servo/components/plugins/utils.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

use rustc::lint::Context;
use rustc::middle::{ty, def};

use syntax::ptr::P;
use syntax::ast;
use syntax::ast::{TyPath, Path, AngleBracketedParameters, PathSegment, Ty};
use syntax::attr::mark_used;

/// Matches a type with a provided string, and returns its type parameters if successful
///
/// Try not to use this for types defined in crates you own, use match_lang_ty instead (for lint passes)
pub fn match_ty_unwrap<'a>(ty: &'a Ty, segments: &[&str]) -> Option<&'a [P<Ty>]> {
    match ty.node {
        TyPath(Path {segments: ref seg, ..}, _, _) => {
            // So ast::Path isn't the full path, just the tokens that were provided.
            // I could muck around with the maps and find the full path
            // however the more efficient way is to simply reverse the iterators and zip them
            // which will compare them in reverse until one of them runs out of segments
            if seg.iter().rev().zip(segments.iter().rev()).all(|(a,b)| a.identifier.as_str() == *b) {
                match seg.as_slice().last() {
                    Some(&PathSegment {parameters: AngleBracketedParameters(ref a), ..}) => {
                        Some(a.types.as_slice())
                    }
                    _ => None
                }
            } else {
                None
            }
        },
        _ => None
    }
}

/// Checks if a type has a #[servo_lang = "str"] attribute
pub fn match_lang_ty(cx: &Context, ty: &Ty, value: &str) -> bool {
    let mut found = false;
    if let TyPath(_, _, ty_id) = ty.node {
        if let Some(def::DefTy(def_id, _)) = cx.tcx.def_map.borrow().get(&ty_id).cloned() {
            // Iterating through attributes is hard because of cross-crate defs
            ty::each_attr(cx.tcx, def_id, |attr| {
                if let ast::MetaNameValue(ref name, ref val) = attr.node.value.node {
                    if name.get() == "servo_lang" {
                        if let ast::LitStr(ref v, _) = val.node {
                            if v.get() == value {
                                mark_used(attr);
                                found = true;
                                // We're done with the loop
                                return false;
                            }
                        }
                    }
                }
                true
            });
        };
    }
    found
}