From f77069a74c4df65c7f69a6476aeb6b52fa8acb48 Mon Sep 17 00:00:00 2001
From: Guillaume Martres <smarter@ubuntu.com>
Date: Fri, 10 Feb 2023 15:36:06 +0100
Subject: [PATCH] ClassfileParser: Avoid cycle when accessing companion in
 inner class lookup

Previously, the call to `info` on the module val could lead to a cycle since the
module val might be in the process of being completed. This commit fixes this by
only using the module class which is all we need to lookup members.

Fixes #15288.
Fixes #14059.

Co-Authored-By: Tom Grigg <tomegrigg@gmail.com>
---
 .../tools/dotc/core/classfile/ClassfileParser.scala      | 8 ++++----
 sbt-test/java-compat/i15288/QueryRequest.java            | 9 +++++++++
 sbt-test/java-compat/i15288/Test.scala                   | 2 ++
 sbt-test/java-compat/i15288/build.sbt                    | 1 +
 sbt-test/java-compat/i15288/test                         | 5 +++++
 5 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 sbt-test/java-compat/i15288/QueryRequest.java
 create mode 100644 sbt-test/java-compat/i15288/Test.scala
 create mode 100644 sbt-test/java-compat/i15288/build.sbt
 create mode 100644 sbt-test/java-compat/i15288/test

diff --git a/compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala b/compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala
index 7702e6a93446..eeeb3767bd34 100644
--- a/compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala
+++ b/compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala
@@ -1086,10 +1086,10 @@ class ClassfileParser(
           if (sym == classRoot.symbol)
             staticScope.lookup(name)
           else {
-            var module = sym.companionModule
-            if (!module.exists && sym.isAbsent())
-              module = sym.scalacLinkedClass
-            module.info.member(name).symbol
+            var moduleClass = sym.registeredCompanion
+            if (!moduleClass.exists && sym.isAbsent())
+              moduleClass = sym.scalacLinkedClass
+            moduleClass.info.member(name).symbol
           }
         else if (sym == classRoot.symbol)
           instanceScope.lookup(name)
diff --git a/sbt-test/java-compat/i15288/QueryRequest.java b/sbt-test/java-compat/i15288/QueryRequest.java
new file mode 100644
index 000000000000..e43487e09449
--- /dev/null
+++ b/sbt-test/java-compat/i15288/QueryRequest.java
@@ -0,0 +1,9 @@
+interface CopyableBuilder<B, T> {}
+interface ToCopyableBuilder<B, T> {}
+
+public class QueryRequest implements ToCopyableBuilder<QueryRequest.Builder, QueryRequest> {
+    public static Builder builder() { throw new UnsupportedOperationException(); }
+    public interface Builder extends CopyableBuilder<Builder, QueryRequest> {
+        void build();
+    }
+}
diff --git a/sbt-test/java-compat/i15288/Test.scala b/sbt-test/java-compat/i15288/Test.scala
new file mode 100644
index 000000000000..e03617ac4c33
--- /dev/null
+++ b/sbt-test/java-compat/i15288/Test.scala
@@ -0,0 +1,2 @@
+class Test:
+  def makeQuery = QueryRequest.builder().build()
diff --git a/sbt-test/java-compat/i15288/build.sbt b/sbt-test/java-compat/i15288/build.sbt
new file mode 100644
index 000000000000..63e314982c41
--- /dev/null
+++ b/sbt-test/java-compat/i15288/build.sbt
@@ -0,0 +1 @@
+scalaVersion := sys.props("plugin.scalaVersion")
diff --git a/sbt-test/java-compat/i15288/test b/sbt-test/java-compat/i15288/test
new file mode 100644
index 000000000000..ad1a8a5987ee
--- /dev/null
+++ b/sbt-test/java-compat/i15288/test
@@ -0,0 +1,5 @@
+## This could just be a pos test checked by FromTastyTests, but
+## ParallelTesting#compileTastyInDir does not support test with multiple files
+## currently.
+> compile
+> doc