From 3e46507ea730a850c982b8126d2604cc9d4845b3 Mon Sep 17 00:00:00 2001
From: Zac Sweers <pandanomic@gmail.com>
Date: Thu, 24 Oct 2024 15:24:00 -0400
Subject: [PATCH] Improve error messaging for error types used as annotation
 arguments (#80)

---
 CHANGELOG.md                                         |  2 ++
 compiler-utils/api/compiler-utils.api                |  1 +
 .../compiler/internal/ksp/KSAnnotationExtensions.kt  | 12 +++++++++++-
 .../squareup/anvil/compiler/internal/ksp/KspUtil.kt  | 11 ++++++-----
 4 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ed99a75f1..a60c8c15c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@
 **Unreleased**
 --------------
 
+- **Enhancement**: Improve error messaging for error types used as annotation arguments.
+
 0.3.3
 -----
 
diff --git a/compiler-utils/api/compiler-utils.api b/compiler-utils/api/compiler-utils.api
index cb02e60a6..89b8c17ca 100644
--- a/compiler-utils/api/compiler-utils.api
+++ b/compiler-utils/api/compiler-utils.api
@@ -112,6 +112,7 @@ public final class com/squareup/anvil/compiler/internal/ksp/KspUtilKt {
 	public static final fun anySymbolsWithAnnotations (Lcom/google/devtools/ksp/processing/Resolver;Ljava/util/Collection;)Z
 	public static final fun atLeastOneAnnotation (Lcom/google/devtools/ksp/symbol/KSClassDeclaration;Ljava/lang/String;Lcom/google/devtools/ksp/symbol/KSType;)Ljava/util/List;
 	public static synthetic fun atLeastOneAnnotation$default (Lcom/google/devtools/ksp/symbol/KSClassDeclaration;Ljava/lang/String;Lcom/google/devtools/ksp/symbol/KSType;ILjava/lang/Object;)Ljava/util/List;
+	public static final fun checkErrorType (Lcom/google/devtools/ksp/symbol/KSType;Lcom/google/devtools/ksp/symbol/KSNode;)Lcom/google/devtools/ksp/symbol/KSType;
 	public static final fun contextualToClassName (Lcom/google/devtools/ksp/symbol/KSType;Lcom/google/devtools/ksp/symbol/KSNode;)Lcom/squareup/kotlinpoet/ClassName;
 	public static final fun contextualToClassName (Lcom/google/devtools/ksp/symbol/KSTypeReference;)Lcom/squareup/kotlinpoet/ClassName;
 	public static final fun contextualToTypeName (Lcom/google/devtools/ksp/symbol/KSType;Lcom/google/devtools/ksp/symbol/KSNode;Lcom/squareup/kotlinpoet/ksp/TypeParameterResolver;)Lcom/squareup/kotlinpoet/TypeName;
diff --git a/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KSAnnotationExtensions.kt b/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KSAnnotationExtensions.kt
index 32711169c..162414f7c 100644
--- a/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KSAnnotationExtensions.kt
+++ b/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KSAnnotationExtensions.kt
@@ -166,7 +166,17 @@ public fun KSAnnotation.classNameArgumentAt(
 public inline fun <reified T> KSAnnotation.argumentOfTypeAt(
   name: String,
 ): T? {
-  return argumentOfTypeWithMapperAt<T, T>(name) { _, value ->
+  return argumentOfTypeWithMapperAt<T, T>(name) { arg, value ->
+    when {
+      value is KSType -> {
+        value.checkErrorType(arg)
+      }
+      value is List<*> && value.firstOrNull() is KSType -> {
+        for (element in value) {
+          (element as KSType).checkErrorType(arg)
+        }
+      }
+    }
     value
   }
 }
diff --git a/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KspUtil.kt b/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KspUtil.kt
index 81906fabd..da51d3ce2 100644
--- a/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KspUtil.kt
+++ b/compiler-utils/src/main/java/com/squareup/anvil/compiler/internal/ksp/KspUtil.kt
@@ -387,18 +387,19 @@ public fun KSType.contextualToClassName(origin: KSNode): ClassName {
   return toClassName()
 }
 
-private fun KSType.checkErrorType(origin: KSNode) {
+@PublishedApi
+internal fun KSType.checkErrorType(origin: KSNode): KSType {
   val (type, node) = if (isError) {
     this to origin
   } else {
     arguments.asSequence()
-      .mapNotNull {
-        it.type?.let {
-          it.resolve() to it
+      .mapNotNull { arg ->
+        arg.type?.let { argType ->
+          argType.resolve() to argType
         }
       }
       .firstOrNull { it.first.isError }
-  } ?: return
+  } ?: return this
 
   val message = buildString {
     appendLine(