Introduce the wasm-bindgen-webidl frontend

This is still a work in progress. Parse WebIDL source text and convert it into
wasm-bindgen AST, so that we can automatically emit bindings for the types and
functions described in the WebIDL.

crates/webidl/src/lib.rs

@@ -0,0 +1,102 @@
+/*!
+# `wasm_bindgen_webidl`
+
+Converts WebIDL into wasm-bindgen's internal AST form, so that bindings can be
+emitted for the types and methods described in the WebIDL.
+ */
+
+#![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
+
+extern crate failure;
+extern crate proc_macro2;
+extern crate syn;
+extern crate wasm_bindgen_backend as backend;
+extern crate webidl;
+
+use failure::ResultExt;
+use proc_macro2::Ident;
+use std::fs;
+use std::io::{self, Read};
+use std::path::Path;
+
+/// Either `Ok(t)` or `Err(failure::Error)`.
+pub type Result<T> = ::std::result::Result<T, failure::Error>;
+
+/// Parse the WebIDL at the given path into a wasm-bindgen AST.
+pub fn parse_file(webidl_path: &Path) -> Result<backend::ast::Program> {
+    let file = fs::File::open(webidl_path).context("opening WebIDL file")?;
+    let mut file = io::BufReader::new(file);
+    let mut source = String::new();
+    file.read_to_string(&mut source)
+        .context("reading WebIDL file")?;
+    parse(&source)
+}
+
+/// Parse a string of WebIDL source text into a wasm-bindgen AST.
+pub fn parse(webidl_source: &str) -> Result<backend::ast::Program> {
+    let definitions = webidl::parse_string(webidl_source).context("parsing WebIDL source text")?;
+
+    let mut program = backend::ast::Program::default();
+    definitions.webidl_parse(&mut program)?;
+
+    Ok(program)
+}
+
+trait WebidlParse {
+    fn webidl_parse(&self, program: &mut backend::ast::Program) -> Result<()>;
+}
+
+impl WebidlParse for Vec<webidl::ast::Definition> {
+    fn webidl_parse(&self, program: &mut backend::ast::Program) -> Result<()> {
+        for def in self {
+            def.webidl_parse(program)?;
+        }
+        Ok(())
+    }
+}
+
+impl WebidlParse for webidl::ast::Definition {
+    fn webidl_parse(&self, program: &mut backend::ast::Program) -> Result<()> {
+        match *self {
+            webidl::ast::Definition::Interface(ref interface) => interface.webidl_parse(program),
+            // TODO
+            webidl::ast::Definition::Callback(..)
+            | webidl::ast::Definition::Dictionary(..)
+            | webidl::ast::Definition::Enum(..)
+            | webidl::ast::Definition::Implements(..)
+            | webidl::ast::Definition::Includes(..)
+            | webidl::ast::Definition::Mixin(..)
+            | webidl::ast::Definition::Namespace(..)
+            | webidl::ast::Definition::Typedef(..) => Ok(()),
+        }
+    }
+}
+
+impl WebidlParse for webidl::ast::Interface {
+    fn webidl_parse(&self, program: &mut backend::ast::Program) -> Result<()> {
+        match *self {
+            webidl::ast::Interface::NonPartial(ref interface) => interface.webidl_parse(program),
+            // TODO
+            webidl::ast::Interface::Callback(..) | webidl::ast::Interface::Partial(..) => Ok(()),
+        }
+    }
+}
+
+impl WebidlParse for webidl::ast::NonPartialInterface {
+    fn webidl_parse(&self, program: &mut backend::ast::Program) -> Result<()> {
+        program.imports.push(backend::ast::Import {
+            module: None,
+            version: None,
+            js_namespace: None,
+            kind: backend::ast::ImportKind::Type(backend::ast::ImportType {
+                vis: syn::Visibility::Public(syn::VisPublic {
+                    pub_token: syn::token::Pub(proc_macro2::Span::call_site()),
+                }),
+                name: Ident::new(&self.name, proc_macro2::Span::call_site()),
+            }),
+        });
+        println!("{:#?}", self);
+        Ok(())
+    }
+}