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//! A procedural attribute-macro to insert `flame` calls into code
//!
//! The feature parity varies between versions of Rust:
//! * On stable and beta, you can annotate functions with `#[flame]`.
//! * On nightly, you can also annotate modules with `#[flame]`.
//!   You will need to add `#![feature(proc_macro_hygiene)]` in the crate root
//!   ([related issue][proc_macro_hygiene tracking issue]).
//!
//! Alas, currently you cannot annotate the whole crate. For details about why,
//! see the [custom inner attributes] issue.
//!
//! You can also annotate modules, functions or other items with `#[noflame]` to
//! omit them from the flame tracing.
//! For any given Rust version, the list of supported items for `#[noflame]` is
//! the same as for `#[flame]`.
//!
//! [proc_macro_hygiene tracking issue]: https://github.com/rust-lang/rust/issues/54727
//! [custom inner attributes]: https://github.com/rust-lang/rust/issues/54726

extern crate proc_macro;
extern crate quote;
extern crate syn;

use self::proc_macro::TokenStream;
use quote::quote;
use syn::fold::{self, Fold};
use syn::parse::{Parse, ParseStream, Result};
use syn::punctuated::Punctuated;

use syn::{
    parse_macro_input, parse_quote, Attribute, ImplItemFn, Item, ItemFn, ItemImpl, ItemMod,
    ItemTrait, Token, TraitItemFn,
};

#[derive(Default)]
struct Flamer {
    id_stack: Vec<String>,
}

impl Flamer {
    fn push(&mut self, ident: String) {
        self.id_stack.push(ident);
    }

    fn pop(&mut self) {
        let _ = self.id_stack.pop();
    }

    fn name(&self) -> String {
        self.id_stack.join("::")
    }

    fn is_noflame(&self, i: &[Attribute]) -> bool {
        i.iter().any(|ref a| {
            if a.path().segments.len() == 1 {
                let ident = &a.path().segments.iter().next().unwrap().ident;
                ident == "flame" || ident == "noflame"
            } else {
                false
            }
        })
    }
}

impl Parse for Flamer {
    fn parse(input: ParseStream) -> Result<Self> {
        let vars = Punctuated::<syn::LitStr, Token![,]>::parse_terminated(input)?;
        Ok(Flamer {
            id_stack: vars.into_iter().map(|s| s.value()).collect::<Vec<_>>(),
        })
    }
}

impl Fold for Flamer {
    fn fold_item_mod(&mut self, i: ItemMod) -> ItemMod {
        if self.is_noflame(&i.attrs) {
            return i;
        }
        self.push(i.ident.to_string());
        let item_mod = fold::fold_item_mod(self, i);
        self.pop();
        item_mod
    }

    fn fold_item_trait(&mut self, i: ItemTrait) -> ItemTrait {
        if self.is_noflame(&i.attrs) {
            return i;
        }
        self.push(i.ident.to_string());
        let t = fold::fold_item_trait(self, i);
        self.pop();
        t
    }

    fn fold_trait_item_fn(&mut self, i: TraitItemFn) -> TraitItemFn {
        if i.sig.constness.is_some() || self.is_noflame(&i.attrs) {
            return i;
        }
        self.push(i.sig.ident.to_string());
        let m = fold::fold_trait_item_fn(self, i);
        self.pop();
        m
    }

    fn fold_item_impl(&mut self, i: ItemImpl) -> ItemImpl {
        if self.is_noflame(&i.attrs) {
            return i;
        }
        if let Some((_, ref path, _)) = i.trait_ {
            self.push(format!("{:?} as {:?}", &i.self_ty, path));
        } else {
            self.push(format!("{:?}", &i.self_ty));
        }
        let ii = fold::fold_item_impl(self, i);
        self.pop();
        ii
    }

    fn fold_impl_item_fn(&mut self, i: ImplItemFn) -> ImplItemFn {
        if i.sig.constness.is_some() || self.is_noflame(&i.attrs) {
            return i;
        }
        self.push(i.sig.ident.to_string());
        let method = fold::fold_impl_item_fn(self, i);
        self.pop();
        method
    }

    fn fold_item_fn(&mut self, i: ItemFn) -> ItemFn {
        if self.is_noflame(&i.attrs) {
            return i;
        }
        if i.sig.constness.is_some() {
            return fold::fold_item_fn(self, i);
        }
        let mut i = i;
        self.push(i.sig.ident.to_string());
        let name = self.name();
        let stmts = ::std::mem::replace(
            &mut i.block.stmts,
            vec![parse_quote! {
                let _flame_guard = ::flame::start_guard(#name);
            }],
        );
        for stmt in stmts {
            i.block.stmts.push(fold::fold_stmt(self, stmt));
        }
        self.pop();
        i
    }
}

#[proc_macro_attribute]
pub fn flame(attrs: TokenStream, code: TokenStream) -> TokenStream {
    let input = parse_macro_input!(code as Item);
    let mut flamer = parse_macro_input!(attrs as Flamer);
    let item = fold::fold_item(&mut flamer, input);
    TokenStream::from(quote!(#item))
}

#[proc_macro_attribute]
pub fn noflame(_attrs: TokenStream, code: TokenStream) -> TokenStream {
    code
}