1 //! Machinery for hygienic macros.
3 //! Inspired by Matthew Flatt et al., “Macros That Work Together: Compile-Time Bindings, Partial
4 //! Expansion, and Definition Contexts,” *Journal of Functional Programming* 22, no. 2
5 //! (March 1, 2012): 181–216, <https://doi.org/10.1017/S0956796812000093>.
7 // Hygiene data is stored in a global variable and accessed via TLS, which
8 // means that accesses are somewhat expensive. (`HygieneData::with`
9 // encapsulates a single access.) Therefore, on hot code paths it is worth
10 // ensuring that multiple HygieneData accesses are combined into a single
11 // `HygieneData::with`.
13 // This explains why `HygieneData`, `SyntaxContext` and `ExpnId` have interfaces
14 // with a certain amount of redundancy in them. For example,
15 // `SyntaxContext::outer_expn_data` combines `SyntaxContext::outer` and
16 // `ExpnId::expn_data` so that two `HygieneData` accesses can be performed within
17 // a single `HygieneData::with` call.
19 // It also explains why many functions appear in `HygieneData` and again in
20 // `SyntaxContext` or `ExpnId`. For example, `HygieneData::outer` and
21 // `SyntaxContext::outer` do the same thing, but the former is for use within a
22 // `HygieneData::with` call while the latter is for use outside such a call.
23 // When modifying this file it is important to understand this distinction,
24 // because getting it wrong can lead to nested `HygieneData::with` calls that
25 // trigger runtime aborts. (Fortunately these are obvious and easy to fix.)
27 use crate::edition::Edition;
28 use crate::symbol::{kw, sym, Symbol};
29 use crate::with_session_globals;
30 use crate::{HashStableContext, Span, DUMMY_SP};
32 use crate::def_id::{CrateNum, DefId, StableCrateId, CRATE_DEF_ID, LOCAL_CRATE};
33 use rustc_data_structures::fingerprint::Fingerprint;
34 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
35 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
36 use rustc_data_structures::sync::{Lock, Lrc};
37 use rustc_data_structures::unhash::UnhashMap;
38 use rustc_index::vec::IndexVec;
39 use rustc_macros::HashStable_Generic;
40 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
45 /// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
46 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
47 pub struct SyntaxContext(u32);
49 #[derive(Debug, Encodable, Decodable, Clone)]
50 pub struct SyntaxContextData {
52 outer_transparency: Transparency,
53 parent: SyntaxContext,
54 /// This context, but with all transparent and semi-transparent expansions filtered away.
55 opaque: SyntaxContext,
56 /// This context, but with all transparent expansions filtered away.
57 opaque_and_semitransparent: SyntaxContext,
58 /// Name of the crate to which `$crate` with this context would resolve.
59 dollar_crate_name: Symbol,
62 rustc_index::newtype_index! {
63 /// A unique ID associated with a macro invocation and expansion.
64 pub struct ExpnIndex {
69 /// A unique ID associated with a macro invocation and expansion.
70 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
73 pub local_id: ExpnIndex,
76 impl fmt::Debug for ExpnId {
77 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
78 // Generate crate_::{{expn_}}.
79 write!(f, "{:?}::{{{{expn{}}}}}", self.krate, self.local_id.private)
83 rustc_index::newtype_index! {
84 /// A unique ID associated with a macro invocation and expansion.
85 pub struct LocalExpnId {
87 DEBUG_FORMAT = "expn{}"
91 /// A unique hash value associated to an expansion.
92 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, Encodable, Decodable, HashStable_Generic)]
93 pub struct ExpnHash(Fingerprint);
96 /// Returns the [StableCrateId] identifying the crate this [ExpnHash]
99 pub fn stable_crate_id(self) -> StableCrateId {
100 StableCrateId(self.0.as_value().0)
103 /// Returns the crate-local part of the [ExpnHash].
107 pub fn local_hash(self) -> u64 {
112 pub fn is_root(self) -> bool {
113 self.0 == Fingerprint::ZERO
116 /// Builds a new [ExpnHash] with the given [StableCrateId] and
117 /// `local_hash`, where `local_hash` must be unique within its crate.
118 fn new(stable_crate_id: StableCrateId, local_hash: u64) -> ExpnHash {
119 ExpnHash(Fingerprint::new(stable_crate_id.0, local_hash))
123 /// A property of a macro expansion that determines how identifiers
124 /// produced by that expansion are resolved.
125 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug, Encodable, Decodable)]
126 #[derive(HashStable_Generic)]
127 pub enum Transparency {
128 /// Identifier produced by a transparent expansion is always resolved at call-site.
129 /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
131 /// Identifier produced by a semi-transparent expansion may be resolved
132 /// either at call-site or at definition-site.
133 /// If it's a local variable, label or `$crate` then it's resolved at def-site.
134 /// Otherwise it's resolved at call-site.
135 /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
136 /// but that's an implementation detail.
138 /// Identifier produced by an opaque expansion is always resolved at definition-site.
139 /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
144 /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
145 pub const ROOT: LocalExpnId = LocalExpnId::from_u32(0);
147 pub fn from_raw(idx: ExpnIndex) -> LocalExpnId {
148 LocalExpnId::from_u32(idx.as_u32())
151 pub fn as_raw(self) -> ExpnIndex {
152 ExpnIndex::from_u32(self.as_u32())
155 pub fn fresh_empty() -> LocalExpnId {
156 HygieneData::with(|data| {
157 let expn_id = data.local_expn_data.push(None);
158 let _eid = data.local_expn_hashes.push(ExpnHash(Fingerprint::ZERO));
159 debug_assert_eq!(expn_id, _eid);
164 pub fn fresh(mut expn_data: ExpnData, ctx: impl HashStableContext) -> LocalExpnId {
165 debug_assert_eq!(expn_data.parent.krate, LOCAL_CRATE);
166 let expn_hash = update_disambiguator(&mut expn_data, ctx);
167 HygieneData::with(|data| {
168 let expn_id = data.local_expn_data.push(Some(expn_data));
169 let _eid = data.local_expn_hashes.push(expn_hash);
170 debug_assert_eq!(expn_id, _eid);
171 let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, expn_id.to_expn_id());
172 debug_assert!(_old_id.is_none());
178 pub fn expn_hash(self) -> ExpnHash {
179 HygieneData::with(|data| data.local_expn_hash(self))
183 pub fn expn_data(self) -> ExpnData {
184 HygieneData::with(|data| data.local_expn_data(self).clone())
188 pub fn to_expn_id(self) -> ExpnId {
189 ExpnId { krate: LOCAL_CRATE, local_id: self.as_raw() }
193 pub fn set_expn_data(self, mut expn_data: ExpnData, ctx: impl HashStableContext) {
194 debug_assert_eq!(expn_data.parent.krate, LOCAL_CRATE);
195 let expn_hash = update_disambiguator(&mut expn_data, ctx);
196 HygieneData::with(|data| {
197 let old_expn_data = &mut data.local_expn_data[self];
198 assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
199 *old_expn_data = Some(expn_data);
200 debug_assert_eq!(data.local_expn_hashes[self].0, Fingerprint::ZERO);
201 data.local_expn_hashes[self] = expn_hash;
202 let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, self.to_expn_id());
203 debug_assert!(_old_id.is_none());
208 pub fn is_descendant_of(self, ancestor: LocalExpnId) -> bool {
209 self.to_expn_id().is_descendant_of(ancestor.to_expn_id())
212 /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
213 /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
215 pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
216 self.to_expn_id().outer_expn_is_descendant_of(ctxt)
219 /// Returns span for the macro which originally caused this expansion to happen.
221 /// Stops backtracing at include! boundary.
223 pub fn expansion_cause(self) -> Option<Span> {
224 self.to_expn_id().expansion_cause()
229 pub fn parent(self) -> LocalExpnId {
230 self.expn_data().parent.as_local().unwrap()
235 /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
236 /// Invariant: we do not create any ExpnId with local_id == 0 and krate != 0.
237 pub const fn root() -> ExpnId {
238 ExpnId { krate: LOCAL_CRATE, local_id: ExpnIndex::from_u32(0) }
242 pub fn expn_hash(self) -> ExpnHash {
243 HygieneData::with(|data| data.expn_hash(self))
247 pub fn from_hash(hash: ExpnHash) -> Option<ExpnId> {
248 HygieneData::with(|data| data.expn_hash_to_expn_id.get(&hash).copied())
252 pub fn as_local(self) -> Option<LocalExpnId> {
253 if self.krate == LOCAL_CRATE { Some(LocalExpnId::from_raw(self.local_id)) } else { None }
258 pub fn expect_local(self) -> LocalExpnId {
259 self.as_local().unwrap()
263 pub fn expn_data(self) -> ExpnData {
264 HygieneData::with(|data| data.expn_data(self).clone())
267 pub fn is_descendant_of(self, ancestor: ExpnId) -> bool {
268 HygieneData::with(|data| data.is_descendant_of(self, ancestor))
271 /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
272 /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
273 pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
274 HygieneData::with(|data| data.is_descendant_of(self, data.outer_expn(ctxt)))
277 /// Returns span for the macro which originally caused this expansion to happen.
279 /// Stops backtracing at include! boundary.
280 pub fn expansion_cause(mut self) -> Option<Span> {
281 let mut last_macro = None;
283 let expn_data = self.expn_data();
284 // Stop going up the backtrace once include! is encountered
285 if expn_data.is_root()
286 || expn_data.kind == ExpnKind::Macro(MacroKind::Bang, sym::include)
290 self = expn_data.call_site.ctxt().outer_expn();
291 last_macro = Some(expn_data.call_site);
298 pub struct HygieneData {
299 /// Each expansion should have an associated expansion data, but sometimes there's a delay
300 /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
301 /// first and then resolved later), so we use an `Option` here.
302 local_expn_data: IndexVec<LocalExpnId, Option<ExpnData>>,
303 local_expn_hashes: IndexVec<LocalExpnId, ExpnHash>,
304 /// Data and hash information from external crates. We may eventually want to remove these
305 /// maps, and fetch the information directly from the other crate's metadata like DefIds do.
306 foreign_expn_data: FxHashMap<ExpnId, ExpnData>,
307 foreign_expn_hashes: FxHashMap<ExpnId, ExpnHash>,
308 expn_hash_to_expn_id: UnhashMap<ExpnHash, ExpnId>,
309 syntax_context_data: Vec<SyntaxContextData>,
310 syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
311 /// Maps the `local_hash` of an `ExpnData` to the next disambiguator value.
312 /// This is used by `update_disambiguator` to keep track of which `ExpnData`s
313 /// would have collisions without a disambiguator.
314 /// The keys of this map are always computed with `ExpnData.disambiguator`
316 expn_data_disambiguators: FxHashMap<u64, u32>,
320 crate fn new(edition: Edition) -> Self {
321 let root_data = ExpnData::default(
325 Some(CRATE_DEF_ID.to_def_id()),
330 local_expn_data: IndexVec::from_elem_n(Some(root_data), 1),
331 local_expn_hashes: IndexVec::from_elem_n(ExpnHash(Fingerprint::ZERO), 1),
332 foreign_expn_data: FxHashMap::default(),
333 foreign_expn_hashes: FxHashMap::default(),
334 expn_hash_to_expn_id: std::iter::once((ExpnHash(Fingerprint::ZERO), ExpnId::root()))
336 syntax_context_data: vec![SyntaxContextData {
337 outer_expn: ExpnId::root(),
338 outer_transparency: Transparency::Opaque,
339 parent: SyntaxContext(0),
340 opaque: SyntaxContext(0),
341 opaque_and_semitransparent: SyntaxContext(0),
342 dollar_crate_name: kw::DollarCrate,
344 syntax_context_map: FxHashMap::default(),
345 expn_data_disambiguators: FxHashMap::default(),
349 pub fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
350 with_session_globals(|session_globals| f(&mut *session_globals.hygiene_data.borrow_mut()))
354 fn local_expn_hash(&self, expn_id: LocalExpnId) -> ExpnHash {
355 self.local_expn_hashes[expn_id]
359 fn expn_hash(&self, expn_id: ExpnId) -> ExpnHash {
360 match expn_id.as_local() {
361 Some(expn_id) => self.local_expn_hashes[expn_id],
362 None => self.foreign_expn_hashes[&expn_id],
366 fn local_expn_data(&self, expn_id: LocalExpnId) -> &ExpnData {
367 self.local_expn_data[expn_id].as_ref().expect("no expansion data for an expansion ID")
370 fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
371 if let Some(expn_id) = expn_id.as_local() {
372 self.local_expn_data[expn_id].as_ref().expect("no expansion data for an expansion ID")
374 &self.foreign_expn_data[&expn_id]
378 fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
379 while expn_id != ancestor {
380 if expn_id == ExpnId::root() {
383 expn_id = self.expn_data(expn_id).parent;
388 fn normalize_to_macros_2_0(&self, ctxt: SyntaxContext) -> SyntaxContext {
389 self.syntax_context_data[ctxt.0 as usize].opaque
392 fn normalize_to_macro_rules(&self, ctxt: SyntaxContext) -> SyntaxContext {
393 self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
396 fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
397 self.syntax_context_data[ctxt.0 as usize].outer_expn
400 fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
401 let data = &self.syntax_context_data[ctxt.0 as usize];
402 (data.outer_expn, data.outer_transparency)
405 fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
406 self.syntax_context_data[ctxt.0 as usize].parent
409 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
410 let outer_mark = self.outer_mark(*ctxt);
411 *ctxt = self.parent_ctxt(*ctxt);
415 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
416 let mut marks = Vec::new();
417 while ctxt != SyntaxContext::root() {
418 debug!("marks: getting parent of {:?}", ctxt);
419 marks.push(self.outer_mark(ctxt));
420 ctxt = self.parent_ctxt(ctxt);
426 fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
427 debug!("walk_chain({:?}, {:?})", span, to);
428 debug!("walk_chain: span ctxt = {:?}", span.ctxt());
429 while span.from_expansion() && span.ctxt() != to {
430 let outer_expn = self.outer_expn(span.ctxt());
431 debug!("walk_chain({:?}): outer_expn={:?}", span, outer_expn);
432 let expn_data = self.expn_data(outer_expn);
433 debug!("walk_chain({:?}): expn_data={:?}", span, expn_data);
434 span = expn_data.call_site;
439 fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
440 let mut scope = None;
441 while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
442 scope = Some(self.remove_mark(ctxt).0);
451 transparency: Transparency,
453 assert_ne!(expn_id, ExpnId::root());
454 if transparency == Transparency::Opaque {
455 return self.apply_mark_internal(ctxt, expn_id, transparency);
458 let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
459 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
460 self.normalize_to_macros_2_0(call_site_ctxt)
462 self.normalize_to_macro_rules(call_site_ctxt)
465 if call_site_ctxt == SyntaxContext::root() {
466 return self.apply_mark_internal(ctxt, expn_id, transparency);
469 // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
470 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
472 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
473 // at their invocation. That is, we pretend that the macros 1.0 definition
474 // was defined at its invocation (i.e., inside the macros 2.0 definition)
475 // so that the macros 2.0 definition remains hygienic.
477 // See the example at `test/ui/hygiene/legacy_interaction.rs`.
478 for (expn_id, transparency) in self.marks(ctxt) {
479 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
481 self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
484 fn apply_mark_internal(
488 transparency: Transparency,
490 let syntax_context_data = &mut self.syntax_context_data;
491 let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
492 let mut opaque_and_semitransparent =
493 syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
495 if transparency >= Transparency::Opaque {
499 .entry((parent, expn_id, transparency))
501 let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
502 syntax_context_data.push(SyntaxContextData {
504 outer_transparency: transparency,
507 opaque_and_semitransparent: new_opaque,
508 dollar_crate_name: kw::DollarCrate,
514 if transparency >= Transparency::SemiTransparent {
515 let parent = opaque_and_semitransparent;
516 opaque_and_semitransparent = *self
518 .entry((parent, expn_id, transparency))
520 let new_opaque_and_semitransparent =
521 SyntaxContext(syntax_context_data.len() as u32);
522 syntax_context_data.push(SyntaxContextData {
524 outer_transparency: transparency,
527 opaque_and_semitransparent: new_opaque_and_semitransparent,
528 dollar_crate_name: kw::DollarCrate,
530 new_opaque_and_semitransparent
535 *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
536 let new_opaque_and_semitransparent_and_transparent =
537 SyntaxContext(syntax_context_data.len() as u32);
538 syntax_context_data.push(SyntaxContextData {
540 outer_transparency: transparency,
543 opaque_and_semitransparent,
544 dollar_crate_name: kw::DollarCrate,
546 new_opaque_and_semitransparent_and_transparent
551 pub fn clear_syntax_context_map() {
552 HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
555 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
556 HygieneData::with(|data| data.walk_chain(span, to))
559 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
560 // The new contexts that need updating are at the end of the list and have `$crate` as a name.
561 let (len, to_update) = HygieneData::with(|data| {
563 data.syntax_context_data.len(),
564 data.syntax_context_data
567 .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate)
571 // The callback must be called from outside of the `HygieneData` lock,
572 // since it will try to acquire it too.
573 let range_to_update = len - to_update..len;
575 range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
576 HygieneData::with(|data| {
577 range_to_update.zip(names).for_each(|(idx, name)| {
578 data.syntax_context_data[idx].dollar_crate_name = name;
583 pub fn debug_hygiene_data(verbose: bool) -> String {
584 HygieneData::with(|data| {
586 format!("{:#?}", data)
588 let mut s = String::from("");
589 s.push_str("Expansions:");
590 let mut debug_expn_data = |(id, expn_data): (&ExpnId, &ExpnData)| {
592 "\n{:?}: parent: {:?}, call_site_ctxt: {:?}, def_site_ctxt: {:?}, kind: {:?}",
595 expn_data.call_site.ctxt(),
596 expn_data.def_site.ctxt(),
600 data.local_expn_data.iter_enumerated().for_each(|(id, expn_data)| {
601 let expn_data = expn_data.as_ref().expect("no expansion data for an expansion ID");
602 debug_expn_data((&id.to_expn_id(), expn_data))
604 data.foreign_expn_data.iter().for_each(debug_expn_data);
605 s.push_str("\n\nSyntaxContexts:");
606 data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
608 "\n#{}: parent: {:?}, outer_mark: ({:?}, {:?})",
609 id, ctxt.parent, ctxt.outer_expn, ctxt.outer_transparency,
619 pub const fn root() -> Self {
624 crate fn as_u32(self) -> u32 {
629 crate fn from_u32(raw: u32) -> SyntaxContext {
633 /// Extend a syntax context with a given expansion and transparency.
634 crate fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
635 HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
638 /// Pulls a single mark off of the syntax context. This effectively moves the
639 /// context up one macro definition level. That is, if we have a nested macro
640 /// definition as follows:
650 /// and we have a SyntaxContext that is referring to something declared by an invocation
651 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
652 /// invocation of f that created g1.
653 /// Returns the mark that was removed.
654 pub fn remove_mark(&mut self) -> ExpnId {
655 HygieneData::with(|data| data.remove_mark(self).0)
658 pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
659 HygieneData::with(|data| data.marks(self))
662 /// Adjust this context for resolution in a scope created by the given expansion.
663 /// For example, consider the following three resolutions of `f`:
666 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
668 /// macro m($f:ident) {
670 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
671 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
673 /// foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
674 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
675 /// //| and it resolves to `::foo::f`.
676 /// bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
677 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
678 /// //| and it resolves to `::bar::f`.
679 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
680 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
681 /// //| and it resolves to `::bar::$f`.
684 /// This returns the expansion whose definition scope we use to privacy check the resolution,
685 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
686 pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
687 HygieneData::with(|data| data.adjust(self, expn_id))
690 /// Like `SyntaxContext::adjust`, but also normalizes `self` to macros 2.0.
691 pub fn normalize_to_macros_2_0_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
692 HygieneData::with(|data| {
693 *self = data.normalize_to_macros_2_0(*self);
694 data.adjust(self, expn_id)
698 /// Adjust this context for resolution in a scope created by the given expansion
699 /// via a glob import with the given `SyntaxContext`.
704 /// macro m($i:ident) {
706 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
707 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
710 /// macro n($j:ident) {
712 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
713 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
714 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
715 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
716 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
717 /// //^ This cannot be glob-adjusted, so this is a resolution error.
721 /// This returns `None` if the context cannot be glob-adjusted.
722 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
723 pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
724 HygieneData::with(|data| {
725 let mut scope = None;
726 let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
727 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
728 scope = Some(data.remove_mark(&mut glob_ctxt).0);
729 if data.remove_mark(self).0 != scope.unwrap() {
733 if data.adjust(self, expn_id).is_some() {
740 /// Undo `glob_adjust` if possible:
743 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
744 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
747 pub fn reverse_glob_adjust(
751 ) -> Option<Option<ExpnId>> {
752 HygieneData::with(|data| {
753 if data.adjust(self, expn_id).is_some() {
757 let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
758 let mut marks = Vec::new();
759 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
760 marks.push(data.remove_mark(&mut glob_ctxt));
763 let scope = marks.last().map(|mark| mark.0);
764 while let Some((expn_id, transparency)) = marks.pop() {
765 *self = data.apply_mark(*self, expn_id, transparency);
771 pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
772 HygieneData::with(|data| {
773 let mut self_normalized = data.normalize_to_macros_2_0(self);
774 data.adjust(&mut self_normalized, expn_id);
775 self_normalized == data.normalize_to_macros_2_0(other)
780 pub fn normalize_to_macros_2_0(self) -> SyntaxContext {
781 HygieneData::with(|data| data.normalize_to_macros_2_0(self))
785 pub fn normalize_to_macro_rules(self) -> SyntaxContext {
786 HygieneData::with(|data| data.normalize_to_macro_rules(self))
790 pub fn outer_expn(self) -> ExpnId {
791 HygieneData::with(|data| data.outer_expn(self))
794 /// `ctxt.outer_expn_data()` is equivalent to but faster than
795 /// `ctxt.outer_expn().expn_data()`.
797 pub fn outer_expn_data(self) -> ExpnData {
798 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
802 pub fn outer_mark(self) -> (ExpnId, Transparency) {
803 HygieneData::with(|data| data.outer_mark(self))
806 pub fn dollar_crate_name(self) -> Symbol {
807 HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
810 pub fn edition(self) -> Edition {
811 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).edition)
815 impl fmt::Debug for SyntaxContext {
816 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
817 write!(f, "#{}", self.0)
822 /// Creates a fresh expansion with given properties.
823 /// Expansions are normally created by macros, but in some cases expansions are created for
824 /// other compiler-generated code to set per-span properties like allowed unstable features.
825 /// The returned span belongs to the created expansion and has the new properties,
826 /// but its location is inherited from the current span.
827 pub fn fresh_expansion(self, expn_data: ExpnData, ctx: impl HashStableContext) -> Span {
828 self.fresh_expansion_with_transparency(expn_data, Transparency::Transparent, ctx)
831 pub fn fresh_expansion_with_transparency(
834 transparency: Transparency,
835 ctx: impl HashStableContext,
837 let expn_id = LocalExpnId::fresh(expn_data, ctx).to_expn_id();
838 HygieneData::with(|data| {
839 self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
843 /// Reuses the span but adds information like the kind of the desugaring and features that are
844 /// allowed inside this span.
845 pub fn mark_with_reason(
847 allow_internal_unstable: Option<Lrc<[Symbol]>>,
848 reason: DesugaringKind,
850 ctx: impl HashStableContext,
852 let expn_data = ExpnData {
853 allow_internal_unstable,
854 ..ExpnData::default(ExpnKind::Desugaring(reason), self, edition, None, None)
856 self.fresh_expansion(expn_data, ctx)
860 /// A subset of properties from both macro definition and macro call available through global data.
861 /// Avoid using this if you have access to the original definition or call structures.
862 #[derive(Clone, Debug, Encodable, Decodable, HashStable_Generic)]
863 pub struct ExpnData {
864 // --- The part unique to each expansion.
865 /// The kind of this expansion - macro or compiler desugaring.
867 /// The expansion that produced this expansion.
869 /// The location of the actual macro invocation or syntax sugar , e.g.
870 /// `let x = foo!();` or `if let Some(y) = x {}`
872 /// This may recursively refer to other macro invocations, e.g., if
873 /// `foo!()` invoked `bar!()` internally, and there was an
874 /// expression inside `bar!`; the call_site of the expression in
875 /// the expansion would point to the `bar!` invocation; that
876 /// call_site span would have its own ExpnData, with the call_site
877 /// pointing to the `foo!` invocation.
879 /// Used to force two `ExpnData`s to have different `Fingerprint`s.
880 /// Due to macro expansion, it's possible to end up with two `ExpnId`s
881 /// that have identical `ExpnData`s. This violates the contract of `HashStable`
882 /// - the two `ExpnId`s are not equal, but their `Fingerprint`s are equal
883 /// (since the numerical `ExpnId` value is not considered by the `HashStable`
886 /// The `disambiguator` field is set by `update_disambiguator` when two distinct
887 /// `ExpnId`s would end up with the same `Fingerprint`. Since `ExpnData` includes
888 /// a `krate` field, this value only needs to be unique within a single crate.
891 // --- The part specific to the macro/desugaring definition.
892 // --- It may be reasonable to share this part between expansions with the same definition,
893 // --- but such sharing is known to bring some minor inconveniences without also bringing
894 // --- noticeable perf improvements (PR #62898).
895 /// The span of the macro definition (possibly dummy).
896 /// This span serves only informational purpose and is not used for resolution.
898 /// List of `#[unstable]`/feature-gated features that the macro is allowed to use
899 /// internally without forcing the whole crate to opt-in
901 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
902 /// Whether the macro is allowed to use `unsafe` internally
903 /// even if the user crate has `#![forbid(unsafe_code)]`.
904 pub allow_internal_unsafe: bool,
905 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
906 /// for a given macro.
907 pub local_inner_macros: bool,
908 /// Edition of the crate in which the macro is defined.
909 pub edition: Edition,
910 /// The `DefId` of the macro being invoked,
911 /// if this `ExpnData` corresponds to a macro invocation
912 pub macro_def_id: Option<DefId>,
913 /// The normal module (`mod`) in which the expanded macro was defined.
914 pub parent_module: Option<DefId>,
917 impl !PartialEq for ExpnData {}
918 impl !Hash for ExpnData {}
926 allow_internal_unstable: Option<Lrc<[Symbol]>>,
927 allow_internal_unsafe: bool,
928 local_inner_macros: bool,
930 macro_def_id: Option<DefId>,
931 parent_module: Option<DefId>,
938 allow_internal_unstable,
939 allow_internal_unsafe,
948 /// Constructs expansion data with default properties.
953 macro_def_id: Option<DefId>,
954 parent_module: Option<DefId>,
958 parent: ExpnId::root(),
961 allow_internal_unstable: None,
962 allow_internal_unsafe: false,
963 local_inner_macros: false,
971 pub fn allow_unstable(
975 allow_internal_unstable: Lrc<[Symbol]>,
976 macro_def_id: Option<DefId>,
977 parent_module: Option<DefId>,
980 allow_internal_unstable: Some(allow_internal_unstable),
981 ..ExpnData::default(kind, call_site, edition, macro_def_id, parent_module)
986 pub fn is_root(&self) -> bool {
987 matches!(self.kind, ExpnKind::Root)
991 fn hash_expn(&self, ctx: &mut impl HashStableContext) -> u64 {
992 let mut hasher = StableHasher::new();
993 self.hash_stable(ctx, &mut hasher);
999 #[derive(Clone, Debug, PartialEq, Encodable, Decodable, HashStable_Generic)]
1001 /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
1003 /// Expansion produced by a macro.
1004 Macro(MacroKind, Symbol),
1005 /// Transform done by the compiler on the AST.
1007 /// Desugaring done by the compiler during HIR lowering.
1008 Desugaring(DesugaringKind),
1014 pub fn descr(&self) -> String {
1016 ExpnKind::Root => kw::PathRoot.to_string(),
1017 ExpnKind::Macro(macro_kind, name) => match macro_kind {
1018 MacroKind::Bang => format!("{}!", name),
1019 MacroKind::Attr => format!("#[{}]", name),
1020 MacroKind::Derive => format!("#[derive({})]", name),
1022 ExpnKind::AstPass(kind) => kind.descr().to_string(),
1023 ExpnKind::Desugaring(kind) => format!("desugaring of {}", kind.descr()),
1024 ExpnKind::Inlined => "inlined source".to_string(),
1029 /// The kind of macro invocation or definition.
1030 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
1031 #[derive(HashStable_Generic)]
1032 pub enum MacroKind {
1033 /// A bang macro `foo!()`.
1035 /// An attribute macro `#[foo]`.
1037 /// A derive macro `#[derive(Foo)]`
1042 pub fn descr(self) -> &'static str {
1044 MacroKind::Bang => "macro",
1045 MacroKind::Attr => "attribute macro",
1046 MacroKind::Derive => "derive macro",
1050 pub fn descr_expected(self) -> &'static str {
1052 MacroKind::Attr => "attribute",
1057 pub fn article(self) -> &'static str {
1059 MacroKind::Attr => "an",
1065 /// The kind of AST transform.
1066 #[derive(Clone, Copy, Debug, PartialEq, Encodable, Decodable, HashStable_Generic)]
1074 pub fn descr(self) -> &'static str {
1076 AstPass::StdImports => "standard library imports",
1077 AstPass::TestHarness => "test harness",
1078 AstPass::ProcMacroHarness => "proc macro harness",
1083 /// The kind of compiler desugaring.
1084 #[derive(Clone, Copy, PartialEq, Debug, Encodable, Decodable, HashStable_Generic)]
1085 pub enum DesugaringKind {
1086 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
1087 /// However, we do not want to blame `c` for unreachability but rather say that `i`
1088 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
1089 /// This also applies to `while` loops.
1093 /// Desugaring of an `impl Trait` in return type position
1094 /// to an `type Foo = impl Trait;` and replacing the
1095 /// `impl Trait` with `Foo`.
1099 ForLoop(ForLoopLoc),
1103 /// A location in the desugaring of a `for` loop
1104 #[derive(Clone, Copy, PartialEq, Debug, Encodable, Decodable, HashStable_Generic)]
1105 pub enum ForLoopLoc {
1110 impl DesugaringKind {
1111 /// The description wording should combine well with "desugaring of {}".
1112 pub fn descr(self) -> &'static str {
1114 DesugaringKind::CondTemporary => "`if` or `while` condition",
1115 DesugaringKind::Async => "`async` block or function",
1116 DesugaringKind::Await => "`await` expression",
1117 DesugaringKind::QuestionMark => "operator `?`",
1118 DesugaringKind::TryBlock => "`try` block",
1119 DesugaringKind::OpaqueTy => "`impl Trait`",
1120 DesugaringKind::ForLoop(_) => "`for` loop",
1121 DesugaringKind::LetElse => "`let...else`",
1127 pub struct HygieneEncodeContext {
1128 /// All `SyntaxContexts` for which we have written `SyntaxContextData` into crate metadata.
1129 /// This is `None` after we finish encoding `SyntaxContexts`, to ensure
1130 /// that we don't accidentally try to encode any more `SyntaxContexts`
1131 serialized_ctxts: Lock<FxHashSet<SyntaxContext>>,
1132 /// The `SyntaxContexts` that we have serialized (e.g. as a result of encoding `Spans`)
1133 /// in the most recent 'round' of serializnig. Serializing `SyntaxContextData`
1134 /// may cause us to serialize more `SyntaxContext`s, so serialize in a loop
1135 /// until we reach a fixed point.
1136 latest_ctxts: Lock<FxHashSet<SyntaxContext>>,
1138 serialized_expns: Lock<FxHashSet<ExpnId>>,
1140 latest_expns: Lock<FxHashSet<ExpnId>>,
1143 impl HygieneEncodeContext {
1144 /// Record the fact that we need to serialize the corresponding `ExpnData`.
1145 pub fn schedule_expn_data_for_encoding(&self, expn: ExpnId) {
1146 if !self.serialized_expns.lock().contains(&expn) {
1147 self.latest_expns.lock().insert(expn);
1151 pub fn encode<T, R>(
1154 mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextData) -> Result<(), R>,
1155 mut encode_expn: impl FnMut(&mut T, ExpnId, &ExpnData, ExpnHash) -> Result<(), R>,
1156 ) -> Result<(), R> {
1157 // When we serialize a `SyntaxContextData`, we may end up serializing
1158 // a `SyntaxContext` that we haven't seen before
1159 while !self.latest_ctxts.lock().is_empty() || !self.latest_expns.lock().is_empty() {
1161 "encode_hygiene: Serializing a round of {:?} SyntaxContextDatas: {:?}",
1162 self.latest_ctxts.lock().len(),
1166 // Consume the current round of SyntaxContexts.
1167 // Drop the lock() temporary early
1168 let latest_ctxts = { std::mem::take(&mut *self.latest_ctxts.lock()) };
1170 // It's fine to iterate over a HashMap, because the serialization
1171 // of the table that we insert data into doesn't depend on insertion
1173 for_all_ctxts_in(latest_ctxts.into_iter(), |index, ctxt, data| {
1174 if self.serialized_ctxts.lock().insert(ctxt) {
1175 encode_ctxt(encoder, index, data)?;
1180 let latest_expns = { std::mem::take(&mut *self.latest_expns.lock()) };
1182 for_all_expns_in(latest_expns.into_iter(), |expn, data, hash| {
1183 if self.serialized_expns.lock().insert(expn) {
1184 encode_expn(encoder, expn, data, hash)?;
1189 debug!("encode_hygiene: Done serializing SyntaxContextData");
1195 /// Additional information used to assist in decoding hygiene data
1196 pub struct HygieneDecodeContext {
1197 // Maps serialized `SyntaxContext` ids to a `SyntaxContext` in the current
1198 // global `HygieneData`. When we deserialize a `SyntaxContext`, we need to create
1199 // a new id in the global `HygieneData`. This map tracks the ID we end up picking,
1200 // so that multiple occurrences of the same serialized id are decoded to the same
1202 remapped_ctxts: Lock<Vec<Option<SyntaxContext>>>,
1205 /// Register an expansion which has been decoded from the on-disk-cache for the local crate.
1206 pub fn register_local_expn_id(data: ExpnData, hash: ExpnHash) -> ExpnId {
1207 HygieneData::with(|hygiene_data| {
1208 let expn_id = hygiene_data.local_expn_data.next_index();
1209 hygiene_data.local_expn_data.push(Some(data));
1210 let _eid = hygiene_data.local_expn_hashes.push(hash);
1211 debug_assert_eq!(expn_id, _eid);
1213 let expn_id = expn_id.to_expn_id();
1215 let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
1216 debug_assert!(_old_id.is_none());
1221 /// Register an expansion which has been decoded from the metadata of a foreign crate.
1222 pub fn register_expn_id(
1224 local_id: ExpnIndex,
1228 let expn_id = ExpnId { krate, local_id };
1229 HygieneData::with(|hygiene_data| {
1230 let _old_data = hygiene_data.foreign_expn_data.insert(expn_id, data);
1231 debug_assert!(_old_data.is_none());
1232 let _old_hash = hygiene_data.foreign_expn_hashes.insert(expn_id, hash);
1233 debug_assert!(_old_hash.is_none());
1234 let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
1235 debug_assert!(_old_id.is_none());
1240 /// Decode an expansion from the metadata of a foreign crate.
1241 pub fn decode_expn_id(
1244 decode_data: impl FnOnce(ExpnId) -> (ExpnData, ExpnHash),
1247 debug!("decode_expn_id: deserialized root");
1248 return ExpnId::root();
1251 let index = ExpnIndex::from_u32(index);
1253 // This function is used to decode metadata, so it cannot decode information about LOCAL_CRATE.
1254 debug_assert_ne!(krate, LOCAL_CRATE);
1255 let expn_id = ExpnId { krate, local_id: index };
1257 // Fast path if the expansion has already been decoded.
1258 if HygieneData::with(|hygiene_data| hygiene_data.foreign_expn_data.contains_key(&expn_id)) {
1262 // Don't decode the data inside `HygieneData::with`, since we need to recursively decode
1264 let (expn_data, hash) = decode_data(expn_id);
1266 register_expn_id(krate, index, expn_data, hash)
1269 // Decodes `SyntaxContext`, using the provided `HygieneDecodeContext`
1270 // to track which `SyntaxContext`s we have already decoded.
1271 // The provided closure will be invoked to deserialize a `SyntaxContextData`
1272 // if we haven't already seen the id of the `SyntaxContext` we are deserializing.
1273 pub fn decode_syntax_context<
1275 F: FnOnce(&mut D, u32) -> Result<SyntaxContextData, D::Error>,
1278 context: &HygieneDecodeContext,
1280 ) -> Result<SyntaxContext, D::Error> {
1281 let raw_id: u32 = Decodable::decode(d)?;
1283 debug!("decode_syntax_context: deserialized root");
1284 // The root is special
1285 return Ok(SyntaxContext::root());
1288 let outer_ctxts = &context.remapped_ctxts;
1290 // Ensure that the lock() temporary is dropped early
1292 if let Some(ctxt) = outer_ctxts.lock().get(raw_id as usize).copied().flatten() {
1297 // Allocate and store SyntaxContext id *before* calling the decoder function,
1298 // as the SyntaxContextData may reference itself.
1299 let new_ctxt = HygieneData::with(|hygiene_data| {
1300 let new_ctxt = SyntaxContext(hygiene_data.syntax_context_data.len() as u32);
1301 // Push a dummy SyntaxContextData to ensure that nobody else can get the
1302 // same ID as us. This will be overwritten after call `decode_Data`
1303 hygiene_data.syntax_context_data.push(SyntaxContextData {
1304 outer_expn: ExpnId::root(),
1305 outer_transparency: Transparency::Transparent,
1306 parent: SyntaxContext::root(),
1307 opaque: SyntaxContext::root(),
1308 opaque_and_semitransparent: SyntaxContext::root(),
1309 dollar_crate_name: kw::Empty,
1311 let mut ctxts = outer_ctxts.lock();
1312 let new_len = raw_id as usize + 1;
1313 if ctxts.len() < new_len {
1314 ctxts.resize(new_len, None);
1316 ctxts[raw_id as usize] = Some(new_ctxt);
1321 // Don't try to decode data while holding the lock, since we need to
1322 // be able to recursively decode a SyntaxContext
1323 let mut ctxt_data = decode_data(d, raw_id)?;
1324 // Reset `dollar_crate_name` so that it will be updated by `update_dollar_crate_names`
1325 // We don't care what the encoding crate set this to - we want to resolve it
1326 // from the perspective of the current compilation session
1327 ctxt_data.dollar_crate_name = kw::DollarCrate;
1329 // Overwrite the dummy data with our decoded SyntaxContextData
1330 HygieneData::with(|hygiene_data| {
1331 let dummy = std::mem::replace(
1332 &mut hygiene_data.syntax_context_data[new_ctxt.as_u32() as usize],
1335 // Make sure nothing weird happening while `decode_data` was running
1336 assert_eq!(dummy.dollar_crate_name, kw::Empty);
1342 fn for_all_ctxts_in<E, F: FnMut(u32, SyntaxContext, &SyntaxContextData) -> Result<(), E>>(
1343 ctxts: impl Iterator<Item = SyntaxContext>,
1345 ) -> Result<(), E> {
1346 let all_data: Vec<_> = HygieneData::with(|data| {
1347 ctxts.map(|ctxt| (ctxt, data.syntax_context_data[ctxt.0 as usize].clone())).collect()
1349 for (ctxt, data) in all_data.into_iter() {
1350 f(ctxt.0, ctxt, &data)?;
1355 fn for_all_expns_in<E>(
1356 expns: impl Iterator<Item = ExpnId>,
1357 mut f: impl FnMut(ExpnId, &ExpnData, ExpnHash) -> Result<(), E>,
1358 ) -> Result<(), E> {
1359 let all_data: Vec<_> = HygieneData::with(|data| {
1360 expns.map(|expn| (expn, data.expn_data(expn).clone(), data.expn_hash(expn))).collect()
1362 for (expn, data, hash) in all_data.into_iter() {
1363 f(expn, &data, hash)?;
1368 impl<E: Encoder> Encodable<E> for LocalExpnId {
1369 fn encode(&self, e: &mut E) -> Result<(), E::Error> {
1370 self.to_expn_id().encode(e)
1374 impl<E: Encoder> Encodable<E> for ExpnId {
1375 default fn encode(&self, _: &mut E) -> Result<(), E::Error> {
1376 panic!("cannot encode `ExpnId` with `{}`", std::any::type_name::<E>());
1380 impl<D: Decoder> Decodable<D> for LocalExpnId {
1381 fn decode(d: &mut D) -> Result<Self, D::Error> {
1382 ExpnId::decode(d).map(ExpnId::expect_local)
1386 impl<D: Decoder> Decodable<D> for ExpnId {
1387 default fn decode(_: &mut D) -> Result<Self, D::Error> {
1388 panic!("cannot decode `ExpnId` with `{}`", std::any::type_name::<D>());
1392 pub fn raw_encode_syntax_context<E: Encoder>(
1393 ctxt: SyntaxContext,
1394 context: &HygieneEncodeContext,
1396 ) -> Result<(), E::Error> {
1397 if !context.serialized_ctxts.lock().contains(&ctxt) {
1398 context.latest_ctxts.lock().insert(ctxt);
1403 impl<E: Encoder> Encodable<E> for SyntaxContext {
1404 default fn encode(&self, _: &mut E) -> Result<(), E::Error> {
1405 panic!("cannot encode `SyntaxContext` with `{}`", std::any::type_name::<E>());
1409 impl<D: Decoder> Decodable<D> for SyntaxContext {
1410 default fn decode(_: &mut D) -> Result<Self, D::Error> {
1411 panic!("cannot decode `SyntaxContext` with `{}`", std::any::type_name::<D>());
1415 /// Updates the `disambiguator` field of the corresponding `ExpnData`
1416 /// such that the `Fingerprint` of the `ExpnData` does not collide with
1417 /// any other `ExpnIds`.
1419 /// This method is called only when an `ExpnData` is first associated
1420 /// with an `ExpnId` (when the `ExpnId` is initially constructed, or via
1421 /// `set_expn_data`). It is *not* called for foreign `ExpnId`s deserialized
1422 /// from another crate's metadata - since `ExpnHash` includes the stable crate id,
1423 /// collisions are only possible between `ExpnId`s within the same crate.
1424 fn update_disambiguator(expn_data: &mut ExpnData, mut ctx: impl HashStableContext) -> ExpnHash {
1425 // This disambiguator should not have been set yet.
1427 expn_data.disambiguator, 0,
1428 "Already set disambiguator for ExpnData: {:?}",
1431 let mut expn_hash = expn_data.hash_expn(&mut ctx);
1433 let disambiguator = HygieneData::with(|data| {
1434 // If this is the first ExpnData with a given hash, then keep our
1435 // disambiguator at 0 (the default u32 value)
1436 let disambig = data.expn_data_disambiguators.entry(expn_hash).or_default();
1437 let disambiguator = *disambig;
1442 if disambiguator != 0 {
1443 debug!("Set disambiguator for expn_data={:?} expn_hash={:?}", expn_data, expn_hash);
1445 expn_data.disambiguator = disambiguator;
1446 expn_hash = expn_data.hash_expn(&mut ctx);
1448 // Verify that the new disambiguator makes the hash unique
1449 #[cfg(debug_assertions)]
1450 HygieneData::with(|data| {
1452 data.expn_data_disambiguators.get(&expn_hash),
1454 "Hash collision after disambiguator update!",
1459 ExpnHash::new(ctx.def_path_hash(LOCAL_CRATE.as_def_id()).stable_crate_id(), expn_hash)
1462 impl<CTX: HashStableContext> HashStable<CTX> for SyntaxContext {
1463 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
1464 const TAG_EXPANSION: u8 = 0;
1465 const TAG_NO_EXPANSION: u8 = 1;
1467 if *self == SyntaxContext::root() {
1468 TAG_NO_EXPANSION.hash_stable(ctx, hasher);
1470 TAG_EXPANSION.hash_stable(ctx, hasher);
1471 let (expn_id, transparency) = self.outer_mark();
1472 expn_id.hash_stable(ctx, hasher);
1473 transparency.hash_stable(ctx, hasher);
1478 impl<CTX: HashStableContext> HashStable<CTX> for ExpnId {
1479 fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
1480 let hash = if *self == ExpnId::root() {
1481 // Avoid fetching TLS storage for a trivial often-used value.
1487 hash.hash_stable(ctx, hasher);