Support decoding maps with boolean keys (#2440)

We ignore quoted/unquoted state when decoding maps with number keys, so it is logical to do the same for boolean maps.

Fixes #2438

formats/json-tests/commonTest/src/kotlinx/serialization/json/JsonMapKeysTest.kt

@@ -5,6 +5,7 @@
 package kotlinx.serialization.json
 
 import kotlinx.serialization.*
+import kotlinx.serialization.builtins.*
 import kotlinx.serialization.descriptors.PrimitiveKind
 import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
 import kotlinx.serialization.descriptors.SerialDescriptor
@@ -41,6 +42,9 @@ class JsonMapKeysTest : JsonTestBase() {
     @Serializable
     private data class WithMap(val map: Map<Long, Long>)
 
+    @Serializable
+    private data class WithBooleanMap(val map: Map<Boolean, Boolean>)
+
     @Serializable
     private data class WithValueKeyMap(val map: Map<PrimitiveCarrier, Long>)
 
@@ -60,13 +64,42 @@ class JsonMapKeysTest : JsonTestBase() {
     private data class WithContextualKey(val map: Map<@Contextual ContextualValue, Long>)
 
     @Test
-    fun testMapKeysShouldBeStrings() = parametrizedTest(default) {
+    fun testMapKeysSupportNumbers() = parametrizedTest {
         assertStringFormAndRestored(
             """{"map":{"10":10,"20":20}}""",
             WithMap(mapOf(10L to 10L, 20L to 20L)),
             WithMap.serializer(),
-            this
+            default
+        )
+    }
+
+    @Test
+    fun testMapKeysSupportBooleans() = parametrizedTest {
+        assertStringFormAndRestored(
+            """{"map":{"true":false,"false":true}}""",
+            WithBooleanMap(mapOf(true to false, false to true)),
+            WithBooleanMap.serializer(),
+            default
+        )
+    }
+
+    // As a result of quoting ignorance when parsing primitives, it is possible to parse unquoted maps if Kotlin keys are non-string primitives.
+    // This is not spec-compliant, but I do not see any problems with it.
+    @Test
+    fun testMapDeserializesUnquotedKeys() = parametrizedTest {
+        assertEquals(WithMap(mapOf(10L to 10L, 20L to 20L)), default.decodeFromString("""{"map":{10:10,20:20}}"""))
+        assertEquals(
+            WithBooleanMap(mapOf(true to false, false to true)),
+            default.decodeFromString("""{"map":{true:false,false:true}}""")
         )
+        assertFailsWithSerial("JsonDecodingException") {
+            default.decodeFromString(
+                MapSerializer(
+                    String.serializer(),
+                    Boolean.serializer()
+                ),"""{"map":{true:false,false:true}}"""
+            )
+        }
     }
 
     @Test

formats/json-tests/commonTest/src/kotlinx/serialization/json/LenientTest.kt

@@ -37,7 +37,7 @@ class LenientTest : JsonTestBase() {
     @Test
     fun testQuotedBoolean() = parametrizedTest {
         val json = """{"i":1, "l":2, "b":"true", "s":"string"}"""
-        assertFailsWithSerial("JsonDecodingException") { default.decodeFromString(Holder.serializer(), json, it) }
+        assertEquals(value, default.decodeFromString(Holder.serializer(), json, it))
         assertEquals(value, lenient.decodeFromString(Holder.serializer(), json, it))
     }
 

formats/json/commonMain/src/kotlinx/serialization/json/internal/StreamingJsonDecoder.kt

@@ -268,23 +268,14 @@ internal open class StreamingJsonDecoder(
         }
     }
 
-
+    /*
+     * The primitives are allowed to be quoted and unquoted
+     * to simplify map key parsing and integrations with third-party API.
+     */
     override fun decodeBoolean(): Boolean {
-        /*
-         * We prohibit any boolean literal that is not strictly 'true' or 'false' as it is considered way too
-         * error-prone, but allow quoted literal in relaxed mode for booleans.
-         */
-        return if (configuration.isLenient) {
-            lexer.consumeBooleanLenient()
-        } else {
-            lexer.consumeBoolean()
-        }
+        return lexer.consumeBooleanLenient()
     }
 
-    /*
-     * The rest of the primitives are allowed to be quoted and unquoted
-     * to simplify integrations with third-party API.
-     */
     override fun decodeByte(): Byte {
         val value = lexer.consumeNumericLiteral()
         // Check for overflow

formats/json/commonMain/src/kotlinx/serialization/json/internal/TreeJsonDecoder.kt

@@ -91,16 +91,7 @@ private sealed class AbstractJsonTreeDecoder(
     override fun decodeTaggedNotNullMark(tag: String): Boolean = currentElement(tag) !== JsonNull
 
     override fun decodeTaggedBoolean(tag: String): Boolean {
-        val value = getPrimitiveValue(tag)
-        if (!json.configuration.isLenient) {
-            val literal = value.asLiteral("boolean")
-            if (literal.isString) throw JsonDecodingException(
-                -1, "Boolean literal for key '$tag' should be unquoted.\n$lenientHint", currentObject().toString()
-            )
-        }
-        return value.primitive("boolean") {
-            booleanOrNull ?: throw IllegalArgumentException() /* Will be handled by 'primitive' */
-        }
+        return getPrimitiveValue(tag).primitive("boolean", JsonPrimitive::booleanOrNull)
     }
 
     override fun decodeTaggedByte(tag: String) = getPrimitiveValue(tag).primitive("byte") {