KTOR-5000 Fix merging nested configs

ktor-server/ktor-server-core/jvmAndNix/src/io/ktor/server/config/MergedApplicationConfig.kt

@@ -30,15 +30,11 @@ internal class MergedApplicationConfig(
         else -> second.propertyOrNull(path)
     }
 
-    override fun config(path: String): ApplicationConfig = when {
-        firstKeys.contains(path) -> first.config(path)
-        else -> second.config(path)
-    }
+    override fun config(path: String): ApplicationConfig =
+        MergedApplicationConfig(first.config(path), second.config(path))
 
-    override fun configList(path: String): List<ApplicationConfig> = when {
-        firstKeys.contains(path) -> first.configList(path)
-        else -> second.configList(path)
-    }
+    override fun configList(path: String): List<ApplicationConfig> =
+        first.configList(path) + second.configList(path)
 
     override fun keys(): Set<String> = firstKeys + second.keys()
 

ktor-server/ktor-server-core/jvmAndNix/test/io/ktor/server/config/MergedApplicationConfigTest.kt

@@ -17,6 +17,39 @@ class MergedApplicationConfigTest {
         assertEquals("value3", config.property("second").getString())
     }
 
+    @Test
+    fun testConfig() {
+        val first = MapApplicationConfig("first.second.third1" to "value1", "first.second.third2" to "value2")
+        val second = MapApplicationConfig("first.second.third1" to "ignored", "first.second.third3" to "value3")
+        val config = MergedApplicationConfig(first, second)
+        val mergedNestedConfig = config.config("first.second")
+        assertEquals("value1", mergedNestedConfig.property("third1").getString())
+        assertEquals("value2", mergedNestedConfig.property("third2").getString())
+        assertEquals("value3", mergedNestedConfig.property("third3").getString())
+        assertEquals(setOf("third1", "third2", "third3"), mergedNestedConfig.keys())
+    }
+
+    @Test
+    fun testConfigList() {
+        val first = MapApplicationConfig(
+            "first.second.size" to "2",
+            "first.second.0.third" to "value1",
+            "first.second.1.third" to "value2"
+        )
+        val second = MapApplicationConfig(
+            "first.second.size" to "2",
+            "first.second.0.third" to "value3",
+            "first.second.1.third" to "value4"
+        )
+        val config = MergedApplicationConfig(first, second)
+        val configs = config.configList("first.second")
+        assertEquals(4, configs.size)
+        assertEquals("value1", configs[0].property("third").getString())
+        assertEquals("value2", configs[1].property("third").getString())
+        assertEquals("value3", configs[2].property("third").getString())
+        assertEquals("value4", configs[3].property("third").getString())
+    }
+
     @Test
     fun testPropertyOrNull() {
         val first = MapApplicationConfig("first" to "value1")