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;
11 use crate::symbol::{kw, 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.expn_info(self))
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(self, ancestor: Mark) -> bool {
116 HygieneData::with(|data| data.is_descendant_of(self, ancestor))
119 /// `mark.outer_is_descendant_of(ctxt)` is equivalent to but faster than
120 /// `mark.is_descendant_of(ctxt.outer())`.
121 pub fn outer_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
122 HygieneData::with(|data| data.is_descendant_of(self, data.outer(ctxt)))
125 /// Computes a mark such that both input marks are descendants of (or equal to) the returned
126 /// mark. That is, the following holds:
129 /// let la = least_ancestor(a, b);
130 /// assert!(a.is_descendant_of(la))
131 /// assert!(b.is_descendant_of(la))
133 pub fn least_ancestor(mut a: Mark, mut b: Mark) -> Mark {
134 HygieneData::with(|data| {
135 // Compute the path from a to the root
136 let mut a_path = FxHashSet::<Mark>::default();
137 while a != Mark::root() {
139 a = data.marks[a.0 as usize].parent;
142 // While the path from b to the root hasn't intersected, move up the tree
143 while !a_path.contains(&b) {
144 b = data.marks[b.0 as usize].parent;
151 // Used for enabling some compatibility fallback in resolve.
153 pub fn looks_like_proc_macro_derive(self) -> bool {
154 HygieneData::with(|data| {
155 let mark_data = &data.marks[self.0 as usize];
156 if mark_data.default_transparency == Transparency::Opaque {
157 if let Some(expn_info) = &mark_data.expn_info {
158 if let ExpnFormat::MacroAttribute(name) = expn_info.format {
159 if name.as_str().starts_with("derive(") {
171 crate struct HygieneData {
172 marks: Vec<MarkData>,
173 syntax_contexts: Vec<SyntaxContextData>,
174 markings: FxHashMap<(SyntaxContext, Mark, Transparency), SyntaxContext>,
178 crate fn new() -> Self {
180 marks: vec![MarkData {
181 parent: Mark::root(),
182 // If the root is opaque, then loops searching for an opaque mark
183 // will automatically stop after reaching it.
184 default_transparency: Transparency::Opaque,
187 syntax_contexts: vec![SyntaxContextData {
188 outer_mark: Mark::root(),
189 transparency: Transparency::Opaque,
190 prev_ctxt: SyntaxContext(0),
191 opaque: SyntaxContext(0),
192 opaque_and_semitransparent: SyntaxContext(0),
193 dollar_crate_name: kw::DollarCrate,
195 markings: FxHashMap::default(),
199 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
200 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
203 fn expn_info(&self, mark: Mark) -> Option<ExpnInfo> {
204 self.marks[mark.0 as usize].expn_info.clone()
207 fn is_descendant_of(&self, mut mark: Mark, ancestor: Mark) -> bool {
208 while mark != ancestor {
209 if mark == Mark::root() {
212 mark = self.marks[mark.0 as usize].parent;
217 fn default_transparency(&self, mark: Mark) -> Transparency {
218 self.marks[mark.0 as usize].default_transparency
221 fn modern(&self, ctxt: SyntaxContext) -> SyntaxContext {
222 self.syntax_contexts[ctxt.0 as usize].opaque
225 fn modern_and_legacy(&self, ctxt: SyntaxContext) -> SyntaxContext {
226 self.syntax_contexts[ctxt.0 as usize].opaque_and_semitransparent
229 fn outer(&self, ctxt: SyntaxContext) -> Mark {
230 self.syntax_contexts[ctxt.0 as usize].outer_mark
233 fn transparency(&self, ctxt: SyntaxContext) -> Transparency {
234 self.syntax_contexts[ctxt.0 as usize].transparency
237 fn prev_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
238 self.syntax_contexts[ctxt.0 as usize].prev_ctxt
241 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> Mark {
242 let outer_mark = self.syntax_contexts[ctxt.0 as usize].outer_mark;
243 *ctxt = self.prev_ctxt(*ctxt);
247 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(Mark, Transparency)> {
248 let mut marks = Vec::new();
249 while ctxt != SyntaxContext::empty() {
250 let outer_mark = self.outer(ctxt);
251 let transparency = self.transparency(ctxt);
252 let prev_ctxt = self.prev_ctxt(ctxt);
253 marks.push((outer_mark, transparency));
260 fn adjust(&self, ctxt: &mut SyntaxContext, expansion: Mark) -> Option<Mark> {
261 let mut scope = None;
262 while !self.is_descendant_of(expansion, self.outer(*ctxt)) {
263 scope = Some(self.remove_mark(ctxt));
268 fn apply_mark_with_transparency(&mut self, ctxt: SyntaxContext, mark: Mark,
269 transparency: Transparency) -> SyntaxContext {
270 assert_ne!(mark, Mark::root());
271 if transparency == Transparency::Opaque {
272 return self.apply_mark_internal(ctxt, mark, transparency);
276 self.expn_info(mark).map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
277 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
278 self.modern(call_site_ctxt)
280 self.modern_and_legacy(call_site_ctxt)
283 if call_site_ctxt == SyntaxContext::empty() {
284 return self.apply_mark_internal(ctxt, mark, transparency);
287 // Otherwise, `mark` is a macros 1.0 definition and the call site is in a
288 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
290 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
291 // at their invocation. That is, we pretend that the macros 1.0 definition
292 // was defined at its invocation (i.e., inside the macros 2.0 definition)
293 // so that the macros 2.0 definition remains hygienic.
295 // See the example at `test/run-pass/hygiene/legacy_interaction.rs`.
296 for (mark, transparency) in self.marks(ctxt) {
297 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, mark, transparency);
299 self.apply_mark_internal(call_site_ctxt, mark, transparency)
302 fn apply_mark_internal(&mut self, ctxt: SyntaxContext, mark: Mark, transparency: Transparency)
304 let syntax_contexts = &mut self.syntax_contexts;
305 let mut opaque = syntax_contexts[ctxt.0 as usize].opaque;
306 let mut opaque_and_semitransparent =
307 syntax_contexts[ctxt.0 as usize].opaque_and_semitransparent;
309 if transparency >= Transparency::Opaque {
310 let prev_ctxt = opaque;
311 opaque = *self.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
312 let new_opaque = SyntaxContext(syntax_contexts.len() as u32);
313 syntax_contexts.push(SyntaxContextData {
318 opaque_and_semitransparent: new_opaque,
319 dollar_crate_name: kw::DollarCrate,
325 if transparency >= Transparency::SemiTransparent {
326 let prev_ctxt = opaque_and_semitransparent;
327 opaque_and_semitransparent =
328 *self.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
329 let new_opaque_and_semitransparent =
330 SyntaxContext(syntax_contexts.len() as u32);
331 syntax_contexts.push(SyntaxContextData {
336 opaque_and_semitransparent: new_opaque_and_semitransparent,
337 dollar_crate_name: kw::DollarCrate,
339 new_opaque_and_semitransparent
343 let prev_ctxt = ctxt;
344 *self.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
345 let new_opaque_and_semitransparent_and_transparent =
346 SyntaxContext(syntax_contexts.len() as u32);
347 syntax_contexts.push(SyntaxContextData {
352 opaque_and_semitransparent,
353 dollar_crate_name: kw::DollarCrate,
355 new_opaque_and_semitransparent_and_transparent
360 pub fn clear_markings() {
361 HygieneData::with(|data| data.markings = FxHashMap::default());
366 pub const fn empty() -> Self {
371 crate fn as_u32(self) -> u32 {
376 crate fn from_u32(raw: u32) -> SyntaxContext {
380 // Allocate a new SyntaxContext with the given ExpnInfo. This is used when
381 // deserializing Spans from the incr. comp. cache.
382 // FIXME(mw): This method does not restore MarkData::parent or
383 // SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things
384 // don't seem to be used after HIR lowering, so everything should be fine
385 // as long as incremental compilation does not kick in before that.
386 pub fn allocate_directly(expansion_info: ExpnInfo) -> Self {
387 HygieneData::with(|data| {
388 data.marks.push(MarkData {
389 parent: Mark::root(),
390 default_transparency: Transparency::SemiTransparent,
391 expn_info: Some(expansion_info),
394 let mark = Mark(data.marks.len() as u32 - 1);
396 data.syntax_contexts.push(SyntaxContextData {
398 transparency: Transparency::SemiTransparent,
399 prev_ctxt: SyntaxContext::empty(),
400 opaque: SyntaxContext::empty(),
401 opaque_and_semitransparent: SyntaxContext::empty(),
402 dollar_crate_name: kw::DollarCrate,
404 SyntaxContext(data.syntax_contexts.len() as u32 - 1)
408 /// Extend a syntax context with a given mark and default transparency for that mark.
409 pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
410 assert_ne!(mark, Mark::root());
411 self.apply_mark_with_transparency(
412 mark, HygieneData::with(|data| data.default_transparency(mark))
416 /// Extend a syntax context with a given mark and transparency
417 pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency)
419 HygieneData::with(|data| data.apply_mark_with_transparency(self, mark, transparency))
422 /// Pulls a single mark off of the syntax context. This effectively moves the
423 /// context up one macro definition level. That is, if we have a nested macro
424 /// definition as follows:
434 /// and we have a SyntaxContext that is referring to something declared by an invocation
435 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
436 /// invocation of f that created g1.
437 /// Returns the mark that was removed.
438 pub fn remove_mark(&mut self) -> Mark {
439 HygieneData::with(|data| data.remove_mark(self))
442 pub fn marks(self) -> Vec<(Mark, Transparency)> {
443 HygieneData::with(|data| data.marks(self))
446 /// Adjust this context for resolution in a scope created by the given expansion.
447 /// For example, consider the following three resolutions of `f`:
450 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
452 /// macro m($f:ident) {
454 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
455 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
457 /// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
458 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
459 /// //| and it resolves to `::foo::f`.
460 /// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
461 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
462 /// //| and it resolves to `::bar::f`.
463 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
464 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
465 /// //| and it resolves to `::bar::$f`.
468 /// This returns the expansion whose definition scope we use to privacy check the resolution,
469 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
470 pub fn adjust(&mut self, expansion: Mark) -> Option<Mark> {
471 HygieneData::with(|data| data.adjust(self, expansion))
474 /// Adjust this context for resolution in a scope created by the given expansion
475 /// via a glob import with the given `SyntaxContext`.
480 /// macro m($i:ident) {
482 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
483 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
486 /// macro n($j:ident) {
488 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
489 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
490 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
491 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
492 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
493 /// //^ This cannot be glob-adjusted, so this is a resolution error.
497 /// This returns `None` if the context cannot be glob-adjusted.
498 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
499 pub fn glob_adjust(&mut self, expansion: Mark, glob_span: Span) -> Option<Option<Mark>> {
500 let mut scope = None;
501 let mut glob_ctxt = glob_span.ctxt().modern();
502 while !expansion.outer_is_descendant_of(glob_ctxt) {
503 scope = Some(glob_ctxt.remove_mark());
504 if self.remove_mark() != scope.unwrap() {
508 if self.adjust(expansion).is_some() {
514 /// Undo `glob_adjust` if possible:
517 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
518 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
521 pub fn reverse_glob_adjust(&mut self, expansion: Mark, glob_span: Span)
522 -> Option<Option<Mark>> {
523 if self.adjust(expansion).is_some() {
527 let mut glob_ctxt = glob_span.ctxt().modern();
528 let mut marks = Vec::new();
529 while !expansion.outer_is_descendant_of(glob_ctxt) {
530 marks.push(glob_ctxt.remove_mark());
533 let scope = marks.last().cloned();
534 while let Some(mark) = marks.pop() {
535 *self = self.apply_mark(mark);
541 pub fn modern(self) -> SyntaxContext {
542 HygieneData::with(|data| data.modern(self))
546 pub fn modern_and_legacy(self) -> SyntaxContext {
547 HygieneData::with(|data| data.modern_and_legacy(self))
551 pub fn outer(self) -> Mark {
552 HygieneData::with(|data| data.outer(self))
555 /// `ctxt.outer_expn_info()` is equivalent to but faster than
556 /// `ctxt.outer().expn_info()`.
558 pub fn outer_expn_info(self) -> Option<ExpnInfo> {
559 HygieneData::with(|data| data.expn_info(data.outer(self)))
562 pub fn dollar_crate_name(self) -> Symbol {
563 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name)
566 pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) {
567 HygieneData::with(|data| {
568 let prev_dollar_crate_name = mem::replace(
569 &mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name
571 assert!(dollar_crate_name == prev_dollar_crate_name ||
572 prev_dollar_crate_name == kw::DollarCrate,
573 "$crate name is reset for a syntax context");
578 impl fmt::Debug for SyntaxContext {
579 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
580 write!(f, "#{}", self.0)
584 /// Extra information for tracking spans of macro and syntax sugar expansion
585 #[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)]
586 pub struct ExpnInfo {
587 /// The location of the actual macro invocation or syntax sugar , e.g.
588 /// `let x = foo!();` or `if let Some(y) = x {}`
590 /// This may recursively refer to other macro invocations, e.g., if
591 /// `foo!()` invoked `bar!()` internally, and there was an
592 /// expression inside `bar!`; the call_site of the expression in
593 /// the expansion would point to the `bar!` invocation; that
594 /// call_site span would have its own ExpnInfo, with the call_site
595 /// pointing to the `foo!` invocation.
597 /// The span of the macro definition itself. The macro may not
598 /// have a sensible definition span (e.g., something defined
599 /// completely inside libsyntax) in which case this is None.
600 /// This span serves only informational purpose and is not used for resolution.
601 pub def_site: Option<Span>,
602 /// The format with which the macro was invoked.
603 pub format: ExpnFormat,
604 /// List of #[unstable]/feature-gated features that the macro is allowed to use
605 /// internally without forcing the whole crate to opt-in
607 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
608 /// Whether the macro is allowed to use `unsafe` internally
609 /// even if the user crate has `#![forbid(unsafe_code)]`.
610 pub allow_internal_unsafe: bool,
611 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
612 /// for a given macro.
613 pub local_inner_macros: bool,
614 /// Edition of the crate in which the macro is defined.
615 pub edition: Edition,
618 /// The source of expansion.
619 #[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
620 pub enum ExpnFormat {
621 /// e.g., #[derive(...)] <item>
622 MacroAttribute(Symbol),
623 /// e.g., `format!()`
625 /// Desugaring done by the compiler during HIR lowering.
626 CompilerDesugaring(CompilerDesugaringKind)
630 pub fn name(&self) -> Symbol {
632 ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name,
633 ExpnFormat::CompilerDesugaring(kind) => kind.name(),
638 /// The kind of compiler desugaring.
639 #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
640 pub enum CompilerDesugaringKind {
641 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
642 /// However, we do not want to blame `c` for unreachability but rather say that `i`
643 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
647 /// Desugaring of an `impl Trait` in return type position
648 /// to an `existential type Foo: Trait;` and replacing the
649 /// `impl Trait` with `Foo`.
650 ExistentialReturnType,
656 impl CompilerDesugaringKind {
657 pub fn name(self) -> Symbol {
658 Symbol::intern(match self {
659 CompilerDesugaringKind::IfTemporary => "if",
660 CompilerDesugaringKind::Async => "async",
661 CompilerDesugaringKind::Await => "await",
662 CompilerDesugaringKind::QuestionMark => "?",
663 CompilerDesugaringKind::TryBlock => "try block",
664 CompilerDesugaringKind::ExistentialReturnType => "existential type",
665 CompilerDesugaringKind::ForLoop => "for loop",
670 impl Encodable for SyntaxContext {
671 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
672 Ok(()) // FIXME(jseyfried) intercrate hygiene
676 impl Decodable for SyntaxContext {
677 fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
678 Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene