From 0ce09551350d817ba15ed5d30209ccf91d7b0ee0 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Thu, 26 Oct 2023 11:18:01 +0100
Subject: [PATCH] Identify structural trees on Match Type qualifiers

Without this change, selecting `v1` on a type `Ifce[(true :
Boolean)]#RT` which widens to a MatchType wouldn't be identified as a
structural tree, which later breaks Erasure.

[Cherry-picked ff90012510dd986381871c425bd9341e9216d3c8]
---
 compiler/src/dotty/tools/dotc/ast/TreeInfo.scala |  2 ++
 tests/neg/i17192.5.scala                         | 12 ++++++++++++
 tests/pos/i17192.scala                           | 11 +++++++++++
 3 files changed, 25 insertions(+)
 create mode 100644 tests/neg/i17192.5.scala
 create mode 100644 tests/pos/i17192.scala

diff --git a/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala b/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
index befac83b824b..7cd6ef96b4f5 100644
--- a/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
+++ b/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
@@ -949,6 +949,8 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
       def hasRefinement(qualtpe: Type): Boolean = qualtpe.dealias match
         case defn.PolyOrErasedFunctionOf(_) =>
           false
+        case tp: MatchType =>
+          hasRefinement(tp.tryNormalize)
         case RefinedType(parent, rname, rinfo) =>
           rname == tree.name || hasRefinement(parent)
         case tp: TypeProxy =>
diff --git a/tests/neg/i17192.5.scala b/tests/neg/i17192.5.scala
new file mode 100644
index 000000000000..2837af36b573
--- /dev/null
+++ b/tests/neg/i17192.5.scala
@@ -0,0 +1,12 @@
+class Ifce[BT <: Boolean]:
+  type RT = BT match
+    case true => this.type { val v1: Int }
+  def cast: RT = this.asInstanceOf[RT]
+
+class Test:
+  def t1: Unit =
+    val full1 = new Ifce[true]().cast
+    val v1 = full1.v1 // error
+//           ^^^^^
+//           Found:    (full1 : Ifce[(true : Boolean)]#RT)
+//           Required: Selectable | Dynamic
diff --git a/tests/pos/i17192.scala b/tests/pos/i17192.scala
new file mode 100644
index 000000000000..129da358b3ba
--- /dev/null
+++ b/tests/pos/i17192.scala
@@ -0,0 +1,11 @@
+class Ifce[BT <: Boolean] extends Selectable:
+  type RT = BT match
+    case true  => this.type { val v1: Int }
+    case false => this.type
+  def cast : RT = this.asInstanceOf[RT]
+  def selectDynamic(key: String): Any = ???
+
+class Test:
+  def t1: Unit =
+    val full = (new Ifce[true]).cast
+    val v1 = full.v1