From fff536ffc63e15749e9515387424a99fb997f63d Mon Sep 17 00:00:00 2001
From: Jan Chyb <jan.chyb.99@gmail.com>
Date: Wed, 17 Sep 2025 15:09:56 +0200
Subject: [PATCH] When unpickling, do not incorrectly set PureInterface flags

Previously, the behavior for setting `NoInits` and `PureInterface` flags
for class symbols in `TreeInfo.defKind` (when compiling from a source)
and in `TreeUnpickler` (when reading Tasty) was inconsistent.
This was problematic, as the `PureInterface` flag dictated whether outer
accessors were generated in `ExplicitOuter` phase (in
the `needsOuterIfReferenced` method), so in the issue minimization,
the inherited trait would have the outer accessors defined, and
the inheriting object would then not implement them. This lead to
runtime `MethodNotFound` errors.
The problem was specifically with lazy vals, which were treated as if
they did not have an rhs.
---
 .../dotty/tools/dotc/core/tasty/TreeUnpickler.scala |  2 +-
 tests/run/i23863-a/BaseTest_1.scala                 | 13 +++++++++++++
 tests/run/i23863-a/Test_2.scala                     |  4 ++++
 tests/run/i23863-b/NestedObject_1.scala             |  3 +++
 tests/run/i23863-b/Test_2.scala                     |  3 +++
 5 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 tests/run/i23863-a/BaseTest_1.scala
 create mode 100644 tests/run/i23863-a/Test_2.scala
 create mode 100644 tests/run/i23863-b/NestedObject_1.scala
 create mode 100644 tests/run/i23863-b/Test_2.scala

diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index 95c9731a0679..c491f15055fa 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -813,7 +813,7 @@ class TreeUnpickler(reader: TastyReader,
             if (sym.isTerm && !sym.isOneOf(DeferredOrLazyOrMethod))
               initsFlags = EmptyFlags
             else if (sym.isClass ||
-              sym.is(Method, butNot = Deferred) && !sym.isConstructor)
+              sym.isOneOf(Method | Lazy, butNot = Deferred) && !sym.isConstructor)
               initsFlags &= NoInits
           case IMPORT | EXPORT =>
             skipTree()
diff --git a/tests/run/i23863-a/BaseTest_1.scala b/tests/run/i23863-a/BaseTest_1.scala
new file mode 100644
index 000000000000..4a23904cb4eb
--- /dev/null
+++ b/tests/run/i23863-a/BaseTest_1.scala
@@ -0,0 +1,13 @@
+abstract class BaseTest {
+  def genName(): String = "outerAccess"
+  trait Fixture {
+    lazy val service: Service = new Service {
+      val a = genName()
+      def doIt(a: String): Int = 0
+    }
+  }
+}
+
+trait Service {
+  def doIt(a: String): Int
+}
diff --git a/tests/run/i23863-a/Test_2.scala b/tests/run/i23863-a/Test_2.scala
new file mode 100644
index 000000000000..9169e6668433
--- /dev/null
+++ b/tests/run/i23863-a/Test_2.scala
@@ -0,0 +1,4 @@
+object Test extends BaseTest {
+  def main(args: Array[String]): Unit =
+    new Fixture { service.doIt("test") }
+}
diff --git a/tests/run/i23863-b/NestedObject_1.scala b/tests/run/i23863-b/NestedObject_1.scala
new file mode 100644
index 000000000000..c792f59894a6
--- /dev/null
+++ b/tests/run/i23863-b/NestedObject_1.scala
@@ -0,0 +1,3 @@
+trait NestedObject {
+  case class A()
+}
diff --git a/tests/run/i23863-b/Test_2.scala b/tests/run/i23863-b/Test_2.scala
new file mode 100644
index 000000000000..99e6b8851200
--- /dev/null
+++ b/tests/run/i23863-b/Test_2.scala
@@ -0,0 +1,3 @@
+object Test extends NestedObject {
+  def main(args: Array[String]): Unit = ()
+}