red #77 tests and docs for jsom map serialization

docs/json_and_kotlin_serialization.md

@@ -98,6 +98,49 @@ formatting and parsing actual Json strings. This is why we use `Json.decodeFromJ
 `Json.decodeFromString`. Such an approach gives satisfactory performance without writing and supporting custom
 `kotlinx.serialization` codecs.
 
+### Pitfall: JSON objects and Map<String, Any?>
+
+Kotlin serialization does not support `Map<String, Any?>` as a serializable type, more general, it can't serialize `Any`. This in particular means that you can deserialize Kotlin `Map<String, T>` as long as `T` is `@Serializable` in Kotlin: 
+
+```kotlin
+@Serializable
+data class TestJson2(
+    val value: Int,
+    val inner: Map<String,Int>
+)
+
+@Test
+fun deserializeMapWithJsonTest() = runTest {
+    val x = eval("""
+        import lyng.serialization
+        { value: 1, inner: { "foo": 1, "bar": 2 }}
+    """.trimIndent()).decodeSerializable<TestJson2>()
+    // That works perfectly well:
+    assertEquals(TestJson2(1, mapOf("foo" to 1, "bar" to 2)), x)
+}
+```
+
+But what if your map has objects of different types? The approach of using polymorphism is partially applicable, but what to do with `{ one: 1, two: "two" }`?
+
+The answer is pretty simple: use `JsonObject` in your deserializable object. This class is capable of holding any JSON types and structures and is sort of a silver bullet for such cases:
+
+~~~kotlin
+@Serializable
+data class TestJson3(
+    val value: Int,
+    val inner: JsonObject
+)
+@Test
+fun deserializeAnyMapWithJsonTest() = runTest {
+    val x = eval("""
+        import lyng.serialization
+        { value: 12, inner: { "foo": 1, "bar": "two" }}
+    """.trimIndent()).decodeSerializable<TestJson3>()
+    assertEquals(TestJson3(12, JsonObject(mapOf("foo" to JsonPrimitive(1), "bar" to Json.encodeToJsonElement("two")))), x)
+}
+~~~
+
+
 # List of supported types
 
 | Lyng type | JSON type | notes       |

lynglib/src/commonTest/kotlin/ScriptTest.kt

@@ -26,6 +26,10 @@ import kotlinx.coroutines.withTimeout
 import kotlinx.datetime.Clock
 import kotlinx.datetime.Instant
 import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.encodeToJsonElement
 import net.sergeych.lyng.*
 import net.sergeych.lyng.obj.*
 import net.sergeych.lyng.pacman.InlineSourcesImportProvider
@@ -3962,4 +3966,33 @@ class ScriptTest {
         """.trimIndent()
         )
     }
+
+    @Serializable
+    data class TestJson2(
+        val value: Int,
+        val inner: Map<String,Int>
+    )
+
+    @Test
+    fun deserializeMapWithJsonTest() = runTest {
+        val x = eval("""
+            import lyng.serialization
+            { value: 1, inner: { "foo": 1, "bar": 2 }}
+        """.trimIndent()).decodeSerializable<TestJson2>()
+        assertEquals(TestJson2(1, mapOf("foo" to 1, "bar" to 2)), x)
+    }
+
+    @Serializable
+    data class TestJson3(
+        val value: Int,
+        val inner: JsonObject
+    )
+    @Test
+    fun deserializeAnyMapWithJsonTest() = runTest {
+        val x = eval("""
+            import lyng.serialization
+            { value: 12, inner: { "foo": 1, "bar": "two" }}
+        """.trimIndent()).decodeSerializable<TestJson3>()println(x)
+        assertEquals(TestJson3(12, JsonObject(mapOf("foo" to JsonPrimitive(1), "bar" to Json.encodeToJsonElement("two")))), x)
+    }
 }