KTOR-5208 Add ApplicationConfig merge with reversed priority (#3258)

KTOR-5208 Add ApplicationConfig merge with reversed priority

KTOR-5208 Add ApplicationConfig merge with reversed priority (#3258)
KTOR-5208 Add ApplicationConfig merge with reversed priority
07210204 · Mariia Skripchenko · GitHub · 4e98d3ba · 07210204 · 07210204
--- a/ktor-server/ktor-server-core/api/ktor-server-core.api
+++ b/ktor-server/ktor-server-core/api/ktor-server-core.api
@@ -314,6 +314,8 @@ protected final class io/ktor/server/config/MapApplicationConfig$MapApplicationC

 public final class io/ktor/server/config/MergedApplicationConfigKt {
 	public static final fun merge (Ljava/util/List;)Lio/ktor/server/config/ApplicationConfig;
+	public static final fun mergeWith (Lio/ktor/server/config/ApplicationConfig;Lio/ktor/server/config/ApplicationConfig;)Lio/ktor/server/config/ApplicationConfig;
+	public static final fun withFallback (Lio/ktor/server/config/ApplicationConfig;Lio/ktor/server/config/ApplicationConfig;)Lio/ktor/server/config/ApplicationConfig;
 }

 public final class io/ktor/server/http/HttpDateJvmKt {

--- a/ktor-server/ktor-server-core/jvmAndNix/src/io/ktor/server/config/MergedApplicationConfig.kt
+++ b/ktor-server/ktor-server-core/jvmAndNix/src/io/ktor/server/config/MergedApplicationConfig.kt
@@ -8,9 +8,30 @@ package io.ktor.server.config
 * Merge configuration combining all their keys.
 * If key is not found in one of the configs, search will continue in the next config in the list.
 */
+@Deprecated("Use mergeWith/withFallback instead.")
 public fun List<ApplicationConfig>.merge(): ApplicationConfig {
    require(isNotEmpty()) { "List of configs can not be empty" }
-    return foldRight(last()) { config, acc -> MergedApplicationConfig(config, acc) }
+    return foldRight(last()) { config, acc -> config.withFallback(acc) }
+}
+
+/**
+ * Merge configuration combining all their keys.
+ * If the key exists in this and [other] config, the value from the [other] config will be used.
+ *
+ * @see [withFallback]
+ */
+public fun ApplicationConfig.mergeWith(other: ApplicationConfig): ApplicationConfig {
+    return MergedApplicationConfig(other, this)
+}
+
+/**
+ * Merge configuration combining all their keys.
+ * If the key exists in this and [other] config, the value from this config will be used.
+ *
+ * @see [mergeWith]
+ */
+public fun ApplicationConfig.withFallback(other: ApplicationConfig): ApplicationConfig {
+    return MergedApplicationConfig(this, other)
 }

 internal class MergedApplicationConfig(

--- a/ktor-server/ktor-server-core/jvmAndNix/test/io/ktor/server/config/MergedApplicationConfigTest.kt
+++ b/ktor-server/ktor-server-core/jvmAndNix/test/io/ktor/server/config/MergedApplicationConfigTest.kt
@@ -98,4 +98,44 @@ class MergedApplicationConfigTest {
        val config = MergedApplicationConfig(first, second)
        assertEquals(mapOf("first" to "value1", "second" to "value3"), config.toMap())
    }
+
+    @Test
+    fun testMergeWith() {
+        val first = MapApplicationConfig(
+            "value1" to "1",
+            "value2" to "2",
+            "value3" to "3",
+            "value4" to "4"
+        )
+        val second = MapApplicationConfig(
+            "value1" to "2",
+            "value2" to "2",
+            "value3" to "1",
+        )
+        val mergedConfig = first.mergeWith(second)
+        assertEquals("2", mergedConfig.property("value1").getString())
+        assertEquals("2", mergedConfig.property("value2").getString())
+        assertEquals("1", mergedConfig.property("value3").getString())
+        assertEquals("4", mergedConfig.property("value4").getString())
+    }
+
+    @Test
+    fun testMergeWithFallback() {
+        val first = MapApplicationConfig(
+            "value1" to "1",
+            "value2" to "2",
+            "value3" to "3"
+        )
+        val second = MapApplicationConfig(
+            "value1" to "2",
+            "value2" to "2",
+            "value3" to "1",
+            "value4" to "4"
+        )
+        val mergedConfig = first.withFallback(second)
+        assertEquals("1", mergedConfig.property("value1").getString())
+        assertEquals("2", mergedConfig.property("value2").getString())
+        assertEquals("3", mergedConfig.property("value3").getString())
+        assertEquals("4", mergedConfig.property("value4").getString())
+    }
 }
--- a/ktor-server/ktor-server-host-common/jvmAndNix/src/io/ktor/server/engine/CommandLine.kt
+++ b/ktor-server/ktor-server-host-common/jvmAndNix/src/io/ktor/server/engine/CommandLine.kt
@@ -101,7 +101,7 @@ internal fun buildApplicationConfig(args: Array<String>): ApplicationConfig {
    val environmentConfig = getConfigFromEnvironment()
    val fileConfig = ConfigLoader.load(configPath)

-    return listOf(commandLineConfig, environmentConfig, fileConfig).merge()
+    return fileConfig.mergeWith(environmentConfig).mergeWith(commandLineConfig)
 }

 internal expect fun ApplicationEngineEnvironmentBuilder.configureSSLConnectors(