Use type parameters' source information for kotlinx.serialization diagnostics

To be more consistent with K1, certain diagnostics should be reported
not on the whole properties' types, but on type arguments inside them.

Note that there is still a difference with K2 because K2 reports on a type argument
including its annotations, while K1 used KtTypeReference.typeElement.

IMO, K2 conveys the same or better meaning here, so I am willing to leave this
difference instead of providing PositioningStrategy.

#KT-53861 Fixed

plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/checkers/FirSerializationPluginClassChecker.kt

@@ -11,10 +11,9 @@ import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.diagnostics.SourceElementPositioningStrategies
 import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.*
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirClassChecker
-import org.jetbrains.kotlin.fir.analysis.checkers.isSingleFieldValueClass
-import org.jetbrains.kotlin.fir.analysis.checkers.toRegularClassSymbol
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.annotationPlatformSupport
 import org.jetbrains.kotlin.fir.declarations.utils.*
@@ -489,7 +488,7 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
                 )
                 checkSerializerNullability(propertyType, customSerializerType, source, reporter)
             } else {
-                checkType(propertyType, source, reporter)
+                checkType(typeRef, source, reporter)
                 checkGenericArrayType(propertyType, source, reporter)
             }
         }
@@ -506,13 +505,15 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
     }
 
     context(CheckerContext)
-    private fun checkTypeArguments(type: ConeKotlinType, source: KtSourceElement?, reporter: DiagnosticReporter) {
+    private fun checkTypeArguments(
-        for (typeArgument in type.typeArguments) {
+        typeRef: FirTypeRef,
-            checkType(
+        fallbackSource: KtSourceElement?,
-                typeArgument.type?.fullyExpandedType(session) ?: continue,
+        reporter: DiagnosticReporter
-                source,
+    ) {
-                reporter
+        val argsRefs = extractArgumentsTypeRefAndSource(typeRef) ?: return
-            )
+        for (typeArgument in argsRefs) {
+            val argTypeRef = typeArgument.typeRef ?: continue
+            checkType(argTypeRef, typeArgument.source ?: fallbackSource, reporter)
         }
     }
 
@@ -526,11 +527,12 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
         get() = isSingleFieldValueClass(session) && !isPrimitiveOrNullablePrimitive
 
     context(CheckerContext)
-    private fun checkType(type: ConeKotlinType, source: KtSourceElement?, reporter: DiagnosticReporter) {
+    private fun checkType(typeRef: FirTypeRef, typeSource: KtSourceElement?, reporter: DiagnosticReporter) {
+        val type = typeRef.coneType.fullyExpandedType(session)
         if (type.lowerBoundIfFlexible().isTypeParameter) return // type parameters always have serializer stored in class' field
         if (type.isUnsupportedInlineType && !canSupportInlineClasses()) {
             reporter.reportOn(
-                source,
+                typeRef.source ?: typeSource,
                 FirSerializationErrors.INLINE_CLASSES_NOT_SUPPORTED,
                 RuntimeVersions.MINIMAL_VERSION_FOR_INLINE_CLASSES.toString(),
                 session.versionReader.runtimeVersions?.implementationVersion.toString()
@@ -541,15 +543,15 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
         if (serializer != null) {
             val classSymbol = type.toRegularClassSymbol(session) ?: return
             type.serializableWith?.fullyExpandedType(session)?.let { serializerType ->
-                checkCustomSerializerMatch(classSymbol, source, type, serializerType, reporter)
+                checkCustomSerializerMatch(classSymbol, typeSource, type, serializerType, reporter)
-                checkCustomSerializerIsNotLocal(source, classSymbol, serializerType, reporter)
+                checkCustomSerializerIsNotLocal(typeSource, classSymbol, serializerType, reporter)
-                checkSerializerNullability(type, serializerType, source, reporter)
+                checkSerializerNullability(type, serializerType, typeSource, reporter)
             }
-            checkTypeArguments(type, source, reporter)
+            checkTypeArguments(typeRef, typeSource, reporter)
         } else {
             if (type.toRegularClassSymbol(session)?.isEnumClass != true) {
                 // enums are always serializable
-                reporter.reportOn(source, FirSerializationErrors.SERIALIZER_NOT_FOUND, type)
+                reporter.reportOn(typeSource, FirSerializationErrors.SERIALIZER_NOT_FOUND, type)
             }
         }
     }
@@ -566,7 +568,6 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
 
         val declarationTypeClassId = declarationType.classId
         if (declarationTypeClassId == null || declarationTypeClassId != serializerForType.classId) {
-            // TODO: report on specific type argument (KT-53861)
             reporter.reportOn(
                 source ?: containingClassSymbol.serializableOrMetaAnnotationSource,
                 FirSerializationErrors.SERIALIZER_TYPE_INCOMPATIBLE,
@@ -576,6 +577,7 @@ object FirSerializationPluginClassChecker : FirClassChecker() {
             )
         }
     }
+
     context(CheckerContext)
     private fun checkCustomSerializerNotAbstract(
         containingClassSymbol: FirClassSymbol<*>,

plugins/kotlinx-serialization/testData/diagnostics/NonSerializable.fir.kt

@@ -1,18 +0,0 @@
-// FIR_DISABLE_LAZY_RESOLVE_CHECKS
-// WITH_STDLIB
-// FIR_DIFFERENCE: KT-53861
-// FILE: test.kt
-import kotlinx.serialization.*
-
-class NonSerializable
-
-@Serializable
-class Basic(val foo: <!SERIALIZER_NOT_FOUND("NonSerializable")!>NonSerializable<!>)
-
-@Serializable
-class Inside(val foo: <!SERIALIZER_NOT_FOUND("NonSerializable")!>List<NonSerializable><!>)
-
-@Serializable
-class WithImplicitType {
-    <!SERIALIZER_NOT_FOUND("NonSerializable")!>val foo = NonSerializable()<!>
-}

plugins/kotlinx-serialization/testData/diagnostics/NonSerializable.kt

@@ -1,6 +1,6 @@
 // FIR_DISABLE_LAZY_RESOLVE_CHECKS
 // WITH_STDLIB
-// FIR_DIFFERENCE: KT-53861
+// FIR_IDENTICAL
 // FILE: test.kt
 import kotlinx.serialization.*
 
@@ -12,6 +12,9 @@ class Basic(val foo: <!SERIALIZER_NOT_FOUND("NonSerializable")!>NonSerializable<
 @Serializable
 class Inside(val foo: List<<!SERIALIZER_NOT_FOUND("NonSerializable")!>NonSerializable<!>>)
 
+@Serializable
+class Inside2(val foo: List<List<<!SERIALIZER_NOT_FOUND("NonSerializable")!>NonSerializable<!>>>)
+
 @Serializable
 class WithImplicitType {
     <!SERIALIZER_NOT_FOUND("NonSerializable")!>val foo = NonSerializable()<!>

plugins/kotlinx-serialization/testData/diagnostics/NonSerializable.txt

@@ -60,6 +60,36 @@ package
     }
 }
 
+@kotlinx.serialization.Serializable public final class Inside2 {
+    @kotlin.Deprecated(level = DeprecationLevel.HIDDEN, message = "This synthesized declaration should not be used directly", replaceWith = kotlin.ReplaceWith(expression = "", imports = {})) internal /*synthesized*/ constructor Inside2(/*0*/ seen1: kotlin.Int, /*1*/ foo: kotlin.collections.List<kotlin.collections.List<NonSerializable>>?, /*2*/ serializationConstructorMarker: kotlinx.serialization.internal.SerializationConstructorMarker?)
+    public constructor Inside2(/*0*/ foo: kotlin.collections.List<kotlin.collections.List<NonSerializable>>)
+    public final val foo: kotlin.collections.List<kotlin.collections.List<NonSerializable>>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    @kotlin.jvm.JvmStatic internal final /*synthesized*/ fun `write$Self`(/*0*/ self: Inside2, /*1*/ output: kotlinx.serialization.encoding.CompositeEncoder, /*2*/ serialDesc: kotlinx.serialization.descriptors.SerialDescriptor): kotlin.Unit
+
+    @kotlin.Deprecated(level = DeprecationLevel.HIDDEN, message = "This synthesized declaration should not be used directly", replaceWith = kotlin.ReplaceWith(expression = "", imports = {})) public object `$serializer` : kotlinx.serialization.internal.GeneratedSerializer<Inside2> {
+        private constructor `$serializer`()
+        public open override /*1*/ /*synthesized*/ val descriptor: kotlinx.serialization.descriptors.SerialDescriptor
+        public open override /*1*/ /*synthesized*/ fun childSerializers(): kotlin.Array<kotlinx.serialization.KSerializer<*>>
+        public open override /*1*/ /*synthesized*/ fun deserialize(/*0*/ decoder: kotlinx.serialization.encoding.Decoder): Inside2
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*synthesized*/ fun serialize(/*0*/ encoder: kotlinx.serialization.encoding.Encoder, /*1*/ value: Inside2): kotlin.Unit
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+        public open override /*1*/ /*fake_override*/ fun typeParametersSerializers(): kotlin.Array<kotlinx.serialization.KSerializer<*>>
+    }
+
+    public companion object Companion {
+        private constructor Companion()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public final /*synthesized*/ fun serializer(): kotlinx.serialization.KSerializer<Inside2>
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
 public final class NonSerializable {
     public constructor NonSerializable()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean

plugins/kotlinx-serialization/testData/diagnostics/SerializerTypeIncompatible.fir.kt

@@ -21,7 +21,10 @@ class Biz(val i: Int)
 class Foo(@Serializable(with = BazSerializer::class) val i: <!SERIALIZER_TYPE_INCOMPATIBLE!>Bar<!>)
 
 @Serializable
-class Foo2(val li: <!SERIALIZER_TYPE_INCOMPATIBLE!>List<@Serializable(with = BazSerializer::class) Bar><!>)
+class Foo2(val li: List<<!SERIALIZER_TYPE_INCOMPATIBLE!>@Serializable(with = BazSerializer::class) Bar<!>>)
+
+@Serializable
+class Foo25(val i: <!SERIALIZER_TYPE_INCOMPATIBLE!>@Serializable(with = BazSerializer::class) Bar<!>)
 
 @Serializable
 class Foo3(@Serializable(with = BazSerializer::class) val i: Baz)

plugins/kotlinx-serialization/testData/diagnostics/SerializerTypeIncompatible.kt

@@ -23,6 +23,9 @@ class Foo(@Serializable(with = BazSerializer::class) val i: <!SERIALIZER_TYPE_IN
 @Serializable
 class Foo2(val li: List<@Serializable(with = BazSerializer::class) <!SERIALIZER_TYPE_INCOMPATIBLE!>Bar<!>>)
 
+@Serializable
+class Foo25(val i: @Serializable(with = BazSerializer::class) <!SERIALIZER_TYPE_INCOMPATIBLE!>Bar<!>)
+
 @Serializable
 class Foo3(@Serializable(with = BazSerializer::class) val i: Baz)