toml_const

TOML compile-time constants

Getting started

use toml_const::{toml_const, toml_const_ws};

// workspace root
// ├── example.toml
// ├── toml_const       <---- you are here
// │   ├── Cargo.toml
// │   └── src
// └── toml_const_macros
//     ├── Cargo.toml
//     └── src

// include a TOML file in your project relative to your manifest directory
toml_const! {
    pub const EXAMPLE_TOML: "../example.toml";
    // multiple definitions are supported
    static CARGO_TOML: "Cargo.toml";
}

// include a file relative to your workspace root
toml_const_ws! {static EXAMPLE_TOML_WS: "example.toml";}

// table keys are capitalized struct fields
const TITLE: &str = EXAMPLE_TOML.TITLE;
assert_eq!(EXAMPLE_TOML.TITLE, EXAMPLE_TOML_WS.TITLE);

Table substitution

File substitution is supported. The first path that exists and satisfies the following conditions will be used. These conditions are, in order of precedence:

• if a substitute path has the use keyword prefixed
• iif a toml file contains use = true at the root level

Multiple substitute files can be specified in the macro expression. The first file containing a use = true key will be merged into the parent file.

These files may contain secrets or other sensitive information that you don't want to check into version control.

use toml_const::toml_const;

toml_const! {
    // example.toml is the template/parent file (must exist)
    pub static EXAMPLE_TOML: "../example.toml" {
        // if Cargo.toml exists, it will be substituted
        use "../Cargo.toml";
        // if Cargo.toml does not exist and example.toml contains
        // `use = true`, it will be substituted
        "../example.toml";
        // files that do not exist are ignored
        "non_existent.toml";
        // .. and so on
    }
}

Limitations

This library does not support the full TOML specification.

It will fail to:

• generate arrays with distinct types (arrays containing different types, arrays of tables with different keys)
• create a struct from a table with a blank key "" = true

It will modify:

• table keys that begin with numbers
• table keys that contain invalid characters for identifiers

TOML data types

All TOML data types are supported. Datetime related structs are re-exported from toml.