From 45cc60c8e99ed75c1c5ed1781c5ba6f54c40dc16 Mon Sep 17 00:00:00 2001
From: Him188 <Him188@mamoe.net>
Date: Mon, 9 Aug 2021 23:43:43 +0800
Subject: [PATCH] Fix `loadService` with fallback implementation

---
 mirai-core-utils/src/androidMain/kotlin/Actuals.kt | 8 +++++---
 mirai-core-utils/src/commonMain/kotlin/Services.kt | 5 +++--
 mirai-core-utils/src/jvmMain/kotlin/Actuals.kt     | 8 +++++---
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/mirai-core-utils/src/androidMain/kotlin/Actuals.kt b/mirai-core-utils/src/androidMain/kotlin/Actuals.kt
index d55d56e15..8645198cf 100644
--- a/mirai-core-utils/src/androidMain/kotlin/Actuals.kt
+++ b/mirai-core-utils/src/androidMain/kotlin/Actuals.kt
@@ -47,17 +47,19 @@ public actual inline fun <reified E> Throwable.unwrap(): Throwable {
 public actual fun <T : Any> loadService(clazz: KClass<out T>, fallbackImplementation: String?): T {
     var suppressed: Throwable? = null
     return ServiceLoader.load(clazz.java).firstOrNull()
-        ?: runCatching { findCreateInstance<T>(fallbackImplementation) }.onFailure { suppressed = it }.getOrNull()
+        ?: (if (fallbackImplementation == null) null
+        else runCatching { findCreateInstance<T>(fallbackImplementation) }.onFailure { suppressed = it }.getOrNull())
         ?: throw NoSuchElementException("Could not find an implementation for service class ${clazz.qualifiedName}").apply {
             if (suppressed != null) addSuppressed(suppressed)
         }
 }
 
-private fun <T : Any> findCreateInstance(fallbackImplementation: String?): T {
+private fun <T : Any> findCreateInstance(fallbackImplementation: String): T {
     return Class.forName(fallbackImplementation).cast<Class<out T>>().kotlin.run { objectInstance ?: createInstance() }
 }
 
 public actual fun <T : Any> loadServiceOrNull(clazz: KClass<out T>, fallbackImplementation: String?): T? {
     return ServiceLoader.load(clazz.java).firstOrNull()
-        ?: runCatching { findCreateInstance<T>(fallbackImplementation) }.getOrNull()
+        ?: if (fallbackImplementation == null) return null
+        else runCatching { findCreateInstance<T>(fallbackImplementation) }.getOrNull()
 }
\ No newline at end of file
diff --git a/mirai-core-utils/src/commonMain/kotlin/Services.kt b/mirai-core-utils/src/commonMain/kotlin/Services.kt
index a5dfd1c36..1da85f04a 100644
--- a/mirai-core-utils/src/commonMain/kotlin/Services.kt
+++ b/mirai-core-utils/src/commonMain/kotlin/Services.kt
@@ -17,5 +17,6 @@ public expect fun <T : Any> loadService(clazz: KClass<out T>, fallbackImplementa
 public inline fun <reified T : Any> loadService(fallbackImplementation: String? = null): T =
     loadService(T::class, fallbackImplementation)
 
-public inline fun <reified T : Any> loadService(noinline fallbackImplementation: () -> T): T =
-    loadServiceOrNull(T::class) ?: fallbackImplementation()
\ No newline at end of file
+// do not inline: T will be inferred to returning type of `fallbackImplementation`
+public fun <T : Any> loadService(clazz: KClass<out T>, fallbackImplementation: () -> T): T =
+    loadServiceOrNull(clazz) ?: fallbackImplementation()
\ No newline at end of file
diff --git a/mirai-core-utils/src/jvmMain/kotlin/Actuals.kt b/mirai-core-utils/src/jvmMain/kotlin/Actuals.kt
index 397e39403..417c334f5 100644
--- a/mirai-core-utils/src/jvmMain/kotlin/Actuals.kt
+++ b/mirai-core-utils/src/jvmMain/kotlin/Actuals.kt
@@ -35,17 +35,19 @@ public actual inline fun <reified E> Throwable.unwrap(): Throwable {
 public actual fun <T : Any> loadService(clazz: KClass<out T>, fallbackImplementation: String?): T {
     var suppressed: Throwable? = null
     return ServiceLoader.load(clazz.java).firstOrNull()
-        ?: runCatching { findCreateInstance<T>(fallbackImplementation) }.onFailure { suppressed = it }.getOrNull()
+        ?: (if (fallbackImplementation == null) null
+        else runCatching { findCreateInstance<T>(fallbackImplementation) }.onFailure { suppressed = it }.getOrNull())
         ?: throw NoSuchElementException("Could not find an implementation for service class ${clazz.qualifiedName}").apply {
             if (suppressed != null) addSuppressed(suppressed)
         }
 }
 
-private fun <T : Any> findCreateInstance(fallbackImplementation: String?): T {
+private fun <T : Any> findCreateInstance(fallbackImplementation: String): T {
     return Class.forName(fallbackImplementation).cast<Class<out T>>().kotlin.run { objectInstance ?: createInstance() }
 }
 
 public actual fun <T : Any> loadServiceOrNull(clazz: KClass<out T>, fallbackImplementation: String?): T? {
     return ServiceLoader.load(clazz.java).firstOrNull()
-        ?: runCatching { findCreateInstance<T>(fallbackImplementation) }.getOrNull()
+        ?: if (fallbackImplementation == null) return null
+        else runCatching { findCreateInstance<T>(fallbackImplementation) }.getOrNull()
 }
\ No newline at end of file