Cargo.toml conventions - The Rust Style Guide

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# `Cargo.toml` conventions

## Formatting conventions

Use the same line width and indentation as Rust code.

Put a blank line between the last key-value pair in a section and the header of the next section. Do not place a blank line between section headers and the key-value pairs in that section, or between key-value pairs in a section.

Version-sort key names within each section, with the exception of the `[package]` section. Put the `[package]` section at the top of the file; put the `name` and `version` keys in that order at the top of that section, followed by the remaining keys other than `description` in order, followed by the `description` at the end of that section.

Don’t use quotes around any standard key names; use bare keys. Only use quoted keys for non-standard keys whose names require them, and avoid introducing such key names when possible. See the TOML specification for details.

Put a single space both before and after the `=` between a key and value. Do not indent any key names; start all key names at the start of a line.

Use multi-line strings (rather than newline escape sequences) for any string values that include multiple lines, such as the crate description.

For array values, such as a list of features, put the entire list on the same line as the key, if it fits. Otherwise, use block indentation: put a newline after the opening square bracket, indent each item by one indentation level, put a comma after each item (including the last), and put the closing square bracket at the start of a line by itself after the last item.

    #![allow(unused)]
    fn main() {
    some_feature = [
        "another_feature",
        "yet_another_feature",
        "some_dependency?/some_feature",
    ]
    }

For table values, such as a crate dependency with a path, write the entire table using curly braces and commas on the same line as the key if it fits. If the entire table does not fit on the same line as the key, separate it out into a separate section with key-value pairs:

    [dependencies]
    crate1 = { path = "crate1", version = "1.2.3" }

    [dependencies.extremely_long_crate_name_goes_here]
    path = "extremely_long_path_name_goes_right_here"
    version = "4.5.6"

## Metadata conventions

The authors list, if present, should consist of strings that each contain an author name followed by an email address in angle brackets: `Full Name <email@address>`. It should not contain bare email addresses, or names without email addresses. (The authors list may also include a mailing list address without an associated name.)

The license field must contain a valid SPDX expression, using valid SPDX license names. (As an exception, by widespread convention, the license field may use `/` in place of `OR`; for example, `MIT/Apache-2.0`.)

The homepage field, if present, must consist of a single URL, including the scheme (e.g. `https://example.org/`, not just `example.org`.)

Within the description field, wrap text at 80 columns. Don’t start the description field with the name of the crate (e.g. “cratename is a …”); just describe the crate itself. If providing a multi-sentence description, the first sentence should go on a line by itself and summarize the crate, like the subject of an email or commit message; subsequent sentences can then describe the crate in more detail.