wasm-bindgen/crates/macro-support/src/lib.rs

//! This crate contains the part of the implementation of the `#[wasm_bindgen]` optsibute that is
//! not in the shared backend crate.

#![doc(html_root_url = "https://docs.rs/wasm-bindgen-macro-support/0.2")]

extern crate proc_macro2;
extern crate quote;
#[macro_use]
extern crate syn;
#[macro_use]
extern crate wasm_bindgen_backend as backend;
extern crate wasm_bindgen_shared as shared;

use backend::{Diagnostic, TryToTokens};
pub use parser::BindgenAttrs;
use quote::ToTokens;
use parser::MacroParse;
use proc_macro2::TokenStream;
use syn::parse::{Parse, ParseStream, Result as SynResult};
use quote::TokenStreamExt;

mod parser;

/// Takes the parsed input from a `#[wasm_bindgen]` macro and returns the generated bindings
pub fn expand(attr: TokenStream, input: TokenStream) -> Result<TokenStream, Diagnostic> {
    parser::reset_attrs_used();
    let item = syn::parse2::<syn::Item>(input)?;
    let opts = syn::parse2(attr)?;

    let mut tokens = proc_macro2::TokenStream::new();
    let mut program = backend::ast::Program::default();
    item.macro_parse(&mut program, (Some(opts), &mut tokens))?;
    program.try_to_tokens(&mut tokens)?;

    // If we successfully got here then we should have used up all attributes
    // and considered all of them to see if they were used. If one was forgotten
    // that's a bug on our end, so sanity check here.
    parser::assert_all_attrs_checked();

    Ok(tokens)
}

/// Takes the parsed input from a `#[wasm_bindgen]` macro and returns the generated bindings
pub fn expand_class_marker(attr: TokenStream, input: TokenStream) -> Result<TokenStream, Diagnostic> {
    parser::reset_attrs_used();
    let mut item = syn::parse2::<syn::ImplItemMethod>(input)?;
    let opts: ClassMarker = syn::parse2(attr)?;

    let mut program = backend::ast::Program::default();
    item.macro_parse(&mut program, (&opts.class, &opts.js_class))?;
    parser::assert_all_attrs_checked(); // same as above

    // This is where things are slightly different, we are being expanded in the
    // context of an impl so we can't inject arbitrary item-like tokens into the
    // output stream. If we were to do that then it wouldn't parse!
    //
    // Instead what we want to do is to generate the tokens for `program` into
    // the header of the function. This'll inject some no_mangle functions and
    // statics and such, and they should all be valid in the context of the
    // start of a function.
    //
    // We manually implement `ToTokens for ImplItemMethod` here, injecting our
    // program's tokens before the actual method's inner body tokens.
    let mut tokens = proc_macro2::TokenStream::new();
    tokens.append_all(item.attrs.iter().filter(|attr| {
        match attr.style {
            syn::AttrStyle::Outer => true,
            _ => false,
        }
    }));
    item.vis.to_tokens(&mut tokens);
    item.sig.to_tokens(&mut tokens);
    let mut err = None;
    item.block.brace_token.surround(&mut tokens, |tokens| {
        if let Err(e) = program.try_to_tokens(tokens) {
            err = Some(e);
        }
        tokens.append_all(item.attrs.iter().filter(|attr| {
            match attr.style {
                syn::AttrStyle::Inner(_) => true,
                _ => false,
            }
        }));
        tokens.append_all(&item.block.stmts);
    });

    if let Some(err) = err {
        return Err(err)
    }

    Ok(tokens)
}

struct ClassMarker {
    class: syn::Ident,
    js_class: String,
}

impl Parse for ClassMarker {
    fn parse(input: ParseStream) -> SynResult<Self> {
        let class = input.parse::<syn::Ident>()?;
        input.parse::<Token![=]>()?;
        let js_class = input.parse::<syn::LitStr>()?.value();
        Ok(ClassMarker { class, js_class })
    }
}