GIR

The GIR is used to generate both the sys level crate and a safe API crate to use the sys level (FFI) crate.

Introduction to gir generation

Using gir requires both a *.toml and a *.gir for generation of the bindings.

The *.gir you need will correspond to the project you want to generate bindings for. You can get them from here or directly on ubuntu website (for example: http://packages.ubuntu.com/zesty/amd64/libgtk-3-dev).

The *.toml is what is used to pass various settings and options to gir for use when generating the bindings - you will likely need to write one to suit your needs, for an example you can take a look to gtk-rs/sys/gir-gtk.toml.

Keep it in mind that since gir is still under development, it generates warnings when running. As long as it's not errors, it's fine. However, if something you asked to be generated wasn't, you should definitely take a look to the warnings to see what failed.

gir Modes

There are two main modes of generation for gir; FFI and API.

There is also a third one used for documentation generation: doc.

The FFI mode is what creates the low-level FFI bindings from the supplied *.gir file - these are essentially direct calls in to the related C library and are typically unsafe. The resulting crate is typically appended with -sys.

The API mode generates another crate for a layer on top of these unsafe (sys) bindings which makes them safe for use in general Rust.

The FFI mode TOML config

In FFI (-m sys) mode, gir generates as much as it can. So in this mode, the TOML file is mostly used to ignore some objects. To do so, you need to add its fullname to an ignore array. Example:

ignore = ["Gtk.Widget", "Gtk.Window"]

And that's all! Neither GtkWidget nor GtkWindow (alongside with their functions) will be generated.

You also need to add any needed external libraries in the "external_libraries" parameter. Example:

external_libraries = [
   "GLib",
   "GObject",
]

You can specify a few other options:

[options]
girs_dir = "../gir-files"
library = "GtkSource"
version = "3.0"
min_cfg_version = "3.0"
target_path = "."
work_mode = "sys"

Also, you can mark some functions that has suffix _utf8 on Windows:

[[object]]
name = "GdkPixbuf.PixbufAnimation"
status = "generate"
    [[object.function]]
    name = "new_from_file"
    is_windows_utf8 = true

Generation in FFI mode

When you're ready, let's generate the FFI part. In the command we'll execute, ../gir-files is where the directory with your .gir files is. (But again, you can just clone the gir-files repository and add your file(s) in it). Then let's run the command:

cargo run --release -- -c YourSysGirFile.toml -d ../gir-files -m sys -o the-output-directory-sys

The generated files will be placed in the-output-directory-sys. Just take care about the dependencies and the crate's name generated in the Cargo.toml file (update them if they don't work as expected).

You now have the sys part of your binding!

The API mode TOML config

This mode requires you to write another TOML file. gtk/Gir.toml is a good example.

This mode generates only the specified objects. You can either add the object's fullname to the generate array or add it to the manual array (but in this case, it won't be generated, just used in other functions/methods instead of generating an "ignored" argument). Example:

generate = ["Gtk.Widget", "Gtk.Window"]
manual = ["Gtk.Button"]

So in here, both GtkWidget and GtkWindow will be fully generated and functions/methods using GtkButton will be uncommented. To generate code for all global functions, add Gtk.* to the generate array.

Sometimes Gir understands the object definition incorrectly or the .gir file contains an incomplete or wrong definition, to fix it, you can use the full object configuration:

[[object]]
# object's fullname
name = "Gtk.SomeClass"
# can be also "manual" and "ignore" but it's simpler to just put the object in the same array
status = "generate"
# replace the parameter name for the child in child properties (instead "child")
child_name = "item"
# don't generate trait SomeClassExt for this object, but implement all functions in impl SomeClass
trait = false
# allow rename result file
module_name = "soome_class"
# prefixed object in mod.rs with #[cfg(mycond)]
cfg_condition = "mycond"
    # define overrides for function
    [[object.function]]
    # filter functions from object
    name = "set_website_label"
    # alternative way to apply override for many functions. Will be used with '^' and '$' on both sides
    # can be used instead of `name` almost anywhere
    # pattern = "[gs]et_value"
    # don't generate function
    ignore = true
    # override starting version
    version = "3.12"
    # prefixed function with #[cfg(mycond)]
    cfg_condition = "mycond"
    # prefixed function with #[doc(hidden)]
    doc_hidden = true
    # disable length_of autodetection
    disable_length_detect = true
        # override for parameter
        [[object.function.parameter]]
        # filter by name
        name = "website_label"
        # allow to remove/add Option<>
        nullable = true
        # allow to make parameter immutable
        const = true
        # parameter is calculated as length of string or array and removed from function declaration
        #  ( for length of return value use "return" )
        length_of = "str"
        # override for return value
        [[object.function.return]]
        # allow to remove/add Option<> to return value
        nullable = true
        # convert bool return types to Result<(), glib::BoolError> with
        # the given error message on failure
        bool_return_is_error = "Function failed doing what it is supposed to do"
    [[object.signal]]
    name = "activate-link"
    # replace trampoline bool return type with `Inhibit`
    inhibit = true
    ignore = true
    version = "3.10"
    doc_hidden = true
        [[object.signal.parameter]]
        name = "path_string"
        # allow to use different names in closure
        new_name = "path"
        # can be also "borrow" and "none": Add some transformation beetween ffi trampoline parameters and rust closure
        transformation = "treepath"
        nullable = true
        [object.signal.return]
        nullable = true
    # override for properties
    [[object.property]]
    name = "baseline-position"
    version = "3.10"
    ignore = true

Since there are no child properties in .gir files, it needs to be added for classes manually:

[[object]]
name = "Gtk.SomeClassWithChildProperties"
status = "generate"
# replace parameter name for child in child properties (instead of "child")
child_name = "item"
# define concrete child type (instead of "Widget")
child_type = "Gtk.MenuItem"
    [[object.child_prop]]
    name = "position"
    type = "gint"
    doc_hidden = true

For enumerations and bitflags, you can configure the members and mark the type as #[must_use]:

[[object]]
name = "Gdk.EventType"
status = "generate"
# generates #[must_use] attribute for the type
must_use = true
    [[object.member]]
    name = "2button_press"
    # allows to skip elements with bad names, other members with same value used instead
    alias = true
    [[object.member]]
    name = "touchpad_pinch"
    # define starting version when member added
    version = "3.18"

For global functions, the members can be configured by configuring the Gtk.* object:

[[object]]
name = "Gtk.*"
status = "generate"
    [[object.function]]
    name = "stock_list_ids"
    # allows to ignore global functions
    ignore = true

Note that you must not place Gtk.* into the generate array and additionally configure its members.

In various cases, GObjects or boxed types can be used from multiple threads and have certain concurrency guarantees. This can be configured with the concurrency setting at the top-level options or per object. It will automatically implement the Send and Sync traits for the resulting object and set appropriate trait bounds for signal callbacks. The default is none, and apart from that send and send+sync are supported.

[[object]]
# object's fullname
name = "Gtk.SomeClass"
# can be also "manual" and "ignore" but it's simpler to just put the object in the same array
status = "generate"
# concurrency of the object, default is set in the top-level options or
# otherwise "none". Valid values are "none", "send" and "send+sync"
concurrency = "send+sync"

Note that send is only valid for types that are either not reference counted (i.e. clone() copies the object) or that are read-only (i.e. no API for mutating the object exists). send+sync is valid if the type can be sent to different threads and all API allows simultaneous calls from different threads due to internal locking via e.g. a mutex.

[[object]]
name = "Gtk.Something"
status = "manual"
# Can also be "ref-mut", "ref-immut"
ref_mode = "ref"

When manually generating bindings, it can happen that the reference mode detected by GIR is different than what was implemented and conversion to the C types are wrong in autogenerated functions that have such objects as argument. This can be overridden with the ref_mode configuration.

Generation in API mode

To generate the Rust-user API level, The command is very similar to the previous one. It's better to not put this output in the same directory as where the FFI files are. Just run:

cargo run --release -- -c YourGirFile.toml -d ../gir-files -o the-output-directory

Now it should be done. Just go to the output directory (so the-output-directory/auto in our case) and try to build using cargo build. Don't forget to update your dependencies in both projects: nothing much to do in the FFI/sys one but the Rust-user API level will need to have a dependency over the FFI/sys one.

Now, at your crate entry point (generally lib.rs), add the following to include all generated files:

pub use auto::*;

Add manual bindings alongside generated code

Unfortunately, gir isn't perfect (yet) and will certainly not be able to generate all the code on its own. So here's what a gir generated folder looks like:

- your_folder
|
|- Cargo.toml
|- src
 |
 |- lib.rs
 |- auto
  |
  |- (all files generated by gir)

You can add your manual bindings directly inside the src folder (at the same level as lib.rs). Then don't forget to reexport them. Let's say you added a Color type in a color.rs file. You need to add in lib.rs:

// We make the type public for the API users.
pub use color::Color;

mod color;

Generating documentation

And finally the last feature! Just run the following command (note the -m doc at the end):

cargo run --release -- -c YourGirFile.toml -d ../gir-files -o the-output-directory -m doc

It'll generate a docs.md if everything went fine. That's where all this crate's documentation is. If you want to put it back into your crate's source code like "normal" doc comments, run:

> cargo install rustdoc-stripper
> rustdoc-stripper -g -o docs.md

And now your crate should be completely documented as expected!

Nightly Rust Only Features

Unions

By default union generation is disabled except for some special cases due to unions not yet being a stable feature. However if you are using nightly rust, then you can enable union generation using cargo run --release --features "use_unions".

Keep in mind that to access union members, you are required to use unsafe blocks, for example;

union myUnion {
    test : u32
}

let testUnion = myUnion { test : 42 };
unsafe { println!("{}", myUnion.test };

This is required as the rust compiler can not guarantee the safety of the union, or that the member being addressed exsits. The union RFC is here and the tracking issue is here.