Intrinsify constValueTuple and summonAll (#18013)

The new implementation instantiates the TupleN/TupleXXL classes
directly.
This avoids the expensive unrolling of tuples using `*:` recursively.

Fixes #15988

Author: nicolasstucki

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

@@ -1520,6 +1520,25 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     }
   }
 
+  /** Creates the tuple containing the given elements */
+  def tupleTree(elems: List[Tree])(using Context): Tree = {
+    val arity = elems.length
+    if arity == 0 then
+      ref(defn.EmptyTupleModule)
+    else if arity <= Definitions.MaxTupleArity then
+      // TupleN[elem1Tpe, ...](elem1, ...)
+      ref(defn.TupleType(arity).nn.typeSymbol.companionModule)
+        .select(nme.apply)
+        .appliedToTypes(elems.map(_.tpe.widenIfUnstable))
+        .appliedToArgs(elems)
+    else
+      // TupleXXL.apply(elems*) // TODO add and use Tuple.apply(elems*) ?
+      ref(defn.TupleXXLModule)
+        .select(nme.apply)
+        .appliedToVarargs(elems.map(_.asInstance(defn.ObjectType)), TypeTree(defn.ObjectType))
+        .asInstance(defn.tupleType(elems.map(elem => elem.tpe.widenIfUnstable)))
+  }
+
   /** Creates the tuple type tree representation of the type trees in `ts` */
   def tupleTypeTree(elems: List[Tree])(using Context): Tree = {
     val arity = elems.length

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -243,8 +243,10 @@ class Definitions {
     @tu lazy val Compiletime_requireConst : Symbol = CompiletimePackageClass.requiredMethod("requireConst")
     @tu lazy val Compiletime_constValue   : Symbol = CompiletimePackageClass.requiredMethod("constValue")
     @tu lazy val Compiletime_constValueOpt: Symbol = CompiletimePackageClass.requiredMethod("constValueOpt")
+    @tu lazy val Compiletime_constValueTuple: Symbol = CompiletimePackageClass.requiredMethod("constValueTuple")
     @tu lazy val Compiletime_summonFrom   : Symbol = CompiletimePackageClass.requiredMethod("summonFrom")
-    @tu lazy val Compiletime_summonInline   : Symbol = CompiletimePackageClass.requiredMethod("summonInline")
+    @tu lazy val Compiletime_summonInline : Symbol = CompiletimePackageClass.requiredMethod("summonInline")
+    @tu lazy val Compiletime_summonAll    : Symbol = CompiletimePackageClass.requiredMethod("summonAll")
   @tu lazy val CompiletimeTestingPackage: Symbol = requiredPackage("scala.compiletime.testing")
     @tu lazy val CompiletimeTesting_typeChecks: Symbol = CompiletimeTestingPackage.requiredMethod("typeChecks")
     @tu lazy val CompiletimeTesting_typeCheckErrors: Symbol = CompiletimeTestingPackage.requiredMethod("typeCheckErrors")
@@ -932,6 +934,8 @@ class Definitions {
   @tu lazy val TupleTypeRef: TypeRef = requiredClassRef("scala.Tuple")
   def TupleClass(using Context): ClassSymbol = TupleTypeRef.symbol.asClass
     @tu lazy val Tuple_cons: Symbol = TupleClass.requiredMethod("*:")
+  @tu lazy val TupleModule: Symbol = requiredModule("scala.Tuple")
+  @tu lazy val EmptyTupleClass: Symbol = requiredClass("scala.EmptyTuple")
   @tu lazy val EmptyTupleModule: Symbol = requiredModule("scala.EmptyTuple")
   @tu lazy val NonEmptyTupleTypeRef: TypeRef = requiredClassRef("scala.NonEmptyTuple")
   def NonEmptyTupleClass(using Context): ClassSymbol = NonEmptyTupleTypeRef.symbol.asClass

compiler/src/dotty/tools/dotc/inlines/Inliner.scala

@@ -497,8 +497,8 @@ class Inliner(val call: tpd.Tree)(using Context):
     // assertAllPositioned(tree)   // debug
     tree.changeOwner(originalOwner, ctx.owner)
 
-  def tryConstValue: Tree =
-    TypeComparer.constValue(callTypeArgs.head.tpe) match {
+  def tryConstValue(tpe: Type): Tree =
+    TypeComparer.constValue(tpe) match {
       case Some(c) => Literal(c).withSpan(call.span)
       case _ => EmptyTree
     }

compiler/src/dotty/tools/dotc/inlines/Inlines.scala

@@ -413,36 +413,67 @@ object Inlines:
             return Intrinsics.codeOf(arg, call.srcPos)
         case _ =>
 
-      // Special handling of `constValue[T]`, `constValueOpt[T], and summonInline[T]`
+      // Special handling of `constValue[T]`, `constValueOpt[T]`, `constValueTuple[T]`, `summonInline[T]` and `summonAll[T]`
       if callTypeArgs.length == 1 then
-        if (inlinedMethod == defn.Compiletime_constValue) {
-          val constVal = tryConstValue
+
+        def constValueOrError(tpe: Type): Tree =
+          val constVal = tryConstValue(tpe)
           if constVal.isEmpty then
-            val msg = NotConstant("cannot take constValue", callTypeArgs.head.tpe)
-            return ref(defn.Predef_undefined).withSpan(call.span).withType(ErrorType(msg))
+            val msg = NotConstant("cannot take constValue", tpe)
+            ref(defn.Predef_undefined).withSpan(callTypeArgs.head.span).withType(ErrorType(msg))
           else
-            return constVal
+            constVal
+
+        def searchImplicitOrError(tpe: Type): Tree =
+          val evTyper = new Typer(ctx.nestingLevel + 1)
+          val evCtx = ctx.fresh.setTyper(evTyper)
+          inContext(evCtx) {
+            val evidence = evTyper.inferImplicitArg(tpe, callTypeArgs.head.span)
+            evidence.tpe match
+              case fail: Implicits.SearchFailureType =>
+                errorTree(call, evTyper.missingArgMsg(evidence, tpe, ""))
+              case _ =>
+                evidence
+          }
+
+        def unrollTupleTypes(tpe: Type): Option[List[Type]] = tpe.dealias match
+          case AppliedType(tycon, args) if defn.isTupleClass(tycon.typeSymbol) =>
+            Some(args)
+          case AppliedType(tycon, head :: tail :: Nil) if tycon.isRef(defn.PairClass) =>
+            unrollTupleTypes(tail).map(head :: _)
+          case tpe: TermRef if tpe.symbol == defn.EmptyTupleModule =>
+            Some(Nil)
+          case _ =>
+            None
+
+        if (inlinedMethod == defn.Compiletime_constValue) {
+          return constValueOrError(callTypeArgs.head.tpe)
         }
         else if (inlinedMethod == defn.Compiletime_constValueOpt) {
-          val constVal = tryConstValue
+          val constVal = tryConstValue(callTypeArgs.head.tpe)
           return (
             if (constVal.isEmpty) ref(defn.NoneModule.termRef)
             else New(defn.SomeClass.typeRef.appliedTo(constVal.tpe), constVal :: Nil)
           )
         }
+        else if (inlinedMethod == defn.Compiletime_constValueTuple) {
+          unrollTupleTypes(callTypeArgs.head.tpe) match
+            case Some(types) =>
+              val constants = types.map(constValueOrError)
+              return Typed(tpd.tupleTree(constants), TypeTree(callTypeArgs.head.tpe)).withSpan(call.span)
+            case _ =>
+              return errorTree(call, em"Tuple element types must be known at compile time")
+        }
         else if (inlinedMethod == defn.Compiletime_summonInline) {
-          def searchImplicit(tpt: Tree) =
-            val evTyper = new Typer(ctx.nestingLevel + 1)
-            val evCtx = ctx.fresh.setTyper(evTyper)
-            inContext(evCtx) {
-              val evidence = evTyper.inferImplicitArg(tpt.tpe, tpt.span)
-              evidence.tpe match
-                case fail: Implicits.SearchFailureType =>
-                  errorTree(call, evTyper.missingArgMsg(evidence, tpt.tpe, ""))
-                case _ =>
-                  evidence
-            }
-          return searchImplicit(callTypeArgs.head)
+          return searchImplicitOrError(callTypeArgs.head.tpe)
+        }
+        else if (inlinedMethod == defn.Compiletime_summonAll) {
+          unrollTupleTypes(callTypeArgs.head.tpe) match
+            case Some(types) =>
+              val implicits = types.map(searchImplicitOrError)
+              return Typed(tpd.tupleTree(implicits), TypeTree(callTypeArgs.head.tpe)).withSpan(call.span)
+            case _ =>
+              return errorTree(call, em"Tuple element types must be known at compile time")
         }
       end if
 

library/src/scala/compiletime/package.scala

@@ -117,13 +117,9 @@ transparent inline def constValue[T]: T =
  *  `(constValue[X1], ..., constValue[Xn])`.
  */
 inline def constValueTuple[T <: Tuple]: T =
-  val res =
-    inline erasedValue[T] match
-      case _: EmptyTuple => EmptyTuple
-      case _: (t *: ts) => constValue[t] *: constValueTuple[ts]
-    end match
-  res.asInstanceOf[T]
-end constValueTuple
+  // implemented in dotty.tools.dotc.typer.Inliner
+  error("Compiler bug: `constValueTuple` was not evaluated by the compiler")
+
 
 /** Summons first given matching one of the listed cases. E.g. in
  *
@@ -168,13 +164,8 @@ transparent inline def summonInline[T]: T =
  *  @return the given values typed as elements of the tuple
  */
 inline def summonAll[T <: Tuple]: T =
-  val res =
-    inline erasedValue[T] match
-      case _: EmptyTuple => EmptyTuple
-      case _: (t *: ts) => summonInline[t] *: summonAll[ts]
-    end match
-  res.asInstanceOf[T]
-end summonAll
+  // implemented in dotty.tools.dotc.typer.Inliner
+  error("Compiler bug: `summonAll` was not evaluated by the compiler")
 
 /** Assertion that an argument is by-name. Used for nullability checking. */
 def byName[T](x: => T): T = x

tests/neg/17211.check

@@ -1,14 +1,14 @@
--- [E182] Type Error: tests/neg/17211.scala:14:12 ----------------------------------------------------------------------
+-- [E182] Type Error: tests/neg/17211.scala:14:13 ----------------------------------------------------------------------
 14 |  constValue[IsInt[Foo.Foo]] // error
-   |  ^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |  IsInt[Foo.Foo] is not a constant type; cannot take constValue
+   |             ^^^^^^^^^^^^^^
+   |             IsInt[Foo.Foo] is not a constant type; cannot take constValue
    |
-   |  Note: a match type could not be fully reduced:
+   |             Note: a match type could not be fully reduced:
    |
-   |    trying to reduce  IsInt[Foo.Foo]
-   |    failed since selector Foo.Foo
-   |    does not match  case Int => (true : Boolean)
-   |    and cannot be shown to be disjoint from it either.
-   |    Therefore, reduction cannot advance to the remaining case
+   |               trying to reduce  IsInt[Foo.Foo]
+   |               failed since selector Foo.Foo
+   |               does not match  case Int => (true : Boolean)
+   |               and cannot be shown to be disjoint from it either.
+   |               Therefore, reduction cannot advance to the remaining case
    |
-   |      case _ => (false : Boolean)
+   |                 case _ => (false : Boolean)

tests/neg/i14177a.scala

@@ -3,4 +3,4 @@ import scala.compiletime.*
 trait C[A]
 
 inline given [Tup <: Tuple]: C[Tup] with
-  val cs = summonAll[Tuple.Map[Tup, C]] // error cannot reduce inline match with
+  val cs = summonAll[Tuple.Map[Tup, C]] // error: Tuple element types must be known at compile time

tests/run/i15988a.scala

@@ -0,0 +1,6 @@
+import scala.compiletime.constValueTuple
+
+@main def Test: Unit =
+  assert(constValueTuple[EmptyTuple] == EmptyTuple)
+  assert(constValueTuple[("foo", 5, 3.14, "bar", false)] == ("foo", 5, 3.14, "bar", false))
+  assert(constValueTuple[(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)] == (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23))

tests/run/i15988b.scala

@@ -0,0 +1,21 @@
+import scala.compiletime.summonAll
+
+@main def Test: Unit =
+  assert(summonAll[EmptyTuple] == EmptyTuple)
+  assert(summonAll[(5, 5, 5)] == (5, 5, 5))
+  assert(
+    summonAll[(
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+    )] == (
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+      5, 5, 5, 5, 5,
+    ))
+
+given 5 = 5