KTOR-7008 Fix toMap() to correctly handle nested values in MergedAppl…

…icationConfig (#4453)

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

@@ -69,5 +69,20 @@ internal class MergedApplicationConfig(
 
     override fun keys(): Set<String> = firstKeys + secondKeys
 
-    override fun toMap(): Map<String, Any?> = second.toMap() + first.toMap()
+    override fun toMap(): Map<String, Any?> = second.toMap().merge(first.toMap())
+
+    @Suppress("UNCHECKED_CAST")
+    private fun Map<String, Any?>.merge(other: Map<String, Any?>): Map<String, Any?> =
+        (this.keys + other.keys).associateWith { key ->
+            val value1 = this[key]
+            val value2 = other[key]
+
+            when {
+                value1 is Map<*, *> && value2 is Map<*, *> -> {
+                    (value1 as Map<String, Any?>).merge(value2 as Map<String, Any?>)
+                }
+
+                else -> value2 ?: value1
+            }
+        }
 }

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

@@ -99,6 +99,22 @@ class MergedApplicationConfigTest {
         assertEquals(mapOf("first" to "value1", "second" to "value3"), config.toMap())
     }
 
+    @Test
+    fun testDeepToMap() {
+        val first = MapApplicationConfig(
+            "nested.nested-value-1" to "value1",
+            "nested.nested-value-2" to "value1",
+        )
+        val second = MapApplicationConfig(
+            "nested.nested-value-2" to "value2",
+            "nested.nested-value-3" to "value2",
+        )
+        val merged = first.mergeWith(second).toMap()["nested"] as Map<*, *>
+        assertEquals("value1", merged["nested-value-1"])
+        assertEquals("value2", merged["nested-value-2"])
+        assertEquals("value2", merged["nested-value-3"])
+    }
+
     @Test
     fun testMergeWith() {
         val first = MapApplicationConfig(