chore: add kotlin code splitter (#11364)

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- **Description:** Adds Kotlin language to `TextSplitter`

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

docs/snippets/modules/data_connection/document_transformers/text_splitters/code_splitter.mdx

@@ -17,6 +17,7 @@ from langchain.text_splitter import (
     ['cpp',
      'go',
      'java',
+     'kotlin',
      'js',
      'ts',
      'php',

libs/langchain/langchain/text_splitter.py

@@ -614,6 +614,7 @@ class Language(str, Enum):
     CPP = "cpp"
     GO = "go"
     JAVA = "java"
+    KOTLIN = "kotlin"
     JS = "js"
     TS = "ts"
     PHP = "php"
@@ -762,6 +763,32 @@ class RecursiveCharacterTextSplitter(TextSplitter):
                 " ",
                 "",
             ]
+        elif language == Language.KOTLIN:
+            return [
+                # Split along class definitions
+                "\nclass ",
+                # Split along method definitions
+                "\npublic ",
+                "\nprotected ",
+                "\nprivate ",
+                "\ninternal ",
+                "\ncompanion ",
+                "\nfun ",
+                "\nval ",
+                "\nvar ",
+                # Split along control flow statements
+                "\nif ",
+                "\nfor ",
+                "\nwhile ",
+                "\nwhen ",
+                "\ncase ",
+                "\nelse ",
+                # Split by the normal type of lines
+                "\n\n",
+                "\n",
+                " ",
+                "",
+            ]
         elif language == Language.JS:
             return [
                 # Split along function definitions

libs/langchain/tests/unit_tests/test_text_splitter.py

@@ -525,6 +525,38 @@ public class HelloWorld {
     ]
 
 
+def test_kotlin_code_splitter() -> None:
+    splitter = RecursiveCharacterTextSplitter.from_language(
+        Language.KOTLIN, chunk_size=CHUNK_SIZE, chunk_overlap=0
+    )
+    code = """
+class HelloWorld {
+    companion object {
+        @JvmStatic
+        fun main(args: Array<String>) {
+            println("Hello, World!")
+        }
+    }
+}
+    """
+    chunks = splitter.split_text(code)
+    assert chunks == [
+        "class",
+        "HelloWorld {",
+        "companion",
+        "object {",
+        "@JvmStatic",
+        "fun",
+        "main(args:",
+        "Array<String>)",
+        "{",
+        'println("Hello,',
+        'World!")',
+        "}\n    }",
+        "}",
+    ]
+
+
 def test_csharp_code_splitter() -> None:
     splitter = RecursiveCharacterTextSplitter.from_language(
         Language.CSHARP, chunk_size=CHUNK_SIZE, chunk_overlap=0