From 4ffa162a304d6dc8cd7444206a17a6a0b38f2c77 Mon Sep 17 00:00:00 2001
From: David Schlosnagle <davids@palantir.com>
Date: Wed, 20 Jul 2022 09:17:55 -0400
Subject: [PATCH] Equals compares collections last

---
 .../conjure/java/types/MethodSpecs.java       | 33 +++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/conjure-java-core/src/main/java/com/palantir/conjure/java/types/MethodSpecs.java b/conjure-java-core/src/main/java/com/palantir/conjure/java/types/MethodSpecs.java
index 5bac5e53f..a70a57a1a 100644
--- a/conjure-java-core/src/main/java/com/palantir/conjure/java/types/MethodSpecs.java
+++ b/conjure-java-core/src/main/java/com/palantir/conjure/java/types/MethodSpecs.java
@@ -19,6 +19,7 @@
 import static com.palantir.logsafe.Preconditions.checkState;
 
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.palantir.conjure.java.util.JavaNameSanitizer;
 import com.palantir.conjure.spec.FieldName;
@@ -27,6 +28,7 @@
 import com.squareup.javapoet.FieldSpec;
 import com.squareup.javapoet.MethodSpec;
 import com.squareup.javapoet.ParameterSpec;
+import com.squareup.javapoet.ParameterizedTypeName;
 import com.squareup.javapoet.TypeName;
 import com.squareup.javapoet.TypeSpec;
 import java.time.OffsetDateTime;
@@ -38,6 +40,8 @@
 
 public final class MethodSpecs {
 
+    private static final ImmutableSet<String> COLLECTION_TYPES =
+            ImmutableSet.of("java.util.List", "java.util.Set", "java.util.Map");
     private static final String MEMOIZED_HASH_CODE = "memoizedHashCode";
 
     public static MethodSpec createEquals(TypeName thisClass) {
@@ -70,8 +74,10 @@ public static MethodSpec createEqualTo(
 
         CodeBlock equalsTo = fields.isEmpty()
                 ? CodeBlock.of("$L", true)
-                : CodeBlocks.of(
-                        fields.stream().map(MethodSpecs::createEqualsStatement).collect(joining(CodeBlock.of(" && "))));
+                : CodeBlocks.of(fields.stream()
+                        .sorted(MethodSpecs::collectionsLastForEquals)
+                        .map(MethodSpecs::createEqualsStatement)
+                        .collect(joining(CodeBlock.of(" && "))));
 
         return MethodSpec.methodBuilder("equalTo")
                 .addModifiers(Modifier.PRIVATE)
@@ -82,6 +88,29 @@ public static MethodSpec createEqualTo(
                 .build();
     }
 
+    private static int collectionsLastForEquals(FieldSpec field1, FieldSpec field2) {
+        if (COLLECTION_TYPES.contains(getTypeForEquals(field1.type))) {
+            if (COLLECTION_TYPES.contains(getTypeForEquals(field2.type))) {
+                return 0; // both are collections, keep in place
+            }
+            return 1; // sort collections last for equals comparison
+        }
+        return 0; // keep in place
+    }
+
+    private static String getTypeForEquals(TypeName typeName) {
+        if (typeName instanceof ParameterizedTypeName) {
+            ParameterizedTypeName parameterizedTypeName = (ParameterizedTypeName) typeName;
+            String canonicalName = parameterizedTypeName.rawType.canonicalName();
+            if ("java.util.Optional".equals(canonicalName)) {
+                return getTypeForEquals(
+                        parameterizedTypeName.typeArguments.iterator().next());
+            }
+            return canonicalName;
+        }
+        return typeName.toString();
+    }
+
     private static CodeBlock createEqualsStatement(FieldSpec field) {
         String thisField = "this." + field.name;
         String otherField = "other." + field.name;