Add kebab-case naming strategy (#2531)

Author: Kantis

formats/json-tests/commonTest/src/kotlinx/serialization/features/JsonNamingStrategyTest.kt

@@ -103,6 +103,52 @@ class JsonNamingStrategyTest : JsonTestBase() {
         }
     }
 
+    @Test
+    fun testKebabCaseStrategy() {
+        fun apply(name: String) =
+            JsonNamingStrategy.KebabCase.serialNameForJson(String.serializer().descriptor, 0, name)
+
+        val cases = mapOf<String, String>(
+            "" to "",
+            "_" to "_",
+            "-" to "-",
+            "___" to "___",
+            "---" to "---",
+            "a" to "a",
+            "A" to "a",
+            "-1" to "-1",
+            "-a" to "-a",
+            "-A" to "-a",
+            "property" to "property",
+            "twoWords" to "two-words",
+            "threeDistinctWords" to "three-distinct-words",
+            "ThreeDistinctWords" to "three-distinct-words",
+            "Oneword" to "oneword",
+            "camel-Case-WithDashes" to "camel-case-with-dashes",
+            "_many----dashes--" to "_many----dashes--",
+            "URLmapping" to "ur-lmapping",
+            "URLMapping" to "url-mapping",
+            "IOStream" to "io-stream",
+            "IOstream" to "i-ostream",
+            "myIo2Stream" to "my-io2-stream",
+            "myIO2Stream" to "my-io2-stream",
+            "myIO2stream" to "my-io2stream",
+            "myIO2streamMax" to "my-io2stream-max",
+            "InURLBetween" to "in-url-between",
+            "myHTTP2APIKey" to "my-http2-api-key",
+            "myHTTP2fastApiKey" to "my-http2fast-api-key",
+            "myHTTP23APIKey" to "my-http23-api-key",
+            "myHttp23ApiKey" to "my-http23-api-key",
+            "theWWW" to "the-www",
+            "theWWW-URL-xxx" to "the-www-url-xxx",
+            "hasDigit123AndPostfix" to "has-digit123-and-postfix"
+        )
+
+        cases.forEach { (input, expected) ->
+            assertEquals(expected, apply(input))
+        }
+    }
+
     @Serializable
     data class DontUseOriginal(val testCase: String)
 

formats/json/api/kotlinx-serialization-json.api

@@ -279,6 +279,7 @@ public abstract interface class kotlinx/serialization/json/JsonNamingStrategy {
 }
 
 public final class kotlinx/serialization/json/JsonNamingStrategy$Builtins {
+	public final fun getKebabCase ()Lkotlinx/serialization/json/JsonNamingStrategy;
 	public final fun getSnakeCase ()Lkotlinx/serialization/json/JsonNamingStrategy;
 }
 

formats/json/commonMain/src/kotlinx/serialization/json/JsonNamingStrategy.kt

@@ -95,39 +95,83 @@ public fun interface JsonNamingStrategy {
          */
         @ExperimentalSerializationApi
         public val SnakeCase: JsonNamingStrategy = object : JsonNamingStrategy {
-            override fun serialNameForJson(descriptor: SerialDescriptor, elementIndex: Int, serialName: String): String =
-                buildString(serialName.length * 2) {
-                    var bufferedChar: Char? = null
-                    var previousUpperCharsCount = 0
+            override fun serialNameForJson(
+                descriptor: SerialDescriptor,
+                elementIndex: Int,
+                serialName: String
+            ): String = convertCamelCase(serialName, '_')
 
-                    serialName.forEach { c ->
-                        if (c.isUpperCase()) {
-                            if (previousUpperCharsCount == 0 && isNotEmpty() && last() != '_')
-                                append('_')
+            override fun toString(): String = "kotlinx.serialization.json.JsonNamingStrategy.SnakeCase"
+        }
+
+        /**
+         * A strategy that transforms serial names from camel case to kebab case — lowercase characters with words separated by dashes.
+         * The descriptor parameter is not used.
+         *
+         * **Transformation rules**
+         *
+         * Words' bounds are defined by uppercase characters. If there is a single uppercase char, it is transformed into lowercase one with a dash in front:
+         * `twoWords` -> `two-words`. No dash is added if it was a beginning of the name: `MyProperty` -> `my-property`. Also, no dash is added if it was already there:
+         * `camel-Case-WithDashes` -> `camel-case-with-dashes`.
+         *
+         * **Acronyms**
+         *
+         * Since acronym rules are quite complex, it is recommended to lowercase all acronyms in source code.
+         * If there is an uppercase acronym — a sequence of uppercase chars — they are considered as a whole word from the start to second-to-last character of the sequence:
+         * `URLMapping` -> `url-mapping`, `myHTTPAuth` -> `my-http-auth`. Non-letter characters allow the word to continue:
+         * `myHTTP2APIKey` -> `my-http2-api-key`,  `myHTTP2fastApiKey` -> `my-http2fast-api-key`.
+         *
+         * **Note on cases**
+         *
+         * Whether a character is in upper case is determined by the result of [Char.isUpperCase] function.
+         * Lowercase transformation is performed by [Char.lowercaseChar], not by [Char.lowercase],
+         * and therefore does not support one-to-many and many-to-one character mappings.
+         * See the documentation of these functions for details.
+         */
+        @ExperimentalSerializationApi
+        public val KebabCase: JsonNamingStrategy = object : JsonNamingStrategy {
+            override fun serialNameForJson(
+                descriptor: SerialDescriptor,
+                elementIndex: Int,
+                serialName: String
+            ): String = convertCamelCase(serialName, '-')
 
-                            bufferedChar?.let(::append)
+            override fun toString(): String = "kotlinx.serialization.json.JsonNamingStrategy.KebabCase"
+        }
 
-                            previousUpperCharsCount++
-                            bufferedChar = c.lowercaseChar()
-                        } else {
-                            if (bufferedChar != null) {
-                                if (previousUpperCharsCount > 1 && c.isLetter()) {
-                                    append('_')
-                                }
-                                append(bufferedChar)
-                                previousUpperCharsCount = 0
-                                bufferedChar = null
+        private fun convertCamelCase(
+            serialName: String,
+            delimiter: Char
+        ) = buildString(serialName.length * 2) {
+                var bufferedChar: Char? = null
+                var previousUpperCharsCount = 0
+
+                serialName.forEach { c ->
+                    if (c.isUpperCase()) {
+                        if (previousUpperCharsCount == 0 && isNotEmpty() && last() != delimiter)
+                            append(delimiter)
+
+                        bufferedChar?.let(::append)
+
+                        previousUpperCharsCount++
+                        bufferedChar = c.lowercaseChar()
+                    } else {
+                        if (bufferedChar != null) {
+                            if (previousUpperCharsCount > 1 && c.isLetter()) {
+                                append(delimiter)
                             }
-                            append(c)
+                            append(bufferedChar)
+                            previousUpperCharsCount = 0
+                            bufferedChar = null
                         }
+                        append(c)
                     }
+                }
 
-                    if(bufferedChar != null) {
-                        append(bufferedChar)
-                    }
+                if (bufferedChar != null) {
+                    append(bufferedChar)
                 }
+            }
 
-            override fun toString(): String = "kotlinx.serialization.json.JsonNamingStrategy.SnakeCase"
-        }
     }
 }