From 50c646417a9d7229b32ba6276b8364a65be5f957 Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Thu, 24 Mar 2022 09:28:00 +0100
Subject: [PATCH] Drop special treatment for Scala-2 code in unapply

It seems our GADT handling is now able to do without.

Fixes #14693
---
 compiler/src/dotty/tools/dotc/core/TypeOps.scala         | 2 +-
 .../src/dotty/tools/dotc/transform/TypeTestsCasts.scala  | 2 +-
 compiler/src/dotty/tools/dotc/typer/Applications.scala   | 4 +---
 compiler/src/dotty/tools/dotc/typer/Inferencing.scala    | 4 ++--
 tests/run/i14693.check                                   | 1 +
 tests/run/i14693.scala                                   | 9 +++++++++
 6 files changed, 15 insertions(+), 7 deletions(-)
 create mode 100644 tests/run/i14693.check
 create mode 100644 tests/run/i14693.scala

diff --git a/compiler/src/dotty/tools/dotc/core/TypeOps.scala b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
index c13d005fa5ac..2cfdd08128ce 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
@@ -827,7 +827,7 @@ object TypeOps:
     }
 
     def instantiate(): Type = {
-      maximizeType(protoTp1, NoSpan, fromScala2x = false)
+      maximizeType(protoTp1, NoSpan)
       wildApprox(protoTp1)
     }
 
diff --git a/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala b/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
index 4db3e9b80c9d..371982a8b442 100644
--- a/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
+++ b/compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
@@ -109,7 +109,7 @@ object TypeTestsCasts {
       // which conform to the skeleton pre.F[_] and X. Then we have to make
       // sure all of them are actually of the type P, which implies that the
       // type arguments in P are trivial (no runtime check needed).
-      maximizeType(P1, span, fromScala2x = false)
+      maximizeType(P1, span)
 
       debug.println("after " + ctx.typerState.constraint.show)
 
diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index 2cf1050a5c67..68c4b357b782 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Applications.scala
@@ -1326,8 +1326,6 @@ trait Applications extends Compatibility {
         unapp
     }
 
-    def fromScala2x = unapplyFn.symbol.exists && (unapplyFn.symbol.owner is Scala2x)
-
     unapplyFn.tpe.widen match {
       case mt: MethodType if mt.paramInfos.length == 1 =>
         val unapplyArgType = mt.paramInfos.head
@@ -1343,7 +1341,7 @@ trait Applications extends Compatibility {
             // Constraining only fails if the pattern cannot possibly match,
             // but useless pattern checks detect more such cases, so we simply rely on them instead.
             withMode(Mode.GadtConstraintInference)(TypeComparer.constrainPatternType(unapplyArgType, selType))
-            val patternBound = maximizeType(unapplyArgType, tree.span, fromScala2x)
+            val patternBound = maximizeType(unapplyArgType, tree.span)
             if (patternBound.nonEmpty) unapplyFn = addBinders(unapplyFn, patternBound)
             unapp.println(i"case 2 $unapplyArgType ${ctx.typerState.constraint}")
             unapplyArgType
diff --git a/compiler/src/dotty/tools/dotc/typer/Inferencing.scala b/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
index 733b95995f05..043f931113ab 100644
--- a/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -399,7 +399,7 @@ object Inferencing {
    *  @return   The list of type symbols that were created
    *            to instantiate undetermined type variables that occur non-variantly
    */
-  def maximizeType(tp: Type, span: Span, fromScala2x: Boolean)(using Context): List[Symbol] = {
+  def maximizeType(tp: Type, span: Span)(using Context): List[Symbol] = {
     Stats.record("maximizeType")
     val vs = variances(tp)
     val patternBindings = new mutable.ListBuffer[(Symbol, TypeParamRef)]
@@ -409,7 +409,7 @@ object Inferencing {
         else if (v == -1) tvar.instantiate(fromBelow = true)
         else {
           val bounds = TypeComparer.fullBounds(tvar.origin)
-          if (bounds.hi <:< bounds.lo || bounds.hi.classSymbol.is(Final) || fromScala2x)
+          if bounds.hi <:< bounds.lo || bounds.hi.classSymbol.is(Final) then
             tvar.instantiate(fromBelow = false)
           else {
             // We do not add the created symbols to GADT constraint immediately, since they may have inter-dependencies.
diff --git a/tests/run/i14693.check b/tests/run/i14693.check
new file mode 100644
index 000000000000..f985b46aff02
--- /dev/null
+++ b/tests/run/i14693.check
@@ -0,0 +1 @@
+Success!
diff --git a/tests/run/i14693.scala b/tests/run/i14693.scala
new file mode 100644
index 000000000000..52d7ca6de4a6
--- /dev/null
+++ b/tests/run/i14693.scala
@@ -0,0 +1,9 @@
+object Test {
+  val a: Array[Long] = Array(1L)
+
+  def test(x: Any) = x match {
+    case Array(i: Long) => println("Success!")
+    case _              => println("Failure!") }
+
+  def main(args: Array[String]): Unit = test(a)
+}
\ No newline at end of file