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));
269 pub fn clear_markings() {
270 HygieneData::with(|data| data.markings = FxHashMap::default());
275 pub const fn empty() -> Self {
280 crate fn as_u32(self) -> u32 {
285 crate fn from_u32(raw: u32) -> SyntaxContext {
289 // Allocate a new SyntaxContext with the given ExpnInfo. This is used when
290 // deserializing Spans from the incr. comp. cache.
291 // FIXME(mw): This method does not restore MarkData::parent or
292 // SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things
293 // don't seem to be used after HIR lowering, so everything should be fine
294 // as long as incremental compilation does not kick in before that.
295 pub fn allocate_directly(expansion_info: ExpnInfo) -> Self {
296 HygieneData::with(|data| {
297 data.marks.push(MarkData {
298 parent: Mark::root(),
299 default_transparency: Transparency::SemiTransparent,
300 expn_info: Some(expansion_info),
303 let mark = Mark(data.marks.len() as u32 - 1);
305 data.syntax_contexts.push(SyntaxContextData {
307 transparency: Transparency::SemiTransparent,
308 prev_ctxt: SyntaxContext::empty(),
309 opaque: SyntaxContext::empty(),
310 opaque_and_semitransparent: SyntaxContext::empty(),
311 dollar_crate_name: kw::DollarCrate,
313 SyntaxContext(data.syntax_contexts.len() as u32 - 1)
317 /// Extend a syntax context with a given mark and default transparency for that mark.
318 pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
319 assert_ne!(mark, Mark::root());
320 self.apply_mark_with_transparency(
321 mark, HygieneData::with(|data| data.default_transparency(mark))
325 /// Extend a syntax context with a given mark and transparency
326 pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency)
328 assert_ne!(mark, Mark::root());
329 if transparency == Transparency::Opaque {
330 return self.apply_mark_internal(mark, transparency);
334 mark.expn_info().map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
335 let call_site_ctxt = if transparency == Transparency::SemiTransparent {
336 call_site_ctxt.modern()
338 call_site_ctxt.modern_and_legacy()
341 if call_site_ctxt == SyntaxContext::empty() {
342 return self.apply_mark_internal(mark, transparency);
345 // Otherwise, `mark` is a macros 1.0 definition and the call site is in a
346 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
348 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
349 // at their invocation. That is, we pretend that the macros 1.0 definition
350 // was defined at its invocation (i.e., inside the macros 2.0 definition)
351 // so that the macros 2.0 definition remains hygienic.
353 // See the example at `test/run-pass/hygiene/legacy_interaction.rs`.
354 let mut ctxt = call_site_ctxt;
355 for (mark, transparency) in self.marks() {
356 ctxt = ctxt.apply_mark_internal(mark, transparency);
358 ctxt.apply_mark_internal(mark, transparency)
361 fn apply_mark_internal(self, mark: Mark, transparency: Transparency) -> SyntaxContext {
362 HygieneData::with(|data| {
363 let syntax_contexts = &mut data.syntax_contexts;
364 let mut opaque = syntax_contexts[self.0 as usize].opaque;
365 let mut opaque_and_semitransparent =
366 syntax_contexts[self.0 as usize].opaque_and_semitransparent;
368 if transparency >= Transparency::Opaque {
369 let prev_ctxt = opaque;
370 opaque = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
371 let new_opaque = SyntaxContext(syntax_contexts.len() as u32);
372 syntax_contexts.push(SyntaxContextData {
377 opaque_and_semitransparent: new_opaque,
378 dollar_crate_name: kw::DollarCrate,
384 if transparency >= Transparency::SemiTransparent {
385 let prev_ctxt = opaque_and_semitransparent;
386 opaque_and_semitransparent =
387 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
388 let new_opaque_and_semitransparent =
389 SyntaxContext(syntax_contexts.len() as u32);
390 syntax_contexts.push(SyntaxContextData {
395 opaque_and_semitransparent: new_opaque_and_semitransparent,
396 dollar_crate_name: kw::DollarCrate,
398 new_opaque_and_semitransparent
402 let prev_ctxt = self;
403 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
404 let new_opaque_and_semitransparent_and_transparent =
405 SyntaxContext(syntax_contexts.len() as u32);
406 syntax_contexts.push(SyntaxContextData {
411 opaque_and_semitransparent,
412 dollar_crate_name: kw::DollarCrate,
414 new_opaque_and_semitransparent_and_transparent
419 /// Pulls a single mark off of the syntax context. This effectively moves the
420 /// context up one macro definition level. That is, if we have a nested macro
421 /// definition as follows:
431 /// and we have a SyntaxContext that is referring to something declared by an invocation
432 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
433 /// invocation of f that created g1.
434 /// Returns the mark that was removed.
435 pub fn remove_mark(&mut self) -> Mark {
436 HygieneData::with(|data| data.remove_mark(self))
439 pub fn marks(self) -> Vec<(Mark, Transparency)> {
440 HygieneData::with(|data| data.marks(self))
443 /// Adjust this context for resolution in a scope created by the given expansion.
444 /// For example, consider the following three resolutions of `f`:
447 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
449 /// macro m($f:ident) {
451 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
452 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
454 /// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
455 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
456 /// //| and it resolves to `::foo::f`.
457 /// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
458 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
459 /// //| and it resolves to `::bar::f`.
460 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
461 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
462 /// //| and it resolves to `::bar::$f`.
465 /// This returns the expansion whose definition scope we use to privacy check the resolution,
466 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
467 pub fn adjust(&mut self, expansion: Mark) -> Option<Mark> {
468 HygieneData::with(|data| data.adjust(self, expansion))
471 /// Adjust this context for resolution in a scope created by the given expansion
472 /// via a glob import with the given `SyntaxContext`.
477 /// macro m($i:ident) {
479 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
480 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
483 /// macro n($j:ident) {
485 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
486 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
487 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
488 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
489 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
490 /// //^ This cannot be glob-adjusted, so this is a resolution error.
494 /// This returns `None` if the context cannot be glob-adjusted.
495 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
496 pub fn glob_adjust(&mut self, expansion: Mark, glob_span: Span) -> Option<Option<Mark>> {
497 let mut scope = None;
498 let mut glob_ctxt = glob_span.ctxt().modern();
499 while !expansion.outer_is_descendant_of(glob_ctxt) {
500 scope = Some(glob_ctxt.remove_mark());
501 if self.remove_mark() != scope.unwrap() {
505 if self.adjust(expansion).is_some() {
511 /// Undo `glob_adjust` if possible:
514 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
515 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
518 pub fn reverse_glob_adjust(&mut self, expansion: Mark, glob_span: Span)
519 -> Option<Option<Mark>> {
520 if self.adjust(expansion).is_some() {
524 let mut glob_ctxt = glob_span.ctxt().modern();
525 let mut marks = Vec::new();
526 while !expansion.outer_is_descendant_of(glob_ctxt) {
527 marks.push(glob_ctxt.remove_mark());
530 let scope = marks.last().cloned();
531 while let Some(mark) = marks.pop() {
532 *self = self.apply_mark(mark);
538 pub fn modern(self) -> SyntaxContext {
539 HygieneData::with(|data| data.modern(self))
543 pub fn modern_and_legacy(self) -> SyntaxContext {
544 HygieneData::with(|data| data.modern_and_legacy(self))
548 pub fn outer(self) -> Mark {
549 HygieneData::with(|data| data.outer(self))
552 /// `ctxt.outer_expn_info()` is equivalent to but faster than
553 /// `ctxt.outer().expn_info()`.
555 pub fn outer_expn_info(self) -> Option<ExpnInfo> {
556 HygieneData::with(|data| data.expn_info(data.outer(self)))
559 pub fn dollar_crate_name(self) -> Symbol {
560 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name)
563 pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) {
564 HygieneData::with(|data| {
565 let prev_dollar_crate_name = mem::replace(
566 &mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name
568 assert!(dollar_crate_name == prev_dollar_crate_name ||
569 prev_dollar_crate_name == kw::DollarCrate,
570 "$crate name is reset for a syntax context");
575 impl fmt::Debug for SyntaxContext {
576 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
577 write!(f, "#{}", self.0)
581 /// Extra information for tracking spans of macro and syntax sugar expansion
582 #[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)]
583 pub struct ExpnInfo {
584 /// The location of the actual macro invocation or syntax sugar , e.g.
585 /// `let x = foo!();` or `if let Some(y) = x {}`
587 /// This may recursively refer to other macro invocations, e.g., if
588 /// `foo!()` invoked `bar!()` internally, and there was an
589 /// expression inside `bar!`; the call_site of the expression in
590 /// the expansion would point to the `bar!` invocation; that
591 /// call_site span would have its own ExpnInfo, with the call_site
592 /// pointing to the `foo!` invocation.
594 /// The span of the macro definition itself. The macro may not
595 /// have a sensible definition span (e.g., something defined
596 /// completely inside libsyntax) in which case this is None.
597 /// This span serves only informational purpose and is not used for resolution.
598 pub def_site: Option<Span>,
599 /// The format with which the macro was invoked.
600 pub format: ExpnFormat,
601 /// List of #[unstable]/feature-gated features that the macro is allowed to use
602 /// internally without forcing the whole crate to opt-in
604 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
605 /// Whether the macro is allowed to use `unsafe` internally
606 /// even if the user crate has `#![forbid(unsafe_code)]`.
607 pub allow_internal_unsafe: bool,
608 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
609 /// for a given macro.
610 pub local_inner_macros: bool,
611 /// Edition of the crate in which the macro is defined.
612 pub edition: Edition,
615 /// The source of expansion.
616 #[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
617 pub enum ExpnFormat {
618 /// e.g., #[derive(...)] <item>
619 MacroAttribute(Symbol),
620 /// e.g., `format!()`
622 /// Desugaring done by the compiler during HIR lowering.
623 CompilerDesugaring(CompilerDesugaringKind)
627 pub fn name(&self) -> Symbol {
629 ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name,
630 ExpnFormat::CompilerDesugaring(kind) => kind.name(),
635 /// The kind of compiler desugaring.
636 #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
637 pub enum CompilerDesugaringKind {
638 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
639 /// However, we do not want to blame `c` for unreachability but rather say that `i`
640 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
644 /// Desugaring of an `impl Trait` in return type position
645 /// to an `existential type Foo: Trait;` and replacing the
646 /// `impl Trait` with `Foo`.
647 ExistentialReturnType,
653 impl CompilerDesugaringKind {
654 pub fn name(self) -> Symbol {
655 Symbol::intern(match self {
656 CompilerDesugaringKind::IfTemporary => "if",
657 CompilerDesugaringKind::Async => "async",
658 CompilerDesugaringKind::Await => "await",
659 CompilerDesugaringKind::QuestionMark => "?",
660 CompilerDesugaringKind::TryBlock => "try block",
661 CompilerDesugaringKind::ExistentialReturnType => "existential type",
662 CompilerDesugaringKind::ForLoop => "for loop",
667 impl Encodable for SyntaxContext {
668 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
669 Ok(()) // FIXME(jseyfried) intercrate hygiene
673 impl Decodable for SyntaxContext {
674 fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
675 Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene