From 9af598d442697529292fb0307a19c84bebb284c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Doeraene?= <sjrdoeraene@gmail.com>
Date: Sat, 31 Dec 2022 15:29:22 +0100
Subject: [PATCH] Subtyping for TypeLambda's.

---
 .../src/main/scala/tastyquery/Subtyping.scala | 18 +++++++++++++++
 .../scala/tastyquery/SubtypingSuite.scala     | 22 +++++++++++++++++++
 .../main/scala/subtyping/TypesFromTASTy.scala |  2 ++
 3 files changed, 42 insertions(+)

diff --git a/tasty-query/shared/src/main/scala/tastyquery/Subtyping.scala b/tasty-query/shared/src/main/scala/tastyquery/Subtyping.scala
index d3dcd062..7689f120 100644
--- a/tasty-query/shared/src/main/scala/tastyquery/Subtyping.scala
+++ b/tasty-query/shared/src/main/scala/tastyquery/Subtyping.scala
@@ -143,6 +143,16 @@ private[tastyquery] object Subtyping:
     case tp2: AppliedType =>
       compareAppliedType2(tp1, tp2)
 
+    case tp2: TypeLambda =>
+      tp1 match
+        case tp1: TypeLambda =>
+          // TODO Check bounds and variances
+          tp1.paramRefs.lengthCompare(tp2.paramRefs) == 0
+            && isSubtype(tp1.resultType, tp2.appliedTo(tp1.paramRefs))
+        case _ =>
+          // TODO? Eta-expand polymorphic type constructors?
+          level4(tp1, tp2)
+
     case tp2: OrType =>
       isSubtype(tp1, tp2.first) || isSubtype(tp1, tp2.second)
         || level4(tp1, tp2)
@@ -269,6 +279,14 @@ private[tastyquery] object Subtyping:
 
       comparePaths || proceedWithWidenedType
 
+    case tp1: TypeLambda =>
+      tp2 match
+        case tp2: TypeLambda =>
+          false // this case is already handled in level3
+        case _ =>
+          tp2.typeParams.lengthCompare(tp1.paramRefs) == 0
+            && isSubtype(tp1.resultType, tp2.appliedTo(tp1.paramRefs))
+
     case tp1: AndType =>
       // TODO Try and simplify first
       isSubtype(tp1.first, tp2) || isSubtype(tp1.second, tp2)
diff --git a/tasty-query/shared/src/test/scala/tastyquery/SubtypingSuite.scala b/tasty-query/shared/src/test/scala/tastyquery/SubtypingSuite.scala
index b6359f25..ce404691 100644
--- a/tasty-query/shared/src/test/scala/tastyquery/SubtypingSuite.scala
+++ b/tasty-query/shared/src/test/scala/tastyquery/SubtypingSuite.scala
@@ -105,6 +105,9 @@ class SubtypingSuite extends UnrestrictedUnpicklingSuite:
   def findTypesFromTASTyNamed(name: String)(using Context): Type =
     ctx.findTopLevelClass("subtyping.TypesFromTASTy").findDecl(termName(name)).declaredType
 
+  def findTypesFromTASTyNamed(name: TypeName)(using Context): Type =
+    ctx.findTopLevelClass("subtyping.TypesFromTASTy").findDecl(name).asInstanceOf[TypeMemberSymbol].aliasedType
+
   testWithContext("same-monomorphic-class") {
     assertEquiv(defn.IntType, defn.IntClass.typeRef).withRef[Int, scala.Int]
     assertEquiv(defn.IntType, defn.IntClass.newTypeRef)
@@ -560,4 +563,23 @@ class SubtypingSuite extends UnrestrictedUnpicklingSuite:
       .withRef[mutable.Seq[? <: Option[Any]], mutable.Seq[? <: Product]]
   }
 
+  testWithContext("type-lambdas") {
+    val Function1Class = ctx.findTopLevelClass("scala.Function1")
+    def fun1Type(argType: Type, resultType: Type): Type =
+      AppliedType(Function1Class.typeRef, argType :: resultType :: Nil)
+
+    def makeTToTTypeLambda() = TypeLambda(typeName("T") :: Nil)(
+      _ => List(defn.NothingAnyBounds),
+      tl => fun1Type(tl.paramRefs(0), tl.paramRefs(0))
+    )
+    val tToTTypeLambda = makeTToTTypeLambda()
+
+    val fromTasty = findTypesFromTASTyNamed(typeName("TToTType"))
+
+    type TToTType = [T] => T => T
+
+    assertEquiv(tToTTypeLambda, makeTToTTypeLambda()).withRef[TToTType, TToTType]
+    assertEquiv(tToTTypeLambda, fromTasty)
+  }
+
 end SubtypingSuite
diff --git a/test-sources/src/main/scala/subtyping/TypesFromTASTy.scala b/test-sources/src/main/scala/subtyping/TypesFromTASTy.scala
index 564b80ba..7bc3cb19 100644
--- a/test-sources/src/main/scala/subtyping/TypesFromTASTy.scala
+++ b/test-sources/src/main/scala/subtyping/TypesFromTASTy.scala
@@ -7,4 +7,6 @@ class TypesFromTASTy:
 
   val orType: Int | String = 1
   val andType: Product & Serializable = Nil
+
+  type TToTType[T] = T => T
 end TypesFromTASTy