From 2bac2f6ab1d76f3eac8f4cdbb3bbc76f22f9b7b1 Mon Sep 17 00:00:00 2001
From: Jan Ouwens <jan.ouwens@gmail.com>
Date: Wed, 29 Nov 2023 13:32:38 +0100
Subject: [PATCH] Support scalac -Xcheckinit

---
 CHANGELOG.md                                  |  4 +++
 .../internal/reflection/FieldIterable.java    |  6 +++-
 .../SyntheticFieldsTest.java                  | 33 +++++++++++++++++++
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f7e5ce20d..4247f75d9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+-   A check for Scala with its `-Xcheckinit` flag switched on. This flag generates a field that should have been marked as synthetic, but isn't, so EqualsVerifier has to check for this field explicitly.
+
 ## [3.15.3] - 2023-11-01
 
 ### Changed
diff --git a/equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/FieldIterable.java b/equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/FieldIterable.java
index d8be8deb0..b50d3f57c 100644
--- a/equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/FieldIterable.java
+++ b/equalsverifier-core/src/main/java/nl/jqno/equalsverifier/internal/reflection/FieldIterable.java
@@ -85,7 +85,11 @@ private List<Field> addFieldsFor(Class<?> c) {
         List<Field> statics = new ArrayList<>();
 
         for (Field field : c.getDeclaredFields()) {
-            if (!field.isSynthetic() && !"__cobertura_counters".equals(field.getName())) {
+            if (
+                !field.isSynthetic() &&
+                !"__cobertura_counters".equals(field.getName()) &&
+                !field.getName().startsWith("bitmap$init$") // Generated by Scala 2.x's -Xcheckinit flag
+            ) {
                 boolean isStatic = Modifier.isStatic(field.getModifiers());
                 if (isStatic && includeStatic) {
                     statics.add(field);
diff --git a/equalsverifier-core/src/test/java/nl/jqno/equalsverifier/integration/extended_contract/SyntheticFieldsTest.java b/equalsverifier-core/src/test/java/nl/jqno/equalsverifier/integration/extended_contract/SyntheticFieldsTest.java
index 211c4b334..20d7f1a21 100644
--- a/equalsverifier-core/src/test/java/nl/jqno/equalsverifier/integration/extended_contract/SyntheticFieldsTest.java
+++ b/equalsverifier-core/src/test/java/nl/jqno/equalsverifier/integration/extended_contract/SyntheticFieldsTest.java
@@ -36,6 +36,11 @@ public void succeed_whenClassIsInstrumentedByCobertura_givenCoberturaDoesntMarkI
         EqualsVerifier.forClass(CoberturaContainer.class).verify();
     }
 
+    @Test
+    public void succeed_whenScalacOptionCheckinitIsEnabled_givenScalaDoesntMarkItsFieldsSynthetic() {
+        EqualsVerifier.forClass(ScalaCheckinit.class).verify();
+    }
+
     static final class LambdaContainer {
 
         private static final Comparator<LambdaContainer> COMPARATOR = (c1, c2) -> 0; // A lambda is a synthetic class
@@ -152,4 +157,32 @@ public int hashCode() {
             return defaultHashCode(this);
         }
     }
+
+    public static final class ScalaCheckinit {
+
+        // CHECKSTYLE OFF: MemberName
+        // This field is generated by the Scala 2.x compiler when -Xcheckinit is switched on.
+        // However, it's not marked as 'synthetic', so EqualsVerifier doesn't ignore it automatically.
+        private volatile byte bitmap$init$0 = 0;
+        // CHECKSTYLE ON: MemberName
+        private final int i;
+
+        public ScalaCheckinit(int i) {
+            this.i = i;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (!(obj instanceof ScalaCheckinit)) {
+                return false;
+            }
+            ScalaCheckinit p = (ScalaCheckinit) obj;
+            return p.i == i;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(i);
+        }
+    }
 }