IssueTracker

Component: Android Public Tracker > App Development > Android Studio > Build Tools > Lint

Studio Build: irrelevant (4.0.1)

Version of Gradle Plugin: 3.6.3 or 4.0.1

Version of Gradle: irrelevant (5.6.4 or 6.5, whichever works with AGP version)

Version of Java: irrelevant (openjdk 1.8.0_242-release)

OS: irrelevant (Windows 10)

Steps to Reproduce:

1. Download DiffUtilEquals.zip
2. Extract it somewhere
3. Run gradlew lint in that folder

Expected: no lint violations Actual: 2 errors (1 in Java and 1 in Kotlin)

  Errors found:

  C:\dev\DiffUtilEquals\src\main\java\com\example\MyDiffUtilCallbackJava.java:18: Error: Suspicious equality check: equals() is not implemented in com.example.IModel [DiffUtilEquals]
     return oldItem.equals(newItem);
                    ~~~~~~~~~~~~~~~
  C:\dev\DiffUtilEquals\src\main\java\com\example\MyDiffUtilCallbackKotlin.kt:17: Error: Suspicious equality check: equals() is not implemented in IModel [DiffUtilEquals]
          oldItem is Model && newItem is Model && oldItem == newItem
                                                          ~~

Despite having a workaround in https://issuetracker.google.com/issues/122928037, we think that DiffUtilEquals should not trigger in these cases:

// Kotlin
oldItem is Model && newItem is Model && oldItem == newItem

// Java
if (oldItem instanceof Model && newItem instanceof Model) {
	return oldItem.equals(newItem);
}

iff Model class has a defined equals method.

This should be especially true in Kotlin where smart casts exist.