gen/src/mod.rs

// Functionality that is shared between the cxx_build::bridge entry point and
// the cxxbridge CLI command.

mod error;
mod file;
pub(super) mod include;
pub(super) mod out;
mod write;

#[cfg(test)]
mod tests;

pub(super) use self::error::Error;
use self::error::{format_err, Result};
use self::file::File;
use crate::syntax::report::Errors;
use crate::syntax::{self, check, Types};
use std::fs;
use std::path::Path;

/// Options for C++ code generation.
///
/// We expect options to be added over time, so this is a non-exhaustive struct.
/// To instantiate one you need to crate a default value and mutate those fields
/// that you want to modify.
///
/// ```
/// # use cxx_gen::Opt;
/// #
/// let impl_annotations = r#"__attribute__((visibility("default")))"#.to_owned();
///
/// let mut opt = Opt::default();
/// opt.cxx_impl_annotations = Some(impl_annotations);
/// ```
#[derive(Default)]
#[non_exhaustive]
pub struct Opt {
    /// Any additional headers to #include. The cxxbridge tool does not parse or
    /// even require the given paths to exist; they simply go into the generated
    /// C++ code as #include lines.
    pub include: Vec<String>,
    /// Optional annotation for implementations of C++ function wrappers that
    /// may be exposed to Rust. You may for example need to provide
    /// `__declspec(dllexport)` or `__attribute__((visibility("default")))` if
    /// Rust code from one shared object or executable depends on these C++
    /// functions in another.
    pub cxx_impl_annotations: Option<String>,
}

/// Results of code generation.
pub struct GeneratedCode {
    /// The bytes of a C++ header file.
    pub header: Vec<u8>,
    /// The bytes of a C++ implementation file (e.g. .cc, cpp etc.)
    pub implementation: Vec<u8>,
}

pub(super) fn do_generate_bridge(path: &Path, opt: &Opt) -> Vec<u8> {
    let header = false;
    generate_from_path(path, opt, header)
}

pub(super) fn do_generate_header(path: &Path, opt: &Opt) -> Vec<u8> {
    let header = true;
    generate_from_path(path, opt, header)
}

fn generate_from_path(path: &Path, opt: &Opt, header: bool) -> Vec<u8> {
    let source = match fs::read_to_string(path) {
        Ok(source) => source,
        Err(err) => format_err(path, "", Error::Io(err)),
    };
    match generate_from_string(&source, opt, header) {
        Ok(out) => out,
        Err(err) => format_err(path, &source, err),
    }
}

fn generate_from_string(source: &str, opt: &Opt, header: bool) -> Result<Vec<u8>> {
    let mut source = source;
    if source.starts_with("#!") && !source.starts_with("#![") {
        let shebang_end = source.find('\n').unwrap_or(source.len());
        source = &source[shebang_end..];
    }
    let syntax: File = syn::parse_str(source)?;
    let generated = generate(syntax, opt, header, !header)?;
    Ok(if header {
        generated.header
    } else {
        generated.implementation
    })
}

pub(super) fn generate(
    syntax: File,
    opt: &Opt,
    gen_header: bool,
    gen_implementation: bool,
) -> Result<GeneratedCode> {
    proc_macro2::fallback::force();
    let ref mut errors = Errors::new();
    let bridge = syntax
        .modules
        .into_iter()
        .next()
        .ok_or(Error::NoBridgeMod)?;
    let ref namespace = bridge.namespace;
    let trusted = bridge.unsafety.is_some();
    let ref apis = syntax::parse_items(errors, bridge.content, trusted);
    let ref types = Types::collect(errors, apis);
    errors.propagate()?;
    check::typecheck(errors, namespace, apis, types);
    errors.propagate()?;
    // Some callers may wish to generate both header and C++
    // from the same token stream to avoid parsing twice. But others
    // only need to generate one or the other.
    Ok(GeneratedCode {
        header: if gen_header {
            write::gen(namespace, apis, types, opt, true).content()
        } else {
            Vec::new()
        },
        implementation: if gen_implementation {
            write::gen(namespace, apis, types, opt, false).content()
        } else {
            Vec::new()
        },
    })
}