feat(p10-1c-jk): tree-sitter-kotlin-ng AST extractor (KotlinAstExtractor)

Uses tree-sitter-kotlin-ng (bare tree-sitter-kotlin is stuck on tree-sitter
0.21-0.23, incompatible with our 0.26). Mirrors JavaAstExtractor (JVM family,
source-side package extraction + class-nesting) with Kotlin grammar quirks:

- Root is `source_file`, not `program`.
- `package_header` child is `qualified_identifier` (its slice text is the
  dotted path); the bare `identifier` shape is also accepted as a fallback.
- `class_declaration` is the single node kind for `class` / `data class` /
  `sealed class` / `interface` / `enum class` — distinguished only by its
  `modifiers` child. Body is `class_body` for non-enum, `enum_class_body`
  for enum class; neither carries a `body` field name, so the extractor
  looks the body up by node kind rather than `child_by_field_name("body")`.
- `companion_object` is its own node kind (NOT object_declaration with a
  modifier); its `name` field is optional, so the extractor fills in the
  implicit Kotlin convention name `Companion`.
- `function_declaration` is allowed at top level (unlike Java), emitted as
  `<pkg>.<fn_name>`; the same node kind nested in `class_body` becomes
  `<pkg>.<...>.<Class>.<method>` via the same mod_path mechanism.
- `secondary_constructor` has no `name` field; symbol uses the enclosing
  class name (Java duplication convention: `<pkg>.<...>.<Class>.<Class>`).
- Enum bodies (`enum_class_body`) are NOT recursed — `enum_entry` is not
  emitted as a unit (matches Java 1차 scope).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
2026-05-20 10:49:57 +00:00
parent ebc4ef2eea
commit 2ce6ae47c5
3 changed files with 658 additions and 0 deletions

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//! `kebab-parse-code::kotlin` — tree-sitter Kotlin AST extractor (P10-1C-JK Task G).
//!
//! Implements [`kebab_core::Extractor`] for [`MediaType::Code("kotlin")`].
//! Mirrors the Java extractor (JVM family, source-side `package` extraction +
//! class-nesting) with Kotlin-specific adjustments:
//!
//! * Root is `source_file` (not `program`).
//! * `package_header` carries a single `qualified_identifier` child whose
//! slice text IS the dotted package path — never a bare `identifier`
//! sub-form for the package (the grammar always wraps a single segment
//! in `qualified_identifier` too).
//! * `class_declaration` covers `class`, `data class`, `sealed class`,
//! `enum class`, AND `interface` — Kotlin uses ONE node kind with a
//! `modifiers` child rather than separate `interface_declaration` /
//! `enum_declaration` nodes (verified via tree-sitter-kotlin-ng
//! `node-types.json`).
//! * The body child of `class_declaration` is either `class_body` (normal
//! classes / interfaces) OR `enum_class_body` (enum class). Neither
//! carries a `body` field name, so it is matched by kind, not by
//! `child_by_field_name("body")`.
//! * `companion_object` is a SEPARATE node kind (not `object_declaration`
//! with a modifier). Its `name` field is OPTIONAL — when omitted (the
//! common case `companion object { ... }`) the symbol uses the
//! implicit Kotlin convention name `Companion`.
//! * `object_declaration` (named singleton) carries a `name` field and a
//! `class_body` child.
//! * `function_declaration` may appear at top level (Kotlin top-level
//! function) AND inside `class_body` — same node kind, the
//! `mod_path` state distinguishes the two emit forms.
//!
//! Enum bodies (`enum_class_body`) are NOT recursed for the 1차 cut —
//! `enum_entry` declarations are not emitted as units, matching the
//! Java extractor's enum policy (design §3.4 1차 scope).
//!
//! Per design §3.4 / §9.1 / §9 versioning.
use anyhow::Result;
use kebab_core::{
Block, CanonicalDocument, CodeBlock, CommonBlock, Extractor, Lang, MediaType, Metadata,
ParserVersion, Provenance, ProvenanceEvent, ProvenanceKind, SourceSpan, SourceType, TrustLevel,
id_for_block, id_for_doc,
};
use serde_json::Map;
use time::OffsetDateTime;
use crate::scaffold::{filename_from_workspace_path, join_symbol, strip_extension};
pub const PARSER_VERSION: &str = "code-kotlin-v1";
/// Kotlin AST extractor. Per-unit blocks via tree-sitter-kotlin-ng 1.1
/// (`LANGUAGE: LanguageFn`) parsed by tree-sitter 0.26.
pub struct KotlinAstExtractor;
impl KotlinAstExtractor {
pub fn new() -> Self {
Self
}
}
impl Default for KotlinAstExtractor {
fn default() -> Self {
Self::new()
}
}
impl Extractor for KotlinAstExtractor {
fn supports(&self, m: &MediaType) -> bool {
matches!(m, MediaType::Code(l) if l == "kotlin")
}
fn parser_version(&self) -> ParserVersion {
ParserVersion(PARSER_VERSION.to_string())
}
fn extract(
&self,
ctx: &kebab_core::ExtractContext<'_>,
bytes: &[u8],
) -> Result<CanonicalDocument> {
let asset = ctx.asset;
if !self.supports(&asset.media_type) {
anyhow::bail!(
"kebab-parse-code: unsupported media_type for KotlinAstExtractor: {:?}",
asset.media_type
);
}
let parser_version = self.parser_version();
let doc_id = id_for_doc(&asset.workspace_path, &asset.asset_id, &parser_version);
let source = String::from_utf8(bytes.to_vec()).map_err(|e| {
anyhow::anyhow!("kebab-parse-code: Kotlin source is not valid UTF-8: {e}")
})?;
let blocks = build_blocks(&source, &doc_id)?;
let unit_count = blocks.len() as u32;
let now = OffsetDateTime::now_utc();
let mut events: Vec<ProvenanceEvent> = Vec::with_capacity(2);
events.push(ProvenanceEvent {
at: asset.discovered_at,
agent: "kb-source-fs".to_string(),
kind: ProvenanceKind::Discovered,
note: None,
});
events.push(ProvenanceEvent {
at: now,
agent: "kb-parse-code".to_string(),
kind: ProvenanceKind::Parsed,
note: Some(format!(
"parser_version={}; unit_count={}",
parser_version.0, unit_count
)),
});
let title = {
let fname = filename_from_workspace_path(&asset.workspace_path.0);
strip_extension(&fname)
};
// Resolve the file's absolute path for repo detection. If the
// source URI carries a relative path, anchor it at the workspace
// root so the `.git/` walk-up starts from the right place.
let abs_path = match &asset.source_uri {
kebab_core::SourceUri::File(p) => {
if p.is_absolute() {
p.clone()
} else {
ctx.workspace_root.join(p)
}
}
kebab_core::SourceUri::Kb(_) => ctx.workspace_root.to_path_buf(),
};
let (repo, git_branch, git_commit) = match crate::repo::detect_repo(&abs_path) {
Some(r) => (Some(r.name), r.branch, r.commit),
None => (None, None, None),
};
let metadata = Metadata {
aliases: Vec::new(),
tags: Vec::new(),
created_at: asset.discovered_at,
updated_at: asset.discovered_at,
source_type: SourceType::Note,
trust_level: TrustLevel::Primary,
user_id_alias: None,
user: Map::new(),
repo,
git_branch,
git_commit,
code_lang: Some("kotlin".to_string()),
};
tracing::debug!(
target: "kebab-parse-code",
"extracted Kotlin doc_id={} workspace_path={} units={}",
doc_id.0,
asset.workspace_path.0,
unit_count
);
Ok(CanonicalDocument {
doc_id,
source_asset_id: asset.asset_id.clone(),
workspace_path: asset.workspace_path.clone(),
title,
lang: Lang("und".to_string()),
blocks,
metadata,
provenance: Provenance { events },
parser_version,
schema_version: 1,
doc_version: 1,
last_chunker_version: None,
last_embedding_version: None,
})
}
}
/// p10-1C-JK: extract `package` declaration text from a tree-sitter-kotlin
/// `source_file`. Returns `None` if no `package_header` (default-package
/// Kotlin file). The package_header's single named child is a
/// `qualified_identifier`; its slice text is the dotted path. Per design
/// §3.4 Kotlin row.
fn extract_package(root: tree_sitter::Node, src: &str) -> Option<String> {
let mut cur = root.walk();
for child in root.named_children(&mut cur) {
if child.kind() == "package_header" {
let mut c2 = child.walk();
for sub in child.named_children(&mut c2) {
let k = sub.kind();
if k == "qualified_identifier" || k == "identifier" {
return Some(src[sub.start_byte()..sub.end_byte()].to_string());
}
}
}
}
None
}
/// Walk preceding `line_comment` / `block_comment` siblings to extend
/// the unit's line range upward, folding leading KDoc / line comments
/// into the unit. Modifiers / annotations live INSIDE the declaration
/// node itself, so their lines are already inside `n.start_position()`.
fn unit_start(n: &tree_sitter::Node) -> u32 {
let mut start = n.start_position().row as u32 + 1;
let mut prev = n.prev_sibling();
while let Some(p) = prev {
let k = p.kind();
if k == "line_comment" || k == "block_comment" {
start = p.start_position().row as u32 + 1;
prev = p.prev_sibling();
} else {
break;
}
}
start
}
fn node_name_text<'a>(n: &tree_sitter::Node, src: &'a str) -> Option<&'a str> {
n.child_by_field_name("name")
.map(|c| &src[c.start_byte()..c.end_byte()])
}
/// Find the first child of a node with one of the given kinds. Used to
/// locate `class_body` / `enum_class_body` on `class_declaration` since
/// the kotlin grammar attaches them without a `body` field name.
fn first_child_of_kinds<'a>(
n: &tree_sitter::Node<'a>,
kinds: &[&str],
) -> Option<tree_sitter::Node<'a>> {
let mut cur = n.walk();
n.named_children(&mut cur)
.find(|child| kinds.contains(&child.kind()))
}
/// `true` iff a `class_declaration` carries the `enum` class modifier.
/// Detected by walking `modifiers` → `class_modifier` and checking the
/// child text. The grammar exposes "enum" / "sealed" / "data" /
/// "annotation" / "inner" as named `class_modifier` children of
/// `modifiers`. We only need to know about "enum" to decide whether to
/// look for `class_body` or `enum_class_body` and whether to skip body
/// recursion.
fn class_decl_is_enum(n: &tree_sitter::Node, src: &str) -> bool {
let mut cur = n.walk();
for child in n.named_children(&mut cur) {
if child.kind() == "modifiers" {
let mut c2 = child.walk();
for sub in child.named_children(&mut c2) {
if sub.kind() == "class_modifier" {
let text = &src[sub.start_byte()..sub.end_byte()];
if text == "enum" {
return true;
}
}
}
}
}
false
}
fn build_blocks(
source: &str,
doc_id: &kebab_core::DocumentId,
) -> anyhow::Result<Vec<kebab_core::Block>> {
let mut parser = tree_sitter::Parser::new();
parser
.set_language(&tree_sitter_kotlin_ng::LANGUAGE.into())
.map_err(|e| anyhow::anyhow!("set tree-sitter-kotlin-ng language: {e}"))?;
let tree = parser
.parse(source.as_bytes(), None)
.ok_or_else(|| anyhow::anyhow!("tree-sitter failed to parse Kotlin source"))?;
let lines: Vec<&str> = source.split('\n').collect();
let root = tree.root_node();
let mod_prefix = extract_package(root, source).unwrap_or_else(|| "<unknown>".to_string());
// units: (symbol, line_start, line_end, is_real_semantic_unit).
// Glue groups are pushed with a sentinel symbol + is_real=false so a
// post-pass can decide `<module>` vs `<top-level>` (JVM family pattern).
let mut units: Vec<(String, u32, u32, bool)> = Vec::new();
// (is_import 0/1, s, e). `is_import` flags `import` — used by the
// glue flush to pick `<module>` vs `<top-level>` provisional label.
let mut glue: Vec<(usize, u32, u32)> = Vec::new();
walk_top(root, source, &mod_prefix, &mut units, &mut glue);
// `<module>` is correct only when the file produced no real unit.
// Otherwise the import-only group becomes `<top-level>` (same
// post-pass as 1B / 1C-Go / Java).
let has_real_unit = units.iter().any(|(_, _, _, is_real)| *is_real);
if has_real_unit {
for (sym, _, _, is_real) in units.iter_mut() {
if !*is_real && sym.ends_with("<module>") {
let pre = &sym[..sym.len() - "<module>".len()];
*sym = format!("{pre}<top-level>");
}
}
}
let total_lines = lines.len() as u32;
let mut blocks = Vec::with_capacity(units.len());
for (ordinal, (symbol, ls, le, _is_real)) in units.into_iter().enumerate() {
let line_start = ls.max(1);
let line_end = le.min(total_lines.max(1));
let span = SourceSpan::Code {
line_start,
line_end,
symbol: Some(symbol),
lang: Some("kotlin".to_string()),
};
let block_id = id_for_block(doc_id, "code", &[], ordinal as u32, &span);
let code = lines[(line_start as usize - 1)..=(line_end as usize - 1)].join("\n");
blocks.push(Block::Code(CodeBlock {
common: CommonBlock {
block_id,
heading_path: Vec::new(),
source_span: span,
},
lang: Some("kotlin".to_string()),
code,
}));
}
Ok(blocks)
}
/// Walk the file's top-level children — `source_file` named children:
/// `package_header` (handled by `extract_package`), `import` (glue),
/// `class_declaration` (class / interface / enum class), `object_declaration`,
/// `function_declaration` (top-level), `property_declaration` (top-level),
/// `type_alias` (currently treated as glue). Class / object bodies are
/// recursed via [`walk_body`] with the type name pushed onto `mod_path`
/// (JVM family pattern). Enum bodies are NOT recursed (1차 cut).
fn walk_top(
node: tree_sitter::Node,
src: &str,
mod_prefix: &str,
units: &mut Vec<(String, u32, u32, bool)>,
glue: &mut Vec<(usize, u32, u32)>,
) {
let mod_path: &[String] = &[];
let mut cur = node.walk();
for child in node.named_children(&mut cur) {
let s = unit_start(&child);
let e = child.end_position().row as u32 + 1;
match child.kind() {
"class_declaration" => {
// Covers class / data class / sealed class / interface /
// enum class — single grammar node, the modifiers child
// distinguishes them. The body is `class_body` for
// non-enum and `enum_class_body` for enum class; both
// attach without a `body` field name.
if let Some(name) = node_name_text(&child, src) {
glue.retain(|(_, gs, _)| *gs < s);
flush_glue(glue, units, mod_prefix, mod_path);
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
let is_enum = class_decl_is_enum(&child, src);
if !is_enum {
if let Some(body) = first_child_of_kinds(&child, &["class_body"]) {
let np: Vec<String> = vec![name.to_string()];
walk_body(body, src, mod_prefix, &np, units);
}
}
// enum_class_body NOT recursed — enum constants are
// not emitted as units (1차 scope, matches Java).
}
}
"object_declaration" => {
// Singleton object — name field is required by the grammar.
if let Some(name) = node_name_text(&child, src) {
glue.retain(|(_, gs, _)| *gs < s);
flush_glue(glue, units, mod_prefix, mod_path);
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
if let Some(body) = first_child_of_kinds(&child, &["class_body"]) {
let np: Vec<String> = vec![name.to_string()];
walk_body(body, src, mod_prefix, &np, units);
}
}
}
"function_declaration" => {
// Top-level Kotlin function (unlike Java).
if let Some(name) = node_name_text(&child, src) {
glue.retain(|(_, gs, _)| *gs < s);
flush_glue(glue, units, mod_prefix, mod_path);
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
}
}
"import" => {
glue.push((1, s, e));
}
// `property_declaration` (top-level val/var) and `type_alias`
// are not emitted as standalone units in the 1차 cut — they
// glue into the import group instead. `package_header` is
// handled by `extract_package` (structural metadata, not a
// unit).
_ => {}
}
}
flush_glue(glue, units, mod_prefix, mod_path);
}
/// Walk a `class_body` (or object's `class_body`). Emits one unit per
/// method / secondary constructor and recurses into nested type
/// declarations + companion objects. Property declarations are NOT
/// emitted (would explode unit count, parallel to Java field policy).
///
/// `companion_object` carries an optional `name` field — when omitted
/// (the common case `companion object { ... }`) the implicit Kotlin
/// convention name `Companion` is used.
///
/// No `glue` parameter: Kotlin imports are file-level only.
fn walk_body(
body: tree_sitter::Node,
src: &str,
mod_prefix: &str,
mod_path: &[String],
units: &mut Vec<(String, u32, u32, bool)>,
) {
let mut cur = body.walk();
for child in body.named_children(&mut cur) {
let s = unit_start(&child);
let e = child.end_position().row as u32 + 1;
match child.kind() {
"function_declaration" => {
if let Some(name) = node_name_text(&child, src) {
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
}
}
"secondary_constructor" => {
// Kotlin secondary constructor — no `name` field on the
// grammar node. Per design §3.4 (Java JVM convention) the
// symbol uses the enclosing class name as the trailing
// segment (matches the Java `<pkg>.<...>.<Class>.<Class>`
// duplication for constructors).
if let Some(class_name) = mod_path.last() {
let sym = join_symbol(mod_prefix, mod_path, class_name);
units.push((sym, s, e, true));
}
}
"companion_object" => {
// Companion's name field is OPTIONAL — fall back to the
// Kotlin implicit name `Companion`.
let name: &str = node_name_text(&child, src).unwrap_or("Companion");
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
if let Some(inner_body) = first_child_of_kinds(&child, &["class_body"]) {
let mut np = mod_path.to_vec();
np.push(name.to_string());
walk_body(inner_body, src, mod_prefix, &np, units);
}
}
"class_declaration" => {
let name = match node_name_text(&child, src) {
Some(n) => n,
None => continue,
};
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
let is_enum = class_decl_is_enum(&child, src);
if !is_enum {
if let Some(inner_body) = first_child_of_kinds(&child, &["class_body"]) {
let mut np = mod_path.to_vec();
np.push(name.to_string());
walk_body(inner_body, src, mod_prefix, &np, units);
}
}
}
"object_declaration" => {
let name = match node_name_text(&child, src) {
Some(n) => n,
None => continue,
};
let sym = join_symbol(mod_prefix, mod_path, name);
units.push((sym, s, e, true));
if let Some(inner_body) = first_child_of_kinds(&child, &["class_body"]) {
let mut np = mod_path.to_vec();
np.push(name.to_string());
walk_body(inner_body, src, mod_prefix, &np, units);
}
}
// property_declaration, anonymous_initializer: NOT emitted.
_ => {}
}
}
}
fn flush_glue(
glue: &mut Vec<(usize, u32, u32)>,
units: &mut Vec<(String, u32, u32, bool)>,
mod_prefix: &str,
mod_path: &[String],
) {
if glue.is_empty() {
return;
}
let s = glue.iter().map(|(_, a, _)| *a).min().unwrap();
let e = glue.iter().map(|(_, _, b)| *b).max().unwrap();
// Provisional label: `<module>` only if the group is exclusively
// imports. The post-pass demotes any `<module>` to `<top-level>` if
// the file produced any real unit.
let only_imports = glue.iter().all(|(is_import, _, _)| *is_import == 1);
let label = if only_imports { "<module>" } else { "<top-level>" };
units.push((join_symbol(mod_prefix, mod_path, label), s, e, false));
glue.clear();
}
#[cfg(test)]
mod tests {
use super::*;
use kebab_core::{Block, MediaType, SourceSpan};
fn extract_fixture() -> kebab_core::CanonicalDocument {
let bytes = std::fs::read(concat!(
env!("CARGO_MANIFEST_DIR"),
"/tests/fixtures/sample.kt"
))
.unwrap();
let asset =
crate::rust::tests_support::fixed_code_asset("crates/x/src/sample.kt", "kotlin");
let cfg = kebab_core::ExtractConfig::default();
let root = std::path::PathBuf::from("/tmp");
let ctx = kebab_core::ExtractContext {
asset: &asset,
workspace_root: &root,
config: &cfg,
};
KotlinAstExtractor::new().extract(&ctx, &bytes).unwrap()
}
#[test]
fn extractor_supports_only_media_code_kotlin() {
let e = KotlinAstExtractor::new();
assert!(e.supports(&MediaType::Code("kotlin".into())));
assert!(!e.supports(&MediaType::Code("java".into())));
assert!(!e.supports(&MediaType::Code("rust".into())));
assert!(!e.supports(&MediaType::Markdown));
}
#[test]
fn kotlin_units_match_design_3_4_symbols() {
let doc = extract_fixture();
let mut syms: Vec<String> = doc
.blocks
.iter()
.filter_map(|b| match b {
Block::Code(c) => match &c.common.source_span {
SourceSpan::Code { symbol, lang, .. } => {
assert_eq!(lang.as_deref(), Some("kotlin"));
symbol.clone()
}
_ => None,
},
_ => None,
})
.collect();
syms.sort();
// package extracted from source = com.kebab.chunk
assert!(
syms.iter()
.any(|s| s == "com.kebab.chunk.MdHeadingV1Chunker"),
"got {syms:?}"
);
assert!(
syms.iter()
.any(|s| s == "com.kebab.chunk.MdHeadingV1Chunker.chunkDoc"),
"got {syms:?}"
);
assert!(
syms.iter()
.any(|s| s == "com.kebab.chunk.MdHeadingV1Chunker.getName"),
"got {syms:?}"
);
// Implicit companion object name = Companion (grammar leaves the
// name field unset; the extractor fills it in).
assert!(
syms.iter()
.any(|s| s == "com.kebab.chunk.MdHeadingV1Chunker.Companion"),
"got {syms:?}"
);
assert!(
syms.iter()
.any(|s| s == "com.kebab.chunk.MdHeadingV1Chunker.Companion.withName"),
"got {syms:?}"
);
// interface — also via class_declaration in the grammar
assert!(
syms.iter().any(|s| s == "com.kebab.chunk.Stringer"),
"got {syms:?}"
);
// enum class — also via class_declaration; body NOT recursed
assert!(
syms.iter().any(|s| s == "com.kebab.chunk.Mode"),
"got {syms:?}"
);
// Kotlin top-level fn — unlike Java
assert!(
syms.iter().any(|s| s == "com.kebab.chunk.freeFunction"),
"got {syms:?}"
);
// Singleton object + its method
assert!(
syms.iter().any(|s| s == "com.kebab.chunk.Singleton"),
"got {syms:?}"
);
assert!(
syms.iter().any(|s| s == "com.kebab.chunk.Singleton.ping"),
"got {syms:?}"
);
// import grouped as <top-level>
assert!(
syms.iter().any(|s| s == "com.kebab.chunk.<top-level>"),
"got {syms:?}"
);
}
#[test]
fn deterministic_across_runs() {
let a = extract_fixture();
for _ in 0..50 {
assert_eq!(extract_fixture().blocks, a.blocks);
}
}
}

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@@ -16,6 +16,7 @@
pub mod go;
pub mod java;
pub mod javascript;
pub mod kotlin;
pub mod lang;
pub mod python;
pub mod repo;
@@ -27,6 +28,7 @@ pub mod typescript;
pub use go::{PARSER_VERSION as GO_PARSER_VERSION, GoAstExtractor};
pub use java::{PARSER_VERSION as JAVA_PARSER_VERSION, JavaAstExtractor};
pub use javascript::{PARSER_VERSION as JS_PARSER_VERSION, JavascriptAstExtractor};
pub use kotlin::{PARSER_VERSION as KOTLIN_PARSER_VERSION, KotlinAstExtractor};
pub use lang::{code_lang_for_path, module_path_for_python, module_path_for_tsjs};
pub use python::{PARSER_VERSION as PYTHON_PARSER_VERSION, PythonAstExtractor};
pub use repo::{RepoMeta, detect_repo};

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// sample.kt
package com.kebab.chunk
import java.util.List
/**
* Heading-aware Markdown chunker.
*/
class MdHeadingV1Chunker(val name: String) {
fun chunkDoc(input: String): List<String> = listOf(name, input)
fun getName(): String = name
companion object {
fun withName(n: String): MdHeadingV1Chunker = MdHeadingV1Chunker(n)
}
}
interface Stringer {
fun asString(): String
}
enum class Mode { DEFAULT, FAST }
fun freeFunction(x: Int): Int = x + 1
object Singleton {
fun ping(): String = "pong"
}