From 7103791b24066a5abb3e55507afbd06cfdee519c Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 29 Apr 2021 13:18:07 +0200
Subject: [PATCH] Don't strip @uncheckedVariance when inferring the type of
 default getters

Fixes #12273
---
 compiler/src/dotty/tools/dotc/core/TypeOps.scala |  4 +++-
 compiler/src/dotty/tools/dotc/typer/Namer.scala  | 10 ++++++----
 tests/pos/i12273.scala                           |  4 ++++
 3 files changed, 13 insertions(+), 5 deletions(-)
 create mode 100644 tests/pos/i12273.scala

diff --git a/compiler/src/dotty/tools/dotc/core/TypeOps.scala b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
index eb353744ae82..09ac61d304b8 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
@@ -164,7 +164,7 @@ object TypeOps:
         // corrective steps, so no widening is wanted.
         simplify(l, theMap) | simplify(r, theMap)
       case AnnotatedType(parent, annot)
-      if !ctx.mode.is(Mode.Type) && annot.symbol == defn.UncheckedVarianceAnnot =>
+      if annot.symbol == defn.UncheckedVarianceAnnot && !ctx.mode.is(Mode.Type) && !theMap.isInstanceOf[SimplifyKeepUnchecked] =>
         simplify(parent, theMap)
       case _: MatchType =>
         val normed = tp.tryNormalize
@@ -180,6 +180,8 @@ object TypeOps:
     def apply(tp: Type): Type = simplify(tp, this)
   }
 
+  class SimplifyKeepUnchecked(using Context) extends SimplifyMap
+
   /** Approximate union type by intersection of its dominators.
    *  That is, replace a union type Tn | ... | Tn
    *  by the smallest intersection type of base-class instances of T1,...,Tn.
diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index 10872e39b516..141e9f67b5f9 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -1550,10 +1550,12 @@ class Namer { typer: Typer =>
           // For justification on the use of `@uncheckedVariance`, see
           // `default-getter-variance.scala`.
           AnnotatedType(defaultTp, Annotation(defn.UncheckedVarianceAnnot))
-        else tp.widenTermRefExpr.simplified match
-          case ctp: ConstantType if isInlineVal => ctp
-          case tp =>
-            TypeComparer.widenInferred(tp, pt)
+        else
+          // don't strip @uncheckedVariance annot for default getters
+          TypeOps.simplify(tp.widenTermRefExpr,
+              if defaultTp.exists then TypeOps.SimplifyKeepUnchecked() else null) match
+            case ctp: ConstantType if isInlineVal => ctp
+            case tp => TypeComparer.widenInferred(tp, pt)
 
       // Replace aliases to Unit by Unit itself. If we leave the alias in
       // it would be erased to BoxedUnit.
diff --git a/tests/pos/i12273.scala b/tests/pos/i12273.scala
new file mode 100644
index 000000000000..1201c2fc62bd
--- /dev/null
+++ b/tests/pos/i12273.scala
@@ -0,0 +1,4 @@
+import scala.annotation.unchecked.uncheckedVariance
+
+final case class Outlet[T](out: T)
+final case class SourceShape[+T](val out: Outlet[T @uncheckedVariance])
\ No newline at end of file