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Add YAML node-types format and converter

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Human-friendly YAML alternative to tree-sitter node-types.json with
three sections: supertypes, named, unnamed. Supports bidirectional
conversion and building Schema objects from YAML.

Includes CLI binary (node_types_yaml) and documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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# YAML Node Types Format
The YAML node-types format is a human-friendly alternative to tree-sitter's
`node-types.json`. It can be converted to and from JSON using the
`node_types_yaml` tool.
## Overview
A YAML node-types file has three top-level sections:
```yaml
supertypes:
# Abstract union types
named:
# Concrete AST nodes and leaf tokens
unnamed:
# Punctuation and keyword tokens
```
All three sections are optional. If omitted, they default to empty.
## Supertypes
Supertypes are abstract groupings of node types (unions). Each supertype maps
to a list of its members:
```yaml
supertypes:
_expression:
- assignment
- binary
- identifier
- call
```
This corresponds to the following JSON:
```json
{
"type": "_expression",
"named": true,
"subtypes": [
{ "type": "assignment", "named": true },
{ "type": "binary", "named": true },
{ "type": "identifier", "named": true },
{ "type": "call", "named": true }
]
}
```
Members are resolved as named or unnamed using the
[type reference rules](#type-references) described below.
## Named nodes
Named nodes are concrete AST node types. Each entry is a node kind mapping to
its fields. A node with no fields (a leaf token like `identifier`) uses an
empty value:
```yaml
named:
identifier:
constant:
```
```json
{"type": "identifier", "named": true, "fields": {}},
{"type": "constant", "named": true, "fields": {}}
```
### Fields
Each field has a name, a multiplicity suffix, and a list of allowed types.
| Suffix | Meaning | JSON `multiple` | JSON `required` |
| ------ | ------------ | --------------- | --------------- |
| (none) | exactly one | `false` | `true` |
| `?` | zero or one | `false` | `false` |
| `+` | one or more | `true` | `true` |
| `*` | zero or more | `true` | `false` |
Example:
```yaml
named:
assignment:
left: _lhs
right: _expression
```
```json
{
"type": "assignment",
"named": true,
"fields": {
"left": {
"multiple": false,
"required": true,
"types": [{ "type": "_lhs", "named": true }]
},
"right": {
"multiple": false,
"required": true,
"types": [{ "type": "_expression", "named": true }]
}
}
}
```
A field with multiple allowed types uses a list:
```yaml
named:
binary:
left: [_expression, _simple_numeric]
operator: ["!=", "+", "&&"]
right: _expression
```
A singleton list can be written as a bare value (as shown with `right` above).
### Unnamed children
Unnamed children (nodes that appear as children without a field name) are
specified using the special `$children` field name, with the same suffixes:
```yaml
named:
argument_list:
$children*: [_expression, block_argument, splat_argument]
```
```json
{
"type": "argument_list",
"named": true,
"fields": {},
"children": {
"multiple": true,
"required": false,
"types": [
{ "type": "_expression", "named": true },
{ "type": "block_argument", "named": true },
{ "type": "splat_argument", "named": true }
]
}
}
```
## Unnamed tokens
Unnamed tokens are punctuation, operators, and keywords that appear in the
parse tree but don't have their own AST node type. They are listed as simple
strings:
```yaml
unnamed:
- "="
- "end"
- "+"
- "&&"
```
```json
{"type": "=", "named": false},
{"type": "end", "named": false},
{"type": "+", "named": false},
{"type": "&&", "named": false}
```
When converting to YAML, unnamed tokens are always wrapped in quotes for
visual clarity. This is purely cosmetic — YAML treats `end` and `"end"` as
the same string.
## Type references
When a type name appears in a field's type list or a supertype's member list,
it needs to be resolved as either named or unnamed. The rules are:
1. If the name only appears in `named` or `supertypes`, it is **named**.
2. If the name only appears in `unnamed`, it is **unnamed**.
3. If the name appears in both, it defaults to **named**.
4. To explicitly reference an unnamed type in the ambiguous case, use the
map form:
```yaml
named:
example:
field: { unnamed: foo }
```
In practice, ambiguity is rare — names like `end`, `+`, `if` are almost
always only unnamed, while names like `identifier`, `assignment` are only
named.
## Complete example
```yaml
supertypes:
_expression:
- assignment
- binary
- identifier
named:
assignment:
left: _expression
right?: _expression
binary:
left: [_expression, _simple_numeric]
operator: ["!=", "+"]
right: _expression
argument_list:
$children*: [_expression, block_argument]
identifier:
constant:
unnamed:
- "!="
- "+"
- "="
- "end"
```
## CLI usage
Convert YAML to JSON:
```
node_types_yaml input.yaml > node-types.json
```
Convert JSON to YAML:
```
node_types_yaml --from-json node-types.json > node-types.yaml
```
Both commands also accept input from stdin if no file argument is given.

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shared/yeast/src/bin/node_types_yaml.rs Normal file
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use clap::Parser;
use std::io::Read;
#[derive(Parser)]
#[clap(
name = "node-types-yaml",
about = "Convert between YAML and JSON node-types formats"
)]
struct Cli {
/// Input file (reads from stdin if not provided)
input: Option<String>,
/// Convert from JSON to YAML (default is YAML to JSON)
#[arg(long)]
from_json: bool,
}
fn main() {
let args = Cli::parse();
let input = match &args.input {
Some(path) => std::fs::read_to_string(path).unwrap_or_else(|e| {
eprintln!("Error reading {path}: {e}");
std::process::exit(1);
}),
None => {
let mut buf = String::new();
std::io::stdin().read_to_string(&mut buf).unwrap_or_else(|e| {
eprintln!("Error reading stdin: {e}");
std::process::exit(1);
});
buf
}
};
let result = if args.from_json {
yeast::node_types_yaml::convert_from_json(&input)
} else {
yeast::node_types_yaml::convert(&input)
};
match result {
Ok(output) => print!("{output}"),
Err(e) => {
eprintln!("Error: {e}");
std::process::exit(1);
}
}
}

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shared/yeast/src/node_types_yaml.rs Normal file
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/// Converts a YAML node-types file to the tree-sitter `node-types.json` format.
///
/// # YAML format
///
/// ```yaml
/// supertypes:
/// _expression:
/// - assignment
/// - binary
///
/// named:
/// assignment:
/// left: _lhs
/// right: _expression
/// identifier:
///
/// unnamed:
/// - "+"
/// - "end"
/// ```
///
/// See the crate-level docs for the full format specification.
use std::collections::{BTreeMap, BTreeSet};
use std::fmt::Write;
use serde::Deserialize;
use serde_json::json;
/// Top-level YAML structure.
#[derive(Deserialize, Default)]
struct YamlNodeTypes {
#[serde(default)]
supertypes: BTreeMap<String, Vec<TypeRef>>,
#[serde(default)]
named: BTreeMap<String, Option<BTreeMap<String, TypeRefOrList>>>,
#[serde(default)]
unnamed: Vec<String>,
}
/// A reference to a node type. Can be:
/// - a plain string (resolved by looking up named vs unnamed)
/// - a map `{unnamed: "name"}` to force unnamed interpretation
#[derive(Deserialize, Debug, Clone)]
#[serde(untagged)]
enum TypeRef {
Name(String),
Explicit { unnamed: String },
}
/// A field value: either a single type ref or a list of them.
#[derive(Deserialize, Debug, Clone)]
#[serde(untagged)]
enum TypeRefOrList {
Single(TypeRef),
List(Vec<TypeRef>),
}
impl TypeRefOrList {
fn into_vec(self) -> Vec<TypeRef> {
match self {
TypeRefOrList::Single(t) => vec![t],
TypeRefOrList::List(v) => v,
}
}
}
/// Parsed field name: base name + multiplicity markers.
struct FieldSpec {
name: Option<String>, // None for $children
multiple: bool,
required: bool,
}
fn parse_field_name(raw: &str) -> FieldSpec {
let is_children = raw == "$children" || raw == "$children?" || raw == "$children*" || raw == "$children+";
let suffix = raw.chars().last().filter(|c| matches!(c, '?' | '*' | '+'));
let (multiple, required) = match suffix {
Some('?') => (false, false),
Some('*') => (true, false),
Some('+') => (true, true),
_ => (false, true), // bare field name = required, single
};
let name = if is_children {
None
} else {
let base = raw.trim_end_matches(|c: char| matches!(c, '?' | '*' | '+'));
Some(base.to_string())
};
FieldSpec {
name,
multiple,
required,
}
}
/// Resolve a TypeRef to a (type, named) pair, given the sets of known named
/// and unnamed types.
fn resolve_type_ref(
type_ref: &TypeRef,
named_types: &BTreeSet<String>,
unnamed_types: &BTreeSet<String>,
) -> serde_json::Value {
match type_ref {
TypeRef::Explicit { unnamed } => {
json!({"type": unnamed, "named": false})
}
TypeRef::Name(name) => {
let is_named = named_types.contains(name);
let is_unnamed = unnamed_types.contains(name);
if is_named && is_unnamed {
// Ambiguous: default to named
json!({"type": name, "named": true})
} else if is_unnamed {
json!({"type": name, "named": false})
} else {
// Named, or unknown (assume named)
json!({"type": name, "named": true})
}
}
}
}
/// Convert YAML string to node-types JSON string.
pub fn convert(yaml_input: &str) -> Result<String, String> {
let yaml: YamlNodeTypes =
serde_yaml::from_str(yaml_input).map_err(|e| format!("Failed to parse YAML: {e}"))?;
// Build the sets of known named and unnamed types for resolution.
let mut named_types = BTreeSet::new();
for name in yaml.supertypes.keys() {
named_types.insert(name.clone());
}
for name in yaml.named.keys() {
named_types.insert(name.clone());
}
let unnamed_types: BTreeSet<String> = yaml.unnamed.iter().cloned().collect();
let mut output = Vec::new();
// 1. Supertypes
for (name, members) in &yaml.supertypes {
let subtypes: Vec<_> = members
.iter()
.map(|m| resolve_type_ref(m, &named_types, &unnamed_types))
.collect();
output.push(json!({
"type": name,
"named": true,
"subtypes": subtypes,
}));
}
// 2. Named nodes
for (name, fields_opt) in &yaml.named {
let fields_map = match fields_opt {
None => {
// Leaf token: no fields, no children, no subtypes
output.push(json!({
"type": name,
"named": true,
"fields": {},
}));
continue;
}
Some(m) if m.is_empty() => {
output.push(json!({
"type": name,
"named": true,
"fields": {},
}));
continue;
}
Some(m) => m,
};
let mut json_fields = serde_json::Map::new();
let mut json_children: Option<serde_json::Value> = None;
for (raw_field_name, type_refs) in fields_map {
let spec = parse_field_name(raw_field_name);
let types: Vec<_> = type_refs
.clone()
.into_vec()
.iter()
.map(|t| resolve_type_ref(t, &named_types, &unnamed_types))
.collect();
// Cloning to make the borrow checker happy
let field_info = json!({
"multiple": spec.multiple,
"required": spec.required,
"types": types,
});
if spec.name.is_none() {
// $children
json_children = Some(field_info);
} else {
json_fields.insert(spec.name.unwrap(), field_info);
}
}
let mut entry = json!({
"type": name,
"named": true,
"fields": json_fields,
});
if let Some(children) = json_children {
entry
.as_object_mut()
.unwrap()
.insert("children".to_string(), children);
}
output.push(entry);
}
// 3. Unnamed tokens
for name in &yaml.unnamed {
output.push(json!({
"type": name,
"named": false,
}));
}
serde_json::to_string_pretty(&output).map_err(|e| format!("Failed to serialize JSON: {e}"))
}
/// Build a Schema from a YAML node-types string.
/// Registers all node kinds and field names found in the YAML.
pub fn schema_from_yaml(yaml_input: &str) -> Result<crate::schema::Schema, String> {
let yaml: YamlNodeTypes =
serde_yaml::from_str(yaml_input).map_err(|e| format!("Failed to parse YAML: {e}"))?;
let mut schema = crate::schema::Schema::new();
// Register all supertypes as node kinds
for name in yaml.supertypes.keys() {
schema.register_kind(name);
}
// Register named node kinds and their fields
for (name, fields_opt) in &yaml.named {
schema.register_kind(name);
if let Some(fields) = fields_opt {
for raw_field_name in fields.keys() {
let spec = parse_field_name(raw_field_name);
if let Some(field_name) = &spec.name {
schema.register_field(field_name);
}
}
}
}
// Register unnamed tokens as node kinds
for name in &yaml.unnamed {
schema.register_kind(name);
}
Ok(schema)
}
/// Build a Schema from a YAML string, extending a tree-sitter Language.
/// The Schema inherits all field/kind names from the Language, plus any
/// additional ones defined in the YAML.
pub fn schema_from_yaml_with_language(yaml_input: &str, language: &tree_sitter::Language) -> Result<crate::schema::Schema, String> {
let yaml: YamlNodeTypes =
serde_yaml::from_str(yaml_input).map_err(|e| format!("Failed to parse YAML: {e}"))?;
let mut schema = crate::schema::Schema::from_language(language);
// Register supertypes
for name in yaml.supertypes.keys() {
schema.register_kind(name);
}
// Register named node kinds and their fields
for (name, fields_opt) in &yaml.named {
schema.register_kind(name);
if let Some(fields) = fields_opt {
for raw_field_name in fields.keys() {
let spec = parse_field_name(raw_field_name);
if let Some(field_name) = &spec.name {
schema.register_field(field_name);
}
}
}
}
// Register unnamed tokens
for name in &yaml.unnamed {
schema.register_kind(name);
}
Ok(schema)
}
// ---------------------------------------------------------------------------
// JSON → YAML conversion
// ---------------------------------------------------------------------------
/// JSON node-types structures (mirrors tree-sitter's format).
#[derive(Deserialize)]
struct JsonNodeInfo {
#[serde(rename = "type")]
kind: String,
named: bool,
#[serde(default)]
fields: BTreeMap<String, JsonFieldInfo>,
children: Option<JsonFieldInfo>,
#[serde(default)]
subtypes: Vec<JsonNodeType>,
}
#[derive(Deserialize)]
struct JsonNodeType {
#[serde(rename = "type")]
kind: String,
named: bool,
}
#[derive(Deserialize)]
struct JsonFieldInfo {
multiple: bool,
required: bool,
types: Vec<JsonNodeType>,
}
/// Convert a tree-sitter node-types.json string to the YAML format.
pub fn convert_from_json(json_input: &str) -> Result<String, String> {
let nodes: Vec<JsonNodeInfo> =
serde_json::from_str(json_input).map_err(|e| format!("Failed to parse JSON: {e}"))?;
// Collect all named and unnamed types for disambiguation decisions.
let mut all_named: BTreeSet<String> = BTreeSet::new();
let mut all_unnamed: BTreeSet<String> = BTreeSet::new();
for node in &nodes {
if node.named {
all_named.insert(node.kind.clone());
} else {
all_unnamed.insert(node.kind.clone());
}
}
let mut supertypes: BTreeMap<String, Vec<JsonNodeType>> = BTreeMap::new();
let mut named: BTreeMap<String, Option<BTreeMap<String, JsonFieldInfo>>> = BTreeMap::new();
let mut unnamed: Vec<String> = Vec::new();
for node in nodes {
if !node.named {
unnamed.push(node.kind);
continue;
}
if !node.subtypes.is_empty() {
supertypes.insert(node.kind, node.subtypes);
continue;
}
if node.fields.is_empty() && node.children.is_none() {
// Leaf token
named.insert(node.kind, None);
} else {
let mut fields = BTreeMap::new();
for (name, info) in node.fields {
fields.insert(name, info);
}
if let Some(children) = node.children {
fields.insert("$children".to_string(), children);
}
named.insert(node.kind, Some(fields));
}
}
// Now emit YAML
let mut out = String::new();
// Supertypes
if !supertypes.is_empty() {
writeln!(out, "supertypes:").unwrap();
for (name, members) in &supertypes {
writeln!(out, " {name}:").unwrap();
for member in members {
let ref_str = format_type_ref(&member.kind, member.named, &all_named, &all_unnamed);
writeln!(out, " - {ref_str}").unwrap();
}
}
writeln!(out).unwrap();
}
// Named
if !named.is_empty() {
writeln!(out, "named:").unwrap();
for (name, fields_opt) in &named {
match fields_opt {
None => {
writeln!(out, " {name}:").unwrap();
}
Some(fields) => {
writeln!(out, " {name}:").unwrap();
for (field_name, info) in fields {
let suffix = field_suffix(info.multiple, info.required);
let yaml_name = if field_name == "$children" {
format!("$children{suffix}")
} else {
format!("{field_name}{suffix}")
};
let type_refs: Vec<String> = info
.types
.iter()
.map(|t| format_type_ref(&t.kind, t.named, &all_named, &all_unnamed))
.collect();
if type_refs.len() == 1 {
writeln!(out, " {yaml_name}: {}", type_refs[0]).unwrap();
} else {
let list = type_refs
.iter()
.map(|s| s.as_str())
.collect::<Vec<_>>()
.join(", ");
writeln!(out, " {yaml_name}: [{list}]").unwrap();
}
}
}
}
}
writeln!(out).unwrap();
}
// Unnamed
if !unnamed.is_empty() {
writeln!(out, "unnamed:").unwrap();
for name in &unnamed {
writeln!(out, " - {}", force_quote(name)).unwrap();
}
}
Ok(out)
}
fn field_suffix(multiple: bool, required: bool) -> &'static str {
match (multiple, required) {
(false, true) => "",
(false, false) => "?",
(true, true) => "+",
(true, false) => "*",
}
}
/// Format a type reference for YAML output. Uses the disambiguation rule:
/// plain string if unambiguous, `{unnamed: name}` if the name exists as both
/// named and unnamed and we need the unnamed interpretation.
fn format_type_ref(
kind: &str,
named: bool,
all_named: &BTreeSet<String>,
_all_unnamed: &BTreeSet<String>,
) -> String {
if named {
quote_yaml(kind)
} else {
let is_also_named = all_named.contains(kind);
if is_also_named {
format!("{{unnamed: {}}}", force_quote(kind))
} else {
force_quote(kind)
}
}
}
/// Always wrap in double quotes. Used for unnamed node references so they're
/// visually distinct from named ones — YAML treats both forms as equivalent strings.
fn force_quote(s: &str) -> String {
format!("\"{}\"", s.replace('\\', "\\\\").replace('"', "\\\""))
}
/// Quote a YAML string value if it contains special characters or could be
/// misinterpreted.
fn quote_yaml(s: &str) -> String {
let needs_quoting = s.is_empty()
|| s.contains(|c: char| {
matches!(
c,
':' | '{' | '}' | '[' | ']' | ',' | '&' | '*' | '#' | '?' | '|' | '-' | '<'
| '>' | '=' | '!' | '%' | '@' | '`' | '"' | '\''
)
})
|| s.starts_with(' ')
|| s.ends_with(' ')
|| s == "true"
|| s == "false"
|| s == "null"
|| s == "yes"
|| s == "no"
|| s.parse::<f64>().is_ok();
if needs_quoting {
format!("\"{}\"", s.replace('\\', "\\\\").replace('"', "\\\""))
} else {
s.to_string()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_basic_conversion() {
let yaml = r#"
supertypes:
_expression:
- assignment
- binary
named:
assignment:
left: _lhs
right: _expression
binary:
left: [_expression, _simple_numeric]
operator: ["!=", "+"]
right: _expression
argument_list:
$children*: [_expression, block_argument]
identifier:
unnamed:
- "!="
- "+"
- "end"
"#;
let json_str = convert(yaml).unwrap();
let result: Vec<serde_json::Value> = serde_json::from_str(&json_str).unwrap();
// Check supertype
let expr = &result[0];
assert_eq!(expr["type"], "_expression");
assert_eq!(expr["named"], true);
assert_eq!(expr["subtypes"].as_array().unwrap().len(), 2);
// Check assignment
let assign = result.iter().find(|n| n["type"] == "assignment").unwrap();
assert_eq!(assign["fields"]["left"]["required"], true);
assert_eq!(assign["fields"]["left"]["multiple"], false);
assert_eq!(assign["fields"]["left"]["types"][0]["type"], "_lhs");
assert_eq!(assign["fields"]["left"]["types"][0]["named"], true);
// Check binary.operator — "!=" and "+" should resolve to unnamed
let binary = result.iter().find(|n| n["type"] == "binary").unwrap();
let op_types = binary["fields"]["operator"]["types"].as_array().unwrap();
assert_eq!(op_types[0]["type"], "!=");
assert_eq!(op_types[0]["named"], false);
assert_eq!(op_types[1]["type"], "+");
assert_eq!(op_types[1]["named"], false);
// Check argument_list has children, not a field
let arg_list = result
.iter()
.find(|n| n["type"] == "argument_list")
.unwrap();
assert!(arg_list.get("children").is_some());
assert_eq!(arg_list["children"]["multiple"], true);
assert_eq!(arg_list["children"]["required"], false);
// Check identifier is a leaf
let ident = result.iter().find(|n| n["type"] == "identifier").unwrap();
assert_eq!(ident["fields"].as_object().unwrap().len(), 0);
// Check unnamed tokens
let end = result.iter().find(|n| n["type"] == "end").unwrap();
assert_eq!(end["named"], false);
}
#[test]
fn test_explicit_unnamed_disambiguation() {
let yaml = r#"
named:
foo:
field: [{unnamed: bar}]
unnamed:
- bar
"#;
let json_str = convert(yaml).unwrap();
let result: Vec<serde_json::Value> = serde_json::from_str(&json_str).unwrap();
let foo = result.iter().find(|n| n["type"] == "foo").unwrap();
assert_eq!(foo["fields"]["field"]["types"][0]["named"], false);
}
#[test]
fn test_field_suffixes() {
let yaml = r#"
named:
test_node:
required_single: foo
optional_single?: foo
required_multiple+: foo
optional_multiple*: foo
"#;
let json_str = convert(yaml).unwrap();
let result: Vec<serde_json::Value> = serde_json::from_str(&json_str).unwrap();
let node = result.iter().find(|n| n["type"] == "test_node").unwrap();
let fields = node["fields"].as_object().unwrap();
assert_eq!(fields["required_single"]["required"], true);
assert_eq!(fields["required_single"]["multiple"], false);
assert_eq!(fields["optional_single"]["required"], false);
assert_eq!(fields["optional_single"]["multiple"], false);
assert_eq!(fields["required_multiple"]["required"], true);
assert_eq!(fields["required_multiple"]["multiple"], true);
assert_eq!(fields["optional_multiple"]["required"], false);
assert_eq!(fields["optional_multiple"]["multiple"], true);
}
#[test]
fn test_json_to_yaml() {
let json = r#"[
{"type": "_expression", "named": true, "subtypes": [
{"type": "assignment", "named": true},
{"type": "identifier", "named": true}
]},
{"type": "assignment", "named": true, "fields": {
"left": {"multiple": false, "required": true, "types": [
{"type": "_expression", "named": true}
]},
"right": {"multiple": false, "required": false, "types": [
{"type": "_expression", "named": true}
]}
}, "children": {
"multiple": true, "required": false, "types": [
{"type": "identifier", "named": true}
]
}},
{"type": "identifier", "named": true, "fields": {}},
{"type": "=", "named": false},
{"type": "end", "named": false}
]"#;
let yaml = convert_from_json(json).unwrap();
// Verify key structures are present
assert!(yaml.contains("supertypes:"));
assert!(yaml.contains("_expression:"));
assert!(yaml.contains("named:"));
assert!(yaml.contains("assignment:"));
assert!(yaml.contains("left:"));
assert!(yaml.contains("right?:"));
assert!(yaml.contains("$children*:"));
assert!(yaml.contains("identifier:"));
assert!(yaml.contains("unnamed:"));
assert!(yaml.contains("\"=\""));
assert!(yaml.contains("end"));
}
#[test]
fn test_round_trip() {
let yaml_input = r#"
supertypes:
_expression:
- assignment
- identifier
named:
assignment:
left: _expression
right?: _expression
$children*: identifier
identifier:
unnamed:
- "="
- end
"#;
// YAML → JSON → YAML
let json = convert(yaml_input).unwrap();
let yaml_output = convert_from_json(&json).unwrap();
// YAML → JSON again (should be identical)
let json2 = convert(&yaml_output).unwrap();
let v1: serde_json::Value = serde_json::from_str(&json).unwrap();
let v2: serde_json::Value = serde_json::from_str(&json2).unwrap();
assert_eq!(v1, v2);
}
}