1 //! Machinery for hygienic macros, inspired by the `MTWT[1]` paper.
3 //! `[1]` Matthew Flatt, Ryan Culpepper, David Darais, and Robert Bruce Findler. 2012.
4 //! *Macros that work together: Compile-time bindings, partial expansion,
5 //! and definition contexts*. J. Funct. Program. 22, 2 (March 2012), 181-216.
6 //! DOI=10.1017/S0956796812000093 <https://doi.org/10.1017/S0956796812000093>
10 use crate::edition::{Edition, DEFAULT_EDITION};
11 use crate::symbol::{keywords, Symbol};
13 use serialize::{Encodable, Decodable, Encoder, Decoder};
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_data_structures::sync::Lrc;
18 /// A SyntaxContext represents a chain of macro expansions (represented by marks).
19 #[derive(Clone, Copy, PartialEq, Eq, Default, PartialOrd, Ord, Hash)]
20 pub struct SyntaxContext(u32);
22 #[derive(Copy, Clone, Debug)]
23 struct SyntaxContextData {
25 transparency: Transparency,
26 prev_ctxt: SyntaxContext,
27 /// This context, but with all transparent and semi-transparent marks filtered away.
28 opaque: SyntaxContext,
29 /// This context, but with all transparent marks filtered away.
30 opaque_and_semitransparent: SyntaxContext,
31 /// Name of the crate to which `$crate` with this context would resolve.
32 dollar_crate_name: Symbol,
35 /// A mark is a unique ID associated with a macro expansion.
36 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
39 #[derive(Clone, Debug)]
42 default_transparency: Transparency,
43 expn_info: Option<ExpnInfo>,
46 /// A property of a macro expansion that determines how identifiers
47 /// produced by that expansion are resolved.
48 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug)]
49 pub enum Transparency {
50 /// Identifier produced by a transparent expansion is always resolved at call-site.
51 /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
53 /// Identifier produced by a semi-transparent expansion may be resolved
54 /// either at call-site or at definition-site.
55 /// If it's a local variable, label or `$crate` then it's resolved at def-site.
56 /// Otherwise it's resolved at call-site.
57 /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
58 /// but that's an implementation detail.
60 /// Identifier produced by an opaque expansion is always resolved at definition-site.
61 /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
66 pub fn fresh(parent: Mark) -> Self {
67 HygieneData::with(|data| {
68 data.marks.push(MarkData {
70 // By default expansions behave like `macro_rules`.
71 default_transparency: Transparency::SemiTransparent,
74 Mark(data.marks.len() as u32 - 1)
78 /// The mark of the theoretical expansion that generates freshly parsed, unexpanded AST.
80 pub fn root() -> Self {
85 pub fn as_u32(self) -> u32 {
90 pub fn from_u32(raw: u32) -> Mark {
95 pub fn parent(self) -> Mark {
96 HygieneData::with(|data| data.marks[self.0 as usize].parent)
100 pub fn expn_info(self) -> Option<ExpnInfo> {
101 HygieneData::with(|data| data.marks[self.0 as usize].expn_info.clone())
105 pub fn set_expn_info(self, info: ExpnInfo) {
106 HygieneData::with(|data| data.marks[self.0 as usize].expn_info = Some(info))
110 pub fn set_default_transparency(self, transparency: Transparency) {
111 assert_ne!(self, Mark::root());
112 HygieneData::with(|data| data.marks[self.0 as usize].default_transparency = transparency)
115 pub fn is_descendant_of(mut self, ancestor: Mark) -> bool {
116 HygieneData::with(|data| {
117 while self != ancestor {
118 if self == Mark::root() {
121 self = data.marks[self.0 as usize].parent;
127 /// Computes a mark such that both input marks are descendants of (or equal to) the returned
128 /// mark. That is, the following holds:
131 /// let la = least_ancestor(a, b);
132 /// assert!(a.is_descendant_of(la))
133 /// assert!(b.is_descendant_of(la))
135 pub fn least_ancestor(mut a: Mark, mut b: Mark) -> Mark {
136 HygieneData::with(|data| {
137 // Compute the path from a to the root
138 let mut a_path = FxHashSet::<Mark>::default();
139 while a != Mark::root() {
141 a = data.marks[a.0 as usize].parent;
144 // While the path from b to the root hasn't intersected, move up the tree
145 while !a_path.contains(&b) {
146 b = data.marks[b.0 as usize].parent;
153 // Used for enabling some compatibility fallback in resolve.
155 pub fn looks_like_proc_macro_derive(self) -> bool {
156 HygieneData::with(|data| {
157 let mark_data = &data.marks[self.0 as usize];
158 if mark_data.default_transparency == Transparency::Opaque {
159 if let Some(expn_info) = &mark_data.expn_info {
160 if let ExpnFormat::MacroAttribute(name) = expn_info.format {
161 if name.as_str().starts_with("derive(") {
173 crate struct HygieneData {
174 marks: Vec<MarkData>,
175 syntax_contexts: Vec<SyntaxContextData>,
176 markings: FxHashMap<(SyntaxContext, Mark, Transparency), SyntaxContext>,
177 default_edition: Edition,
181 crate fn new() -> Self {
183 marks: vec![MarkData {
184 parent: Mark::root(),
185 // If the root is opaque, then loops searching for an opaque mark
186 // will automatically stop after reaching it.
187 default_transparency: Transparency::Opaque,
190 syntax_contexts: vec![SyntaxContextData {
191 outer_mark: Mark::root(),
192 transparency: Transparency::Opaque,
193 prev_ctxt: SyntaxContext(0),
194 opaque: SyntaxContext(0),
195 opaque_and_semitransparent: SyntaxContext(0),
196 dollar_crate_name: keywords::DollarCrate.name(),
198 markings: FxHashMap::default(),
199 default_edition: DEFAULT_EDITION,
203 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
204 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
208 pub fn default_edition() -> Edition {
209 HygieneData::with(|data| data.default_edition)
212 pub fn set_default_edition(edition: Edition) {
213 HygieneData::with(|data| data.default_edition = edition);
216 pub fn clear_markings() {
217 HygieneData::with(|data| data.markings = FxHashMap::default());
222 pub const fn empty() -> Self {
227 crate fn as_u32(self) -> u32 {
232 crate fn from_u32(raw: u32) -> SyntaxContext {
236 // Allocate a new SyntaxContext with the given ExpnInfo. This is used when
237 // deserializing Spans from the incr. comp. cache.
238 // FIXME(mw): This method does not restore MarkData::parent or
239 // SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things
240 // don't seem to be used after HIR lowering, so everything should be fine
241 // as long as incremental compilation does not kick in before that.
242 pub fn allocate_directly(expansion_info: ExpnInfo) -> Self {
243 HygieneData::with(|data| {
244 data.marks.push(MarkData {
245 parent: Mark::root(),
246 default_transparency: Transparency::SemiTransparent,
247 expn_info: Some(expansion_info),
250 let mark = Mark(data.marks.len() as u32 - 1);
252 data.syntax_contexts.push(SyntaxContextData {
254 transparency: Transparency::SemiTransparent,
255 prev_ctxt: SyntaxContext::empty(),
256 opaque: SyntaxContext::empty(),
257 opaque_and_semitransparent: SyntaxContext::empty(),
258 dollar_crate_name: keywords::DollarCrate.name(),
260 SyntaxContext(data.syntax_contexts.len() as u32 - 1)
264 /// Extend a syntax context with a given mark and default transparency for that mark.
265 pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
266 assert_ne!(mark, Mark::root());
267 self.apply_mark_with_transparency(
268 mark, HygieneData::with(|data| data.marks[mark.0 as usize].default_transparency)
272 /// Extend a syntax context with a given mark and transparency
273 pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency)
275 assert_ne!(mark, Mark::root());
276 if transparency == Transparency::Opaque {
277 return self.apply_mark_internal(mark, transparency);
281 mark.expn_info().map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
282 let call_site_ctxt = if transparency == Transparency::SemiTransparent {
283 call_site_ctxt.modern()
285 call_site_ctxt.modern_and_legacy()
288 if call_site_ctxt == SyntaxContext::empty() {
289 return self.apply_mark_internal(mark, transparency);
292 // Otherwise, `mark` is a macros 1.0 definition and the call site is in a
293 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
295 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
296 // at their invocation. That is, we pretend that the macros 1.0 definition
297 // was defined at its invocation (i.e., inside the macros 2.0 definition)
298 // so that the macros 2.0 definition remains hygienic.
300 // See the example at `test/run-pass/hygiene/legacy_interaction.rs`.
301 let mut ctxt = call_site_ctxt;
302 for (mark, transparency) in self.marks() {
303 ctxt = ctxt.apply_mark_internal(mark, transparency);
305 ctxt.apply_mark_internal(mark, transparency)
308 fn apply_mark_internal(self, mark: Mark, transparency: Transparency) -> SyntaxContext {
309 HygieneData::with(|data| {
310 let syntax_contexts = &mut data.syntax_contexts;
311 let mut opaque = syntax_contexts[self.0 as usize].opaque;
312 let mut opaque_and_semitransparent =
313 syntax_contexts[self.0 as usize].opaque_and_semitransparent;
315 if transparency >= Transparency::Opaque {
316 let prev_ctxt = opaque;
317 opaque = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
318 let new_opaque = SyntaxContext(syntax_contexts.len() as u32);
319 syntax_contexts.push(SyntaxContextData {
324 opaque_and_semitransparent: new_opaque,
325 dollar_crate_name: keywords::DollarCrate.name(),
331 if transparency >= Transparency::SemiTransparent {
332 let prev_ctxt = opaque_and_semitransparent;
333 opaque_and_semitransparent =
334 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
335 let new_opaque_and_semitransparent =
336 SyntaxContext(syntax_contexts.len() as u32);
337 syntax_contexts.push(SyntaxContextData {
342 opaque_and_semitransparent: new_opaque_and_semitransparent,
343 dollar_crate_name: keywords::DollarCrate.name(),
345 new_opaque_and_semitransparent
349 let prev_ctxt = self;
350 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
351 let new_opaque_and_semitransparent_and_transparent =
352 SyntaxContext(syntax_contexts.len() as u32);
353 syntax_contexts.push(SyntaxContextData {
358 opaque_and_semitransparent,
359 dollar_crate_name: keywords::DollarCrate.name(),
361 new_opaque_and_semitransparent_and_transparent
366 /// Pulls a single mark off of the syntax context. This effectively moves the
367 /// context up one macro definition level. That is, if we have a nested macro
368 /// definition as follows:
378 /// and we have a SyntaxContext that is referring to something declared by an invocation
379 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
380 /// invocation of f that created g1.
381 /// Returns the mark that was removed.
382 pub fn remove_mark(&mut self) -> Mark {
383 HygieneData::with(|data| {
384 let outer_mark = data.syntax_contexts[self.0 as usize].outer_mark;
385 *self = data.syntax_contexts[self.0 as usize].prev_ctxt;
390 pub fn marks(mut self) -> Vec<(Mark, Transparency)> {
391 HygieneData::with(|data| {
392 let mut marks = Vec::new();
393 while self != SyntaxContext::empty() {
394 let ctxt_data = &data.syntax_contexts[self.0 as usize];
395 marks.push((ctxt_data.outer_mark, ctxt_data.transparency));
396 self = ctxt_data.prev_ctxt;
403 /// Adjust this context for resolution in a scope created by the given expansion.
404 /// For example, consider the following three resolutions of `f`:
407 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
409 /// macro m($f:ident) {
411 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
412 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
414 /// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
415 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
416 /// //| and it resolves to `::foo::f`.
417 /// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
418 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
419 /// //| and it resolves to `::bar::f`.
420 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
421 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
422 /// //| and it resolves to `::bar::$f`.
425 /// This returns the expansion whose definition scope we use to privacy check the resolution,
426 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
427 pub fn adjust(&mut self, expansion: Mark) -> Option<Mark> {
428 let mut scope = None;
429 while !expansion.is_descendant_of(self.outer()) {
430 scope = Some(self.remove_mark());
435 /// Adjust this context for resolution in a scope created by the given expansion
436 /// via a glob import with the given `SyntaxContext`.
441 /// macro m($i:ident) {
443 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
444 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
447 /// macro n($j:ident) {
449 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
450 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
451 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
452 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
453 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
454 /// //^ This cannot be glob-adjusted, so this is a resolution error.
458 /// This returns `None` if the context cannot be glob-adjusted.
459 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
460 pub fn glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext)
461 -> Option<Option<Mark>> {
462 let mut scope = None;
463 while !expansion.is_descendant_of(glob_ctxt.outer()) {
464 scope = Some(glob_ctxt.remove_mark());
465 if self.remove_mark() != scope.unwrap() {
469 if self.adjust(expansion).is_some() {
475 /// Undo `glob_adjust` if possible:
478 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
479 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
482 pub fn reverse_glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext)
483 -> Option<Option<Mark>> {
484 if self.adjust(expansion).is_some() {
488 let mut marks = Vec::new();
489 while !expansion.is_descendant_of(glob_ctxt.outer()) {
490 marks.push(glob_ctxt.remove_mark());
493 let scope = marks.last().cloned();
494 while let Some(mark) = marks.pop() {
495 *self = self.apply_mark(mark);
501 pub fn modern(self) -> SyntaxContext {
502 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque)
506 pub fn modern_and_legacy(self) -> SyntaxContext {
507 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque_and_semitransparent)
511 pub fn outer(self) -> Mark {
512 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].outer_mark)
515 pub fn dollar_crate_name(self) -> Symbol {
516 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name)
519 pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) {
520 HygieneData::with(|data| {
521 let prev_dollar_crate_name = mem::replace(
522 &mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name
524 assert!(dollar_crate_name == prev_dollar_crate_name ||
525 prev_dollar_crate_name == keywords::DollarCrate.name(),
526 "$crate name is reset for a syntax context");
531 impl fmt::Debug for SyntaxContext {
532 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
533 write!(f, "#{}", self.0)
537 /// Extra information for tracking spans of macro and syntax sugar expansion
538 #[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)]
539 pub struct ExpnInfo {
540 /// The location of the actual macro invocation or syntax sugar , e.g.
541 /// `let x = foo!();` or `if let Some(y) = x {}`
543 /// This may recursively refer to other macro invocations, e.g., if
544 /// `foo!()` invoked `bar!()` internally, and there was an
545 /// expression inside `bar!`; the call_site of the expression in
546 /// the expansion would point to the `bar!` invocation; that
547 /// call_site span would have its own ExpnInfo, with the call_site
548 /// pointing to the `foo!` invocation.
550 /// The span of the macro definition itself. The macro may not
551 /// have a sensible definition span (e.g., something defined
552 /// completely inside libsyntax) in which case this is None.
553 /// This span serves only informational purpose and is not used for resolution.
554 pub def_site: Option<Span>,
555 /// The format with which the macro was invoked.
556 pub format: ExpnFormat,
557 /// List of #[unstable]/feature-gated features that the macro is allowed to use
558 /// internally without forcing the whole crate to opt-in
560 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
561 /// Whether the macro is allowed to use `unsafe` internally
562 /// even if the user crate has `#![forbid(unsafe_code)]`.
563 pub allow_internal_unsafe: bool,
564 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
565 /// for a given macro.
566 pub local_inner_macros: bool,
567 /// Edition of the crate in which the macro is defined.
568 pub edition: Edition,
571 /// The source of expansion.
572 #[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
573 pub enum ExpnFormat {
574 /// e.g., #[derive(...)] <item>
575 MacroAttribute(Symbol),
576 /// e.g., `format!()`
578 /// Desugaring done by the compiler during HIR lowering.
579 CompilerDesugaring(CompilerDesugaringKind)
583 pub fn name(&self) -> Symbol {
585 ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name,
586 ExpnFormat::CompilerDesugaring(kind) => kind.name(),
591 /// The kind of compiler desugaring.
592 #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
593 pub enum CompilerDesugaringKind {
594 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
595 /// However, we do not want to blame `c` for unreachability but rather say that `i`
596 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
600 /// Desugaring of an `impl Trait` in return type position
601 /// to an `existential type Foo: Trait;` and replacing the
602 /// `impl Trait` with `Foo`.
603 ExistentialReturnType,
609 impl CompilerDesugaringKind {
610 pub fn name(self) -> Symbol {
611 Symbol::intern(match self {
612 CompilerDesugaringKind::IfTemporary => "if",
613 CompilerDesugaringKind::Async => "async",
614 CompilerDesugaringKind::Await => "await",
615 CompilerDesugaringKind::QuestionMark => "?",
616 CompilerDesugaringKind::TryBlock => "try block",
617 CompilerDesugaringKind::ExistentialReturnType => "existential type",
618 CompilerDesugaringKind::ForLoop => "for loop",
623 impl Encodable for SyntaxContext {
624 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
625 Ok(()) // FIXME(jseyfried) intercrate hygiene
629 impl Decodable for SyntaxContext {
630 fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
631 Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene