Add checks for synthetic functions and erased functions.

* Add `isSyntheticFunction` checks for synthetic functions such as FuntionN
for N > 22 and ImplicitFunctionN for N >= 0.
* Add `erasedFunctionClass` to get the erased verion of synthetic functions.
* Change the semantics of `isFunctionClass` to return  true if it is any kind of
FunctionN or ImplicitFunctionN.

7 files changed, 111 insertions, 52 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index 2797bb8a6..69ab6c21a 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -635,13 +635,9 @@ class Definitions {
       FunctionType(args.length, isImplicit).appliedTo(args ::: resultType :: Nil)
     def unapply(ft: Type)(implicit ctx: Context) = {
       val tsym = ft.typeSymbol
-      val isImplicitFun = isImplicitFunctionClass(tsym)
-      if (isImplicitFun || isFunctionClass(tsym)) {
-        val targs = ft.argInfos
-        val numArgs = targs.length - 1
-        if (numArgs >= 0 && FunctionType(numArgs, isImplicitFun).symbol == tsym)
-          Some(targs.init, targs.last, isImplicitFun)
-        else None
+      if (isFunctionClass(tsym)) {
+        val targs = ft.dealias.argInfos
+        Some(targs.init, targs.last, tsym.name.isImplicitFunction)
       }
       else None
     }
@@ -694,20 +690,17 @@ class Definitions {
   lazy val TupleType = mkArityArray("scala.Tuple", MaxTupleArity, 2)
   lazy val ProductNType = mkArityArray("scala.Product", MaxTupleArity, 0)
 
-  def FunctionClass(n: Int)(implicit ctx: Context) =
-    if (n < MaxImplementedFunctionArity) FunctionClassPerRun()(ctx)(n)
+  def FunctionClass(n: Int, isImplicit: Boolean = false)(implicit ctx: Context) =
+    if (isImplicit) ctx.requiredClass("scala.ImplicitFunction" + n.toString)
+    else if (n <= MaxImplementedFunctionArity) FunctionClassPerRun()(ctx)(n)
     else ctx.requiredClass("scala.Function" + n.toString)
 
     lazy val Function0_applyR = ImplementedFunctionType(0).symbol.requiredMethodRef(nme.apply)
     def Function0_apply(implicit ctx: Context) = Function0_applyR.symbol
 
-  def ImplicitFunctionClass(n: Int)(implicit ctx: Context) =
-    ctx.requiredClass("scala.ImplicitFunction" + n.toString)
-
   def FunctionType(n: Int, isImplicit: Boolean = false)(implicit ctx: Context): TypeRef =
-    if (isImplicit && !ctx.erasedTypes) ImplicitFunctionClass(n).typeRef
-    else if (n < MaxImplementedFunctionArity) ImplementedFunctionType(n)
-    else FunctionClass(n).typeRef
+    if (n <= MaxImplementedFunctionArity && (!isImplicit || ctx.erasedTypes)) ImplementedFunctionType(n)
+    else FunctionClass(n, isImplicit).typeRef
 
   private lazy val TupleTypes: Set[TypeRef] = TupleType.toSet
   private lazy val ProductTypes: Set[TypeRef] = ProductNType.toSet
@@ -731,14 +724,61 @@ class Definitions {
   def isBottomType(tp: Type) =
     tp.derivesFrom(NothingClass) || tp.derivesFrom(NullClass)
 
-  def isFunctionClass(cls: Symbol) = isVarArityClass(cls, tpnme.Function)
-  def isImplicitFunctionClass(cls: Symbol) = isVarArityClass(cls, tpnme.ImplicitFunction)
-  /** Is a class that will be erased to FunctionXXL */
-  def isXXLFunctionClass(cls: Symbol) = cls.name.functionArity > MaxImplementedFunctionArity
+  /** Is a function class.
+   *   - FunctionN for N >= 0
+   *   - ImplicitFunctionN for N >= 0
+   */
+  def isFunctionClass(cls: Symbol) = scalaClassName(cls).isFunction
+
+  /** Is an implicit function class.
+   *   - ImplicitFunctionN for N >= 0
+   */
+  def isImplicitFunctionClass(cls: Symbol) = scalaClassName(cls).isImplicitFunction
+
+  /** Is a class that will be erased to FunctionXXL
+   *   - FunctionN for N >= 22
+   *   - ImplicitFunctionN for N >= 22
+   */
+  def isXXLFunctionClass(cls: Symbol) = scalaClassName(cls).functionArity > MaxImplementedFunctionArity
+
+  /** Is a synthetic function class
+   *    - FunctionN for N > 22
+   *    - ImplicitFunctionN for N >= 0
+   */
+  def isSyntheticFunctionClass(cls: Symbol) = scalaClassName(cls).isSyntheticFunction
+
   def isAbstractFunctionClass(cls: Symbol) = isVarArityClass(cls, tpnme.AbstractFunction)
   def isTupleClass(cls: Symbol) = isVarArityClass(cls, tpnme.Tuple)
   def isProductClass(cls: Symbol) = isVarArityClass(cls, tpnme.Product)
 
+  /** Returns the erased class of the function class `cls`
+   *    - FunctionN for N > 22 becomes FunctionXXL
+   *    - FunctionN for 22 > N >= 0 remains as FunctionN
+   *    - ImplicitFunctionN for N > 22 becomes FunctionXXL
+   *    - ImplicitFunctionN for 22 > N >= 0 becomes FunctionN
+   *    - anything else becomes a NoSymbol
+   */
+  def erasedFunctionClass(cls: Symbol): Symbol = {
+    val arity = scalaClassName(cls).functionArity
+    if (arity > 22) defn.FunctionXXLClass
+    else if (arity >= 0) defn.FunctionClass(arity)
+    else NoSymbol
+  }
+
+  /** Returns the erased type of the function class `cls`
+   *    - FunctionN for N > 22 becomes FunctionXXL
+   *    - FunctionN for 22 > N >= 0 remains as FunctionN
+   *    - ImplicitFunctionN for N > 22 becomes FunctionXXL
+   *    - ImplicitFunctionN for 22 > N >= 0 becomes FunctionN
+   *    - anything else becomes a NoType
+   */
+  def erasedFunctionType(cls: Symbol): Type = {
+    val arity = scalaClassName(cls).functionArity
+    if (arity > 22) defn.FunctionXXLType
+    else if (arity >= 0) defn.FunctionType(arity)
+    else NoType
+  }
+
   val predefClassNames: Set[Name] =
     Set("Predef$", "DeprecatedPredef", "LowPriorityImplicits").map(_.toTypeName)
 
@@ -809,16 +849,13 @@ class Definitions {
   def isFunctionType(tp: Type)(implicit ctx: Context) = {
     val arity = functionArity(tp)
     val sym = tp.dealias.typeSymbol
-    arity >= 0 && (
-      isFunctionClass(sym) && tp.isRef(FunctionType(arity, isImplicit = false).typeSymbol) ||
-      isImplicitFunctionClass(sym) && tp.isRef(FunctionType(arity, isImplicit = true).typeSymbol)
-    )
+    arity >= 0 && isFunctionClass(sym) && tp.isRef(FunctionType(arity, sym.name.isImplicitFunction).typeSymbol)
   }
 
   def functionArity(tp: Type)(implicit ctx: Context) = tp.dealias.argInfos.length - 1
 
   def isImplicitFunctionType(tp: Type)(implicit ctx: Context) =
-    isFunctionType(tp) && tp.dealias.typeSymbol.name.startsWith(tpnme.ImplicitFunction)
+    isFunctionType(tp) && tp.dealias.typeSymbol.name.isImplicitFunction
 
   // ----- primitive value class machinery ------------------------------------------
 
@@ -892,9 +929,6 @@ class Definitions {
 
   // ----- Initialization ---------------------------------------------------
 
-  private def maxImplemented(name: Name) =
-    if (name `startsWith` tpnme.Function) MaxImplementedFunctionArity else 0
-
   /** Give the scala package a scope where a FunctionN trait is automatically
    *  added when someone looks for it.
    */
@@ -904,7 +938,7 @@ class Definitions {
     val newDecls = new MutableScope(oldDecls) {
       override def lookupEntry(name: Name)(implicit ctx: Context): ScopeEntry = {
         val res = super.lookupEntry(name)
-        if (res == null && name.isTypeName && name.functionArity > maxImplemented(name))
+        if (res == null && name.isTypeName && name.isSyntheticFunction)
           newScopeEntry(newFunctionNTrait(name.asTypeName))
         else res
       }
diff --git a/compiler/src/dotty/tools/dotc/core/NameOps.scala b/compiler/src/dotty/tools/dotc/core/NameOps.scala
index c037d1ce7..cd3ae2a25 100644
--- a/compiler/src/dotty/tools/dotc/core/NameOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/NameOps.scala
@@ -8,6 +8,7 @@ import Names._, StdNames._, Contexts._, Symbols._, Flags._
 import Decorators.StringDecorator
 import util.{Chars, NameTransformer}
 import Chars.isOperatorPart
+import Definitions._
 
 object NameOps {
 
@@ -231,13 +232,43 @@ object NameOps {
       }
     }
 
-    def functionArity: Int = {
-      def test(prefix: Name): Int =
-        if (name.startsWith(prefix))
-          try name.drop(prefix.length).toString.toInt
-          catch { case ex: NumberFormatException => -1 }
-        else -1
-      test(tpnme.Function) max test(tpnme.ImplicitFunction)
+    /** Is a synthetic function name
+     *    - N for FunctionN
+     *    - N for ImplicitFunctionN
+      *   - (-1) otherwise
+     */
+    def functionArity: Int =
+      functionArityFor(tpnme.Function) max functionArityFor(tpnme.ImplicitFunction)
+
+    /** Is a function name
+     *    - FunctionN for N >= 0
+     *    - ImplicitFunctionN for N >= 0
+     *    - false otherwise
+     */
+    def isFunction: Boolean = functionArity >= 0
+
+    /** Is a implicit function name
+     *    - ImplicitFunctionN for N >= 0
+     *    - false otherwise
+     */
+    def isImplicitFunction: Boolean = functionArityFor(tpnme.ImplicitFunction) >= 0
+
+    /** Is a synthetic function name
+     *    - FunctionN for N > 22
+     *    - ImplicitFunctionN for N >= 0
+     *    - false otherwise
+     */
+    def isSyntheticFunction: Boolean = {
+      functionArityFor(tpnme.Function) > MaxImplementedFunctionArity ||
+        functionArityFor(tpnme.ImplicitFunction) >= 0
+    }
+
+    /** Parsed function arity for function with some specific prefix */
+    private def functionArityFor(prefix: Name): Int = {
+      if (name.startsWith(prefix))
+        try name.toString.substring(prefix.length).toInt
+        catch { case _: NumberFormatException => -1 }
+      else -1
     }
 
     /** The name of the generic runtime operation corresponding to an array operation */
diff --git a/compiler/src/dotty/tools/dotc/core/TypeErasure.scala b/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
index 2a341390b..ff99008bb 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
@@ -44,7 +44,7 @@ object TypeErasure {
       val sym = tp.symbol
       sym.isClass &&
       sym != defn.AnyClass && sym != defn.ArrayClass &&
-      !defn.isXXLFunctionClass(sym) && !defn.isImplicitFunctionClass(sym)
+      !defn.isSyntheticFunctionClass(sym)
     case _: TermRef =>
       true
     case JavaArrayType(elem) =>
@@ -358,8 +358,7 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
       if (!sym.isClass) this(tp.info)
       else if (semiEraseVCs && isDerivedValueClass(sym)) eraseDerivedValueClassRef(tp)
       else if (sym == defn.ArrayClass) apply(tp.appliedTo(TypeBounds.empty)) // i966 shows that we can hit a raw Array type.
-      else if (defn.isXXLFunctionClass(sym)) defn.FunctionXXLType
-      else if (defn.isImplicitFunctionClass(sym)) apply(defn.FunctionType(sym.name.functionArity))
+      else if (defn.isSyntheticFunctionClass(sym)) defn.erasedFunctionType(sym)
       else eraseNormalClassRef(tp)
     case tp: RefinedType =>
       val parent = tp.parent
@@ -370,7 +369,7 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
     case SuperType(thistpe, supertpe) =>
       SuperType(this(thistpe), this(supertpe))
     case ExprType(rt) =>
-      defn.FunctionClass(0).typeRef
+      defn.FunctionType(0)
     case AndType(tp1, tp2) =>
       erasedGlb(this(tp1), this(tp2), isJava)
     case OrType(tp1, tp2) =>
@@ -496,8 +495,8 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
           val erasedVCRef = eraseDerivedValueClassRef(tp)
           if (erasedVCRef.exists) return sigName(erasedVCRef)
         }
-        if (defn.isImplicitFunctionClass(sym))
-          sigName(defn.FunctionType(sym.name.functionArity))
+        if (defn.isSyntheticFunctionClass(sym))
+          sigName(defn.erasedFunctionType(sym))
         else
           normalizeClass(sym.asClass).fullName.asTypeName
       case defn.ArrayOf(elem) =>
diff --git a/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala b/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala
index 5b75df6b2..3d952f425 100644
--- a/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala
+++ b/compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala
@@ -126,8 +126,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       case AppliedType(tycon, args) =>
         val cls = tycon.typeSymbol
         if (tycon.isRepeatedParam) return toTextLocal(args.head) ~ "*"
-        if (defn.isFunctionClass(cls)) return toTextFunction(args, isImplicit = false)
-        if (defn.isImplicitFunctionClass(cls)) return toTextFunction(args, isImplicit = true)
+        if (defn.isFunctionClass(cls)) return toTextFunction(args, cls.name.isImplicitFunction)
         if (defn.isTupleClass(cls)) return toTextTuple(args)
         return (toTextLocal(tycon) ~ "[" ~ Text(args map argText, ", ") ~ "]").close
       case tp: TypeRef =>
diff --git a/compiler/src/dotty/tools/dotc/transform/Erasure.scala b/compiler/src/dotty/tools/dotc/transform/Erasure.scala
index bba97c4c2..34ea2bc6f 100644
--- a/compiler/src/dotty/tools/dotc/transform/Erasure.scala
+++ b/compiler/src/dotty/tools/dotc/transform/Erasure.scala
@@ -349,10 +349,8 @@ object Erasure extends TypeTestsCasts{
           if ((owner eq defn.AnyClass) || (owner eq defn.AnyValClass)) {
             assert(sym.isConstructor, s"${sym.showLocated}")
             defn.ObjectClass
-          } else if (defn.isXXLFunctionClass(owner))
-            defn.FunctionXXLClass
-          else if (defn.isImplicitFunctionClass(owner))
-            recur(defn.FunctionClass(owner.name.functionArity))
+          } else if (defn.isSyntheticFunctionClass(owner))
+            defn.erasedFunctionClass(owner)
           else
             owner
         recur(sym.owner)
diff --git a/compiler/src/dotty/tools/dotc/transform/TreeChecker.scala b/compiler/src/dotty/tools/dotc/transform/TreeChecker.scala
index eee429a87..b2b99160b 100644
--- a/compiler/src/dotty/tools/dotc/transform/TreeChecker.scala
+++ b/compiler/src/dotty/tools/dotc/transform/TreeChecker.scala
@@ -81,7 +81,7 @@ class TreeChecker extends Phase with SymTransformer {
     val sym = symd.symbol
 
     if (sym.isClass && !sym.isAbsent) {
-      val validSuperclass = sym.isPrimitiveValueClass ||  defn.syntheticCoreClasses.contains(sym) ||
+      val validSuperclass = sym.isPrimitiveValueClass || defn.syntheticCoreClasses.contains(sym) ||
         (sym eq defn.ObjectClass) || (sym is NoSuperClass) || (sym.asClass.superClass.exists)
       if (!validSuperclass)
         printError(s"$sym has no superclass set")
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index ded8993fb..e04667223 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -664,9 +664,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def typedFunction(tree: untpd.Function, pt: Type)(implicit ctx: Context) = track("typedFunction") {
     val untpd.Function(args, body) = tree
     if (ctx.mode is Mode.Type) {
-      val funCls =
-        if (tree.isInstanceOf[untpd.ImplicitFunction]) defn.ImplicitFunctionClass(args.length)
-        else defn.FunctionClass(args.length)
+      val funCls = defn.FunctionClass(args.length, tree.isInstanceOf[untpd.ImplicitFunction])
       typed(cpy.AppliedTypeTree(tree)(
         untpd.TypeTree(funCls.typeRef), args :+ body), pt)
     }
@@ -1937,7 +1935,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
             !untpd.isImplicitClosure(tree) &&
             !isApplyProto(pt) &&
             !ctx.isAfterTyper) {
-          typr.println("insert apply on implicit $tree")
+          typr.println(i"insert apply on implicit $tree")
           typed(untpd.Select(untpd.TypedSplice(tree), nme.apply), pt)
         }
         else if (ctx.mode is Mode.Pattern) {