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The first bug-fix release of tomllib (0.1.2) is out! Get it on!

tomlkit is coming! Here's a taste of what you can do with version 0.1.2:

Get the package name, version, whether it has a license and all dependencies of Cargo.toml files:

find . -name 'Cargo.toml' | ./toml_parser/target/debug/tomlkit -g,package.version --has-value package.license,package.description -c dependencies --set-true "has license","has description" --set-false "no license","no description"
"methodtest", "0.1.0", no license, no description, [nom]
"mtailtest", "0.1.0", no license, no description, [mtaillib]
"multitail", "0.1.0", no license, no description, [term, notify, getopts]
"mtaillib", "0.1.0", no license, no description, [notify, libc]
"nomplusplus", "0.1.0", has license, has description, [radix_trie, regex, lazy_static]
"rproxy", "0.1.0", no license, no description, [radix_trie]
"radix_trie", "0.0.8", has license, has description, [nibble_vec]
"rustfmt", "0.2.1", has license, has description, [toml, rustc-serialize, unicode-segmentation, regex, term, strings, diff, syntex_syntax, log, env_logger, getopts]
"test", "0.1.0", no license, no description, []
"tomllib", "0.1.2", has license, has description, [nom, regex, log, env_logger, pirate, csv]
"tomllib", "0.1.0", has license, has description, [nom, regex, log, env_logger]
"tomllib", "0.1.1", has license, has description, [nom, regex, log, env_logger]
"tomllib", "0.1.2", has license, has description, [nom, regex, log, env_logger, pirate, csv]
"trietest", "0.1.0", no license, no description, [radix_trie]
  • Don't like quotes? --strip-quotes (you won't be able to tell the difference between 435 the integer, 435 the basic string, 435 the multi-line basic string, 435 the literal string, and 435 the multi-line literal string, but whatever).
  • Want each value on a new line? --separator $'\n'
  • Hate standard array notation? --array-begin "" --array-end "" --array-separator $'\n', you won't be able to tell where the array begins and ends but who needs to know that? Alternatively there's --array-length which ditches the beginning and ending array characters and starts the array with an extra usize that tells you the length of the following array.

I wrote a blog post about my adventures in creating method macros in nom. Give it a read!

tomllib is a parser, modifier, and generator for TOML files that doesn't judge you!

######It is written in Rust using nom. tomlkit is the command line tool with the same functionality as tomllib that is coming soon after the release of tomllib. Build Status Coverage Status

####What does it mean that it doesn't judge me?###

tomlib respects your crazy indentation and whitespace scheme. It respects the order you place things. It doesn't try to reformat the file based on somebody else's views on file format purity. It only makes changes that you tell it to make and leaves the rest alone. Want 20 tabs between every key and = in a key value pair? Have at it! Want to put a comment and 5 newlines after every array value? We won't try to change your mind! Randomly placed tables and nested tables? It's your file! Do whatever you want and as long as it is within spec; we won't try to change it.

Reference documentation can be found here.


Based on my version of the official TOML ABNF (at least until they merge my changes). Currently can parse entire Unicode TOML files and reconstruct them into a perfect copy, preserving order and all whitespace. Tested with perfect output on the toml README example, the regular, hard, and unicode hard examples in the toml test directory as well as all of the valid and invalid tests in BurntSushi/toml-test (except for one invalid test that is actually valid).


Here's how you would parse a TOML document and then get and set values (note that due to the way the parse method works it takes ownership of the parser, then returns it in a tuple with the ParseResult):

use tomllib::TOMLParser;
use tomllib::types::Value;

let parser = TOMLParser::new();
let toml_doc = r#"
[table] # This is a comment
 "A Key" = "A Value" # This line is indented
  SomeKey = "Some Value" # This line is indented twice
let (mut parser, result) = parser.parse(toml_doc);
parser.get_value("table.SomeKey"); // gets "Some Value"
parser.set_value("table.\"A Key\"", Value::float(9.876));
parser.set_value("table.SomeKey", Value::bool(false));

Tables and inline tables have subkeys while arrays of tables and arrays use array indexing starting at 0 for example:

an_array = ["A", "B", "C"]
inline_table = {first = 1.1, second = 1.3}
foo = "D"
bar = "F"
nested = {third = [{fourth = "okay"}, {fifth = "something", sixth = "baz"}]

In the above example the key of "C" is an_array[2], the key of 1.3 is inline_table.second, the key of "D" is array_of_table[1].foo, and the key "F" is You can nest inline table and arrays, so for example the of "baz" is fruit[0].type.nested.third[1].sixth

Here's a quick example of using the returned ParseResult any ParseErrors:

use tomllib::TOMLParser;
use tomllib::types::{Value, ParseResult, ParseError};

let parser = TOMLParser::new();
let toml_doc = r#"
 mixed_array = [5, true]
let (mut parser, result) = parser.parse(toml_doc);
// For brevity's sake we're only matching `FullError` `ParseResult`s and `MixedArray` `ParseError`s
match result {
  ParseResult::FullError(rrc_errors) => {
    println!("Parsed the full document, but with errors:");
    for error in rrc_errors.borrow().iter() {
      match error {
        &ParseError::MixedArray(ref key, ref line, ref column) => {
          println!("A mixed array with key {} was encountered on line {}, column {}.", key, line, column);
          assert_eq!("array_of_tables[0].has_error.mixed_array", *key);
          assert_eq!(4, *line);
          assert_eq!(0, *column); // column reporting is unimplemented so it will always be zero        
        _ => assert!(false),
  _ => assert!(false),

In this first release you can parse any TOML document, lookup any value, get the sub-keys of any key, and modify any value to be any other value of any type. And throughout it all, it will preserve the original formatting and comments, with the exception of changes to the structure of an Array or InlineTable. The caveats are that if you change the number of elements in an array or inline table then formatting is not preserved. If you keep the number elements in an array or inline table the same, but change some or all of the values then all formatting is preserved.

Some things that you can't do yet, but are planned for the next release are:

  • Key/Val insertion
  • Key/Val deletion
  • Table and Array of Table insertion
  • Table and Array of Table deletion
  • Key modification
  • Table and Array of Table modification
  • More error reporting

For future releases here some things I plan on adding:

  • Method to strip extraneous spaces, newlines and comments
  • User defined whitespace schemes
  • Element re-ordering
  • Conversion to JSON and YAML

Getting Started

To get the source simply git clone I took a dependency on regex_macros which requires you be on the beta version of Rust. Fortunately multirust makes this dead simple without forcing all of your Rust evironment to be on Beta.

Install multirust (you'll have to uninstall currently installed versions of Rust) first:

curl -sf | sh

Change into the toml_parser directory and set that directory (and that directory only) to use Beta Rust:

cd toml_parser
multirust override beta

You can always go back to stable or beta with multirust override (beta|stable). To make changes fork the repository, then clone it, make changes, and issue a pull request. If you have any problems enter an issue in the issue tracker.

I would love to hear your feedback. If there's something you would like this project to do then feel free to write up an issue about it. If you're not comfortable writing an issue out in the open you can email me at


A format-preserving TOML file parser and manipulator in Rust using nom




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