Crate toml_edit

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This crate allows you to parse and modify toml documents, while preserving comments, spaces* and relative order* or items.

It is primarily tailored to the needs of cargo-edit.


use toml_edit::{Document, value};

let toml = r#"
"hello" = 'toml!' # comment
let mut doc = toml.parse::<Document>().expect("invalid doc");
assert_eq!(doc.to_string(), toml);
// let's add a new key/value pair inside a.b: c = {d = "hello"}
doc["a"]["b"]["c"]["d"] = value("hello");
// autoformat inline table a.b.c: { d = "hello" }
doc["a"]["b"]["c"].as_inline_table_mut().map(|t| t.fmt());
let expected = r#"
"hello" = 'toml!' # comment
c = { d = "hello" }
assert_eq!(doc.to_string(), expected);


Things it does not preserve:

  • Different quotes and spaces around the same table key, e.g.
[ 'a'. b]
[ "a"  .c]

will be represented as (spaces are removed, the first encountered quote type is used)

  • Children tables before parent table (tables are reordered by default, see test).
  • Scattered array of tables (tables are reordered by default, see test).

The reason behind the first limitation is that Table does not store its header, allowing us to safely swap two tables (we store a mapping in each table: child key -> child table).

This last two limitations allow us to represent a toml document as a tree-like data structure, which enables easier implementation of editing operations and an easy to use and type-safe API. If you care about the above two cases, you can use Document::to_string_in_original_order() to reconstruct tables in their original order.


Type representing a TOML array, payload of the Value::Array variant’s value
Type representing a TOML array of tables
A prefix and suffix, including comments, whitespaces and newlines.
Type representing a TOML document
Type representing a TOML inline table, payload of the Value::InlineTable variant
Key as part of a Key/Value Pair or a table header.
Type representing a TOML non-inline table
Type representing a TOML parse error


Type representing either a value, a table, an array of tables, or none.
Representation of a TOML Value (as part of a Key/Value Pair).


This trait represents either a Table, or an InlineTable.


Returns an empty array of tables.
Sets the prefix and the suffix for value.
Returns an empty table.
Returns a formatted value.

Type Definitions

An iterator type over Array’s values.
An iterator type over Table’s key/value pairs.
A mutable iterator type over Table’s key/value pairs.