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

use std::cell::Cell;

use backend::ast;
use backend::util::{ident_ty, ShortHash};
use backend::Diagnostic;
use proc_macro2::{Delimiter, Ident, Span, TokenStream, TokenTree};
use quote::ToTokens;
use shared;
use syn;
use syn::parse::{Parse, ParseStream, Result as SynResult};

thread_local!(static ATTRS: AttributeParseState = Default::default());

#[derive(Default)]
struct AttributeParseState {
    parsed: Cell<usize>,
    checks: Cell<usize>,
}

/// Parsed attributes from a `#[wasm_bindgen(..)]`.
#[cfg_attr(feature = "extra-traits", derive(Debug, PartialEq, Eq))]
pub struct BindgenAttrs {
    /// List of parsed attributes
    pub attrs: Vec<(Cell<bool>, BindgenAttr)>,
}

macro_rules! attrgen {
    ($mac:ident) => {
        $mac! {
            (catch, Catch(Span)),
            (constructor, Constructor(Span)),
            (method, Method(Span)),
            (static_method_of, StaticMethodOf(Span, Ident)),
            (js_namespace, JsNamespace(Span, Ident)),
            (module, Module(Span, String, Span)),
            (raw_module, RawModule(Span, String, Span)),
            (inline_js, InlineJs(Span, String, Span)),
            (getter, Getter(Span, Option<Ident>)),
            (setter, Setter(Span, Option<Ident>)),
            (indexing_getter, IndexingGetter(Span)),
            (indexing_setter, IndexingSetter(Span)),
            (indexing_deleter, IndexingDeleter(Span)),
            (structural, Structural(Span)),
            (r#final, Final(Span)),
            (readonly, Readonly(Span)),
            (js_name, JsName(Span, String, Span)),
            (js_class, JsClass(Span, String, Span)),
            (inspectable, Inspectable(Span)),
            (is_type_of, IsTypeOf(Span, syn::Expr)),
            (extends, Extends(Span, syn::Path)),
            (vendor_prefix, VendorPrefix(Span, Ident)),
            (variadic, Variadic(Span)),
            (typescript_custom_section, TypescriptCustomSection(Span)),
            (start, Start(Span)),
            (skip, Skip(Span)),

            // For testing purposes only.
            (assert_no_shim, AssertNoShim(Span)),
        }
    };
}

macro_rules! methods {
    ($(($name:ident, $variant:ident($($contents:tt)*)),)*) => {
        $(methods!(@method $name, $variant($($contents)*));)*

        #[cfg(feature = "strict-macro")]
        fn check_used(self) -> Result<(), Diagnostic> {
            // Account for the fact this method was called
            ATTRS.with(|state| state.checks.set(state.checks.get() + 1));

            let mut errors = Vec::new();
            for (used, attr) in self.attrs.iter() {
                if used.get() {
                    continue
                }
                // The check below causes rustc to crash on powerpc64 platforms
                // with an LLVM error. To avoid this, we instead use #[cfg()]
                // and duplicate the function below. See #58516 for details.
                /*if !cfg!(feature = "strict-macro") {
                    continue
                }*/
                let span = match attr {
                    $(BindgenAttr::$variant(span, ..) => span,)*
                };
                errors.push(Diagnostic::span_error(*span, "unused #[wasm_bindgen] attribute"));
            }
            Diagnostic::from_vec(errors)
        }

        #[cfg(not(feature = "strict-macro"))]
        fn check_used(self) -> Result<(), Diagnostic> {
            // Account for the fact this method was called
            ATTRS.with(|state| state.checks.set(state.checks.get() + 1));
            Ok(())
        }
    };

    (@method $name:ident, $variant:ident(Span, String, Span)) => {
        fn $name(&self) -> Option<(&str, Span)> {
            self.attrs
                .iter()
                .filter_map(|a| match &a.1 {
                    BindgenAttr::$variant(_, s, span) => {
                        a.0.set(true);
                        Some((&s[..], *span))
                    }
                    _ => None,
                })
                .next()
        }
    };

    (@method $name:ident, $variant:ident(Span, $($other:tt)*)) => {
        #[allow(unused)]
        fn $name(&self) -> Option<&$($other)*> {
            self.attrs
                .iter()
                .filter_map(|a| match &a.1 {
                    BindgenAttr::$variant(_, s) => {
                        a.0.set(true);
                        Some(s)
                    }
                    _ => None,
                })
                .next()
        }
    };

    (@method $name:ident, $variant:ident($($other:tt)*)) => {
        #[allow(unused)]
        fn $name(&self) -> Option<&$($other)*> {
            self.attrs
                .iter()
                .filter_map(|a| match &a.1 {
                    BindgenAttr::$variant(s) => {
                        a.0.set(true);
                        Some(s)
                    }
                    _ => None,
                })
                .next()
        }
    };
}

impl BindgenAttrs {
    /// Find and parse the wasm_bindgen attributes.
    fn find(attrs: &mut Vec<syn::Attribute>) -> Result<BindgenAttrs, Diagnostic> {
        let mut ret = BindgenAttrs::default();
        loop {
            let pos = attrs
                .iter()
                .enumerate()
                .find(|&(_, ref m)| m.path.segments[0].ident == "wasm_bindgen")
                .map(|a| a.0);
            let pos = match pos {
                Some(i) => i,
                None => return Ok(ret),
            };
            let attr = attrs.remove(pos);
            let mut tts = attr.tokens.clone().into_iter();
            let group = match tts.next() {
                Some(TokenTree::Group(d)) => d,
                Some(_) => bail_span!(attr, "malformed #[wasm_bindgen] attribute"),
                None => continue,
            };
            if tts.next().is_some() {
                bail_span!(attr, "malformed #[wasm_bindgen] attribute");
            }
            if group.delimiter() != Delimiter::Parenthesis {
                bail_span!(attr, "malformed #[wasm_bindgen] attribute");
            }
            let mut attrs: BindgenAttrs = syn::parse2(group.stream())?;
            ret.attrs.extend(attrs.attrs.drain(..));
            attrs.check_used()?;
        }
    }

    attrgen!(methods);
}

impl Default for BindgenAttrs {
    fn default() -> BindgenAttrs {
        // Add 1 to the list of parsed attribute sets. We'll use this counter to
        // sanity check that we call `check_used` an appropriate number of
        // times.
        ATTRS.with(|state| state.parsed.set(state.parsed.get() + 1));
        BindgenAttrs { attrs: Vec::new() }
    }
}

impl Parse for BindgenAttrs {
    fn parse(input: ParseStream) -> SynResult<Self> {
        let mut attrs = BindgenAttrs::default();
        if input.is_empty() {
            return Ok(attrs);
        }

        let opts = syn::punctuated::Punctuated::<_, syn::token::Comma>::parse_terminated(input)?;
        attrs.attrs = opts.into_iter().map(|c| (Cell::new(false), c)).collect();
        Ok(attrs)
    }
}

macro_rules! gen_bindgen_attr {
    ($(($method:ident, $($variants:tt)*),)*) => {
        /// The possible attributes in the `#[wasm_bindgen]`.
        #[cfg_attr(feature = "extra-traits", derive(Debug, PartialEq, Eq))]
        pub enum BindgenAttr {
            $($($variants)*,)*
        }
    }
}
attrgen!(gen_bindgen_attr);

impl Parse for BindgenAttr {
    fn parse(input: ParseStream) -> SynResult<Self> {
        let original = input.fork();
        let attr: AnyIdent = input.parse()?;
        let attr = attr.0;
        let attr_span = attr.span();
        let attr_string = attr.to_string();
        let raw_attr_string = format!("r#{}", attr_string);

        macro_rules! parsers {
            ($(($name:ident, $($contents:tt)*),)*) => {
                $(
                    if attr_string == stringify!($name) || raw_attr_string == stringify!($name) {
                        parsers!(
                            @parser
                            $($contents)*
                        );
                    }
                )*
            };

            (@parser $variant:ident(Span)) => ({
                return Ok(BindgenAttr::$variant(attr_span));
            });

            (@parser $variant:ident(Span, Ident)) => ({
                input.parse::<Token![=]>()?;
                let ident = input.parse::<AnyIdent>()?.0;
                return Ok(BindgenAttr::$variant(attr_span, ident))
            });

            (@parser $variant:ident(Span, Option<Ident>)) => ({
                if input.parse::<Token![=]>().is_ok() {
                    let ident = input.parse::<AnyIdent>()?.0;
                    return Ok(BindgenAttr::$variant(attr_span, Some(ident)))
                } else {
                    return Ok(BindgenAttr::$variant(attr_span, None));
                }
            });

            (@parser $variant:ident(Span, syn::Path)) => ({
                input.parse::<Token![=]>()?;
                return Ok(BindgenAttr::$variant(attr_span, input.parse()?));
            });

            (@parser $variant:ident(Span, syn::Expr)) => ({
                input.parse::<Token![=]>()?;
                return Ok(BindgenAttr::$variant(attr_span, input.parse()?));
            });

            (@parser $variant:ident(Span, String, Span)) => ({
                input.parse::<Token![=]>()?;
                let (val, span) = match input.parse::<syn::LitStr>() {
                    Ok(str) => (str.value(), str.span()),
                    Err(_) => {
                        let ident = input.parse::<AnyIdent>()?.0;
                        (ident.to_string(), ident.span())
                    }
                };
                return Ok(BindgenAttr::$variant(attr_span, val, span))
            });
        }

        attrgen!(parsers);

        return Err(original.error("unknown attribute"));
    }
}

struct AnyIdent(Ident);

impl Parse for AnyIdent {
    fn parse(input: ParseStream) -> SynResult<Self> {
        input.step(|cursor| match cursor.ident() {
            Some((ident, remaining)) => Ok((AnyIdent(ident), remaining)),
            None => Err(cursor.error("expected an identifier")),
        })
    }
}

/// Conversion trait with context.
///
/// Used to convert syn tokens into an AST, that we can then use to generate glue code. The context
/// (`Ctx`) is used to pass in the attributes from the `#[wasm_bindgen]`, if needed.
trait ConvertToAst<Ctx> {
    /// What we are converting to.
    type Target;
    /// Convert into our target.
    ///
    /// Since this is used in a procedural macro, use panic to fail.
    fn convert(self, context: Ctx) -> Result<Self::Target, Diagnostic>;
}

impl<'a> ConvertToAst<BindgenAttrs> for &'a mut syn::ItemStruct {
    type Target = ast::Struct;

    fn convert(self, attrs: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
        if self.generics.params.len() > 0 {
            bail_span!(
                self.generics,
                "structs with #[wasm_bindgen] cannot have lifetime or \
                 type parameters currently"
            );
        }
        let mut fields = Vec::new();
        let js_name = attrs
            .js_name()
            .map(|s| s.0.to_string())
            .unwrap_or(self.ident.to_string());
        let is_inspectable = attrs.inspectable().is_some();
        for (i, field) in self.fields.iter_mut().enumerate() {
            match field.vis {
                syn::Visibility::Public(..) => {}
                _ => continue,
            }
            let (name_str, member) = match &field.ident {
                Some(ident) => (ident.to_string(), syn::Member::Named(ident.clone())),
                None => (i.to_string(), syn::Member::Unnamed(i.into())),
            };

            let attrs = BindgenAttrs::find(&mut field.attrs)?;
            assert_not_variadic(&attrs)?;
            if attrs.skip().is_some() {
                attrs.check_used()?;
                continue;
            }

            let comments = extract_doc_comments(&field.attrs);
            let getter = shared::struct_field_get(&js_name, &name_str);
            let setter = shared::struct_field_set(&js_name, &name_str);

            fields.push(ast::StructField {
                name: member,
                struct_name: self.ident.clone(),
                readonly: attrs.readonly().is_some(),
                ty: field.ty.clone(),
                getter: Ident::new(&getter, Span::call_site()),
                setter: Ident::new(&setter, Span::call_site()),
                comments,
            });
            attrs.check_used()?;
        }
        let comments: Vec<String> = extract_doc_comments(&self.attrs);
        attrs.check_used()?;
        Ok(ast::Struct {
            rust_name: self.ident.clone(),
            js_name,
            fields,
            comments,
            is_inspectable,
        })
    }
}

impl<'a> ConvertToAst<(BindgenAttrs, &'a ast::ImportModule)> for syn::ForeignItemFn {
    type Target = ast::ImportKind;

    fn convert(
        self,
        (opts, module): (BindgenAttrs, &'a ast::ImportModule),
    ) -> Result<Self::Target, Diagnostic> {
        let wasm = function_from_decl(
            &self.sig.ident,
            &opts,
            self.sig.clone(),
            self.attrs.clone(),
            self.vis.clone(),
            false,
            None,
        )?
        .0;
        let catch = opts.catch().is_some();
        let variadic = opts.variadic().is_some();
        let js_ret = if catch {
            // TODO: this assumes a whole bunch:
            //
            // * The outer type is actually a `Result`
            // * The error type is a `JsValue`
            // * The actual type is the first type parameter
            //
            // should probably fix this one day...
            extract_first_ty_param(wasm.ret.as_ref())?
        } else {
            wasm.ret.clone()
        };

        let operation_kind = operation_kind(&opts);

        let kind = if opts.method().is_some() {
            let class = wasm.arguments.get(0).ok_or_else(|| {
                err_span!(self, "imported methods must have at least one argument")
            })?;
            let class = match &*class.ty {
                syn::Type::Reference(syn::TypeReference {
                    mutability: None,
                    elem,
                    ..
                }) => &**elem,
                _ => bail_span!(
                    class.ty,
                    "first argument of method must be a shared reference"
                ),
            };
            let class_name = match *class {
                syn::Type::Path(syn::TypePath {
                    qself: None,
                    ref path,
                }) => path,
                _ => bail_span!(class, "first argument of method must be a path"),
            };
            let class_name = extract_path_ident(class_name)?;
            let class_name = opts
                .js_class()
                .map(|p| p.0.into())
                .unwrap_or_else(|| class_name.to_string());

            let kind = ast::MethodKind::Operation(ast::Operation {
                is_static: false,
                kind: operation_kind,
            });

            ast::ImportFunctionKind::Method {
                class: class_name,
                ty: class.clone(),
                kind,
            }
        } else if let Some(cls) = opts.static_method_of() {
            let class = opts
                .js_class()
                .map(|p| p.0.into())
                .unwrap_or_else(|| cls.to_string());
            let ty = ident_ty(cls.clone());

            let kind = ast::MethodKind::Operation(ast::Operation {
                is_static: true,
                kind: operation_kind,
            });

            ast::ImportFunctionKind::Method { class, ty, kind }
        } else if opts.constructor().is_some() {
            let class = match js_ret {
                Some(ref ty) => ty,
                _ => bail_span!(self, "constructor returns must be bare types"),
            };
            let class_name = match *class {
                syn::Type::Path(syn::TypePath {
                    qself: None,
                    ref path,
                }) => path,
                _ => bail_span!(self, "return value of constructor must be a bare path"),
            };
            let class_name = extract_path_ident(class_name)?;
            let class_name = opts
                .js_class()
                .map(|p| p.0.into())
                .unwrap_or_else(|| class_name.to_string());

            ast::ImportFunctionKind::Method {
                class: class_name.to_string(),
                ty: class.clone(),
                kind: ast::MethodKind::Constructor,
            }
        } else {
            ast::ImportFunctionKind::Normal
        };

        let shim = {
            let ns = match kind {
                ast::ImportFunctionKind::Normal => (0, "n"),
                ast::ImportFunctionKind::Method { ref class, .. } => (1, &class[..]),
            };
            let data = (ns, &self.sig.ident, module);
            format!(
                "__wbg_{}_{}",
                wasm.name
                    .chars()
                    .filter(|c| c.is_ascii_alphanumeric())
                    .collect::<String>(),
                ShortHash(data)
            )
        };
        if let Some(span) = opts.r#final() {
            if opts.structural().is_some() {
                let msg = "cannot specify both `structural` and `final`";
                return Err(Diagnostic::span_error(*span, msg));
            }
        }
        let assert_no_shim = opts.assert_no_shim().is_some();
        let ret = ast::ImportKind::Function(ast::ImportFunction {
            function: wasm,
            assert_no_shim,
            kind,
            js_ret,
            catch,
            variadic,
            structural: opts.structural().is_some() || opts.r#final().is_none(),
            rust_name: self.sig.ident.clone(),
            shim: Ident::new(&shim, Span::call_site()),
            doc_comment: None,
        });
        opts.check_used()?;

        Ok(ret)
    }
}

impl ConvertToAst<BindgenAttrs> for syn::ForeignItemType {
    type Target = ast::ImportKind;

    fn convert(self, attrs: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
        assert_not_variadic(&attrs)?;
        let js_name = attrs
            .js_name()
            .map(|s| s.0)
            .map_or_else(|| self.ident.to_string(), |s| s.to_string());
        let is_type_of = attrs.is_type_of().cloned();
        let shim = format!("__wbg_instanceof_{}_{}", self.ident, ShortHash(&self.ident));
        let mut extends = Vec::new();
        let mut vendor_prefixes = Vec::new();
        for (used, attr) in attrs.attrs.iter() {
            match attr {
                BindgenAttr::Extends(_, e) => {
                    extends.push(e.clone());
                    used.set(true);
                }
                BindgenAttr::VendorPrefix(_, e) => {
                    vendor_prefixes.push(e.clone());
                    used.set(true);
                }
                _ => {}
            }
        }
        attrs.check_used()?;
        Ok(ast::ImportKind::Type(ast::ImportType {
            vis: self.vis,
            attrs: self.attrs,
            doc_comment: None,
            instanceof_shim: shim,
            is_type_of,
            rust_name: self.ident,
            js_name,
            extends,
            vendor_prefixes,
        }))
    }
}

impl<'a> ConvertToAst<(BindgenAttrs, &'a ast::ImportModule)> for syn::ForeignItemStatic {
    type Target = ast::ImportKind;

    fn convert(
        self,
        (opts, module): (BindgenAttrs, &'a ast::ImportModule),
    ) -> Result<Self::Target, Diagnostic> {
        if self.mutability.is_some() {
            bail_span!(self.mutability, "cannot import mutable globals yet")
        }
        assert_not_variadic(&opts)?;
        let default_name = self.ident.to_string();
        let js_name = opts
            .js_name()
            .map(|p| p.0)
            .unwrap_or(&default_name)
            .to_string();
        let shim = format!(
            "__wbg_static_accessor_{}_{}",
            self.ident,
            ShortHash((&js_name, module, &self.ident)),
        );
        opts.check_used()?;
        Ok(ast::ImportKind::Static(ast::ImportStatic {
            ty: *self.ty,
            vis: self.vis,
            rust_name: self.ident.clone(),
            js_name,
            shim: Ident::new(&shim, Span::call_site()),
        }))
    }
}

impl ConvertToAst<BindgenAttrs> for syn::ItemFn {
    type Target = ast::Function;

    fn convert(self, attrs: BindgenAttrs) -> Result<Self::Target, Diagnostic> {
        match self.vis {
            syn::Visibility::Public(_) => {}
            _ => bail_span!(self, "can only #[wasm_bindgen] public functions"),
        }
        if self.sig.constness.is_some() {
            bail_span!(
                self.sig.constness,
                "can only #[wasm_bindgen] non-const functions"
            );
        }
        if self.sig.unsafety.is_some() {
            bail_span!(self.sig.unsafety, "can only #[wasm_bindgen] safe functions");
        }
        assert_not_variadic(&attrs)?;

        let ret = function_from_decl(
            &self.sig.ident,
            &attrs,
            self.sig.clone(),
            self.attrs,
            self.vis,
            false,
            None,
        )?;
        attrs.check_used()?;
        Ok(ret.0)
    }
}

/// Construct a function (and gets the self type if appropriate) for our AST from a syn function.
fn function_from_decl(
    decl_name: &syn::Ident,
    opts: &BindgenAttrs,
    sig: syn::Signature,
    attrs: Vec<syn::Attribute>,
    vis: syn::Visibility,
    allow_self: bool,
    self_ty: Option<&Ident>,
) -> Result<(ast::Function, Option<ast::MethodSelf>), Diagnostic> {
    if sig.variadic.is_some() {
        bail_span!(sig.variadic, "can't #[wasm_bindgen] variadic functions");
    }
    if sig.generics.params.len() > 0 {
        bail_span!(
            sig.generics,
            "can't #[wasm_bindgen] functions with lifetime or type parameters",
        );
    }

    assert_no_lifetimes(&sig)?;

    let syn::Signature { inputs, output, .. } = sig;

    let replace_self = |t: syn::Type| {
        let self_ty = match self_ty {
            Some(i) => i,
            None => return t,
        };
        let path = match t {
            syn::Type::Path(syn::TypePath { qself: None, path }) => path,
            other => return other,
        };
        let new_path = if path.segments.len() == 1 && path.segments[0].ident == "Self" {
            self_ty.clone().into()
        } else {
            path
        };
        syn::Type::Path(syn::TypePath {
            qself: None,
            path: new_path,
        })
    };

    let mut method_self = None;
    let arguments = inputs
        .into_iter()
        .filter_map(|arg| match arg {
            syn::FnArg::Typed(mut c) => {
                c.ty = Box::new(replace_self(*c.ty));
                Some(c)
            }
            syn::FnArg::Receiver(r) => {
                if !allow_self {
                    panic!("arguments cannot be `self`")
                }
                assert!(method_self.is_none());
                if r.reference.is_none() {
                    method_self = Some(ast::MethodSelf::ByValue);
                } else if r.mutability.is_some() {
                    method_self = Some(ast::MethodSelf::RefMutable);
                } else {
                    method_self = Some(ast::MethodSelf::RefShared);
                }
                None
            }
        })
        .collect::<Vec<_>>();

    let ret = match output {
        syn::ReturnType::Default => None,
        syn::ReturnType::Type(_, ty) => Some(replace_self(*ty)),
    };

    let (name, name_span, renamed_via_js_name) =
        if let Some((js_name, js_name_span)) = opts.js_name() {
            (js_name.to_string(), js_name_span, true)
        } else {
            (decl_name.to_string(), decl_name.span(), false)
        };
    Ok((
        ast::Function {
            arguments,
            name_span,
            name,
            renamed_via_js_name,
            ret,
            rust_attrs: attrs,
            rust_vis: vis,
            r#async: sig.asyncness.is_some(),
        },
        method_self,
    ))
}

pub(crate) trait MacroParse<Ctx> {
    /// Parse the contents of an object into our AST, with a context if necessary.
    ///
    /// The context is used to have access to the attributes on `#[wasm_bindgen]`, and to allow
    /// writing to the output `TokenStream`.
    fn macro_parse(self, program: &mut ast::Program, context: Ctx) -> Result<(), Diagnostic>;
}

impl<'a> MacroParse<(Option<BindgenAttrs>, &'a mut TokenStream)> for syn::Item {
    fn macro_parse(
        self,
        program: &mut ast::Program,
        (opts, tokens): (Option<BindgenAttrs>, &'a mut TokenStream),
    ) -> Result<(), Diagnostic> {
        match self {
            syn::Item::Fn(mut f) => {
                let no_mangle = f
                    .attrs
                    .iter()
                    .enumerate()
                    .filter_map(|(i, m)| m.parse_meta().ok().map(|m| (i, m)))
                    .find(|(_, m)| m.path().is_ident("no_mangle"));
                match no_mangle {
                    Some((i, _)) => {
                        f.attrs.remove(i);
                    }
                    _ => {}
                }
                let comments = extract_doc_comments(&f.attrs);
                f.to_tokens(tokens);
                let opts = opts.unwrap_or_default();
                if opts.start().is_some() {
                    if f.sig.generics.params.len() > 0 {
                        bail_span!(&f.sig.generics, "the start function cannot have generics",);
                    }
                    if f.sig.inputs.len() > 0 {
                        bail_span!(&f.sig.inputs, "the start function cannot have arguments",);
                    }
                }
                let method_kind = ast::MethodKind::Operation(ast::Operation {
                    is_static: true,
                    kind: operation_kind(&opts),
                });
                let rust_name = f.sig.ident.clone();
                let start = opts.start().is_some();
                program.exports.push(ast::Export {
                    comments,
                    function: f.convert(opts)?,
                    js_class: None,
                    method_kind,
                    method_self: None,
                    rust_class: None,
                    rust_name,
                    start,
                });
            }
            syn::Item::Struct(mut s) => {
                let opts = opts.unwrap_or_default();
                program.structs.push((&mut s).convert(opts)?);
                s.to_tokens(tokens);
            }
            syn::Item::Impl(mut i) => {
                let opts = opts.unwrap_or_default();
                (&mut i).macro_parse(program, opts)?;
                i.to_tokens(tokens);
            }
            syn::Item::ForeignMod(mut f) => {
                let opts = match opts {
                    Some(opts) => opts,
                    None => BindgenAttrs::find(&mut f.attrs)?,
                };
                f.macro_parse(program, opts)?;
            }
            syn::Item::Enum(e) => {
                if let Some(opts) = opts {
                    opts.check_used()?;
                }
                e.to_tokens(tokens);
                e.macro_parse(program, ())?;
            }
            syn::Item::Const(mut c) => {
                let opts = match opts {
                    Some(opts) => opts,
                    None => BindgenAttrs::find(&mut c.attrs)?,
                };
                c.macro_parse(program, opts)?;
            }
            _ => {
                bail_span!(
                    self,
                    "#[wasm_bindgen] can only be applied to a function, \
                     struct, enum, impl, or extern block",
                );
            }
        }

        Ok(())
    }
}

impl<'a> MacroParse<BindgenAttrs> for &'a mut syn::ItemImpl {
    fn macro_parse(
        self,
        _program: &mut ast::Program,
        opts: BindgenAttrs,
    ) -> Result<(), Diagnostic> {
        if self.defaultness.is_some() {
            bail_span!(
                self.defaultness,
                "#[wasm_bindgen] default impls are not supported"
            );
        }
        if self.unsafety.is_some() {
            bail_span!(
                self.unsafety,
                "#[wasm_bindgen] unsafe impls are not supported"
            );
        }
        if let Some((_, path, _)) = &self.trait_ {
            bail_span!(path, "#[wasm_bindgen] trait impls are not supported");
        }
        if self.generics.params.len() > 0 {
            bail_span!(
                self.generics,
                "#[wasm_bindgen] generic impls aren't supported"
            );
        }
        let name = match *self.self_ty {
            syn::Type::Path(syn::TypePath {
                qself: None,
                ref path,
            }) => extract_path_ident(path)?,
            _ => bail_span!(
                self.self_ty,
                "unsupported self type in #[wasm_bindgen] impl"
            ),
        };
        let mut errors = Vec::new();
        for item in self.items.iter_mut() {
            if let Err(e) = prepare_for_impl_recursion(item, &name, &opts) {
                errors.push(e);
            }
        }
        Diagnostic::from_vec(errors)?;
        opts.check_used()?;
        Ok(())
    }
}

// Prepare for recursion into an `impl` block. Here we want to attach an
// internal attribute, `__wasm_bindgen_class_marker`, with any metadata we need
// to pass from the impl to the impl item. Recursive macro expansion will then
// expand the `__wasm_bindgen_class_marker` attribute.
//
// Note that we currently do this because inner items may have things like cfgs
// on them, so we want to expand the impl first, let the insides get cfg'd, and
// then go for the rest.
fn prepare_for_impl_recursion(
    item: &mut syn::ImplItem,
    class: &Ident,
    impl_opts: &BindgenAttrs,
) -> Result<(), Diagnostic> {
    let method = match item {
        syn::ImplItem::Method(m) => m,
        syn::ImplItem::Const(_) => {
            bail_span!(
                &*item,
                "const definitions aren't supported with #[wasm_bindgen]"
            );
        }
        syn::ImplItem::Type(_) => bail_span!(
            &*item,
            "type definitions in impls aren't supported with #[wasm_bindgen]"
        ),
        syn::ImplItem::Macro(_) => {
            // In theory we want to allow this, but we have no way of expanding
            // the macro and then placing our magical attributes on the expanded
            // functions. As a result, just disallow it for now to hopefully
            // ward off buggy results from this macro.
            bail_span!(&*item, "macros in impls aren't supported");
        }
        syn::ImplItem::Verbatim(_) => panic!("unparsed impl item?"),
        other => bail_span!(other, "failed to parse this item as a known item"),
    };

    let js_class = impl_opts
        .js_class()
        .map(|s| s.0.to_string())
        .unwrap_or(class.to_string());

    method.attrs.insert(
        0,
        syn::Attribute {
            pound_token: Default::default(),
            style: syn::AttrStyle::Outer,
            bracket_token: Default::default(),
            path: syn::parse_quote! { wasm_bindgen::prelude::__wasm_bindgen_class_marker },
            tokens: quote::quote! { (#class = #js_class) }.into(),
        },
    );

    Ok(())
}

impl<'a, 'b> MacroParse<(&'a Ident, &'a str)> for &'b mut syn::ImplItemMethod {
    fn macro_parse(
        self,
        program: &mut ast::Program,
        (class, js_class): (&'a Ident, &'a str),
    ) -> Result<(), Diagnostic> {
        match self.vis {
            syn::Visibility::Public(_) => {}
            _ => return Ok(()),
        }
        if self.defaultness.is_some() {
            panic!("default methods are not supported");
        }
        if self.sig.constness.is_some() {
            bail_span!(
                self.sig.constness,
                "can only #[wasm_bindgen] non-const functions",
            );
        }
        if self.sig.unsafety.is_some() {
            bail_span!(self.sig.unsafety, "can only bindgen safe functions",);
        }

        let opts = BindgenAttrs::find(&mut self.attrs)?;
        let comments = extract_doc_comments(&self.attrs);
        let (function, method_self) = function_from_decl(
            &self.sig.ident,
            &opts,
            self.sig.clone(),
            self.attrs.clone(),
            self.vis.clone(),
            true,
            Some(class),
        )?;
        let method_kind = if opts.constructor().is_some() {
            ast::MethodKind::Constructor
        } else {
            let is_static = method_self.is_none();
            let kind = operation_kind(&opts);
            ast::MethodKind::Operation(ast::Operation { is_static, kind })
        };
        program.exports.push(ast::Export {
            comments,
            function,
            js_class: Some(js_class.to_string()),
            method_kind,
            method_self,
            rust_class: Some(class.clone()),
            rust_name: self.sig.ident.clone(),
            start: false,
        });
        opts.check_used()?;
        Ok(())
    }
}

impl MacroParse<()> for syn::ItemEnum {
    fn macro_parse(self, program: &mut ast::Program, (): ()) -> Result<(), Diagnostic> {
        match self.vis {
            syn::Visibility::Public(_) => {}
            _ => bail_span!(self, "only public enums are allowed with #[wasm_bindgen]"),
        }

        if self.variants.len() == 0 {
            bail_span!(self, "cannot export empty enums to JS");
        }

        let has_discriminant = self.variants[0].discriminant.is_some();

        let variants = self
            .variants
            .iter()
            .enumerate()
            .map(|(i, v)| {
                match v.fields {
                    syn::Fields::Unit => (),
                    _ => bail_span!(v.fields, "only C-Style enums allowed with #[wasm_bindgen]"),
                }

                // Require that everything either has a discriminant or doesn't.
                // We don't really want to get in the business of emulating how
                // rustc assigns values to enums.
                if v.discriminant.is_some() != has_discriminant {
                    bail_span!(
                        v,
                        "must either annotate discriminant of all variants or none"
                    );
                }

                let value = match &v.discriminant {
                    Some((
                        _,
                        syn::Expr::Lit(syn::ExprLit {
                            attrs: _,
                            lit: syn::Lit::Int(int_lit),
                        }),
                    )) => match int_lit.base10_digits().parse::<u32>() {
                        Ok(v) => v,
                        Err(_) => {
                            bail_span!(
                                int_lit,
                                "enums with #[wasm_bindgen] can only support \
                                 numbers that can be represented as u32"
                            );
                        }
                    },
                    None => i as u32,
                    Some((_, expr)) => bail_span!(
                        expr,
                        "enums with #[wasm_bidngen] may only have \
                         number literal values",
                    ),
                };

                Ok(ast::Variant {
                    name: v.ident.clone(),
                    value,
                })
            })
            .collect::<Result<Vec<_>, Diagnostic>>()?;

        let mut values = variants.iter().map(|v| v.value).collect::<Vec<_>>();
        values.sort();
        let hole = values
            .windows(2)
            .filter_map(|window| {
                if window[0] + 1 != window[1] {
                    Some(window[0] + 1)
                } else {
                    None
                }
            })
            .next()
            .unwrap_or(*values.last().unwrap() + 1);
        for value in values {
            assert!(hole != value);
        }

        let comments = extract_doc_comments(&self.attrs);
        program.enums.push(ast::Enum {
            name: self.ident,
            variants,
            comments,
            hole,
        });
        Ok(())
    }
}

impl MacroParse<BindgenAttrs> for syn::ItemConst {
    fn macro_parse(self, program: &mut ast::Program, opts: BindgenAttrs) -> Result<(), Diagnostic> {
        // Shortcut
        if opts.typescript_custom_section().is_none() {
            bail_span!(self, "#[wasm_bindgen] will not work on constants unless you are defining a #[wasm_bindgen(typescript_custom_section)].");
        }

        match *self.expr {
            syn::Expr::Lit(syn::ExprLit {
                lit: syn::Lit::Str(litstr),
                ..
            }) => {
                program.typescript_custom_sections.push(litstr.value());
            }
            _ => {
                bail_span!(self, "Expected a string literal to be used with #[wasm_bindgen(typescript_custom_section)].");
            }
        }

        opts.check_used()?;

        Ok(())
    }
}

impl MacroParse<BindgenAttrs> for syn::ItemForeignMod {
    fn macro_parse(self, program: &mut ast::Program, opts: BindgenAttrs) -> Result<(), Diagnostic> {
        let mut errors = Vec::new();
        match self.abi.name {
            Some(ref l) if l.value() == "C" => {}
            None => {}
            Some(ref other) => {
                errors.push(err_span!(
                    other,
                    "only foreign mods with the `C` ABI are allowed"
                ));
            }
        }
        let module = if let Some((name, span)) = opts.module() {
            if opts.inline_js().is_some() {
                let msg = "cannot specify both `module` and `inline_js`";
                errors.push(Diagnostic::span_error(span, msg));
            }
            if opts.raw_module().is_some() {
                let msg = "cannot specify both `module` and `raw_module`";
                errors.push(Diagnostic::span_error(span, msg));
            }
            ast::ImportModule::Named(name.to_string(), span)
        } else if let Some((name, span)) = opts.raw_module() {
            if opts.inline_js().is_some() {
                let msg = "cannot specify both `raw_module` and `inline_js`";
                errors.push(Diagnostic::span_error(span, msg));
            }
            ast::ImportModule::RawNamed(name.to_string(), span)
        } else if let Some((js, span)) = opts.inline_js() {
            let i = program.inline_js.len();
            program.inline_js.push(js.to_string());
            ast::ImportModule::Inline(i, span)
        } else {
            ast::ImportModule::None
        };
        for item in self.items.into_iter() {
            if let Err(e) = item.macro_parse(program, module.clone()) {
                errors.push(e);
            }
        }
        Diagnostic::from_vec(errors)?;
        opts.check_used()?;
        Ok(())
    }
}

impl MacroParse<ast::ImportModule> for syn::ForeignItem {
    fn macro_parse(
        mut self,
        program: &mut ast::Program,
        module: ast::ImportModule,
    ) -> Result<(), Diagnostic> {
        let item_opts = {
            let attrs = match self {
                syn::ForeignItem::Fn(ref mut f) => &mut f.attrs,
                syn::ForeignItem::Type(ref mut t) => &mut t.attrs,
                syn::ForeignItem::Static(ref mut s) => &mut s.attrs,
                _ => panic!("only foreign functions/types allowed for now"),
            };
            BindgenAttrs::find(attrs)?
        };
        let js_namespace = item_opts.js_namespace().cloned();
        let kind = match self {
            syn::ForeignItem::Fn(f) => f.convert((item_opts, &module))?,
            syn::ForeignItem::Type(t) => t.convert(item_opts)?,
            syn::ForeignItem::Static(s) => s.convert((item_opts, &module))?,
            _ => panic!("only foreign functions/types allowed for now"),
        };

        program.imports.push(ast::Import {
            module,
            js_namespace,
            kind,
        });

        Ok(())
    }
}

/// Get the first type parameter of a generic type, errors on incorrect input.
fn extract_first_ty_param(ty: Option<&syn::Type>) -> Result<Option<syn::Type>, Diagnostic> {
    let t = match ty {
        Some(t) => t,
        None => return Ok(None),
    };
    let path = match *t {
        syn::Type::Path(syn::TypePath {
            qself: None,
            ref path,
        }) => path,
        _ => bail_span!(t, "must be Result<...>"),
    };
    let seg = path
        .segments
        .last()
        .ok_or_else(|| err_span!(t, "must have at least one segment"))?;
    let generics = match seg.arguments {
        syn::PathArguments::AngleBracketed(ref t) => t,
        _ => bail_span!(t, "must be Result<...>"),
    };
    let generic = generics
        .args
        .first()
        .ok_or_else(|| err_span!(t, "must have at least one generic parameter"))?;
    let ty = match generic {
        syn::GenericArgument::Type(t) => t,
        other => bail_span!(other, "must be a type parameter"),
    };
    match ty {
        syn::Type::Tuple(t) if t.elems.len() == 0 => return Ok(None),
        _ => {}
    }
    Ok(Some(ty.clone()))
}

/// Extract the documentation comments from a Vec of attributes
fn extract_doc_comments(attrs: &[syn::Attribute]) -> Vec<String> {
    attrs
        .iter()
        .filter_map(|a| {
            // if the path segments include an ident of "doc" we know this
            // this is a doc comment
            if a.path.segments.iter().any(|s| s.ident.to_string() == "doc") {
                Some(
                    // We want to filter out any Puncts so just grab the Literals
                    a.tokens.clone().into_iter().filter_map(|t| match t {
                        TokenTree::Literal(lit) => {
                            // this will always return the quoted string, we deal with
                            // that in the cli when we read in the comments
                            Some(lit.to_string())
                        }
                        _ => None,
                    }),
                )
            } else {
                None
            }
        })
        //Fold up the [[String]] iter we created into Vec<String>
        .fold(vec![], |mut acc, a| {
            acc.extend(a);
            acc
        })
}

/// Check there are no lifetimes on the function.
fn assert_no_lifetimes(sig: &syn::Signature) -> Result<(), Diagnostic> {
    struct Walk {
        diagnostics: Vec<Diagnostic>,
    }

    impl<'ast> syn::visit::Visit<'ast> for Walk {
        fn visit_lifetime(&mut self, i: &'ast syn::Lifetime) {
            self.diagnostics.push(err_span!(
                &*i,
                "it is currently not sound to use lifetimes in function \
                 signatures"
            ));
        }
    }
    let mut walk = Walk {
        diagnostics: Vec::new(),
    };
    syn::visit::Visit::visit_signature(&mut walk, sig);
    Diagnostic::from_vec(walk.diagnostics)
}

/// This method always fails if the BindgenAttrs contain variadic
fn assert_not_variadic(attrs: &BindgenAttrs) -> Result<(), Diagnostic> {
    if let Some(span) = attrs.variadic() {
        let msg = "the `variadic` attribute can only be applied to imported \
                   (`extern`) functions";
        return Err(Diagnostic::span_error(*span, msg));
    }
    Ok(())
}

/// If the path is a single ident, return it.
fn extract_path_ident(path: &syn::Path) -> Result<Ident, Diagnostic> {
    if path.leading_colon.is_some() {
        bail_span!(path, "global paths are not supported yet");
    }
    if path.segments.len() != 1 {
        bail_span!(path, "multi-segment paths are not supported yet");
    }
    let value = &path.segments[0];
    match value.arguments {
        syn::PathArguments::None => {}
        _ => bail_span!(path, "paths with type parameters are not supported yet"),
    }
    Ok(value.ident.clone())
}

pub fn reset_attrs_used() {
    ATTRS.with(|state| {
        state.parsed.set(0);
        state.checks.set(0);
    })
}

pub fn assert_all_attrs_checked() {
    ATTRS.with(|state| {
        assert_eq!(state.parsed.get(), state.checks.get());
    })
}

fn operation_kind(opts: &BindgenAttrs) -> ast::OperationKind {
    let mut operation_kind = ast::OperationKind::Regular;
    if let Some(g) = opts.getter() {
        operation_kind = ast::OperationKind::Getter(g.clone());
    }
    if let Some(s) = opts.setter() {
        operation_kind = ast::OperationKind::Setter(s.clone());
    }
    if opts.indexing_getter().is_some() {
        operation_kind = ast::OperationKind::IndexingGetter;
    }
    if opts.indexing_setter().is_some() {
        operation_kind = ast::OperationKind::IndexingSetter;
    }
    if opts.indexing_deleter().is_some() {
        operation_kind = ast::OperationKind::IndexingDeleter;
    }
    operation_kind
}