//! 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 <https://doi.org/10.1017/S0956796812000093>
use GLOBALS;
use Span;
use edition::{Edition, DEFAULT_EDITION};
use symbol::{keywords, Symbol};
use serialize::{Encodable, Decodable, Encoder, Decoder};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use std::{fmt, mem};
/// A SyntaxContext represents a chain of macro expansions (represented by marks).
#[derive(Clone, Copy, PartialEq, Eq, Default, PartialOrd, Ord, Hash)]
pub struct SyntaxContext(u32);
#[derive(Copy, Clone, Debug)]
struct SyntaxContextData {
outer_mark: Mark,
transparency: Transparency,
prev_ctxt: SyntaxContext,
// This context, but with all transparent and semi-transparent marks filtered away.
opaque: SyntaxContext,
// This context, but with all transparent marks filtered away.
opaque_and_semitransparent: SyntaxContext,
// Name of the crate to which `$crate` with this context would resolve.
dollar_crate_name: Symbol,
}
/// A mark is a unique id associated with a macro expansion.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
pub struct Mark(u32);
#[derive(Clone, Debug)]
struct MarkData {
parent: Mark,
default_transparency: Transparency,
expn_info: Option<ExpnInfo>,
}
/// A property of a macro expansion that determines how identifiers
/// produced by that expansion are resolved.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug)]
pub enum Transparency {
/// Identifier produced by a transparent expansion is always resolved at call-site.
/// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
Transparent,
/// Identifier produced by a semi-transparent expansion may be resolved
/// either at call-site or at definition-site.
/// If it's a local variable, label or `$crate` then it's resolved at def-site.
/// Otherwise it's resolved at call-site.
/// `macro_rules` macros behave like this, built-in macros currently behave like this too,
/// but that's an implementation detail.
SemiTransparent,
/// Identifier produced by an opaque expansion is always resolved at definition-site.
/// Def-site spans in procedural macros, identifiers from `macro` by default use this.
Opaque,
}
impl Mark {
pub fn fresh(parent: Mark) -> Self {
HygieneData::with(|data| {
data.marks.push(MarkData {
parent,
// By default expansions behave like `macro_rules`.
default_transparency: Transparency::SemiTransparent,
expn_info: None,
});
Mark(data.marks.len() as u32 - 1)
})
}
/// The mark of the theoretical expansion that generates freshly parsed, unexpanded AST.
#[inline]
pub fn root() -> Self {
Mark(0)
}
#[inline]
pub fn as_u32(self) -> u32 {
self.0
}
#[inline]
pub fn from_u32(raw: u32) -> Mark {
Mark(raw)
}
#[inline]
pub fn parent(self) -> Mark {
HygieneData::with(|data| data.marks[self.0 as usize].parent)
}
#[inline]
pub fn expn_info(self) -> Option<ExpnInfo> {
HygieneData::with(|data| data.marks[self.0 as usize].expn_info.clone())
}
#[inline]
pub fn set_expn_info(self, info: ExpnInfo) {
HygieneData::with(|data| data.marks[self.0 as usize].expn_info = Some(info))
}
#[inline]
pub fn set_default_transparency(self, transparency: Transparency) {
assert_ne!(self, Mark::root());
HygieneData::with(|data| data.marks[self.0 as usize].default_transparency = transparency)
}
pub fn is_descendant_of(mut self, ancestor: Mark) -> bool {
HygieneData::with(|data| {
while self != ancestor {
if self == Mark::root() {
return false;
}
self = data.marks[self.0 as usize].parent;
}
true
})
}
/// Computes a mark such that both input marks are descendants of (or equal to) the returned
/// mark. That is, the following holds:
///
/// ```rust
/// let la = least_ancestor(a, b);
/// assert!(a.is_descendant_of(la))
/// assert!(b.is_descendant_of(la))
/// ```
pub fn least_ancestor(mut a: Mark, mut b: Mark) -> Mark {
HygieneData::with(|data| {
// Compute the path from a to the root
let mut a_path = FxHashSet::<Mark>::default();
while a != Mark::root() {
a_path.insert(a);
a = data.marks[a.0 as usize].parent;
}
// While the path from b to the root hasn't intersected, move up the tree
while !a_path.contains(&b) {
b = data.marks[b.0 as usize].parent;
}
b
})
}
// Used for enabling some compatibility fallback in resolve.
#[inline]
pub fn looks_like_proc_macro_derive(self) -> bool {
HygieneData::with(|data| {
let mark_data = &data.marks[self.0 as usize];
if mark_data.default_transparency == Transparency::Opaque {
if let Some(expn_info) = &mark_data.expn_info {
if let ExpnFormat::MacroAttribute(name) = expn_info.format {
if name.as_str().starts_with("derive(") {
return true;
}
}
}
}
false
})
}
}
#[derive(Debug)]
crate struct HygieneData {
marks: Vec<MarkData>,
syntax_contexts: Vec<SyntaxContextData>,
markings: FxHashMap<(SyntaxContext, Mark, Transparency), SyntaxContext>,
default_edition: Edition,
}
impl HygieneData {
crate fn new() -> Self {
HygieneData {
marks: vec![MarkData {
parent: Mark::root(),
// If the root is opaque, then loops searching for an opaque mark
// will automatically stop after reaching it.
default_transparency: Transparency::Opaque,
expn_info: None,
}],
syntax_contexts: vec![SyntaxContextData {
outer_mark: Mark::root(),
transparency: Transparency::Opaque,
prev_ctxt: SyntaxContext(0),
opaque: SyntaxContext(0),
opaque_and_semitransparent: SyntaxContext(0),
dollar_crate_name: keywords::DollarCrate.name(),
}],
markings: FxHashMap::default(),
default_edition: DEFAULT_EDITION,
}
}
fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
}
}
pub fn default_edition() -> Edition {
HygieneData::with(|data| data.default_edition)
}
pub fn set_default_edition(edition: Edition) {
HygieneData::with(|data| data.default_edition = edition);
}
pub fn clear_markings() {
HygieneData::with(|data| data.markings = FxHashMap::default());
}
impl SyntaxContext {
pub const fn empty() -> Self {
SyntaxContext(0)
}
crate fn as_u32(self) -> u32 {
self.0
}
crate fn from_u32(raw: u32) -> SyntaxContext {
SyntaxContext(raw)
}
// Allocate a new SyntaxContext with the given ExpnInfo. This is used when
// deserializing Spans from the incr. comp. cache.
// FIXME(mw): This method does not restore MarkData::parent or
// SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things
// don't seem to be used after HIR lowering, so everything should be fine
// as long as incremental compilation does not kick in before that.
pub fn allocate_directly(expansion_info: ExpnInfo) -> Self {
HygieneData::with(|data| {
data.marks.push(MarkData {
parent: Mark::root(),
default_transparency: Transparency::SemiTransparent,
expn_info: Some(expansion_info),
});
let mark = Mark(data.marks.len() as u32 - 1);
data.syntax_contexts.push(SyntaxContextData {
outer_mark: mark,
transparency: Transparency::SemiTransparent,
prev_ctxt: SyntaxContext::empty(),
opaque: SyntaxContext::empty(),
opaque_and_semitransparent: SyntaxContext::empty(),
dollar_crate_name: keywords::DollarCrate.name(),
});
SyntaxContext(data.syntax_contexts.len() as u32 - 1)
})
}
/// Extend a syntax context with a given mark and default transparency for that mark.
pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
assert_ne!(mark, Mark::root());
self.apply_mark_with_transparency(
mark, HygieneData::with(|data| data.marks[mark.0 as usize].default_transparency)
)
}
/// Extend a syntax context with a given mark and transparency
pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency)
-> SyntaxContext {
assert_ne!(mark, Mark::root());
if transparency == Transparency::Opaque {
return self.apply_mark_internal(mark, transparency);
}
let call_site_ctxt =
mark.expn_info().map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
let call_site_ctxt = if transparency == Transparency::SemiTransparent {
call_site_ctxt.modern()
} else {
call_site_ctxt.modern_and_legacy()
};
if call_site_ctxt == SyntaxContext::empty() {
return self.apply_mark_internal(mark, transparency);
}
// Otherwise, `mark` is a macros 1.0 definition and the call site is in a
// macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
//
// In this case, the tokens from the macros 1.0 definition inherit the hygiene
// at their invocation. That is, we pretend that the macros 1.0 definition
// was defined at its invocation (i.e., inside the macros 2.0 definition)
// so that the macros 2.0 definition remains hygienic.
//
// See the example at `test/run-pass/hygiene/legacy_interaction.rs`.
let mut ctxt = call_site_ctxt;
for (mark, transparency) in self.marks() {
ctxt = ctxt.apply_mark_internal(mark, transparency);
}
ctxt.apply_mark_internal(mark, transparency)
}
fn apply_mark_internal(self, mark: Mark, transparency: Transparency) -> SyntaxContext {
HygieneData::with(|data| {
let syntax_contexts = &mut data.syntax_contexts;
let mut opaque = syntax_contexts[self.0 as usize].opaque;
let mut opaque_and_semitransparent =
syntax_contexts[self.0 as usize].opaque_and_semitransparent;
if transparency >= Transparency::Opaque {
let prev_ctxt = opaque;
opaque = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
let new_opaque = SyntaxContext(syntax_contexts.len() as u32);
syntax_contexts.push(SyntaxContextData {
outer_mark: mark,
transparency,
prev_ctxt,
opaque: new_opaque,
opaque_and_semitransparent: new_opaque,
dollar_crate_name: keywords::DollarCrate.name(),
});
new_opaque
});
}
if transparency >= Transparency::SemiTransparent {
let prev_ctxt = opaque_and_semitransparent;
opaque_and_semitransparent =
*data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
let new_opaque_and_semitransparent =
SyntaxContext(syntax_contexts.len() as u32);
syntax_contexts.push(SyntaxContextData {
outer_mark: mark,
transparency,
prev_ctxt,
opaque,
opaque_and_semitransparent: new_opaque_and_semitransparent,
dollar_crate_name: keywords::DollarCrate.name(),
});
new_opaque_and_semitransparent
});
}
let prev_ctxt = self;
*data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
let new_opaque_and_semitransparent_and_transparent =
SyntaxContext(syntax_contexts.len() as u32);
syntax_contexts.push(SyntaxContextData {
outer_mark: mark,
transparency,
prev_ctxt,
opaque,
opaque_and_semitransparent,
dollar_crate_name: keywords::DollarCrate.name(),
});
new_opaque_and_semitransparent_and_transparent
})
})
}
/// Pulls a single mark off of the syntax context. This effectively moves the
/// context up one macro definition level. That is, if we have a nested macro
/// definition as follows:
///
/// ```rust
/// macro_rules! f {
/// macro_rules! g {
/// ...
/// }
/// }
/// ```
///
/// and we have a SyntaxContext that is referring to something declared by an invocation
/// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
/// invocation of f that created g1.
/// Returns the mark that was removed.
pub fn remove_mark(&mut self) -> Mark {
HygieneData::with(|data| {
let outer_mark = data.syntax_contexts[self.0 as usize].outer_mark;
*self = data.syntax_contexts[self.0 as usize].prev_ctxt;
outer_mark
})
}
pub fn marks(mut self) -> Vec<(Mark, Transparency)> {
HygieneData::with(|data| {
let mut marks = Vec::new();
while self != SyntaxContext::empty() {
let ctxt_data = &data.syntax_contexts[self.0 as usize];
marks.push((ctxt_data.outer_mark, ctxt_data.transparency));
self = ctxt_data.prev_ctxt;
}
marks.reverse();
marks
})
}
/// Adjust this context for resolution in a scope created by the given expansion.
/// For example, consider the following three resolutions of `f`:
///
/// ```rust
/// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
/// m!(f);
/// macro m($f:ident) {
/// mod bar {
/// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
/// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
/// }
/// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
/// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
/// //| and it resolves to `::foo::f`.
/// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
/// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
/// //| and it resolves to `::bar::f`.
/// bar::$f(); // `f`'s `SyntaxContext` is empty.
/// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
/// //| and it resolves to `::bar::$f`.
/// }
/// ```
/// This returns the expansion whose definition scope we use to privacy check the resolution,
/// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
pub fn adjust(&mut self, expansion: Mark) -> Option<Mark> {
let mut scope = None;
while !expansion.is_descendant_of(self.outer()) {
scope = Some(self.remove_mark());
}
scope
}
/// Adjust this context for resolution in a scope created by the given expansion
/// via a glob import with the given `SyntaxContext`.
/// For example:
///
/// ```rust
/// m!(f);
/// macro m($i:ident) {
/// mod foo {
/// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
/// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
/// }
/// n(f);
/// macro n($j:ident) {
/// use foo::*;
/// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
/// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
/// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
/// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
/// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
/// //^ This cannot be glob-adjusted, so this is a resolution error.
/// }
/// }
/// ```
/// This returns `None` if the context cannot be glob-adjusted.
/// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
pub fn glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext)
-> Option<Option<Mark>> {
let mut scope = None;
while !expansion.is_descendant_of(glob_ctxt.outer()) {
scope = Some(glob_ctxt.remove_mark());
if self.remove_mark() != scope.unwrap() {
return None;
}
}
if self.adjust(expansion).is_some() {
return None;
}
Some(scope)
}
/// Undo `glob_adjust` if possible:
///
/// ```rust
/// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
/// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
/// }
/// ```
pub fn reverse_glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext)
-> Option<Option<Mark>> {
if self.adjust(expansion).is_some() {
return None;
}
let mut marks = Vec::new();
while !expansion.is_descendant_of(glob_ctxt.outer()) {
marks.push(glob_ctxt.remove_mark());
}
let scope = marks.last().cloned();
while let Some(mark) = marks.pop() {
*self = self.apply_mark(mark);
}
Some(scope)
}
#[inline]
pub fn modern(self) -> SyntaxContext {
HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque)
}
#[inline]
pub fn modern_and_legacy(self) -> SyntaxContext {
HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque_and_semitransparent)
}
#[inline]
pub fn outer(self) -> Mark {
HygieneData::with(|data| data.syntax_contexts[self.0 as usize].outer_mark)
}
pub fn dollar_crate_name(self) -> Symbol {
HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name)
}
pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) {
HygieneData::with(|data| {
let prev_dollar_crate_name = mem::replace(
&mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name
);
assert!(dollar_crate_name == prev_dollar_crate_name ||
prev_dollar_crate_name == keywords::DollarCrate.name(),
"$crate name is reset for a syntax context");
})
}
}
impl fmt::Debug for SyntaxContext {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "#{}", self.0)
}
}
/// Extra information for tracking spans of macro and syntax sugar expansion
#[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)]
pub struct ExpnInfo {
/// The location of the actual macro invocation or syntax sugar , e.g.
/// `let x = foo!();` or `if let Some(y) = x {}`
///
/// This may recursively refer to other macro invocations, e.g., if
/// `foo!()` invoked `bar!()` internally, and there was an
/// expression inside `bar!`; the call_site of the expression in
/// the expansion would point to the `bar!` invocation; that
/// call_site span would have its own ExpnInfo, with the call_site
/// pointing to the `foo!` invocation.
pub call_site: Span,
/// The span of the macro definition itself. The macro may not
/// have a sensible definition span (e.g., something defined
/// completely inside libsyntax) in which case this is None.
/// This span serves only informational purpose and is not used for resolution.
pub def_site: Option<Span>,
/// The format with which the macro was invoked.
pub format: ExpnFormat,
/// Whether the macro is allowed to use #[unstable]/feature-gated
/// features internally without forcing the whole crate to opt-in
/// to them.
pub allow_internal_unstable: bool,
/// Whether the macro is allowed to use `unsafe` internally
/// even if the user crate has `#![forbid(unsafe_code)]`.
pub allow_internal_unsafe: bool,
/// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
/// for a given macro.
pub local_inner_macros: bool,
/// Edition of the crate in which the macro is defined.
pub edition: Edition,
}
/// The source of expansion.
#[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
pub enum ExpnFormat {
/// e.g., #[derive(...)] <item>
MacroAttribute(Symbol),
/// e.g., `format!()`
MacroBang(Symbol),
/// Desugaring done by the compiler during HIR lowering.
CompilerDesugaring(CompilerDesugaringKind)
}
impl ExpnFormat {
pub fn name(&self) -> Symbol {
match *self {
ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name,
ExpnFormat::CompilerDesugaring(kind) => kind.name(),
}
}
}
/// The kind of compiler desugaring.
#[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
pub enum CompilerDesugaringKind {
QuestionMark,
TryBlock,
/// Desugaring of an `impl Trait` in return type position
/// to an `existential type Foo: Trait;` + replacing the
/// `impl Trait` with `Foo`.
ExistentialReturnType,
Async,
ForLoop,
}
impl CompilerDesugaringKind {
pub fn name(self) -> Symbol {
Symbol::intern(match self {
CompilerDesugaringKind::Async => "async",
CompilerDesugaringKind::QuestionMark => "?",
CompilerDesugaringKind::TryBlock => "try block",
CompilerDesugaringKind::ExistentialReturnType => "existential type",
CompilerDesugaringKind::ForLoop => "for loop",
})
}
}
impl Encodable for SyntaxContext {
fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
Ok(()) // FIXME(jseyfried) intercrate hygiene
}
}
impl Decodable for SyntaxContext {
fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene
}
}