From 09efbe20379034083517b954afe7e46a1d9a2fa9 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Sat, 26 Aug 2023 14:03:52 -0600
Subject: [PATCH] Fix MT separate compilation bug (bis)

---
 .../src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala   | 8 +++++++-
 tests/pos/i18261.bis.min/Main_0.scala                     | 7 +++++++
 tests/pos/i18261.bis.min/Test_1.scala                     | 4 ++++
 tests/pos/i18261.bis/DFBits_0.scala                       | 7 +++++++
 tests/pos/i18261.bis/Foo_0.scala                          | 4 ++++
 tests/pos/i18261.bis/Test_1.scala                         | 5 +++++
 6 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i18261.bis.min/Main_0.scala
 create mode 100644 tests/pos/i18261.bis.min/Test_1.scala
 create mode 100644 tests/pos/i18261.bis/DFBits_0.scala
 create mode 100644 tests/pos/i18261.bis/Foo_0.scala
 create mode 100644 tests/pos/i18261.bis/Test_1.scala

diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index 7fa335afbf44..4f48519c4a92 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -1452,7 +1452,13 @@ class TreeUnpickler(reader: TastyReader,
               val args = until(end)(readTpt())
               val tree = untpd.AppliedTypeTree(tycon, args)
               val ownType = ctx.typeAssigner.processAppliedType(tree, tycon.tpe.safeAppliedTo(args.tpes))
-              tree.withType(postProcessFunction(ownType))
+              val tp = postProcessFunction(ownType)
+              // Much like in the MATCHtpt case,
+              // normalize the type to avoid differences in the type of trees,
+              // (between joint compilation and separate compilation)
+              // which affects how types are compared in subtyping.
+              val tpn = tp.normalized
+              tree.withType(tpn)
             case ANNOTATEDtpt =>
               Annotated(readTpt(), readTree())
             case LAMBDAtpt =>
diff --git a/tests/pos/i18261.bis.min/Main_0.scala b/tests/pos/i18261.bis.min/Main_0.scala
new file mode 100644
index 000000000000..18d746f60d42
--- /dev/null
+++ b/tests/pos/i18261.bis.min/Main_0.scala
@@ -0,0 +1,7 @@
+trait VAL
+
+type Foo[T, M] = M match { case VAL => T }
+
+class Cand[A]
+object Cand:
+  given inst[X, Y <: Foo[X, VAL]]: Cand[Y] = new Cand[Y]
diff --git a/tests/pos/i18261.bis.min/Test_1.scala b/tests/pos/i18261.bis.min/Test_1.scala
new file mode 100644
index 000000000000..c5d62cc12267
--- /dev/null
+++ b/tests/pos/i18261.bis.min/Test_1.scala
@@ -0,0 +1,4 @@
+class Test:
+  def test: Unit =
+    summon[Cand[Int]]
+    summon[Cand[Long]]
diff --git a/tests/pos/i18261.bis/DFBits_0.scala b/tests/pos/i18261.bis/DFBits_0.scala
new file mode 100644
index 000000000000..0313faf04523
--- /dev/null
+++ b/tests/pos/i18261.bis/DFBits_0.scala
@@ -0,0 +1,7 @@
+trait DFBits[W <: Int]
+
+trait Candidate[R]:
+  type OutW <: Int
+object Candidate:
+  given [W <: Int, R <: Foo[DFBits[W], VAL]]: Candidate[R] with
+    type OutW = W
diff --git a/tests/pos/i18261.bis/Foo_0.scala b/tests/pos/i18261.bis/Foo_0.scala
new file mode 100644
index 000000000000..47dd67b0984d
--- /dev/null
+++ b/tests/pos/i18261.bis/Foo_0.scala
@@ -0,0 +1,4 @@
+trait VAL
+
+type Foo[T, M] = M match
+  case VAL => T
diff --git a/tests/pos/i18261.bis/Test_1.scala b/tests/pos/i18261.bis/Test_1.scala
new file mode 100644
index 000000000000..3b91847e3326
--- /dev/null
+++ b/tests/pos/i18261.bis/Test_1.scala
@@ -0,0 +1,5 @@
+def baz[L](lhs: L)(using icL: Candidate[L]): DFBits[Int] = ???
+object Test:
+  val x: DFBits[8] = ???
+  val z: DFBits[Int] = baz(x)
+  summon[Candidate[z.type]]