tags)
             case Splice(expr) =>
               this(x, expr)(using spliceContext)
+            case SplicePattern(body, args) =>
+              this(this(x, body)(using spliceContext), args)
             case Hole(_, _, args, content) =>
               this(this(x, args), content)
             case _ =>

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -399,6 +399,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def Inlined(call: tpd.Tree, bindings: List[MemberDef], expansion: Tree)(implicit src: SourceFile): Inlined = new Inlined(call, bindings, expansion)
   def Quote(body: Tree, tags: List[Tree])(implicit src: SourceFile): Quote = new Quote(body, tags)
   def Splice(expr: Tree)(implicit src: SourceFile): Splice = new Splice(expr)
+  def SplicePattern(body: Tree, args: List[Tree])(implicit src: SourceFile): SplicePattern = new SplicePattern(body, args)
   def TypeTree()(implicit src: SourceFile): TypeTree = new TypeTree()
   def InferredTypeTree()(implicit src: SourceFile): TypeTree = new InferredTypeTree()
   def SingletonTypeTree(ref: Tree)(implicit src: SourceFile): SingletonTypeTree = new SingletonTypeTree(ref)

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1750,10 +1750,10 @@ object Parsers {
     def splice(isType: Boolean): Tree =
       val start = in.offset
       atSpan(in.offset) {
+        val inPattern = (staged & StageKind.QuotedPattern) != 0
         val expr =
           if (in.name.length == 1) {
             in.nextToken()
-            val inPattern = (staged & StageKind.QuotedPattern) != 0
             withinStaged(StageKind.Spliced)(if (inPattern) inBraces(pattern()) else stagedBlock())
           }
           else atSpan(in.offset + 1) {
@@ -1769,6 +1769,8 @@ object Parsers {
             else "To use a given Type[T] in a quote just write T directly"
           syntaxError(em"$msg\n\nHint: $hint", Span(start, in.lastOffset))
           Ident(nme.ERROR.toTypeName)
+        else if inPattern then
+          SplicePattern(expr, Nil)
         else
           Splice(expr)
       }

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -735,6 +735,12 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       case Splice(expr) =>
         val spliceTypeText = (keywordStr("[") ~ toTextGlobal(tree.typeOpt) ~ keywordStr("]")).provided(printDebug && tree.typeOpt.exists)
         keywordStr("$") ~ spliceTypeText ~ keywordStr("{") ~ toTextGlobal(expr) ~ keywordStr("}")
+      case SplicePattern(pattern, args) =>
+        val spliceTypeText = (keywordStr("[") ~ toTextGlobal(tree.typeOpt) ~ keywordStr("]")).provided(printDebug && tree.typeOpt.exists)
+        keywordStr("$") ~ spliceTypeText ~ {
+          if args.isEmpty then keywordStr("{") ~ inPattern(toText(pattern)) ~ keywordStr("}")
+          else toText(pattern.symbol.name) ~ "(" ~ toTextGlobal(args, ", ") ~ ")"
+        }
       case Hole(isTerm, idx, args, content) =>
         val (prefix, postfix) = if isTerm then ("{{{", "}}}") else ("[[[", "]]]")
         val argsText = toTextGlobal(args, ", ")

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1097,7 +1097,7 @@ trait Applications extends Compatibility {
         }
       else {
         val app = tree.fun match
-          case _: untpd.Splice if ctx.mode.is(Mode.QuotedPattern) => typedAppliedSplice(tree, pt)
+          case _: untpd.SplicePattern => typedAppliedSplice(tree, pt)
           case _ => realApply
         app match {
           case Apply(fn @ Select(left, _), right :: Nil) if fn.hasType =>

compiler/src/dotty/tools/dotc/typer/QuotesAndSplices.scala

@@ -17,6 +17,7 @@ import dotty.tools.dotc.core.Types._
 import dotty.tools.dotc.inlines.PrepareInlineable
 import dotty.tools.dotc.staging.StagingLevel.*
 import dotty.tools.dotc.transform.SymUtils._
+import dotty.tools.dotc.typer.ErrorReporting.errorTree
 import dotty.tools.dotc.typer.Implicits._
 import dotty.tools.dotc.typer.Inferencing._
 import dotty.tools.dotc.util.Spans._
@@ -74,45 +75,55 @@ trait QuotesAndSplices {
   def typedSplice(tree: untpd.Splice, pt: Type)(using Context): Tree = {
     record("typedSplice")
     checkSpliceOutsideQuote(tree)
+    assert(!ctx.mode.is(Mode.QuotedPattern))
     tree.expr match {
       case untpd.Quote(innerExpr, Nil) if innerExpr.isTerm =>
         report.warning("Canceled quote directly inside a splice. ${ '{ XYZ } } is equivalent to XYZ.", tree.srcPos)
         return typed(innerExpr, pt)
       case _ =>
     }
-    if (ctx.mode.is(Mode.QuotedPattern))
-      if (isFullyDefined(pt, ForceDegree.flipBottom)) {
-        def spliceOwner(ctx: Context): Symbol =
-          if (ctx.mode.is(Mode.QuotedPattern)) spliceOwner(ctx.outer) else ctx.owner
-        val pat = typedPattern(tree.expr, defn.QuotedExprClass.typeRef.appliedTo(pt))(
-          using spliceContext.retractMode(Mode.QuotedPattern).addMode(Mode.Pattern).withOwner(spliceOwner(ctx)))
-        val baseType = pat.tpe.baseType(defn.QuotedExprClass)
-        val argType = if baseType != NoType then baseType.argTypesHi.head else defn.NothingType
-        Splice(pat, argType).withSpan(tree.span)
-      }
-      else {
-        report.error(em"Type must be fully defined.\nConsider annotating the splice using a type ascription:\n  ($tree: XYZ).", tree.expr.srcPos)
-        tree.withType(UnspecifiedErrorType)
-      }
-    else {
-      if (level == 0) {
-        // Mark the first inline method from the context as a macro
-        def markAsMacro(c: Context): Unit =
-          if (c.owner eq c.outer.owner) markAsMacro(c.outer)
-          else if (c.owner.isInlineMethod) c.owner.setFlag(Macro)
-          else if (!c.outer.owner.is(Package)) markAsMacro(c.outer)
-          else assert(ctx.reporter.hasErrors) // Did not find inline def to mark as macro
-        markAsMacro(ctx)
-      }
-
-      // TODO typecheck directly (without `exprSplice`)
-      val internalSplice =
-        untpd.Apply(untpd.ref(defn.QuotedRuntime_exprSplice.termRef), tree.expr)
-      typedApply(internalSplice, pt)(using spliceContext).withSpan(tree.span) match
-        case tree @ Apply(TypeApply(_, tpt :: Nil), spliced :: Nil) if tree.symbol == defn.QuotedRuntime_exprSplice =>
-          cpy.Splice(tree)(spliced)
-        case tree => tree
+    if (level == 0) {
+      // Mark the first inline method from the context as a macro
+      def markAsMacro(c: Context): Unit =
+        if (c.owner eq c.outer.owner) markAsMacro(c.outer)
+        else if (c.owner.isInlineMethod) c.owner.setFlag(Macro)
+        else if (!c.outer.owner.is(Package)) markAsMacro(c.outer)
+        else assert(ctx.reporter.hasErrors) // Did not find inline def to mark as macro
+      markAsMacro(ctx)
     }
+
+    // TODO typecheck directly (without `exprSplice`)
+    val internalSplice =
+      untpd.Apply(untpd.ref(defn.QuotedRuntime_exprSplice.termRef), tree.expr)
+    typedApply(internalSplice, pt)(using spliceContext).withSpan(tree.span) match
+      case tree @ Apply(TypeApply(_, tpt :: Nil), spliced :: Nil) if tree.symbol == defn.QuotedRuntime_exprSplice =>
+        cpy.Splice(tree)(spliced)
+      case tree => tree
+  }
+
+  def typedSplicePattern(tree: untpd.SplicePattern, pt: Type)(using Context): Tree = {
+    record("typedSplicePattern")
+    if isFullyDefined(pt, ForceDegree.flipBottom) then
+      def patternOuterContext(ctx: Context): Context =
+        if (ctx.mode.is(Mode.QuotedPattern)) patternOuterContext(ctx.outer) else ctx
+      val typedArgs = tree.args.map {
+        case arg: untpd.Ident =>
+          typedExpr(arg)
+        case arg =>
+          report.error("Open pattern expected an identifier", arg.srcPos)
+          EmptyTree
+      }
+      for arg <- typedArgs if arg.symbol.is(Mutable) do // TODO support these patterns. Possibly using scala.quoted.util.Var
+        report.error("References to `var`s cannot be used in higher-order pattern", arg.srcPos)
+      val argTypes = typedArgs.map(_.tpe.widenTermRefExpr)
+      val patType = if tree.args.isEmpty then pt else defn.FunctionOf(argTypes, pt)
+      val pat = typedPattern(tree.body, defn.QuotedExprClass.typeRef.appliedTo(patType))(
+        using spliceContext.retractMode(Mode.QuotedPattern).addMode(Mode.Pattern).withOwner(patternOuterContext(ctx).owner))
+      val baseType = pat.tpe.baseType(defn.QuotedExprClass)
+      val argType = if baseType.exists then baseType.argTypesHi.head else defn.NothingType
+      untpd.cpy.SplicePattern(tree)(pat, typedArgs).withType(pt)
+    else
+      errorTree(tree, em"Type must be fully defined.\nConsider annotating the splice using a type ascription:\n  ($tree: XYZ).", tree.body.srcPos)
   }
 
   def typedHole(tree: untpd.Hole, pt: Type)(using Context): Tree =
@@ -127,29 +138,17 @@ trait QuotesAndSplices {
    */
   def typedAppliedSplice(tree: untpd.Apply, pt: Type)(using Context): Tree = {
     assert(ctx.mode.is(Mode.QuotedPattern))
-    val untpd.Apply(splice: untpd.Splice, args) = tree: @unchecked
-    def isInBraces: Boolean = splice.span.end != splice.expr.span.end
-    if !isFullyDefined(pt, ForceDegree.flipBottom) then
-      report.error(em"Type must be fully defined.", splice.srcPos)
-      tree.withType(UnspecifiedErrorType)
-    else if isInBraces then // ${x}(...) match an application
+    val untpd.Apply(splice: untpd.SplicePattern, args) = tree: @unchecked
+    def isInBraces: Boolean = splice.span.end != splice.body.span.end
+    if isInBraces then // ${x}(...) match an application
       val typedArgs = args.map(arg => typedExpr(arg))
       val argTypes = typedArgs.map(_.tpe.widenTermRefExpr)
-      val splice1 = typedSplice(splice, defn.FunctionOf(argTypes, pt))
-      Apply(splice1.select(nme.apply), typedArgs).withType(pt).withSpan(tree.span)
+      val splice1 = typedSplicePattern(splice, defn.FunctionOf(argTypes, pt))
+      untpd.cpy.Apply(tree)(splice1.select(nme.apply), typedArgs).withType(pt)
     else // $x(...) higher-order quasipattern
-      val typedArgs = args.map {
-        case arg: untpd.Ident =>
-          typedExpr(arg)
-        case arg =>
-          report.error("Open pattern expected an identifier", arg.srcPos)
-          EmptyTree
-      }
       if args.isEmpty then
-        report.error("Missing arguments for open pattern", tree.srcPos)
-      val argTypes = typedArgs.map(_.tpe.widenTermRefExpr)
-      val typedPat = typedSplice(splice, defn.FunctionOf(argTypes, pt))
-      ref(defn.QuotedRuntimePatterns_patternHigherOrderHole).appliedToType(pt).appliedTo(typedPat, SeqLiteral(typedArgs, TypeTree(defn.AnyType)))
+         report.error("Missing arguments for open pattern", tree.srcPos)
+      typedSplicePattern(untpd.cpy.SplicePattern(tree)(splice.body, args), pt)
   }
 
   /** Type a pattern variable name `t` in quote pattern as `${given t$giveni: Type[t @ _]}`.
@@ -227,29 +226,16 @@ trait QuotesAndSplices {
       val freshTypeBindingsBuff = new mutable.ListBuffer[Tree]
       val typePatBuf = new mutable.ListBuffer[Tree]
       override def transform(tree: Tree)(using Context) = tree match {
-        case Typed(splice: Splice, tpt) if !tpt.tpe.derivesFrom(defn.RepeatedParamClass) =>
+        case Typed(splice @ SplicePattern(pat, Nil), tpt) if !tpt.tpe.derivesFrom(defn.RepeatedParamClass) =>
           transform(tpt) // Collect type bindings
           transform(splice)
-        case Apply(TypeApply(fn, targs), Splice(pat) :: args :: Nil) if fn.symbol == defn.QuotedRuntimePatterns_patternHigherOrderHole =>
-          args match // TODO support these patterns. Possibly using scala.quoted.util.Var
-            case SeqLiteral(args, _) =>
-              for arg <- args; if arg.symbol.is(Mutable) do
-                report.error("References to `var`s cannot be used in higher-order pattern", arg.srcPos)
-          try ref(defn.QuotedRuntimePatterns_higherOrderHole.termRef).appliedToTypeTrees(targs).appliedTo(args).withSpan(tree.span)
-          finally {
-            val patType = pat.tpe.widen
-            val patType1 = patType.translateFromRepeated(toArray = false)
-            val pat1 = if (patType eq patType1) pat else pat.withType(patType1)
-            patBuf += pat1
-          }
-        case Splice(pat) =>
-          try ref(defn.QuotedRuntimePatterns_patternHole.termRef).appliedToType(tree.tpe).withSpan(tree.span)
-          finally {
-            val patType = pat.tpe.widen
-            val patType1 = patType.translateFromRepeated(toArray = false)
-            val pat1 = if (patType eq patType1) pat else pat.withType(patType1)
-            patBuf += pat1
-          }
+        case SplicePattern(pat, args) =>
+          val patType = pat.tpe.widen
+          val patType1 = patType.translateFromRepeated(toArray = false)
+          val pat1 = if (patType eq patType1) pat else pat.withType(patType1)
+          patBuf += pat1
+          if args.isEmpty then ref(defn.QuotedRuntimePatterns_patternHole.termRef).appliedToType(tree.tpe).withSpan(tree.span)
+          else ref(defn.QuotedRuntimePatterns_higherOrderHole.termRef).appliedToType(tree.tpe).appliedTo(SeqLiteral(args, TypeTree(defn.AnyType))).withSpan(tree.span)
         case Select(pat: Bind, _) if tree.symbol.isTypeSplice =>
           val sym = tree.tpe.dealias.typeSymbol
           if sym.exists then

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3096,6 +3096,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
           case untpd.EmptyTree => tpd.EmptyTree
           case tree: untpd.Quote => typedQuote(tree, pt)
           case tree: untpd.Splice => typedSplice(tree, pt)
+          case tree: untpd.SplicePattern => typedSplicePattern(tree, pt)
           case tree: untpd.MacroTree => report.error("Unexpected macro", tree.srcPos); tpd.nullLiteral  // ill-formed code may reach here
           case tree: untpd.Hole => typedHole(tree, pt)
           case _ => typedUnadapted(desugar(tree, pt), pt, locked)