# crowbook-intl

A library to localize strings, translating them according to runtime options.

Basically, this library allows your project to generate a `lformat!` macro, that behaves
similarly to `format!`, except the message string (the first argument) might get translated
(if you can find the appropriate string for the language).

## Usage

First, you'll need to add the following to your `Cargo.toml` file:

```toml
build = "build.rs"

[build-dependencies]
crowbook-intl = "0.1.0"

[dependencies]
crowbook-intl-runtime = "0.1.0"
```

You'll then need to create the `build.rs` file, which can look like this:

```rust,ignore
extern crate crowbook_intl;
use crowbook_intl::{Localizer, Extractor};

fn main() {
    // Generate a `lang/default.pot` containing strings used to call `lformat!`
    let mut extractor = Extractor::new();
    extractor.add_messages_from_dir(concat!(env!("CARGO_MANIFEST_DIR"), "/src")).unwrap();
    extractor.write_pot_file(concat!(env!("CARGO_MANIFEST_DIR"), "/lang/default.pot")).unwrap();

    // Generate the `localize_macros.rs` file
    let mut localizer = Localizer::new(&extractor);
    // Use env::var instead of env! to avoid problems when cross-compiling
    let dest_path = Path::new(&env::var("OUT_DIR").unwrap())
       .join("localize_macros.rs");
    localizer.write_macro_file(dest_path).unwrap();
}
```

This will create a `localize_macros.rs` at build time somewhere in `OUT_DIR`, containing the `lformat!` macro.
To actually use this macro, you have to create a `src/localize_macros.rs` file that includes it:

```rust,ignore
include!(concat!(env!("OUT_DIR"), "/localize_macros.rs"));
```

To use it, the last step is to modify your `src/lib/lib.rs` file:

```rust,ignore
extern crate crowbook_intl_runtime;
#[macro_use] mod localize_macros;
```

Once this is done, you can start replacing your calls to `format!` with calls to `lformat!`.

In order to get translation, you'll need to actually translate the strings in separate
files, and set your `build.rs` to load them.

E.g., if you have the following code:

```rust,ignore
println!("{}", lformat!("Hello, world!"));
```

and you want it translated in french, you'll have to create a `lang/fr.po` file
from the `lang/default.pot` file containing:

```text
msgid "Hello, world!";
msgstr "Bonjour le monde !";
```

And load it in your `build.rs` file:

```rust,ignore
let mut localizer = Localizer::new();
localizer.add_lang("fr", include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/lang/fr.mp"))).unwrap();
(...)
```

Once *this* is done, you can use the `localize_macros::set_lang` function
to switch the language at runtime:

```rust,ignore
use crowbook_intl_runtime::set_lang;
set_lang("en");
println!("{}", lformat!("Hello, world!")); // prints "Hello, world!"
set_lang("fr");
println!("{}", lformat!("Hello, world!")); // prints "Bonjour le monde !"
```

## Updating your translation

When you add new strings that need to be translated (by more calls to `lformat!`),
or when you change the content of existing strings, you can use [Gettext's `msgmerge` and `msgcmp`](https://www.gnu.org/software/gettext/manual/html_node/msgmerge-Invocation.html)
commands to update your translation. While it is not guaranteed that the formats are
strictly identical, it should work. (That is, it is a bug if it doesn't; but at this
stage, this library is absolutely not guaranteed to be bug-free.)

## Known limitations and bugs

* Currently, `crowbook-intl` doesn't handle correctly raw string literals in `lformat!`
  (they won't be translated correctly).
* Multiple calls to the same string, but formatted differently (e.g. using a backslash
  before a newline to separate a string on multiple lines) will also cause problems.

## Warning

In case the complexity of the operation didn't discourage you, I should warn you
that this library is highly experimental at this time.

## License

This is free software, published under the [Mozilla Public License,
version 2.0](https://www.mozilla.org/en-US/MPL/2.0/).

## Documentation ##

See the
[documentation on docs.rs](https://docs.rs/crowbook-intl).

## ChangeLog ##

See [the ChangeLog file](ChangeLog.md).

## Author ##

[Élisabeth Henry](http://lise-henry.github.io/) <liz.henry@ouvaton.org>.