rust_icu: low-level rust language bindings for the ICU library

| Item | Description | | ---- | ----------- | | ICU 64/65/66 | Build Status <code>master</code> | | Source | https://github.com/google/rusticu | | README | https://github.com/google/rusticu/blob/master/README.md | | Coverage | View report | Docs | https://github.com/google/rust_icu/blob/master/docs/README.md |

This is a library of low level native rust language bindings for the International Components for Unicode (ICU) library for C (a.k.a. ICU4C).

See: http://icu-project.org for details about the ICU library. The library source can be viewed on Github at https://github.com/unicode-org/icu.

The latest version of this file is available at https://github.com/google/rust_icu.

This is not an officially supported Google product.

Why wrap ICU (vs. doing anything else)?

Structure of the repository

The repository is organized as a cargo workspace of rust crates. Each crate corresponds to the respective header in the ICU4C library's C API. For example, rust_icu_uenum implements the functionality that one would find in the uenum.h header file.

Please consult the coverage report for details about function coverage in the headers given above.

| Crate | Description | | ----- | ----------- | | rusticusys| Low-level bindings code | | rusticucommon| Commonly used low-level wrappings of the bindings. | | rusticuucal| Implements ucal.h C API header from the ICU library. | | rusticuudat| Implements udat.h C API header from the ICU library. | | rusticuudata| Implements udata.h C API header from the ICU library. | | rusticuuenum| Implements uenum.h C API header from the ICU library. Mainly UEnumeration and friends. | | rusticuuloc| Implements uloc.h C API header from the ICU library. | | rusticuustring| Implements ustring.h C API header from the ICU library. | | rusticuutext| Implements utext.h C API header from the ICU library. |

Limitations

The generated rust language binding methods of today limit the availability of language bindings to the available C API. The ICU library's C API (sometimes referred to as ICU4C in the documentation) is distinct from the ICU C++ API.

The bindings offered by this library have somewhat limited applicability, which means it may sometimes not work for you out of the box. If you come across such a case, feel free to file a bug for us to fix. Pull requests are welcome.

The limitations we know of today are as follows:

Compatibility

The table below shows the support matrix that has been verified so far. Any versions not mentioned explicitly have not been tested. Feel free to test a version and send a pull request to add to this matrix once you confirm the functionality. Each row is for a particular ICU library version. The column headers of columns 2 and onwards are features set combos. The coverage reflects the feature set and version points that we needed up to this point. The version semver in each cell denotes the version point that was tested.

| ICU version | default | renaming | renaming, icu_version_in_env| | ----------- | ------------------- | ---------------------- | ----- | | 63.x | ??? | ??? | ??? | | 64.2 | 0.0.{3,4,5} | ??? | ??? | | 65.1 | 0.0.5 | 0.0.5 | 0.0.5 | | 66.0.1 | 0.0.5 | ??? | ??? |

API versions that differ in the minor version number only should be compatible; but since it is time consuming to test all versions and relatively easy to keep only the last major edition of the library around, we keep only one minor version per library in the table, until need arises to do something else.

Features

The rust_icu library is intended to be compiled with cargo, with one of several features enabled. Compilation with cargo allows us to do some library detection in a custom build.rs file in the rust_icu_sys library and adapt the build process to your build environment. However, since not every development environment will use the same settings, we opted to offer certain features (below) as configuration options.

While our intention is to keep the list of features below up to date with the actual list in Cargo.toml, the list may periodically go out of date.

To use any of the features, you will need to activate the feature in all the rust_icu_* crates that you intend to use. Failing to do this will result in confusing compilation end result.

| Feature | Default? | Description | | ------- | -------- | ----------- | | bindgen | Yes | If set, cargo will run bindgen to generate bindings based on the installed ICU library. The program icu-config must be in $PATH for this to work. In the future there may be other approaches for auto-detecting libraries, such as via pkg-config. | | renaming | Yes | If set, ICU bindings are generated with version numbers appended. This is called "renaming" in ICU, and is normally needed only when linking against specific ICU version is required, for example to work around having to link different ICU versions. See the ICU documentation for a discussion of renaming. | | icu_config | Yes | If set, the binary icu-config will be used to configure the library. Turn this feature off if you do not want build.rs to try to autodetect the build environment. You will want to skip this feature if your build environment configures ICU in a different way. | | icu_version_in_env | No | If set, ICU bindings are made for the ICU version specified in the environment variable RUST_ICU_MAJOR_VERSION_NUMBER, which is made available to cargo at build time. See section below for details on how to use this feature. |

Prerequisites

Required

Optional

Testing

There are a few options to run the test for rust_icu.

Cargo

Building and testing using cargo is the

The following tests should all build and pass. Note that because the libraries needed are in a custom location, we need to set LD_LIBRARY_PATH when running the tests.

bash env LD_LIBRARY_PATH="$(icu-config --libdir)" cargo test

GNU Make

The easiest way is to use GNU Make and run:

make test

You may want to use this method if you are working on rust_icu, have your development environment all set up and would like a shorthand to run the tests.

Docker-based

See optional dependencies section above.

To run a hermetic build and test of the rust_icu source code, issue the following command:

bash make docker-test

This will run docker-based build and test of the source code on your local machine. This is a good way to test that your code works with a specific reference version of ICU.

Prior art

There is plenty of prior art that has been considered:

The current state of things is that I'd like to do a few experiments on my own first, then see if the work can be folded into any of the above efforts.

See also:

Assumptions

There are a few competing approaches for ICU bindings. However, it seems, at least based on information available in rust's RFC repos, that the work on ICU support in rust is still ongoing.

These are the assumptions made in the making of this library:

Additional instructions

ICU installation instructions

These instructions follow the "out-of-tree" build instructions from the ICU repository.

Assumptions

The instructions below are not self-contained. They assume that:

Compilation

mkdir -p $HOME/local mkdir -p $HOME/tmp cd $HOME/tmp git clone https://github.com/unicode-org/icu.git mkdir icu4c-build cd icu4c-build ../icu/icu4c/source/runConfigureICU Linux \ --prefix=$HOME/local \ --enable-static make make install make doc

If the compilation finishes with success, the directory $HOME/local/bin will have the file icu-config which is necessary to discover the library configuration.

You can also do a

bash make check

to run the unit tests.

If you add $HOME/local/bin to $PATH, or move icu-config to a directory that is listed in your $PATH you should be all set to compile rust_icu.

ICU rebuilding instructions

If you change the configuration of the ICU library with an intention to rebuild the library from source you should probably add an intervening make clean command.

Since the ICU build is not hermetic, this ensures there are no remnants of the old compilation process sitting around in the build directory. You need to do this for example if you upgrade the major version of the ICU library. If you forget to do so, you may see unexpected errors while compiling ICU, or while linking or running your programs.

Compiling for a set version of ICU

Assumptions

OR:

The following is a tested example.

bash env LD_LIBRARY_PATH=$HOME/local/lib RUST_ICU_MAJOR_VERSION_NUMBER=65 bash -c `cargo test`

The following would be an as of yet untested example of compiling rust_icu against a preexisting ICU version 66.

bash env LD_LIBRARY_PATH=$HOME/local/lib RUST_ICU_MAJOR_VERSION_NUMBER=66 bash -c `cargo test`

Adding support for a new version of ICU.

In general, as long as icu-config approach is supported, it should be possible to generate the library wrappers for newer versions of the ICU library, assuming that the underlying C APIs do not diverge too much.

An approach that yielded easy support for ICU 65.1 consisted of the following steps. Below, $RUST_ICU_SOURCE_DIR is the directory where you extracted the ICU source code.

These files lib_XX.rs may need to be generated again if build.rs is changed to include more features.

Adding more bindings

When adding more ICU wrappers, make sure to do the following: