Give a compile time error when defining an anonymous mappie object (#238)

* 237 give a more specific error when defining an anonymous mappie object

* 237 Added changelog

Author: stefankoppier

compiler-plugin/src/main/kotlin/tech/mappie/fir/MappieAdditionalCheckersExtension.kt

@@ -1,6 +1,8 @@
 package tech.mappie.fir
 
 import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.DeclarationCheckers
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirAnonymousObjectChecker
 import org.jetbrains.kotlin.fir.analysis.checkers.expression.ExpressionCheckers
 import org.jetbrains.kotlin.fir.analysis.checkers.expression.FirFunctionCallChecker
 import org.jetbrains.kotlin.fir.analysis.extensions.FirAdditionalCheckersExtension
@@ -21,4 +23,10 @@ class MappieAdditionalCheckersExtension(session: FirSession) : FirAdditionalChec
             ToCallChecker(),
         )
     }
+
+    override val declarationCheckers: DeclarationCheckers = object : DeclarationCheckers() {
+        override val anonymousObjectCheckers: Set<FirAnonymousObjectChecker> = setOf(
+            AnonymousMappieObjectChecker()
+        )
+    }
 }

compiler-plugin/src/main/kotlin/tech/mappie/fir/analysis/AnonymousMappieObjectChecker.kt

@@ -0,0 +1,27 @@
+package tech.mappie.fir.analysis
+
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.SourceElementPositioningStrategies.WHOLE_ELEMENT
+import org.jetbrains.kotlin.diagnostics.error1
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.MppCheckerKind
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirAnonymousObjectChecker
+import org.jetbrains.kotlin.fir.declarations.FirAnonymousObject
+import org.jetbrains.kotlin.psi.KtElement
+import tech.mappie.fir.util.isSubclassOfAnMappie
+
+class AnonymousMappieObjectChecker : FirAnonymousObjectChecker(MppCheckerKind.Common) {
+
+    context(context: CheckerContext, reporter: DiagnosticReporter)
+    override fun check(declaration: FirAnonymousObject) {
+        if (declaration.symbol.isSubclassOfAnMappie()) {
+            reporter.reportOn(declaration.source, INVALID_ANONYMOUS_OBJECT, INVALID_ANONYMOUS_OBJECT_MESSAGE)
+        }
+    }
+
+    companion object {
+        private val INVALID_ANONYMOUS_OBJECT by error1<KtElement, String>(WHOLE_ELEMENT)
+        private const val INVALID_ANONYMOUS_OBJECT_MESSAGE = "Anonymous Mappie objects are not supported"
+    }
+}

compiler-plugin/src/main/kotlin/tech/mappie/fir/util/Util.kt

@@ -46,6 +46,11 @@ context(context: CheckerContext)
 internal fun FirClassSymbol<*>.isSubclassOfAnObjectMappie() =
     isSubclassOfObjectMappie() || isSubclassOfObjectMappie2() || isSubclassOfObjectMappie3() || isSubclassOfObjectMappie4() || isSubclassOfObjectMappie5()
 
+context(context: CheckerContext)
+internal fun FirClassSymbol<*>.isSubclassOfAnMappie() =
+    isSubclassOfAnObjectMappie() || isSubclassOfEnumMappie()
+
+
 @OptIn(SymbolInternals::class)
 context (context: CheckerContext)
 fun FirExpression.toConstant(): FirLiteralExpression? =

compiler-plugin/src/test/kotlin/tech/mappie/testing/AnonymousMappieObjectTest.kt

@@ -0,0 +1,35 @@
+package tech.mappie.testing
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.io.TempDir
+import tech.mappie.testing.compilation.compile
+
+import java.io.File
+
+class AnonymousMappieObjectTest {
+
+    data class Input(val text: String)
+    data class Output(val text: String)
+
+    @TempDir
+    lateinit var directory: File
+
+    @Test
+    fun `anonymous mappie object should fail`() {
+        compile(directory) {
+            file("Test.kt",
+                """
+                import tech.mappie.api.ObjectMappie
+                import tech.mappie.testing.AnonymousMappieObjectTest.*
+
+                fun test() {
+                    val x = object : ObjectMappie<Int, String>() { }
+                }
+                """
+            )
+        } satisfies {
+            isCompilationError()
+            hasErrorMessage(5, "Anonymous Mappie objects are not supported")
+        }
+    }
+}

website/src/changelog.md

@@ -2,6 +2,10 @@
 title: "Changelog"
 layout: "layouts/changelog.html"
 changelog:
+  - date: "tbd"
+    title: "v2.2.0-1.5.0"
+    items:
+      - "[#237](https://github.com/Mr-Mappie/mappie/issues/237) Added compile time error when defining anonymous mappie objects."
   - date: "2025-08-11"
     title: "v2.2.0-1.4-1"
     items: