Move the macro support code into its own crate (#529)

crates/macro-support/src/lib.rs

@@ -0,0 +1,26 @@
+//! 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;
+extern crate wasm_bindgen_backend as backend;
+extern crate wasm_bindgen_shared as shared;
+
+pub use parser::BindgenAttrs;
+use parser::MacroParse;
+use quote::ToTokens;
+
+mod parser;
+
+/// Takes the parsed input from a `#[wasm_bindgen]` macro and returns the generated bindings
+pub fn expand(item: syn::Item, opts: parser::BindgenAttrs) -> proc_macro2::TokenStream {
+    let mut tokens = proc_macro2::TokenStream::new();
+    let mut program = backend::ast::Program::default();
+    item.macro_parse(&mut program, (Some(opts), &mut tokens));
+    program.to_tokens(&mut tokens);
+    tokens
+}