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#![warn(clippy::all, clippy::pedantic, clippy::cargo)]
//! This crate provides a set of functions to facilitate compiling flatbuffers to Rust from within
//! Rust. This is particularly helpful for use in `build.rs` scripts. Please note that for
//! compatiblity this crate will only support a single version of the `flatc` compiler. Please
//! check what version that is against whatever version is installed on your system.That said, due
//! to flatbuffers' versioning policy, it could be ok to mix patch and even minor versions.
//!
//! ## Usage
//!
//! If you're not sure where to start, take a look at [`BuilderOptions`]. Please also look at the
//! [`flatbuffers-example`](https://github.com/rdelfin/flatbuffers-build/tree/main/flatbuffers-example)
//! folder in the repo for an example. However, we'll explain the full functionality here.
//!
//! As an example, imagine a crate with the following folder structure:
//! ```bash
//! ├── build.rs
//! ├── Cargo.toml
//! ├── schemas
//! │ ├── example.fbs
//! │ └── weapon.fbs
//! └── src
//! └── main.rs
//! ```
//! In order to compile and use the code generated from both `example.fbs` and `weapon.fbs`, first
//! you need to add `flatbuffers-build` to your build dependencies, as well as a matching version
//! of `flatbuffers`:
//! ```toml
//! # Cargo.toml
//! # [...]
//! [dependencies]
//! flatbuffers = "=24.3.25"
//!
//! [build-dependencies]
//! flatbuffers-build = "=24.3.25"
//! # [...]
//! ```
//!
//! You can then have a very simple `build.rs` as follows:
//! ```no_run
//! use flatbuffers_build::BuilderOptions;
//!
//! BuilderOptions::new_with_files(["schemas/weapon.fbs", "schemas/example.fbs"])
//! .set_symlink_directory("src/gen_flatbuffers")
//! .compile()
//! .expect("flatbuffer compilation failed");
//! ```
//!
//! Note here that `weapon.fbs` and `example.fbs` are based on the schemas provided by
//! `flatbuffers` as an example. The namespace is `MyGame.Sample` and it contains multiple tables
//! and structs, including a `Monster` table.
//!
//! This will just compile the flatbuffers and drop them in `${OUT_DIR}/flatbuffers` and will
//! create a symlink under `src/gen_flatbuffers`. You can then use them in `lib.rs` like so:
//!
//! ```rust,ignore
//! #[allow(warnings)]
//! mod gen_flatbuffers;
//!
//! use gen_flatbuffers::my_game::sample::Monster;
//!
//! fn some_fn() {
//! // Make use of `Monster`
//! }
//! ```
//!
//! Note that since this will generate a symlink under `src/gen_flatbuffers`, you need to add this
//! file to your gitignore as this symlink will dynamically change at runtime.
//!
//! ## On file ordering
//!
//! Unfortunately due to a quirk in the `flatc` compiler the order you provide the `fbs` files does
//! matter. From some experimentation, the guidance is to always list files _after_ their
//! dependencies. Otherwise, the resulting `mod.rs` will be unusable. As an example, we have a
//! `weapon.fbs` and `example.fbs`. Since the latter has an `include` directive for `weapon.fbs`,
//! it should go after in the list. If you were to put `example.fbs` _before_ `weapon.fbs`, you'd
//! end up only being able to import the contents of `weapon.fbs` and with compilation errors if
//! you tried to use any other components.
use std::{
ffi::{OsStr, OsString},
path::{Path, PathBuf},
process::Command,
};
const FLATC_VERSION_PREFIX: &str = "flatc version ";
const FLATC_BUILD_PATH: Option<&str> = option_env!("FLATC_PATH");
/// Version of `flatc` supported by this library. Make sure this matches exactly with the `flatc`
/// binary you're using and the version of the `flatbuffers` rust library.
pub const SUPPORTED_FLATC_VERSION: &str = "24.3.25";
/// Primary error type returned when you compile your flatbuffer specifications to Rust.
#[derive(thiserror::Error, Debug)]
pub enum Error {
/// Returned when `flatc` returns with an non-zero status code for a reason not covered
/// elsewhere in this enum.
#[error("flatc exited unexpectedly with status code {status_code:?}\n-- stdout:\n{stdout}\n-- stderr:\n{stderr}\n")]
FlatcErrorCode {
/// Status code returned by `flatc` (none if program was terminated by a signal).
status_code: Option<i32>,
/// Standard output stream contents of the program
stdout: String,
/// Standard error stream contents of the program
stderr: String,
},
/// Returned if `flatc --version` generates output we cannot parse. Usually means that the
/// binary requested is not, in fact, flatc.
#[error("flatc returned invalid output for --version: {0}")]
InvalidFlatcOutput(String),
/// Returned if the version of `flatc` does not match the supported version. Please refer to
/// [`SUPPORTED_FLATC_VERSION`] for that.
#[error("flatc version '{0}' is unsupported by this version of the library. Please match your library with your flatc version")]
UnsupportedFlatcVersion(String),
/// Returned if we fail to spawn a process with `flatc`. Usually means the supplied path to
/// flatc does not exist.
#[error("flatc failed to spawn: {0}")]
FlatcSpawnFailure(#[source] std::io::Error),
/// Returned if you failed to set either the output path or the `OUT_DIR` environment variable.
#[error(
"output directory was not set. Either call .set_output_path() or set the `OUT_DIR` env var"
)]
OutputDirNotSet,
/// Returned when an issue arrises when creating the symlink. Typically this will be things
/// like permissions, a directory existing already at the file location, or other filesystem
/// errors.
#[error("failed to create symlink path requested: {0}")]
SymlinkCreationFailure(#[source] std::io::Error),
}
/// Alias for a Result that uses [`Error`] as the default error type.
pub type Result<T = (), E = Error> = std::result::Result<T, E>;
/// Builder for options to the flatc compiler options. When consumed using
/// [`BuilderOptions::compile`], this generates rust code from the flatbuffer definition files
/// provided. The basic usage for this struct looks something like this:
/// ```no_run
/// use flatbuffers_build::BuilderOptions;
///
/// BuilderOptions::new_with_files(["some_file.fbs", "some_other_file.fbs"])
/// .compile()
/// .expect("flatbuffer compilation failed");
/// ```
///
/// This struct operates as a builder pattern, so you can do things like set the `flatc` path:
/// ```no_run
/// # use flatbuffers_build::BuilderOptions;
/// BuilderOptions::new_with_files(["some_file.fbs", "some_other_file.fbs"])
/// .set_compiler("/some/path/to/flatc")
/// .compile()
/// .expect("flatbuffer compilation failed");
/// ```
///
/// Consult the functions bellow for more details.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct BuilderOptions {
files: Vec<PathBuf>,
compiler: Option<String>,
output_path: Option<PathBuf>,
symlink_path: Option<PathBuf>,
supress_buildrs_directives: bool,
}
impl BuilderOptions {
/// Create a new builder for the compiler options. We purely initialise with an iterable of
/// files to compile. To actually build, refer to the [`Self::compile`] function. Note that the
/// order of the files is actually important, as incorrect ordering will result in incorrect
/// generated code with missing components. You should always put dependencies of other files
/// earlier in the list. In other words, if `schema_a.fbs` imports `schema_b.fbs`, then you'd
/// want to call this with:
///
/// ```rust
/// # use flatbuffers_build::BuilderOptions;
/// BuilderOptions::new_with_files(["schema_b.fbs", "schema_a.fbs"]);
/// ```
///
/// # Arguments
/// * `files` - An iterable of files that should be compiled into rust code. No glob resolution
/// happens here, and all paths MUST match to real files, either as absolute paths
/// or relative to the current working directory.
#[must_use]
pub fn new_with_files<P: AsRef<Path>, I: IntoIterator<Item = P>>(files: I) -> Self {
BuilderOptions {
files: files.into_iter().map(|f| f.as_ref().into()).collect(),
compiler: None,
output_path: None,
symlink_path: None,
supress_buildrs_directives: false,
}
}
/// Set the path of the `flatc` binary to use as a compiler. If no such path is provided, we
/// will default to first using whatever's set in the `FLATC_PATH` environment variable, or if
/// that's not set, we will let the system resolve using standard `PATH` resolution.
///
/// # Arguments
/// * `compiler` - Path to the compiler to run. This can also be a name that we should resolve
/// using standard `PATH` resolution.
#[must_use]
pub fn set_compiler<S: AsRef<str>>(self, compiler: S) -> Self {
BuilderOptions {
compiler: Some(compiler.as_ref().into()),
..self
}
}
/// Call this to set the output directory of the protobufs. If you don't set this, we will
/// default to writing to `${OUT_DIR}/flatbuffers`.
///
/// # Arguments
/// * `output_path` - The directory to write the files to.
#[must_use]
pub fn set_output_path<P: AsRef<Path>>(self, output_path: P) -> Self {
BuilderOptions {
output_path: Some(output_path.as_ref().into()),
..self
}
}
/// Set a path to create a symlink that points to the output files. This is commonly used to
/// symlink to a folder under `src` so you can normally pull in the generated code as a module.
/// We recommend always calling this and setting it to `src/generated` or something similar.
///
/// # Arguments
/// * `symlink_path` - Path to generate the symlink to.
#[must_use]
pub fn set_symlink_directory<P: AsRef<Path>>(self, symlink_path: P) -> Self {
BuilderOptions {
symlink_path: Some(symlink_path.as_ref().into()),
..self
}
}
/// Set this if you're not running from a `build.rs` script and don't want us to print the
/// build.rs instructions/directives that we would otherwise print in stdout.
#[must_use]
pub fn supress_buildrs_directives(self) -> Self {
BuilderOptions {
supress_buildrs_directives: true,
..self
}
}
/// Call this function to trigger compilation. Will write the compiled protobufs to the
/// specified directory, or to `${OUT_DIR}/flatbuffers` by default.
///
/// # Errors
/// Will fail if any error happens during compilation, including:
/// - Invalid protoc files
/// - Unsupported flatc version
/// - flatc exiting with a non-zero error code
/// For more details, see [`Error`].
pub fn compile(self) -> Result {
compile(self)
}
}
fn compile(builder_options: BuilderOptions) -> Result {
let files_str: Vec<_> = builder_options
.files
.iter()
.map(|p| p.clone().into_os_string())
.collect();
let compiler = builder_options.compiler.unwrap_or_else(|| {
if let Some(build_flatc) = FLATC_BUILD_PATH {
build_flatc.to_owned()
} else {
std::env::var("FLATC_PATH").unwrap_or("flatc".into())
}
});
let output_path = builder_options.output_path.map_or_else(
|| {
std::env::var_os("OUT_DIR")
.ok_or(Error::OutputDirNotSet)
.map(|mut s| {
s.push(OsString::from("/flatbuffers"));
s
})
},
|p| Ok(p.into_os_string()),
)?;
confirm_flatc_version(&compiler)?;
let mut args = vec![
OsString::from("--rust"),
OsString::from("--rust-module-root-file"),
OsString::from("-o"),
output_path.clone(),
];
args.extend(files_str);
run_flatc(&compiler, &args)?;
if let Some(symlink_path) = builder_options.symlink_path {
generate_symlink(&symlink_path, PathBuf::from(output_path))?;
if !builder_options.supress_buildrs_directives {
println!("cargo::rerun-if-changed={}", symlink_path.display());
}
}
if !builder_options.supress_buildrs_directives {
for file in builder_options.files {
println!("cargo::rerun-if-changed={}", file.display());
}
}
Ok(())
}
fn generate_symlink<P: AsRef<Path>, Q: AsRef<Path>>(symlink_path: P, output_path: Q) -> Result {
if symlink_path.as_ref().exists() {
std::fs::remove_file(&symlink_path).map_err(Error::SymlinkCreationFailure)?;
}
std::os::unix::fs::symlink(output_path, symlink_path).map_err(Error::SymlinkCreationFailure)?;
Ok(())
}
fn confirm_flatc_version(compiler: &str) -> Result {
// Output shows up in stdout
let output = run_flatc(compiler, ["--version"])?;
if output.stdout.starts_with(FLATC_VERSION_PREFIX) {
let version_str = output.stdout[FLATC_VERSION_PREFIX.len()..].trim_end();
if version_str == SUPPORTED_FLATC_VERSION {
Ok(())
} else {
Err(Error::UnsupportedFlatcVersion(version_str.into()))
}
} else {
Err(Error::InvalidFlatcOutput(output.stdout))
}
}
struct ProgramOutput {
pub stdout: String,
pub _stderr: String,
}
fn run_flatc<I: IntoIterator<Item = S>, S: AsRef<OsStr>>(
compiler: &str,
args: I,
) -> Result<ProgramOutput> {
let output = Command::new(compiler)
.args(args)
.output()
.map_err(Error::FlatcSpawnFailure)?;
let stdout = String::from_utf8_lossy(&output.stdout).into_owned();
let stderr = String::from_utf8_lossy(&output.stderr).into_owned();
if output.status.success() {
Ok(ProgramOutput {
stdout,
_stderr: stderr,
})
} else {
Err(Error::FlatcErrorCode {
status_code: output.status.code(),
stdout,
stderr,
})
}
}