#1232: Include type hint into KSErrorType.

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/processing/impl/ResolverImpl.kt

@@ -691,7 +691,8 @@ class ResolverImpl(
                 builtIns.arrayType.replace(typeArgs)
             }
             else -> {
-                getClassDeclarationByName(psiType.canonicalText)?.asStarProjectedType() ?: KSErrorType
+                getClassDeclarationByName(psiType.canonicalText)?.asStarProjectedType()
+                    ?: KSErrorType(psiType.canonicalText)
             }
         }
     }
@@ -1053,7 +1054,7 @@ class ResolverImpl(
             }
         }
         // if substitution fails, fallback to the type from the property
-        return KSErrorType
+        return KSErrorType.fromReferenceBestEffort(property.type)
     }
 
     internal fun asMemberOf(
@@ -1246,7 +1247,7 @@ class ResolverImpl(
     }
 
     // Convert type arguments for Java wildcard, recursively.
-    private fun KotlinType.toWildcard(mode: TypeMappingMode): KotlinType? {
+    private fun KotlinType.toWildcard(mode: TypeMappingMode): KotlinType {
         val parameters = constructor.parameters
         val arguments = arguments
 
@@ -1257,16 +1258,18 @@ class ResolverImpl(
                 argument.projectionKind != org.jetbrains.kotlin.types.Variance.INVARIANT
             ) {
                 // conflicting variances
-                // TODO: error message
-                return null
+                throw IllegalArgumentException(
+                    "Conflicting variance: variance '${parameter.variance.label}' vs projection " +
+                        "'${argument.projectionKind.label}'"
+                )
             }
 
             val argMode = mode.updateFromAnnotations(argument.type)
             val variance = KotlinTypeMapper.getVarianceForWildcard(parameter, argument, argMode)
             val genericMode = argMode.toGenericArgumentMode(
                 getEffectiveVariance(parameter.variance, argument.projectionKind)
             )
-            TypeProjectionImpl(variance, argument.type.toWildcard(genericMode) ?: return null)
+            TypeProjectionImpl(variance, argument.type.toWildcard(genericMode))
         }
 
         return replace(wildcardArguments)
@@ -1368,19 +1371,17 @@ class ResolverImpl(
             if (position == RefPosition.SUPER_TYPE &&
                 argument.projectionKind != org.jetbrains.kotlin.types.Variance.INVARIANT
             ) {
-                // Type projection isn't allowed in immediate arguments to supertypes.
-                // TODO: error message
-                return KSTypeReferenceSyntheticImpl.getCached(KSErrorType, null)
+                throw IllegalArgumentException("Type projection isn't allowed in immediate arguments to supertypes")
             }
         }
 
-        val wildcardType = kotlinType.toWildcard(typeMappingMode)?.let {
+        val wildcardType = kotlinType.toWildcard(typeMappingMode).let {
             var candidate: KotlinType = it
             for (i in indexes.reversed()) {
                 candidate = candidate.arguments[i].type
             }
             getKSTypeCached(candidate)
-        } ?: KSErrorType
+        }
 
         return KSTypeReferenceSyntheticImpl.getCached(wildcardType, null)
     }

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSAnnotationDescriptorImpl.kt

@@ -62,7 +62,9 @@ import org.jetbrains.kotlin.load.kotlin.getContainingKotlinJvmBinaryClass
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.psi.KtClassLiteralExpression
 import org.jetbrains.kotlin.psi.KtCollectionLiteralExpression
+import org.jetbrains.kotlin.psi.KtExpression
 import org.jetbrains.kotlin.psi.KtParameter
 import org.jetbrains.kotlin.resolve.AnnotationResolverImpl
 import org.jetbrains.kotlin.resolve.BindingContext
@@ -161,7 +163,7 @@ private fun <T> ConstantValue<T>.toValue(parent: KSNode): Any? = when (this) {
         } else classValue.classId.findKSType()
         is KClassValue.Value.LocalClass -> getKSTypeCached(classValue.type)
     }
-    is ErrorValue -> KSErrorType
+    is ErrorValue -> KSErrorType(toString())
     is NullValue -> null
     else -> value
 }
@@ -211,7 +213,7 @@ fun LazyAnnotationDescriptor.getValueArguments(): Map<Name, ConstantValue<*>> {
         } else if (resolvedArgument is DefaultValueArgument) {
             valueParameter.name to DefaultConstantValue
         } else {
-            c.annotationResolver.getAnnotationArgumentValue(c.trace, valueParameter, resolvedArgument)?.let { value ->
+            c.annotationResolver.getAnnotationArgumentValue(c.trace, valueParameter, resolvedArgument).let { value ->
                 val argExp = resolvedArgument.arguments.lastOrNull()?.getArgumentExpression()
                 // When some elements are not available, the expected and actual size of an array argument will
                 // be different. In such case, we need to reconstruct the array.
@@ -224,17 +226,22 @@ fun LazyAnnotationDescriptor.getValueArguments(): Map<Name, ConstantValue<*>> {
                     val bc = ResolverImpl.instance!!.bindingTrace.bindingContext
                     val args = argExp.innerExpressions.map {
                         bc.get(BindingContext.COMPILE_TIME_VALUE, it)?.toConstantValue(value.type)
-                            ?: ErrorValue.create("<ERROR VALUE>")
+                            ?: it.asErrorValue()
                     }
                     valueParameter.name to TypedArrayValue(args, value.type)
                 } else {
-                    valueParameter.name to value
+                    valueParameter.name to (value ?: argExp?.asErrorValue() ?: ErrorValue.create("ERROR VALUE"))
                 }
-            } ?: (valueParameter.name to ErrorValue.create("<ERROR VALUE>"))
+            }
         }
     }.toMap()
 }
 
+private fun KtExpression.asErrorValue(): ErrorValue {
+    val reprExpr = (this as? KtClassLiteralExpression)?.receiverExpression ?: this
+    return ErrorValue.create(reprExpr.text)
+}
+
 fun AnnotationDescriptor.createKSValueArguments(ownerAnnotation: KSAnnotation): List<KSValueArgument> {
     val allValueArgs = if (this is LazyAnnotationDescriptor) {
         this.getValueArguments()
@@ -419,14 +426,14 @@ fun ValueParameterDescriptor.getDefaultValue(ownerAnnotation: KSAnnotation): Any
                 if (!this.type.isError) {
                     defaultValue?.convert(this.type)?.toValue(ownerAnnotation)
                 } else {
-                    KSErrorType
+                    KSErrorType.fromKtErrorType(type)
                 }
             }
         }
         is KtParameter -> if (!this.type.isError) {
             ResolverImpl.instance!!.evaluateConstant(psi.defaultValue, this.type)?.toValue(ownerAnnotation)
         } else {
-            KSErrorType
+            KSErrorType.fromKtErrorType(type)
         }
         is PsiAnnotationMethod -> {
             when (psi.defaultValue) {

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/binary/KSClassDeclarationDescriptorImpl.kt

@@ -153,7 +153,7 @@ class KSClassDeclarationDescriptorImpl private constructor(val descriptor: Class
     override fun asType(typeArguments: List<KSTypeArgument>): KSType =
         descriptor.defaultType.replaceTypeArguments(typeArguments)?.let {
             getKSTypeCached(it, typeArguments)
-        } ?: KSErrorType
+        } ?: KSErrorType()
 
     override fun asStarProjectedType(): KSType {
         return getKSTypeCached(descriptor.defaultType.replaceArgumentsWithStarProjections())

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSClassDeclarationJavaEnumEntryImpl.kt

@@ -97,7 +97,7 @@ class KSClassDeclarationJavaEnumEntryImpl private constructor(val psi: PsiEnumCo
     // Enum can't have type parameters.
     override fun asType(typeArguments: List<KSTypeArgument>): KSType {
         if (typeArguments.isNotEmpty())
-            return KSErrorType
+            return KSErrorType()
         return asStarProjectedType()
     }
 

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSClassDeclarationJavaImpl.kt

@@ -157,13 +157,13 @@ class KSClassDeclarationJavaImpl private constructor(val psi: PsiClass) :
             it.defaultType.replaceTypeArguments(typeArguments)?.let {
                 getKSTypeCached(it, typeArguments)
             }
-        } ?: KSErrorType
+        } ?: KSErrorType()
     }
 
     override fun asStarProjectedType(): KSType {
         return descriptor?.let {
             getKSTypeCached(it.defaultType.replaceArgumentsWithStarProjections())
-        } ?: KSErrorType
+        } ?: KSErrorType()
     }
 
     override fun <D, R> accept(visitor: KSVisitor<D, R>, data: D): R {

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSTypeReferenceJavaImpl.kt

@@ -124,11 +124,13 @@ class KSTypeReferenceJavaImpl private constructor(val psi: PsiType, override val
             .mapNotNull {
                 (it.annotationType.resolve() as? KSTypeImpl)?.kotlinType?.constructor?.declarationDescriptor?.fqNameSafe
             }
-        val resolved = if ((resolvedType.declaration as? KSClassDeclarationDescriptorImpl)
-            ?.descriptor is NotFoundClasses.MockClassDescriptor
-        ) {
-            KSErrorType
-        } else resolvedType
+        val resolved = when (val declaration = resolvedType.declaration) {
+            is KSClassDeclarationDescriptorImpl -> when (val descriptor = declaration.descriptor) {
+                is NotFoundClasses.MockClassDescriptor -> KSErrorType(descriptor.name.asString())
+                else -> resolvedType
+            }
+            else -> resolvedType
+        }
         val hasNotNull = relatedAnnotations.any { it in NOT_NULL_ANNOTATIONS }
         val hasNullable = relatedAnnotations.any { it in NULLABLE_ANNOTATIONS }
         return if (hasNullable && !hasNotNull) {

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/java/KSTypeReferenceLiteJavaImpl.kt

@@ -47,13 +47,14 @@ class KSTypeReferenceLiteJavaImpl private constructor(val psiElement: PsiElement
     val type: KSType by lazy {
         when (psiElement) {
             is PsiAnnotation -> {
-                val psiClass = psiElement.nameReferenceElement!!.resolve() as? PsiClass
+                val nameReferenceElement = psiElement.nameReferenceElement!!
+                val psiClass = nameReferenceElement.resolve() as? PsiClass
                 psiClass?.let {
                     (psiElement.containingFile as? PsiJavaFile)?.let {
                         ResolverImpl.instance!!.incrementalContext.recordLookup(it, psiClass.qualifiedName!!)
                     }
                     KSClassDeclarationJavaImpl.getCached(psiClass).asStarProjectedType()
-                } ?: KSErrorType
+                } ?: KSErrorType(nameReferenceElement.text)
             }
             is PsiMethod -> {
                 KSClassDeclarationJavaImpl.getCached(psiElement.containingClass!!).asStarProjectedType()

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSClassDeclarationImpl.kt

@@ -124,7 +124,7 @@ class KSClassDeclarationImpl private constructor(val ktClassOrObject: KtClassOrO
     override fun asType(typeArguments: List<KSTypeArgument>): KSType {
         return descriptor.defaultType.replaceTypeArguments(typeArguments)?.let {
             getKSTypeCached(it, typeArguments)
-        } ?: KSErrorType
+        } ?: KSErrorType()
     }
 
     override fun asStarProjectedType(): KSType {

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSErrorType.kt

@@ -19,17 +19,28 @@ package com.google.devtools.ksp.symbol.impl.kotlin
 
 import com.google.devtools.ksp.symbol.*
 import com.google.devtools.ksp.symbol.impl.synthetic.KSErrorTypeClassDeclaration
+import org.jetbrains.kotlin.types.FlexibleType
+import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.error.ErrorType
+import org.jetbrains.kotlin.types.error.ErrorTypeKind
 
-object KSErrorType : KSType {
-    override val annotations: Sequence<KSAnnotation> = emptySequence()
+class KSErrorType(
+    val nameHint: String? = null,
+) : KSType {
+    override val annotations: Sequence<KSAnnotation>
+        get() = emptySequence()
 
-    override val arguments: List<KSTypeArgument> = emptyList()
+    override val arguments: List<KSTypeArgument>
+        get() = emptyList()
 
-    override val declaration: KSDeclaration = KSErrorTypeClassDeclaration
+    override val declaration: KSDeclaration
+        get() = KSErrorTypeClassDeclaration(this)
 
-    override val isError: Boolean = true
+    override val isError: Boolean
+        get() = true
 
-    override val nullability: Nullability = Nullability.NULLABLE
+    override val nullability: Nullability
+        get() = Nullability.NULLABLE
 
     override fun isAssignableFrom(that: KSType): Boolean {
         return false
@@ -51,7 +62,8 @@ object KSErrorType : KSType {
         return this
     }
 
-    override val isMarkedNullable: Boolean = false
+    override val isMarkedNullable: Boolean
+        get() = false
 
     override fun replace(arguments: List<KSTypeArgument>): KSType {
         return this
@@ -61,11 +73,51 @@ object KSErrorType : KSType {
         return this
     }
 
-    override fun toString(): String {
-        return "<ERROR TYPE>"
-    }
+    override fun toString(): String = nameHint?.let { "<ERROR TYPE: $it>" } ?: "<ERROR TYPE>"
+
+    override val isFunctionType: Boolean
+        get() = false
+
+    override val isSuspendFunctionType: Boolean
+        get() = false
 
-    override val isFunctionType: Boolean = false
+    override fun hashCode() = nameHint.hashCode()
 
-    override val isSuspendFunctionType: Boolean = false
+    override fun equals(other: Any?): Boolean {
+        return this === other || other is KSErrorType && other.nameHint == nameHint
+    }
+
+    companion object {
+        fun fromReferenceBestEffort(reference: KSTypeReference?): KSErrorType {
+            return when (val type = reference?.resolve()) {
+                is KSErrorType -> type
+                null -> KSErrorType(reference?.element?.toString())
+                else -> KSErrorType(type.toString())
+            }
+        }
+
+        fun fromKtErrorType(ktType: KotlinType): KSErrorType {
+            // Logic is in sync with `KotlinType.isError`
+            val errorType: ErrorType = when (val unwrapped = ktType.unwrap()) {
+                is ErrorType -> unwrapped
+                is FlexibleType -> unwrapped.delegate as? ErrorType
+                else -> null
+            } ?: throw IllegalArgumentException("Not an error type: $ktType")
+
+            val hint = when (errorType.kind) {
+                // Handle "Unresolved types" group
+                ErrorTypeKind.UNRESOLVED_TYPE,
+                ErrorTypeKind.UNRESOLVED_CLASS_TYPE,
+                ErrorTypeKind.UNRESOLVED_JAVA_CLASS,
+                ErrorTypeKind.UNRESOLVED_DECLARATION,
+                ErrorTypeKind.UNRESOLVED_KCLASS_CONSTANT_VALUE,
+                ErrorTypeKind.UNRESOLVED_TYPE_ALIAS -> errorType.formatParams.first()
+
+                // TODO: Handle more ErrorTypeKinds where it's possible to extract a name for the error type.
+                else -> errorType.debugMessage
+            }
+
+            return KSErrorType(hint)
+        }
+    }
 }

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSFunctionErrorImpl.kt

@@ -29,18 +29,19 @@ class KSFunctionErrorImpl(
 ) : KSFunction {
     override val isError: Boolean = true
 
-    override val returnType: KSType = KSErrorType
+    override val returnType: KSType
+        get() = KSErrorType.fromReferenceBestEffort(declaration.returnType)
 
     override val parameterTypes: List<KSType?>
         get() = declaration.parameters.map {
-            KSErrorType
+            KSErrorType.fromReferenceBestEffort(it.type)
         }
     override val typeParameters: List<KSTypeParameter>
         get() = emptyList()
 
     override val extensionReceiverType: KSType?
         get() = declaration.extensionReceiver?.let {
-            KSErrorType
+            KSErrorType.fromReferenceBestEffort(it)
         }
 
     override fun equals(other: Any?): Boolean {

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSPropertyDeclarationImpl.kt

@@ -97,7 +97,7 @@ class KSPropertyDeclarationImpl private constructor(val ktProperty: KtProperty)
             KSTypeReferenceDeferredImpl.getCached(this) {
                 val desc = propertyDescriptor as? VariableDescriptorWithAccessors
                 if (desc == null) {
-                    KSErrorType
+                    KSErrorType()
                 } else {
                     getKSTypeCached(desc.type)
                 }

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSTypeImpl.kt

@@ -97,7 +97,7 @@ class KSTypeImpl private constructor(
     override fun replace(arguments: List<KSTypeArgument>): KSType {
         return kotlinType.replaceTypeArguments(arguments)?.let {
             getKSTypeCached(it, arguments, annotations)
-        } ?: KSErrorType
+        } ?: KSErrorType()
     }
 
     override fun starProjection(): KSType {
@@ -136,10 +136,12 @@ fun getKSTypeCached(
     ksTypeArguments: List<KSTypeArgument>? = null,
     annotations: Sequence<KSAnnotation> = sequenceOf()
 ): KSType {
-    return if (kotlinType.isError ||
-        kotlinType.constructor.declarationDescriptor is NotFoundClasses.MockClassDescriptor
-    ) {
-        KSErrorType
+    if (kotlinType.isError) {
+        return KSErrorType.fromKtErrorType(kotlinType)
+    }
+    val descriptor = kotlinType.constructor.declarationDescriptor
+    return if (descriptor is NotFoundClasses.MockClassDescriptor) {
+        KSErrorType(descriptor.name.asString())
     } else {
         KSTypeImpl.getCached(
             kotlinType,

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/symbol/impl/kotlin/KSValueParameterImpl.kt

@@ -112,7 +112,7 @@ class KSValueParameterImpl private constructor(val ktParameter: KtParameter) : K
 
     override val type: KSTypeReference by lazy {
         ktParameter.typeReference?.let { KSTypeReferenceImpl.getCached(it) }
-            ?: findPropertyForAccessor()?.type ?: KSTypeReferenceSyntheticImpl.getCached(KSErrorType, this)
+            ?: findPropertyForAccessor()?.type ?: KSTypeReferenceSyntheticImpl.getCached(KSErrorType(), this)
     }
 
     override val hasDefault: Boolean = ktParameter.hasDefaultValue()