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>
8 // Hygiene data is stored in a global variable and accessed via TLS, which
9 // means that accesses are somewhat expensive. (`HygieneData::with`
10 // encapsulates a single access.) Therefore, on hot code paths it is worth
11 // ensuring that multiple HygieneData accesses are combined into a single
12 // `HygieneData::with`.
14 // This explains why `HygieneData`, `SyntaxContext` and `ExpnId` have interfaces
15 // with a certain amount of redundancy in them. For example,
16 // `SyntaxContext::outer_expn_data` combines `SyntaxContext::outer` and
17 // `ExpnId::expn_data` so that two `HygieneData` accesses can be performed within
18 // a single `HygieneData::with` call.
20 // It also explains why many functions appear in `HygieneData` and again in
21 // `SyntaxContext` or `ExpnId`. For example, `HygieneData::outer` and
22 // `SyntaxContext::outer` do the same thing, but the former is for use within a
23 // `HygieneData::with` call while the latter is for use outside such a call.
24 // When modifying this file it is important to understand this distinction,
25 // because getting it wrong can lead to nested `HygieneData::with` calls that
26 // trigger runtime aborts. (Fortunately these are obvious and easy to fix.)
28 use crate::edition::Edition;
29 use crate::symbol::{kw, sym, Symbol};
31 use crate::{Span, DUMMY_SP};
33 use rustc_data_structures::fx::FxHashMap;
34 use rustc_data_structures::sync::Lrc;
35 use rustc_macros::HashStable_Generic;
36 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
39 /// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
40 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
41 pub struct SyntaxContext(u32);
44 struct SyntaxContextData {
46 outer_transparency: Transparency,
47 parent: SyntaxContext,
48 /// This context, but with all transparent and semi-transparent expansions filtered away.
49 opaque: SyntaxContext,
50 /// This context, but with all transparent expansions filtered away.
51 opaque_and_semitransparent: SyntaxContext,
52 /// Name of the crate to which `$crate` with this context would resolve.
53 dollar_crate_name: Symbol,
56 /// A unique ID associated with a macro invocation and expansion.
57 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
58 pub struct ExpnId(u32);
60 /// A property of a macro expansion that determines how identifiers
61 /// produced by that expansion are resolved.
74 pub enum Transparency {
75 /// Identifier produced by a transparent expansion is always resolved at call-site.
76 /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
78 /// Identifier produced by a semi-transparent expansion may be resolved
79 /// either at call-site or at definition-site.
80 /// If it's a local variable, label or `$crate` then it's resolved at def-site.
81 /// Otherwise it's resolved at call-site.
82 /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
83 /// but that's an implementation detail.
85 /// Identifier produced by an opaque expansion is always resolved at definition-site.
86 /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
91 pub fn fresh(expn_data: Option<ExpnData>) -> Self {
92 HygieneData::with(|data| data.fresh_expn(expn_data))
95 /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
97 pub fn root() -> Self {
102 pub fn as_u32(self) -> u32 {
107 pub fn from_u32(raw: u32) -> ExpnId {
112 pub fn expn_data(self) -> ExpnData {
113 HygieneData::with(|data| data.expn_data(self).clone())
117 pub fn set_expn_data(self, expn_data: ExpnData) {
118 HygieneData::with(|data| {
119 let old_expn_data = &mut data.expn_data[self.0 as usize];
120 assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
121 *old_expn_data = Some(expn_data);
125 pub fn is_descendant_of(self, ancestor: ExpnId) -> bool {
126 HygieneData::with(|data| data.is_descendant_of(self, ancestor))
129 /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
130 /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
131 pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
132 HygieneData::with(|data| data.is_descendant_of(self, data.outer_expn(ctxt)))
135 /// Returns span for the macro which originally caused this expansion to happen.
137 /// Stops backtracing at include! boundary.
138 pub fn expansion_cause(mut self) -> Option<Span> {
139 let mut last_macro = None;
141 let expn_data = self.expn_data();
142 // Stop going up the backtrace once include! is encountered
143 if expn_data.is_root() || expn_data.kind.descr() == sym::include {
146 self = expn_data.call_site.ctxt().outer_expn();
147 last_macro = Some(expn_data.call_site);
154 crate struct HygieneData {
155 /// Each expansion should have an associated expansion data, but sometimes there's a delay
156 /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
157 /// first and then resolved later), so we use an `Option` here.
158 expn_data: Vec<Option<ExpnData>>,
159 syntax_context_data: Vec<SyntaxContextData>,
160 syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
164 crate fn new(edition: Edition) -> Self {
166 expn_data: vec![Some(ExpnData::default(ExpnKind::Root, DUMMY_SP, edition))],
167 syntax_context_data: vec![SyntaxContextData {
168 outer_expn: ExpnId::root(),
169 outer_transparency: Transparency::Opaque,
170 parent: SyntaxContext(0),
171 opaque: SyntaxContext(0),
172 opaque_and_semitransparent: SyntaxContext(0),
173 dollar_crate_name: kw::DollarCrate,
175 syntax_context_map: FxHashMap::default(),
179 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
180 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
183 fn fresh_expn(&mut self, expn_data: Option<ExpnData>) -> ExpnId {
184 self.expn_data.push(expn_data);
185 ExpnId(self.expn_data.len() as u32 - 1)
188 fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
189 self.expn_data[expn_id.0 as usize].as_ref().expect("no expansion data for an expansion ID")
192 fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
193 while expn_id != ancestor {
194 if expn_id == ExpnId::root() {
197 expn_id = self.expn_data(expn_id).parent;
202 fn modern(&self, ctxt: SyntaxContext) -> SyntaxContext {
203 self.syntax_context_data[ctxt.0 as usize].opaque
206 fn modern_and_legacy(&self, ctxt: SyntaxContext) -> SyntaxContext {
207 self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
210 fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
211 self.syntax_context_data[ctxt.0 as usize].outer_expn
214 fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
215 let data = &self.syntax_context_data[ctxt.0 as usize];
216 (data.outer_expn, data.outer_transparency)
219 fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
220 self.syntax_context_data[ctxt.0 as usize].parent
223 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
224 let outer_mark = self.outer_mark(*ctxt);
225 *ctxt = self.parent_ctxt(*ctxt);
229 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
230 let mut marks = Vec::new();
231 while ctxt != SyntaxContext::root() {
232 marks.push(self.outer_mark(ctxt));
233 ctxt = self.parent_ctxt(ctxt);
239 fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
240 while span.from_expansion() && span.ctxt() != to {
241 span = self.expn_data(self.outer_expn(span.ctxt())).call_site;
246 fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
247 let mut scope = None;
248 while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
249 scope = Some(self.remove_mark(ctxt).0);
258 transparency: Transparency,
260 assert_ne!(expn_id, ExpnId::root());
261 if transparency == Transparency::Opaque {
262 return self.apply_mark_internal(ctxt, expn_id, transparency);
265 let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
266 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
267 self.modern(call_site_ctxt)
269 self.modern_and_legacy(call_site_ctxt)
272 if call_site_ctxt == SyntaxContext::root() {
273 return self.apply_mark_internal(ctxt, expn_id, transparency);
276 // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
277 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
279 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
280 // at their invocation. That is, we pretend that the macros 1.0 definition
281 // was defined at its invocation (i.e., inside the macros 2.0 definition)
282 // so that the macros 2.0 definition remains hygienic.
284 // See the example at `test/ui/hygiene/legacy_interaction.rs`.
285 for (expn_id, transparency) in self.marks(ctxt) {
286 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
288 self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
291 fn apply_mark_internal(
295 transparency: Transparency,
297 let syntax_context_data = &mut self.syntax_context_data;
298 let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
299 let mut opaque_and_semitransparent =
300 syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
302 if transparency >= Transparency::Opaque {
306 .entry((parent, expn_id, transparency))
308 let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
309 syntax_context_data.push(SyntaxContextData {
311 outer_transparency: transparency,
314 opaque_and_semitransparent: new_opaque,
315 dollar_crate_name: kw::DollarCrate,
321 if transparency >= Transparency::SemiTransparent {
322 let parent = opaque_and_semitransparent;
323 opaque_and_semitransparent = *self
325 .entry((parent, expn_id, transparency))
327 let new_opaque_and_semitransparent =
328 SyntaxContext(syntax_context_data.len() as u32);
329 syntax_context_data.push(SyntaxContextData {
331 outer_transparency: transparency,
334 opaque_and_semitransparent: new_opaque_and_semitransparent,
335 dollar_crate_name: kw::DollarCrate,
337 new_opaque_and_semitransparent
342 *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
343 let new_opaque_and_semitransparent_and_transparent =
344 SyntaxContext(syntax_context_data.len() as u32);
345 syntax_context_data.push(SyntaxContextData {
347 outer_transparency: transparency,
350 opaque_and_semitransparent,
351 dollar_crate_name: kw::DollarCrate,
353 new_opaque_and_semitransparent_and_transparent
358 pub fn clear_syntax_context_map() {
359 HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
362 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
363 HygieneData::with(|data| data.walk_chain(span, to))
366 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
367 // The new contexts that need updating are at the end of the list and have `$crate` as a name.
368 let (len, to_update) = HygieneData::with(|data| {
370 data.syntax_context_data.len(),
371 data.syntax_context_data
374 .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate)
378 // The callback must be called from outside of the `HygieneData` lock,
379 // since it will try to acquire it too.
380 let range_to_update = len - to_update..len;
382 range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
383 HygieneData::with(|data| {
384 range_to_update.zip(names.into_iter()).for_each(|(idx, name)| {
385 data.syntax_context_data[idx].dollar_crate_name = name;
390 pub fn debug_hygiene_data(verbose: bool) -> String {
391 HygieneData::with(|data| {
393 format!("{:#?}", data)
395 let mut s = String::from("");
396 s.push_str("Expansions:");
397 data.expn_data.iter().enumerate().for_each(|(id, expn_info)| {
398 let expn_info = expn_info.as_ref().expect("no expansion data for an expansion ID");
400 "\n{}: parent: {:?}, call_site_ctxt: {:?}, kind: {:?}",
403 expn_info.call_site.ctxt(),
407 s.push_str("\n\nSyntaxContexts:");
408 data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
410 "\n#{}: parent: {:?}, outer_mark: ({:?}, {:?})",
411 id, ctxt.parent, ctxt.outer_expn, ctxt.outer_transparency,
421 pub const fn root() -> Self {
426 crate fn as_u32(self) -> u32 {
431 crate fn from_u32(raw: u32) -> SyntaxContext {
435 /// Extend a syntax context with a given expansion and transparency.
436 crate fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
437 HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
440 /// Pulls a single mark off of the syntax context. This effectively moves the
441 /// context up one macro definition level. That is, if we have a nested macro
442 /// definition as follows:
452 /// and we have a SyntaxContext that is referring to something declared by an invocation
453 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
454 /// invocation of f that created g1.
455 /// Returns the mark that was removed.
456 pub fn remove_mark(&mut self) -> ExpnId {
457 HygieneData::with(|data| data.remove_mark(self).0)
460 pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
461 HygieneData::with(|data| data.marks(self))
464 /// Adjust this context for resolution in a scope created by the given expansion.
465 /// For example, consider the following three resolutions of `f`:
468 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
470 /// macro m($f:ident) {
472 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
473 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
475 /// foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
476 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
477 /// //| and it resolves to `::foo::f`.
478 /// bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
479 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
480 /// //| and it resolves to `::bar::f`.
481 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
482 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
483 /// //| and it resolves to `::bar::$f`.
486 /// This returns the expansion whose definition scope we use to privacy check the resolution,
487 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
488 pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
489 HygieneData::with(|data| data.adjust(self, expn_id))
492 /// Like `SyntaxContext::adjust`, but also modernizes `self`.
493 pub fn modernize_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
494 HygieneData::with(|data| {
495 *self = data.modern(*self);
496 data.adjust(self, expn_id)
500 /// Adjust this context for resolution in a scope created by the given expansion
501 /// via a glob import with the given `SyntaxContext`.
506 /// macro m($i:ident) {
508 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
509 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
512 /// macro n($j:ident) {
514 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
515 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
516 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
517 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
518 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
519 /// //^ This cannot be glob-adjusted, so this is a resolution error.
523 /// This returns `None` if the context cannot be glob-adjusted.
524 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
525 pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
526 HygieneData::with(|data| {
527 let mut scope = None;
528 let mut glob_ctxt = data.modern(glob_span.ctxt());
529 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
530 scope = Some(data.remove_mark(&mut glob_ctxt).0);
531 if data.remove_mark(self).0 != scope.unwrap() {
535 if data.adjust(self, expn_id).is_some() {
542 /// Undo `glob_adjust` if possible:
545 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
546 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
549 pub fn reverse_glob_adjust(
553 ) -> Option<Option<ExpnId>> {
554 HygieneData::with(|data| {
555 if data.adjust(self, expn_id).is_some() {
559 let mut glob_ctxt = data.modern(glob_span.ctxt());
560 let mut marks = Vec::new();
561 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
562 marks.push(data.remove_mark(&mut glob_ctxt));
565 let scope = marks.last().map(|mark| mark.0);
566 while let Some((expn_id, transparency)) = marks.pop() {
567 *self = data.apply_mark(*self, expn_id, transparency);
573 pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
574 HygieneData::with(|data| {
575 let mut self_modern = data.modern(self);
576 data.adjust(&mut self_modern, expn_id);
577 self_modern == data.modern(other)
582 pub fn modern(self) -> SyntaxContext {
583 HygieneData::with(|data| data.modern(self))
587 pub fn modern_and_legacy(self) -> SyntaxContext {
588 HygieneData::with(|data| data.modern_and_legacy(self))
592 pub fn outer_expn(self) -> ExpnId {
593 HygieneData::with(|data| data.outer_expn(self))
596 /// `ctxt.outer_expn_data()` is equivalent to but faster than
597 /// `ctxt.outer_expn().expn_data()`.
599 pub fn outer_expn_data(self) -> ExpnData {
600 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
604 pub fn outer_mark_with_data(self) -> (ExpnId, Transparency, ExpnData) {
605 HygieneData::with(|data| {
606 let (expn_id, transparency) = data.outer_mark(self);
607 (expn_id, transparency, data.expn_data(expn_id).clone())
611 pub fn dollar_crate_name(self) -> Symbol {
612 HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
616 impl fmt::Debug for SyntaxContext {
617 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
618 write!(f, "#{}", self.0)
623 /// Creates a fresh expansion with given properties.
624 /// Expansions are normally created by macros, but in some cases expansions are created for
625 /// other compiler-generated code to set per-span properties like allowed unstable features.
626 /// The returned span belongs to the created expansion and has the new properties,
627 /// but its location is inherited from the current span.
628 pub fn fresh_expansion(self, expn_data: ExpnData) -> Span {
629 self.fresh_expansion_with_transparency(expn_data, Transparency::Transparent)
632 pub fn fresh_expansion_with_transparency(
635 transparency: Transparency,
637 HygieneData::with(|data| {
638 let expn_id = data.fresh_expn(Some(expn_data));
639 self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
644 /// A subset of properties from both macro definition and macro call available through global data.
645 /// Avoid using this if you have access to the original definition or call structures.
646 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
647 pub struct ExpnData {
648 // --- The part unique to each expansion.
649 /// The kind of this expansion - macro or compiler desugaring.
651 /// The expansion that produced this expansion.
652 #[stable_hasher(ignore)]
654 /// The location of the actual macro invocation or syntax sugar , e.g.
655 /// `let x = foo!();` or `if let Some(y) = x {}`
657 /// This may recursively refer to other macro invocations, e.g., if
658 /// `foo!()` invoked `bar!()` internally, and there was an
659 /// expression inside `bar!`; the call_site of the expression in
660 /// the expansion would point to the `bar!` invocation; that
661 /// call_site span would have its own ExpnData, with the call_site
662 /// pointing to the `foo!` invocation.
665 // --- The part specific to the macro/desugaring definition.
666 // --- It may be reasonable to share this part between expansions with the same definition,
667 // --- but such sharing is known to bring some minor inconveniences without also bringing
668 // --- noticeable perf improvements (PR #62898).
669 /// The span of the macro definition (possibly dummy).
670 /// This span serves only informational purpose and is not used for resolution.
672 /// List of #[unstable]/feature-gated features that the macro is allowed to use
673 /// internally without forcing the whole crate to opt-in
675 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
676 /// Whether the macro is allowed to use `unsafe` internally
677 /// even if the user crate has `#![forbid(unsafe_code)]`.
678 pub allow_internal_unsafe: bool,
679 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
680 /// for a given macro.
681 pub local_inner_macros: bool,
682 /// Edition of the crate in which the macro is defined.
683 pub edition: Edition,
687 /// Constructs expansion data with default properties.
688 pub fn default(kind: ExpnKind, call_site: Span, edition: Edition) -> ExpnData {
691 parent: ExpnId::root(),
694 allow_internal_unstable: None,
695 allow_internal_unsafe: false,
696 local_inner_macros: false,
701 pub fn allow_unstable(
705 allow_internal_unstable: Lrc<[Symbol]>,
708 allow_internal_unstable: Some(allow_internal_unstable),
709 ..ExpnData::default(kind, call_site, edition)
714 pub fn is_root(&self) -> bool {
715 if let ExpnKind::Root = self.kind { true } else { false }
720 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
722 /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
724 /// Expansion produced by a macro.
725 Macro(MacroKind, Symbol),
726 /// Transform done by the compiler on the AST.
728 /// Desugaring done by the compiler during HIR lowering.
729 Desugaring(DesugaringKind),
733 pub fn descr(&self) -> Symbol {
735 ExpnKind::Root => kw::PathRoot,
736 ExpnKind::Macro(_, descr) => descr,
737 ExpnKind::AstPass(kind) => Symbol::intern(kind.descr()),
738 ExpnKind::Desugaring(kind) => Symbol::intern(kind.descr()),
743 /// The kind of macro invocation or definition.
756 /// A bang macro `foo!()`.
758 /// An attribute macro `#[foo]`.
760 /// A derive macro `#[derive(Foo)]`
765 pub fn descr(self) -> &'static str {
767 MacroKind::Bang => "macro",
768 MacroKind::Attr => "attribute macro",
769 MacroKind::Derive => "derive macro",
773 pub fn descr_expected(self) -> &'static str {
775 MacroKind::Attr => "attribute",
780 pub fn article(self) -> &'static str {
782 MacroKind::Attr => "an",
788 /// The kind of AST transform.
789 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
797 fn descr(self) -> &'static str {
799 AstPass::StdImports => "standard library imports",
800 AstPass::TestHarness => "test harness",
801 AstPass::ProcMacroHarness => "proc macro harness",
806 /// The kind of compiler desugaring.
807 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
808 pub enum DesugaringKind {
809 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
810 /// However, we do not want to blame `c` for unreachability but rather say that `i`
811 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
812 /// This also applies to `while` loops.
816 /// Desugaring of an `impl Trait` in return type position
817 /// to an `type Foo = impl Trait;` and replacing the
818 /// `impl Trait` with `Foo`.
825 impl DesugaringKind {
826 /// The description wording should combine well with "desugaring of {}".
827 fn descr(self) -> &'static str {
829 DesugaringKind::CondTemporary => "`if` or `while` condition",
830 DesugaringKind::Async => "`async` block or function",
831 DesugaringKind::Await => "`await` expression",
832 DesugaringKind::QuestionMark => "operator `?`",
833 DesugaringKind::TryBlock => "`try` block",
834 DesugaringKind::OpaqueTy => "`impl Trait`",
835 DesugaringKind::ForLoop => "`for` loop",
840 impl Encodable for ExpnId {
841 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
842 Ok(()) // FIXME(jseyfried) intercrate hygiene
846 impl Decodable for ExpnId {
847 fn decode<D: Decoder>(_: &mut D) -> Result<Self, D::Error> {
848 Ok(ExpnId::root()) // FIXME(jseyfried) intercrate hygiene