Allow sealed classes to be Moshi-compatible (#431)

* Allow enums to be Moshi compatible

* Run spotless

* Support sealed interfaces with moshi-sealed

* Support primitives in collections

* Support sealed classes

* Run spotless

* Clarify comment

* Edit comment formatting

Author: ywu96

slack-lint-checks/src/main/java/slack/lint/JsonInflaterMoshiCompatibilityDetector.kt

@@ -172,9 +172,28 @@ class JsonInflaterMoshiCompatibilityDetector : Detector(), SourceCodeScanner {
   }
 
   private fun isAbstractOrNonPublicClass(psiClass: PsiClass): Boolean {
-    return !psiClass.isInterface &&
-      (psiClass.hasModifierProperty(PsiModifier.ABSTRACT) ||
-        !psiClass.hasModifierProperty(PsiModifier.PUBLIC))
+    if (psiClass.isInterface) return false
+
+    // We return false for sealed classes here even though they are technically considered abstract
+    // by PsiClass. From a Moshi perspective, sealed classes can be compatible, while abstract
+    // classes cannot.
+    if (isSealedClass(psiClass)) return false
+
+    return (psiClass.hasModifierProperty(PsiModifier.ABSTRACT) ||
+      !psiClass.hasModifierProperty(PsiModifier.PUBLIC))
+  }
+
+  private fun isSealedClass(psiClass: PsiClass): Boolean {
+    if (psiClass.isInterface) return false
+
+    // For Kotlin classes, check using Kotlin PSI
+    if (psiClass is KtLightClass) {
+      val ktClass = psiClass.kotlinOrigin
+      return ktClass?.hasModifier(KtTokens.SEALED_KEYWORD) == true
+    }
+
+    // Fallback for Java classes (Java doesn't have sealed classes in older versions)
+    return psiClass.hasModifierProperty(PsiModifier.SEALED)
   }
 
   private fun isSealedInterface(psiClass: PsiClass): Boolean {

slack-lint-checks/src/test/java/slack/lint/JsonInflaterMoshiCompatibilityDetectorTest.kt

@@ -686,4 +686,97 @@ class JsonInflaterMoshiCompatibilityDetectorTest : LintDetectorTest() {
       """
       )
   }
+
+  @Test
+  fun testSealedClass() {
+    lint()
+      .files(
+        jsonClassStub,
+        jsonInflaterStub,
+        typeLabelStub,
+        defaultObjectStub,
+        kotlin(
+          """
+        package test
+
+        import com.squareup.moshi.JsonClass
+        import slack.commons.json.JsonInflater
+        import dev.zacsweers.moshix.sealed.annotations.TypeLabel
+        import dev.zacsweers.moshix.sealed.annotations.DefaultObject
+
+        @JsonClass(generateAdapter = true, generator = "sealed:type")
+        sealed class Animal {
+            @TypeLabel("dog")
+            @JsonClass(generateAdapter = true)
+            data class Dog(val name: String) : Animal()
+
+            @TypeLabel("cat")
+            @JsonClass(generateAdapter = true)
+            data class Cat(val age: Int) : Animal()
+
+            @DefaultObject
+            object Default : Animal()
+        }
+
+        fun useJsonInflater(jsonInflater: JsonInflater) {
+            val model = jsonInflater.inflate("{}", Animal::class.java)
+            val json = jsonInflater.deflate(model, Animal::class.java)
+        }
+      """
+        ),
+      )
+      .run()
+      .expectClean()
+  }
+
+  @Test
+  fun testSealedClassMissingJsonClassAnnotation() {
+    lint()
+      .files(
+        jsonClassStub,
+        jsonInflaterStub,
+        typeLabelStub,
+        defaultObjectStub,
+        kotlin(
+          """
+        package test
+
+        import com.squareup.moshi.JsonClass
+        import slack.commons.json.JsonInflater
+        import dev.zacsweers.moshix.sealed.annotations.TypeLabel
+        import dev.zacsweers.moshix.sealed.annotations.DefaultObject
+
+        sealed class Animal {
+            @TypeLabel("dog")
+            @JsonClass(generateAdapter = true)
+            data class Dog(val name: String) : Animal()
+
+            @TypeLabel("cat")
+            @JsonClass(generateAdapter = true)
+            data class Cat(val age: Int) : Animal()
+
+            @DefaultObject
+            object Default : Animal()
+        }
+
+        fun useJsonInflater(jsonInflater: JsonInflater) {
+            val model = jsonInflater.inflate("{}", Animal::class.java)
+            val json = jsonInflater.deflate(model, Animal::class.java)
+        }
+      """
+        ),
+      )
+      .run()
+      .expect(
+        """
+            src/test/Animal.kt:23: Error: Using JsonInflater.inflate/deflate with a Moshi-incompatible type. [JsonInflaterMoshiIncompatibleType]
+                        val model = jsonInflater.inflate("{}", Animal::class.java)
+                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+            src/test/Animal.kt:24: Error: Using JsonInflater.inflate/deflate with a Moshi-incompatible type. [JsonInflaterMoshiIncompatibleType]
+                        val json = jsonInflater.deflate(model, Animal::class.java)
+                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+            2 errors
+      """
+      )
+  }
 }