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(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 /// `mark.outer_is_descendant_of(ctxt)` is equivalent to but faster than
128 /// `mark.is_descendant_of(ctxt.outer())`.
129 pub fn outer_is_descendant_of(mut self, ctxt: SyntaxContext) -> bool {
130 HygieneData::with(|data| {
131 let outer = data.syntax_contexts[ctxt.0 as usize].outer_mark;
132 while self != outer {
133 if self == Mark::root() {
136 self = data.marks[self.0 as usize].parent;
142 /// Computes a mark such that both input marks are descendants of (or equal to) the returned
143 /// mark. That is, the following holds:
146 /// let la = least_ancestor(a, b);
147 /// assert!(a.is_descendant_of(la))
148 /// assert!(b.is_descendant_of(la))
150 pub fn least_ancestor(mut a: Mark, mut b: Mark) -> Mark {
151 HygieneData::with(|data| {
152 // Compute the path from a to the root
153 let mut a_path = FxHashSet::<Mark>::default();
154 while a != Mark::root() {
156 a = data.marks[a.0 as usize].parent;
159 // While the path from b to the root hasn't intersected, move up the tree
160 while !a_path.contains(&b) {
161 b = data.marks[b.0 as usize].parent;
168 // Used for enabling some compatibility fallback in resolve.
170 pub fn looks_like_proc_macro_derive(self) -> bool {
171 HygieneData::with(|data| {
172 let mark_data = &data.marks[self.0 as usize];
173 if mark_data.default_transparency == Transparency::Opaque {
174 if let Some(expn_info) = &mark_data.expn_info {
175 if let ExpnFormat::MacroAttribute(name) = expn_info.format {
176 if name.as_str().starts_with("derive(") {
188 crate struct HygieneData {
189 marks: Vec<MarkData>,
190 syntax_contexts: Vec<SyntaxContextData>,
191 markings: FxHashMap<(SyntaxContext, Mark, Transparency), SyntaxContext>,
195 crate fn new() -> Self {
197 marks: vec![MarkData {
198 parent: Mark::root(),
199 // If the root is opaque, then loops searching for an opaque mark
200 // will automatically stop after reaching it.
201 default_transparency: Transparency::Opaque,
204 syntax_contexts: vec![SyntaxContextData {
205 outer_mark: Mark::root(),
206 transparency: Transparency::Opaque,
207 prev_ctxt: SyntaxContext(0),
208 opaque: SyntaxContext(0),
209 opaque_and_semitransparent: SyntaxContext(0),
210 dollar_crate_name: kw::DollarCrate,
212 markings: FxHashMap::default(),
216 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
217 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
221 pub fn clear_markings() {
222 HygieneData::with(|data| data.markings = FxHashMap::default());
227 pub const fn empty() -> Self {
232 crate fn as_u32(self) -> u32 {
237 crate fn from_u32(raw: u32) -> SyntaxContext {
241 // Allocate a new SyntaxContext with the given ExpnInfo. This is used when
242 // deserializing Spans from the incr. comp. cache.
243 // FIXME(mw): This method does not restore MarkData::parent or
244 // SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things
245 // don't seem to be used after HIR lowering, so everything should be fine
246 // as long as incremental compilation does not kick in before that.
247 pub fn allocate_directly(expansion_info: ExpnInfo) -> Self {
248 HygieneData::with(|data| {
249 data.marks.push(MarkData {
250 parent: Mark::root(),
251 default_transparency: Transparency::SemiTransparent,
252 expn_info: Some(expansion_info),
255 let mark = Mark(data.marks.len() as u32 - 1);
257 data.syntax_contexts.push(SyntaxContextData {
259 transparency: Transparency::SemiTransparent,
260 prev_ctxt: SyntaxContext::empty(),
261 opaque: SyntaxContext::empty(),
262 opaque_and_semitransparent: SyntaxContext::empty(),
263 dollar_crate_name: kw::DollarCrate,
265 SyntaxContext(data.syntax_contexts.len() as u32 - 1)
269 /// Extend a syntax context with a given mark and default transparency for that mark.
270 pub fn apply_mark(self, mark: Mark) -> SyntaxContext {
271 assert_ne!(mark, Mark::root());
272 self.apply_mark_with_transparency(
273 mark, HygieneData::with(|data| data.marks[mark.0 as usize].default_transparency)
277 /// Extend a syntax context with a given mark and transparency
278 pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency)
280 assert_ne!(mark, Mark::root());
281 if transparency == Transparency::Opaque {
282 return self.apply_mark_internal(mark, transparency);
286 mark.expn_info().map_or(SyntaxContext::empty(), |info| info.call_site.ctxt());
287 let call_site_ctxt = if transparency == Transparency::SemiTransparent {
288 call_site_ctxt.modern()
290 call_site_ctxt.modern_and_legacy()
293 if call_site_ctxt == SyntaxContext::empty() {
294 return self.apply_mark_internal(mark, transparency);
297 // Otherwise, `mark` is a macros 1.0 definition and the call site is in a
298 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
300 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
301 // at their invocation. That is, we pretend that the macros 1.0 definition
302 // was defined at its invocation (i.e., inside the macros 2.0 definition)
303 // so that the macros 2.0 definition remains hygienic.
305 // See the example at `test/run-pass/hygiene/legacy_interaction.rs`.
306 let mut ctxt = call_site_ctxt;
307 for (mark, transparency) in self.marks() {
308 ctxt = ctxt.apply_mark_internal(mark, transparency);
310 ctxt.apply_mark_internal(mark, transparency)
313 fn apply_mark_internal(self, mark: Mark, transparency: Transparency) -> SyntaxContext {
314 HygieneData::with(|data| {
315 let syntax_contexts = &mut data.syntax_contexts;
316 let mut opaque = syntax_contexts[self.0 as usize].opaque;
317 let mut opaque_and_semitransparent =
318 syntax_contexts[self.0 as usize].opaque_and_semitransparent;
320 if transparency >= Transparency::Opaque {
321 let prev_ctxt = opaque;
322 opaque = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
323 let new_opaque = SyntaxContext(syntax_contexts.len() as u32);
324 syntax_contexts.push(SyntaxContextData {
329 opaque_and_semitransparent: new_opaque,
330 dollar_crate_name: kw::DollarCrate,
336 if transparency >= Transparency::SemiTransparent {
337 let prev_ctxt = opaque_and_semitransparent;
338 opaque_and_semitransparent =
339 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
340 let new_opaque_and_semitransparent =
341 SyntaxContext(syntax_contexts.len() as u32);
342 syntax_contexts.push(SyntaxContextData {
347 opaque_and_semitransparent: new_opaque_and_semitransparent,
348 dollar_crate_name: kw::DollarCrate,
350 new_opaque_and_semitransparent
354 let prev_ctxt = self;
355 *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| {
356 let new_opaque_and_semitransparent_and_transparent =
357 SyntaxContext(syntax_contexts.len() as u32);
358 syntax_contexts.push(SyntaxContextData {
363 opaque_and_semitransparent,
364 dollar_crate_name: kw::DollarCrate,
366 new_opaque_and_semitransparent_and_transparent
371 /// Pulls a single mark off of the syntax context. This effectively moves the
372 /// context up one macro definition level. That is, if we have a nested macro
373 /// definition as follows:
383 /// and we have a SyntaxContext that is referring to something declared by an invocation
384 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
385 /// invocation of f that created g1.
386 /// Returns the mark that was removed.
387 pub fn remove_mark(&mut self) -> Mark {
388 HygieneData::with(|data| {
389 let outer_mark = data.syntax_contexts[self.0 as usize].outer_mark;
390 *self = data.syntax_contexts[self.0 as usize].prev_ctxt;
395 pub fn marks(mut self) -> Vec<(Mark, Transparency)> {
396 HygieneData::with(|data| {
397 let mut marks = Vec::new();
398 while self != SyntaxContext::empty() {
399 let ctxt_data = &data.syntax_contexts[self.0 as usize];
400 marks.push((ctxt_data.outer_mark, ctxt_data.transparency));
401 self = ctxt_data.prev_ctxt;
408 /// Adjust this context for resolution in a scope created by the given expansion.
409 /// For example, consider the following three resolutions of `f`:
412 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
414 /// macro m($f:ident) {
416 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
417 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
419 /// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
420 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
421 /// //| and it resolves to `::foo::f`.
422 /// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m`
423 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
424 /// //| and it resolves to `::bar::f`.
425 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
426 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
427 /// //| and it resolves to `::bar::$f`.
430 /// This returns the expansion whose definition scope we use to privacy check the resolution,
431 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
432 pub fn adjust(&mut self, expansion: Mark) -> Option<Mark> {
433 let mut scope = None;
434 while !expansion.outer_is_descendant_of(*self) {
435 scope = Some(self.remove_mark());
440 /// Adjust this context for resolution in a scope created by the given expansion
441 /// via a glob import with the given `SyntaxContext`.
446 /// macro m($i:ident) {
448 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`.
449 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
452 /// macro n($j:ident) {
454 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
455 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
456 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
457 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
458 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
459 /// //^ This cannot be glob-adjusted, so this is a resolution error.
463 /// This returns `None` if the context cannot be glob-adjusted.
464 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
465 pub fn glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext)
466 -> Option<Option<Mark>> {
467 let mut scope = None;
468 while !expansion.outer_is_descendant_of(glob_ctxt) {
469 scope = Some(glob_ctxt.remove_mark());
470 if self.remove_mark() != scope.unwrap() {
474 if self.adjust(expansion).is_some() {
480 /// Undo `glob_adjust` if possible:
483 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
484 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
487 pub fn reverse_glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext)
488 -> Option<Option<Mark>> {
489 if self.adjust(expansion).is_some() {
493 let mut marks = Vec::new();
494 while !expansion.outer_is_descendant_of(glob_ctxt) {
495 marks.push(glob_ctxt.remove_mark());
498 let scope = marks.last().cloned();
499 while let Some(mark) = marks.pop() {
500 *self = self.apply_mark(mark);
506 pub fn modern(self) -> SyntaxContext {
507 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque)
511 pub fn modern_and_legacy(self) -> SyntaxContext {
512 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque_and_semitransparent)
516 pub fn outer(self) -> Mark {
517 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].outer_mark)
520 /// `ctxt.outer_expn_info()` is equivalent to but faster than
521 /// `ctxt.outer().expn_info()`.
523 pub fn outer_expn_info(self) -> Option<ExpnInfo> {
524 HygieneData::with(|data| {
525 let outer = data.syntax_contexts[self.0 as usize].outer_mark;
526 data.marks[outer.0 as usize].expn_info.clone()
530 pub fn dollar_crate_name(self) -> Symbol {
531 HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name)
534 pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) {
535 HygieneData::with(|data| {
536 let prev_dollar_crate_name = mem::replace(
537 &mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name
539 assert!(dollar_crate_name == prev_dollar_crate_name ||
540 prev_dollar_crate_name == kw::DollarCrate,
541 "$crate name is reset for a syntax context");
546 impl fmt::Debug for SyntaxContext {
547 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
548 write!(f, "#{}", self.0)
552 /// Extra information for tracking spans of macro and syntax sugar expansion
553 #[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)]
554 pub struct ExpnInfo {
555 /// The location of the actual macro invocation or syntax sugar , e.g.
556 /// `let x = foo!();` or `if let Some(y) = x {}`
558 /// This may recursively refer to other macro invocations, e.g., if
559 /// `foo!()` invoked `bar!()` internally, and there was an
560 /// expression inside `bar!`; the call_site of the expression in
561 /// the expansion would point to the `bar!` invocation; that
562 /// call_site span would have its own ExpnInfo, with the call_site
563 /// pointing to the `foo!` invocation.
565 /// The span of the macro definition itself. The macro may not
566 /// have a sensible definition span (e.g., something defined
567 /// completely inside libsyntax) in which case this is None.
568 /// This span serves only informational purpose and is not used for resolution.
569 pub def_site: Option<Span>,
570 /// The format with which the macro was invoked.
571 pub format: ExpnFormat,
572 /// List of #[unstable]/feature-gated features that the macro is allowed to use
573 /// internally without forcing the whole crate to opt-in
575 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
576 /// Whether the macro is allowed to use `unsafe` internally
577 /// even if the user crate has `#![forbid(unsafe_code)]`.
578 pub allow_internal_unsafe: bool,
579 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
580 /// for a given macro.
581 pub local_inner_macros: bool,
582 /// Edition of the crate in which the macro is defined.
583 pub edition: Edition,
586 /// The source of expansion.
587 #[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
588 pub enum ExpnFormat {
589 /// e.g., #[derive(...)] <item>
590 MacroAttribute(Symbol),
591 /// e.g., `format!()`
593 /// Desugaring done by the compiler during HIR lowering.
594 CompilerDesugaring(CompilerDesugaringKind)
598 pub fn name(&self) -> Symbol {
600 ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name,
601 ExpnFormat::CompilerDesugaring(kind) => kind.name(),
606 /// The kind of compiler desugaring.
607 #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)]
608 pub enum CompilerDesugaringKind {
609 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
610 /// However, we do not want to blame `c` for unreachability but rather say that `i`
611 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
615 /// Desugaring of an `impl Trait` in return type position
616 /// to an `existential type Foo: Trait;` and replacing the
617 /// `impl Trait` with `Foo`.
618 ExistentialReturnType,
624 impl CompilerDesugaringKind {
625 pub fn name(self) -> Symbol {
626 Symbol::intern(match self {
627 CompilerDesugaringKind::IfTemporary => "if",
628 CompilerDesugaringKind::Async => "async",
629 CompilerDesugaringKind::Await => "await",
630 CompilerDesugaringKind::QuestionMark => "?",
631 CompilerDesugaringKind::TryBlock => "try block",
632 CompilerDesugaringKind::ExistentialReturnType => "existential type",
633 CompilerDesugaringKind::ForLoop => "for loop",
638 impl Encodable for SyntaxContext {
639 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
640 Ok(()) // FIXME(jseyfried) intercrate hygiene
644 impl Decodable for SyntaxContext {
645 fn decode<D: Decoder>(_: &mut D) -> Result<SyntaxContext, D::Error> {
646 Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene