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// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Machinery for hygienic macros, inspired by the MTWT[1] paper.
//!
//! [1] Matthew Flatt, Ryan Culpepper, David Darais, and Robert Bruce Findler.
//! 2012. *Macros that work together: Compile-time bindings, partial expansion,
//! and definition contexts*. J. Funct. Program. 22, 2 (March 2012), 181-216.
//! DOI=10.1017/S0956796812000093 http://dx.doi.org/10.1017/S0956796812000093
use std::cell::RefCell;
use std::collections::HashMap;
use std::fmt;
/// A SyntaxContext represents a chain of macro expansions (represented by marks).
#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Default)]
pub struct SyntaxContext(u32);
#[derive(Copy, Clone)]
pub struct SyntaxContextData {
pub outer_mark: Mark,
pub prev_ctxt: SyntaxContext,
}
/// A mark represents a unique id associated with a macro expansion.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Default)]
pub struct Mark(u32);
impl Mark {
pub fn fresh() -> Self {
HygieneData::with(|data| {
let next_mark = Mark(data.next_mark.0 + 1);
::std::mem::replace(&mut data.next_mark, next_mark)
})
}
}
struct HygieneData {
syntax_contexts: Vec<SyntaxContextData>,
markings: HashMap<(SyntaxContext, Mark), SyntaxContext>,
next_mark: Mark,
}
impl HygieneData {
fn new() -> Self {
HygieneData {
syntax_contexts: vec![SyntaxContextData {
outer_mark: Mark(0), // the null mark
prev_ctxt: SyntaxContext(0), // the empty context
}],
markings: HashMap::new(),
next_mark: Mark(1),
}
}
fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
thread_local! {
static HYGIENE_DATA: RefCell<HygieneData> = RefCell::new(HygieneData::new());
}
HYGIENE_DATA.with(|data| f(&mut *data.borrow_mut()))
}
}
pub fn reset_hygiene_data() {
HygieneData::with(|data| *data = HygieneData::new())
}
impl SyntaxContext {
pub const fn empty() -> Self {
SyntaxContext(0)
}
pub fn data(self) -> SyntaxContextData {
HygieneData::with(|data| data.syntax_contexts[self.0 as usize])
}
/// Extend a syntax context with a given mark
pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
// Applying the same mark twice is a no-op
let ctxt_data = self.data();
if mark == ctxt_data.outer_mark {
return ctxt_data.prev_ctxt;
}
HygieneData::with(|data| {
let syntax_contexts = &mut data.syntax_contexts;
*data.markings.entry((self, mark)).or_insert_with(|| {
syntax_contexts.push(SyntaxContextData {
outer_mark: mark,
prev_ctxt: self,
});
SyntaxContext(syntax_contexts.len() as u32 - 1)
})
})
}
/// If `ident` is macro expanded, return the source ident from the macro definition
/// and the mark of the expansion that created the macro definition.
pub fn source(self) -> (Self /* source context */, Mark /* source macro */) {
let macro_def_ctxt = self.data().prev_ctxt.data();
(macro_def_ctxt.prev_ctxt, macro_def_ctxt.outer_mark)
}
}
impl fmt::Debug for SyntaxContext {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "#{}", self.0)
}
}
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