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.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(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 outer(&self, ctxt: SyntaxContext) -> Mark {
204 self.syntax_contexts[ctxt.0 as usize].outer_mark
207 fn expn_info(&self, mark: Mark) -> Option<ExpnInfo> {
208 self.marks[mark.0 as usize].expn_info.clone()
211 fn is_descendant_of(&self, mut mark: Mark, ancestor: Mark) -> bool {
212 while mark != ancestor {
213 if mark == Mark::root() {
216 mark = self.marks[mark.0 as usize].parent;
222 pub fn clear_markings() {
223 HygieneData::with(|data| data.markings = FxHashMap::default());
228 pub const fn empty() -> Self {
233 crate fn as_u32(self) -> u32 {
238 crate fn from_u32(raw: u32) -> SyntaxContext {
242 // Allocate a new SyntaxContext with the given ExpnInfo. This is used when
243 // deserializing Spans from the incr. comp. cache.
244 // FIXME(mw): This method does not restore MarkData::parent or
245 // SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things
246 // don't seem to be used after HIR lowering, so everything should be fine
247 // as long as incremental compilation does not kick in before that.
248 pub fn allocate_directly(expansion_info: ExpnInfo) -> Self {
249 HygieneData::with(|data| {
250 data.marks.push(MarkData {
251 parent: Mark::root(),
252 default_transparency: Transparency::SemiTransparent,
253 expn_info: Some(expansion_info),
256 let mark = Mark(data.marks.len() as u32 - 1);
258 data.syntax_contexts.push(SyntaxContextData {
260 transparency: Transparency::SemiTransparent,
261 prev_ctxt: SyntaxContext::empty(),
262 opaque: SyntaxContext::empty(),
263 opaque_and_semitransparent: SyntaxContext::empty(),
264 dollar_crate_name: kw::DollarCrate,
266 SyntaxContext(data.syntax_contexts.len() as u32 - 1)
270 /// Extend a syntax context with a given mark and default transparency for that mark.
271 pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
272 assert_ne!(mark, Mark::root());
273 self.apply_mark_with_transparency(
274 mark, HygieneData::with(|data| data.marks[mark.0 as usize].default_transparency)
278 /// Extend a syntax context with a given mark and transparency
279 pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency)
281 assert_ne!(mark, Mark::root());
282 if transparency == Transparency::Opaque {
283 return self.apply_mark_internal(mark, transparency);
287 mark.expn_info().map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
288 let call_site_ctxt = if transparency == Transparency::SemiTransparent {
289 call_site_ctxt.modern()
291 call_site_ctxt.modern_and_legacy()
294 if call_site_ctxt == SyntaxContext::empty() {
295 return self.apply_mark_internal(mark, transparency);
298 // Otherwise, `mark` is a macros 1.0 definition and the call site is in a
299 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
301 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
302 // at their invocation. That is, we pretend that the macros 1.0 definition
303 // was defined at its invocation (i.e., inside the macros 2.0 definition)
304 // so that the macros 2.0 definition remains hygienic.
306 // See the example at `test/run-pass/hygiene/legacy_interaction.rs`.
307 let mut ctxt = call_site_ctxt;
308 for (mark, transparency) in self.marks() {
309 ctxt = ctxt.apply_mark_internal(mark, transparency);
311 ctxt.apply_mark_internal(mark, transparency)
314 fn apply_mark_internal(self, mark: Mark, transparency: Transparency) -> SyntaxContext {
315 HygieneData::with(|data| {
316 let syntax_contexts = &mut data.syntax_contexts;
317 let mut opaque = syntax_contexts[self.0 as usize].opaque;
318 let mut opaque_and_semitransparent =
319 syntax_contexts[self.0 as usize].opaque_and_semitransparent;
321 if transparency >= Transparency::Opaque {
322 let prev_ctxt = opaque;
323 opaque = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
324 let new_opaque = SyntaxContext(syntax_contexts.len() as u32);
325 syntax_contexts.push(SyntaxContextData {
330 opaque_and_semitransparent: new_opaque,
331 dollar_crate_name: kw::DollarCrate,
337 if transparency >= Transparency::SemiTransparent {
338 let prev_ctxt = opaque_and_semitransparent;
339 opaque_and_semitransparent =
340 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
341 let new_opaque_and_semitransparent =
342 SyntaxContext(syntax_contexts.len() as u32);
343 syntax_contexts.push(SyntaxContextData {
348 opaque_and_semitransparent: new_opaque_and_semitransparent,
349 dollar_crate_name: kw::DollarCrate,
351 new_opaque_and_semitransparent
355 let prev_ctxt = self;
356 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
357 let new_opaque_and_semitransparent_and_transparent =
358 SyntaxContext(syntax_contexts.len() as u32);
359 syntax_contexts.push(SyntaxContextData {
364 opaque_and_semitransparent,
365 dollar_crate_name: kw::DollarCrate,
367 new_opaque_and_semitransparent_and_transparent
372 /// Pulls a single mark off of the syntax context. This effectively moves the
373 /// context up one macro definition level. That is, if we have a nested macro
374 /// definition as follows:
384 /// and we have a SyntaxContext that is referring to something declared by an invocation
385 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
386 /// invocation of f that created g1.
387 /// Returns the mark that was removed.
388 pub fn remove_mark(&mut self) -> Mark {
389 HygieneData::with(|data| {
390 let outer_mark = data.syntax_contexts[self.0 as usize].outer_mark;
391 *self = data.syntax_contexts[self.0 as usize].prev_ctxt;
396 pub fn marks(mut self) -> Vec<(Mark, Transparency)> {
397 HygieneData::with(|data| {
398 let mut marks = Vec::new();
399 while self != SyntaxContext::empty() {
400 let ctxt_data = &data.syntax_contexts[self.0 as usize];
401 marks.push((ctxt_data.outer_mark, ctxt_data.transparency));
402 self = ctxt_data.prev_ctxt;
409 /// Adjust this context for resolution in a scope created by the given expansion.
410 /// For example, consider the following three resolutions of `f`:
413 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
415 /// macro m($f:ident) {
417 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
418 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
420 /// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
421 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
422 /// //| and it resolves to `::foo::f`.
423 /// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
424 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
425 /// //| and it resolves to `::bar::f`.
426 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
427 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
428 /// //| and it resolves to `::bar::$f`.
431 /// This returns the expansion whose definition scope we use to privacy check the resolution,
432 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
433 pub fn adjust(&mut self, expansion: Mark) -> Option<Mark> {
434 let mut scope = None;
435 while !expansion.outer_is_descendant_of(*self) {
436 scope = Some(self.remove_mark());
441 /// Adjust this context for resolution in a scope created by the given expansion
442 /// via a glob import with the given `SyntaxContext`.
447 /// macro m($i:ident) {
449 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
450 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
453 /// macro n($j:ident) {
455 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
456 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
457 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
458 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
459 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
460 /// //^ This cannot be glob-adjusted, so this is a resolution error.
464 /// This returns `None` if the context cannot be glob-adjusted.
465 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
466 pub fn glob_adjust(&mut self, expansion: Mark, glob_span: Span) -> Option<Option<Mark>> {
467 let mut scope = None;
468 let mut glob_ctxt = glob_span.ctxt().modern();
469 while !expansion.outer_is_descendant_of(glob_ctxt) {
470 scope = Some(glob_ctxt.remove_mark());
471 if self.remove_mark() != scope.unwrap() {
475 if self.adjust(expansion).is_some() {
481 /// Undo `glob_adjust` if possible:
484 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
485 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
488 pub fn reverse_glob_adjust(&mut self, expansion: Mark, glob_span: Span)
489 -> Option<Option<Mark>> {
490 if self.adjust(expansion).is_some() {
494 let mut glob_ctxt = glob_span.ctxt().modern();
495 let mut marks = Vec::new();
496 while !expansion.outer_is_descendant_of(glob_ctxt) {
497 marks.push(glob_ctxt.remove_mark());
500 let scope = marks.last().cloned();
501 while let Some(mark) = marks.pop() {
502 *self = self.apply_mark(mark);
508 pub fn modern(self) -> SyntaxContext {
509 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque)
513 pub fn modern_and_legacy(self) -> SyntaxContext {
514 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque_and_semitransparent)
518 pub fn outer(self) -> Mark {
519 HygieneData::with(|data| data.outer(self))
522 /// `ctxt.outer_expn_info()` is equivalent to but faster than
523 /// `ctxt.outer().expn_info()`.
525 pub fn outer_expn_info(self) -> Option<ExpnInfo> {
526 HygieneData::with(|data| data.expn_info(data.outer(self)))
529 pub fn dollar_crate_name(self) -> Symbol {
530 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name)
533 pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) {
534 HygieneData::with(|data| {
535 let prev_dollar_crate_name = mem::replace(
536 &mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name
538 assert!(dollar_crate_name == prev_dollar_crate_name ||
539 prev_dollar_crate_name == kw::DollarCrate,
540 "$crate name is reset for a syntax context");
545 impl fmt::Debug for SyntaxContext {
546 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
547 write!(f, "#{}", self.0)
551 /// Extra information for tracking spans of macro and syntax sugar expansion
552 #[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)]
553 pub struct ExpnInfo {
554 /// The location of the actual macro invocation or syntax sugar , e.g.
555 /// `let x = foo!();` or `if let Some(y) = x {}`
557 /// This may recursively refer to other macro invocations, e.g., if
558 /// `foo!()` invoked `bar!()` internally, and there was an
559 /// expression inside `bar!`; the call_site of the expression in
560 /// the expansion would point to the `bar!` invocation; that
561 /// call_site span would have its own ExpnInfo, with the call_site
562 /// pointing to the `foo!` invocation.
564 /// The span of the macro definition itself. The macro may not
565 /// have a sensible definition span (e.g., something defined
566 /// completely inside libsyntax) in which case this is None.
567 /// This span serves only informational purpose and is not used for resolution.
568 pub def_site: Option<Span>,
569 /// The format with which the macro was invoked.
570 pub format: ExpnFormat,
571 /// List of #[unstable]/feature-gated features that the macro is allowed to use
572 /// internally without forcing the whole crate to opt-in
574 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
575 /// Whether the macro is allowed to use `unsafe` internally
576 /// even if the user crate has `#![forbid(unsafe_code)]`.
577 pub allow_internal_unsafe: bool,
578 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
579 /// for a given macro.
580 pub local_inner_macros: bool,
581 /// Edition of the crate in which the macro is defined.
582 pub edition: Edition,
585 /// The source of expansion.
586 #[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
587 pub enum ExpnFormat {
588 /// e.g., #[derive(...)] <item>
589 MacroAttribute(Symbol),
590 /// e.g., `format!()`
592 /// Desugaring done by the compiler during HIR lowering.
593 CompilerDesugaring(CompilerDesugaringKind)
597 pub fn name(&self) -> Symbol {
599 ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name,
600 ExpnFormat::CompilerDesugaring(kind) => kind.name(),
605 /// The kind of compiler desugaring.
606 #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
607 pub enum CompilerDesugaringKind {
608 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
609 /// However, we do not want to blame `c` for unreachability but rather say that `i`
610 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
614 /// Desugaring of an `impl Trait` in return type position
615 /// to an `existential type Foo: Trait;` and replacing the
616 /// `impl Trait` with `Foo`.
617 ExistentialReturnType,
623 impl CompilerDesugaringKind {
624 pub fn name(self) -> Symbol {
625 Symbol::intern(match self {
626 CompilerDesugaringKind::IfTemporary => "if",
627 CompilerDesugaringKind::Async => "async",
628 CompilerDesugaringKind::Await => "await",
629 CompilerDesugaringKind::QuestionMark => "?",
630 CompilerDesugaringKind::TryBlock => "try block",
631 CompilerDesugaringKind::ExistentialReturnType => "existential type",
632 CompilerDesugaringKind::ForLoop => "for loop",
637 impl Encodable for SyntaxContext {
638 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
639 Ok(()) // FIXME(jseyfried) intercrate hygiene
643 impl Decodable for SyntaxContext {
644 fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
645 Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene