2 files changed, 40 insertions, 0 deletions
diff --git a/src/dotty/tools/dotc/core/SymDenotations.scala b/src/dotty/tools/dotc/core/SymDenotations.scala
index 606966be9..46484e6cc 100644
--- a/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -324,6 +324,9 @@ object SymDenotations {
     final def isRefinementClass(implicit ctx: Context): Boolean =
       name.decode == tpnme.REFINE_CLASS
 
+    final def isLambdaTrait(implicit ctx: Context): Boolean =
+      isClass && name.startsWith(tpnme.LambdaPrefix)
+
     /** Is this symbol a package object or its module class? */
     def isPackageObject(implicit ctx: Context): Boolean = {
       val poName = if (isType) nme.PACKAGE_CLS else nme.PACKAGE
diff --git a/src/dotty/tools/dotc/core/TypeApplications.scala b/src/dotty/tools/dotc/core/TypeApplications.scala
index c4845a249..428178b81 100644
--- a/src/dotty/tools/dotc/core/TypeApplications.scala
+++ b/src/dotty/tools/dotc/core/TypeApplications.scala
@@ -8,7 +8,9 @@ import Decorators._
 import util.Stats._
 import util.common._
 import Names._
+import NameOps._
 import Flags._
+import StdNames.tpnme
 import util.Positions.Position
 import config.Printers._
 import collection.mutable
@@ -108,6 +110,41 @@ class TypeApplications(val self: Type) extends AnyVal {
   def uninstantiatedTypeParams(implicit ctx: Context): List[TypeSymbol] =
     typeParams filter (tparam => self.member(tparam.name).symbol == tparam)
 
+ /** If type `tp` is equal, aliased-to, or upperbounded-by a type of the form
+   *  `LambdaXYZ { ... }`, the class symbol of that type, otherwise NoSymbol.
+   *  @param forcing  if set, might force completion. If not, never forces
+   *                  but returns NoSymbol when it would have to otherwise.
+   */
+  def LambdaClass(forcing: Boolean)(implicit ctx: Context): Symbol = ctx.traceIndented(i"LambdaClass($self)", hk) { self.stripTypeVar match {
+    case self: TypeRef =>
+      val sym = self.symbol
+      if (sym.isLambdaTrait) sym
+      else if (sym.isClass || sym.isCompleting && !forcing) NoSymbol
+      else self.info.LambdaClass(forcing)
+    case self: TermRef =>
+      NoSymbol
+    case self: TypeProxy =>
+      self.underlying.LambdaClass(forcing)
+    case _ =>
+      NoSymbol
+  }}
+
+  /** Is type `tp` equal, aliased-to, or upperbounded-by a type of the form
+   *  `LambdaXYZ { ... }`?
+   */
+  def isLambda(implicit ctx: Context): Boolean =
+    LambdaClass(forcing = true).exists
+
+  /** Same is `isLambda`, except that symbol denotations are not forced
+   *  Symbols in completion count as not lambdas.
+   */
+  def isSafeLambda(implicit ctx: Context): Boolean =
+    LambdaClass(forcing = false).exists
+
+  /** Is type `tp` a Lambda with all Arg$ fields fully instantiated? */
+  def isInstantiatedLambda(tp: Type)(implicit ctx: Context): Boolean =
+    tp.isSafeLambda && tp.typeParams.forall(_.name == tpnme.Apply)
+
   /** Encode the type resulting from applying this type to given arguments */
   final def appliedTo(args: List[Type])(implicit ctx: Context): Type = /*>|>*/ track("appliedTo") /*<|<*/ {