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.)
29 use crate::{Span, DUMMY_SP};
30 use crate::edition::Edition;
31 use crate::symbol::{kw, sym, Symbol};
33 use rustc_serialize::{Encodable, Decodable, Encoder, Decoder};
34 use rustc_data_structures::fx::FxHashMap;
35 use rustc_data_structures::sync::Lrc;
38 /// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
39 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
40 pub struct SyntaxContext(u32);
43 struct SyntaxContextData {
45 outer_transparency: Transparency,
46 parent: SyntaxContext,
47 /// This context, but with all transparent and semi-transparent expansions filtered away.
48 opaque: SyntaxContext,
49 /// This context, but with all transparent expansions filtered away.
50 opaque_and_semitransparent: SyntaxContext,
51 /// Name of the crate to which `$crate` with this context would resolve.
52 dollar_crate_name: Symbol,
55 /// A unique ID associated with a macro invocation and expansion.
56 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
57 pub struct ExpnId(u32);
59 /// A property of a macro expansion that determines how identifiers
60 /// produced by that expansion are resolved.
61 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug, RustcEncodable, RustcDecodable)]
62 pub enum Transparency {
63 /// Identifier produced by a transparent expansion is always resolved at call-site.
64 /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
66 /// Identifier produced by a semi-transparent expansion may be resolved
67 /// either at call-site or at definition-site.
68 /// If it's a local variable, label or `$crate` then it's resolved at def-site.
69 /// Otherwise it's resolved at call-site.
70 /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
71 /// but that's an implementation detail.
73 /// Identifier produced by an opaque expansion is always resolved at definition-site.
74 /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
79 pub fn fresh(expn_data: Option<ExpnData>) -> Self {
80 HygieneData::with(|data| data.fresh_expn(expn_data))
83 /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
85 pub fn root() -> Self {
90 pub fn as_u32(self) -> u32 {
95 pub fn from_u32(raw: u32) -> ExpnId {
100 pub fn expn_data(self) -> ExpnData {
101 HygieneData::with(|data| data.expn_data(self).clone())
105 pub fn set_expn_data(self, expn_data: ExpnData) {
106 HygieneData::with(|data| {
107 let old_expn_data = &mut data.expn_data[self.0 as usize];
108 assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
109 *old_expn_data = Some(expn_data);
113 pub fn is_descendant_of(self, ancestor: ExpnId) -> bool {
114 HygieneData::with(|data| data.is_descendant_of(self, ancestor))
117 /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
118 /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
119 pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
120 HygieneData::with(|data| data.is_descendant_of(self, data.outer_expn(ctxt)))
123 /// Returns span for the macro which originally caused this expansion to happen.
125 /// Stops backtracing at include! boundary.
126 pub fn expansion_cause(mut self) -> Option<Span> {
127 let mut last_macro = None;
129 let expn_data = self.expn_data();
130 // Stop going up the backtrace once include! is encountered
131 if expn_data.is_root() || expn_data.kind.descr() == sym::include {
134 self = expn_data.call_site.ctxt().outer_expn();
135 last_macro = Some(expn_data.call_site);
142 crate struct HygieneData {
143 /// Each expansion should have an associated expansion data, but sometimes there's a delay
144 /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
145 /// first and then resolved later), so we use an `Option` here.
146 expn_data: Vec<Option<ExpnData>>,
147 syntax_context_data: Vec<SyntaxContextData>,
148 syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
152 crate fn new(edition: Edition) -> Self {
154 expn_data: vec![Some(ExpnData::default(ExpnKind::Root, DUMMY_SP, edition))],
155 syntax_context_data: vec![SyntaxContextData {
156 outer_expn: ExpnId::root(),
157 outer_transparency: Transparency::Opaque,
158 parent: SyntaxContext(0),
159 opaque: SyntaxContext(0),
160 opaque_and_semitransparent: SyntaxContext(0),
161 dollar_crate_name: kw::DollarCrate,
163 syntax_context_map: FxHashMap::default(),
167 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
168 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
171 fn fresh_expn(&mut self, expn_data: Option<ExpnData>) -> ExpnId {
172 self.expn_data.push(expn_data);
173 ExpnId(self.expn_data.len() as u32 - 1)
176 fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
177 self.expn_data[expn_id.0 as usize].as_ref()
178 .expect("no expansion data for an expansion ID")
181 fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
182 while expn_id != ancestor {
183 if expn_id == ExpnId::root() {
186 expn_id = self.expn_data(expn_id).parent;
191 fn modern(&self, ctxt: SyntaxContext) -> SyntaxContext {
192 self.syntax_context_data[ctxt.0 as usize].opaque
195 fn modern_and_legacy(&self, ctxt: SyntaxContext) -> SyntaxContext {
196 self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
199 fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
200 self.syntax_context_data[ctxt.0 as usize].outer_expn
203 fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
204 let data = &self.syntax_context_data[ctxt.0 as usize];
205 (data.outer_expn, data.outer_transparency)
208 fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
209 self.syntax_context_data[ctxt.0 as usize].parent
212 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
213 let outer_mark = self.outer_mark(*ctxt);
214 *ctxt = self.parent_ctxt(*ctxt);
218 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
219 let mut marks = Vec::new();
220 while ctxt != SyntaxContext::root() {
221 marks.push(self.outer_mark(ctxt));
222 ctxt = self.parent_ctxt(ctxt);
228 fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
229 while span.from_expansion() && span.ctxt() != to {
230 span = self.expn_data(self.outer_expn(span.ctxt())).call_site;
235 fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
236 let mut scope = None;
237 while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
238 scope = Some(self.remove_mark(ctxt).0);
244 &mut self, ctxt: SyntaxContext, expn_id: ExpnId, transparency: Transparency
246 assert_ne!(expn_id, ExpnId::root());
247 if transparency == Transparency::Opaque {
248 return self.apply_mark_internal(ctxt, expn_id, transparency);
251 let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
252 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
253 self.modern(call_site_ctxt)
255 self.modern_and_legacy(call_site_ctxt)
258 if call_site_ctxt == SyntaxContext::root() {
259 return self.apply_mark_internal(ctxt, expn_id, transparency);
262 // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
263 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
265 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
266 // at their invocation. That is, we pretend that the macros 1.0 definition
267 // was defined at its invocation (i.e., inside the macros 2.0 definition)
268 // so that the macros 2.0 definition remains hygienic.
270 // See the example at `test/ui/hygiene/legacy_interaction.rs`.
271 for (expn_id, transparency) in self.marks(ctxt) {
272 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
274 self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
277 fn apply_mark_internal(
278 &mut self, ctxt: SyntaxContext, expn_id: ExpnId, transparency: Transparency
280 let syntax_context_data = &mut self.syntax_context_data;
281 let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
282 let mut opaque_and_semitransparent =
283 syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
285 if transparency >= Transparency::Opaque {
287 opaque = *self.syntax_context_map.entry((parent, expn_id, transparency))
289 let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
290 syntax_context_data.push(SyntaxContextData {
292 outer_transparency: transparency,
295 opaque_and_semitransparent: new_opaque,
296 dollar_crate_name: kw::DollarCrate,
302 if transparency >= Transparency::SemiTransparent {
303 let parent = opaque_and_semitransparent;
304 opaque_and_semitransparent =
305 *self.syntax_context_map.entry((parent, expn_id, transparency))
307 let new_opaque_and_semitransparent =
308 SyntaxContext(syntax_context_data.len() as u32);
309 syntax_context_data.push(SyntaxContextData {
311 outer_transparency: transparency,
314 opaque_and_semitransparent: new_opaque_and_semitransparent,
315 dollar_crate_name: kw::DollarCrate,
317 new_opaque_and_semitransparent
322 *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
323 let new_opaque_and_semitransparent_and_transparent =
324 SyntaxContext(syntax_context_data.len() as u32);
325 syntax_context_data.push(SyntaxContextData {
327 outer_transparency: transparency,
330 opaque_and_semitransparent,
331 dollar_crate_name: kw::DollarCrate,
333 new_opaque_and_semitransparent_and_transparent
338 pub fn clear_syntax_context_map() {
339 HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
342 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
343 HygieneData::with(|data| data.walk_chain(span, to))
346 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
347 // The new contexts that need updating are at the end of the list and have `$crate` as a name.
348 let (len, to_update) = HygieneData::with(|data| (
349 data.syntax_context_data.len(),
350 data.syntax_context_data.iter().rev()
351 .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate).count()
353 // The callback must be called from outside of the `HygieneData` lock,
354 // since it will try to acquire it too.
355 let range_to_update = len - to_update .. len;
357 range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
358 HygieneData::with(|data| range_to_update.zip(names.into_iter()).for_each(|(idx, name)| {
359 data.syntax_context_data[idx].dollar_crate_name = name;
363 pub fn debug_hygiene_data(verbose: bool) -> String {
364 HygieneData::with(|data| {
366 format!("{:#?}", data)
368 let mut s = String::from("");
369 s.push_str("Expansions:");
370 data.expn_data.iter().enumerate().for_each(|(id, expn_info)| {
371 let expn_info = expn_info.as_ref().expect("no expansion data for an expansion ID");
373 "\n{}: parent: {:?}, call_site_ctxt: {:?}, kind: {:?}",
376 expn_info.call_site.ctxt(),
380 s.push_str("\n\nSyntaxContexts:");
381 data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
383 "\n#{}: parent: {:?}, outer_mark: ({:?}, {:?})",
387 ctxt.outer_transparency,
397 pub const fn root() -> Self {
402 crate fn as_u32(self) -> u32 {
407 crate fn from_u32(raw: u32) -> SyntaxContext {
411 /// Extend a syntax context with a given expansion and transparency.
412 crate fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
413 HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
416 /// Pulls a single mark off of the syntax context. This effectively moves the
417 /// context up one macro definition level. That is, if we have a nested macro
418 /// definition as follows:
428 /// and we have a SyntaxContext that is referring to something declared by an invocation
429 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
430 /// invocation of f that created g1.
431 /// Returns the mark that was removed.
432 pub fn remove_mark(&mut self) -> ExpnId {
433 HygieneData::with(|data| data.remove_mark(self).0)
436 pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
437 HygieneData::with(|data| data.marks(self))
440 /// Adjust this context for resolution in a scope created by the given expansion.
441 /// For example, consider the following three resolutions of `f`:
444 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
446 /// macro m($f:ident) {
448 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
449 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
451 /// foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
452 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
453 /// //| and it resolves to `::foo::f`.
454 /// bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
455 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
456 /// //| and it resolves to `::bar::f`.
457 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
458 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
459 /// //| and it resolves to `::bar::$f`.
462 /// This returns the expansion whose definition scope we use to privacy check the resolution,
463 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
464 pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
465 HygieneData::with(|data| data.adjust(self, expn_id))
468 /// Like `SyntaxContext::adjust`, but also modernizes `self`.
469 pub fn modernize_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
470 HygieneData::with(|data| {
471 *self = data.modern(*self);
472 data.adjust(self, expn_id)
476 /// Adjust this context for resolution in a scope created by the given expansion
477 /// via a glob import with the given `SyntaxContext`.
482 /// macro m($i:ident) {
484 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
485 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
488 /// macro n($j:ident) {
490 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
491 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
492 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
493 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
494 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
495 /// //^ This cannot be glob-adjusted, so this is a resolution error.
499 /// This returns `None` if the context cannot be glob-adjusted.
500 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
501 pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
502 HygieneData::with(|data| {
503 let mut scope = None;
504 let mut glob_ctxt = data.modern(glob_span.ctxt());
505 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
506 scope = Some(data.remove_mark(&mut glob_ctxt).0);
507 if data.remove_mark(self).0 != scope.unwrap() {
511 if data.adjust(self, expn_id).is_some() {
518 /// Undo `glob_adjust` if possible:
521 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
522 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
525 pub fn reverse_glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span)
526 -> Option<Option<ExpnId>> {
527 HygieneData::with(|data| {
528 if data.adjust(self, expn_id).is_some() {
532 let mut glob_ctxt = data.modern(glob_span.ctxt());
533 let mut marks = Vec::new();
534 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
535 marks.push(data.remove_mark(&mut glob_ctxt));
538 let scope = marks.last().map(|mark| mark.0);
539 while let Some((expn_id, transparency)) = marks.pop() {
540 *self = data.apply_mark(*self, expn_id, transparency);
546 pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
547 HygieneData::with(|data| {
548 let mut self_modern = data.modern(self);
549 data.adjust(&mut self_modern, expn_id);
550 self_modern == data.modern(other)
555 pub fn modern(self) -> SyntaxContext {
556 HygieneData::with(|data| data.modern(self))
560 pub fn modern_and_legacy(self) -> SyntaxContext {
561 HygieneData::with(|data| data.modern_and_legacy(self))
565 pub fn outer_expn(self) -> ExpnId {
566 HygieneData::with(|data| data.outer_expn(self))
569 /// `ctxt.outer_expn_data()` is equivalent to but faster than
570 /// `ctxt.outer_expn().expn_data()`.
572 pub fn outer_expn_data(self) -> ExpnData {
573 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
577 pub fn outer_mark_with_data(self) -> (ExpnId, Transparency, ExpnData) {
578 HygieneData::with(|data| {
579 let (expn_id, transparency) = data.outer_mark(self);
580 (expn_id, transparency, data.expn_data(expn_id).clone())
584 pub fn dollar_crate_name(self) -> Symbol {
585 HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
589 impl fmt::Debug for SyntaxContext {
590 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
591 write!(f, "#{}", self.0)
596 /// Creates a fresh expansion with given properties.
597 /// Expansions are normally created by macros, but in some cases expansions are created for
598 /// other compiler-generated code to set per-span properties like allowed unstable features.
599 /// The returned span belongs to the created expansion and has the new properties,
600 /// but its location is inherited from the current span.
601 pub fn fresh_expansion(self, expn_data: ExpnData) -> Span {
602 self.fresh_expansion_with_transparency(expn_data, Transparency::Transparent)
605 pub fn fresh_expansion_with_transparency(
606 self, expn_data: ExpnData, transparency: Transparency
608 HygieneData::with(|data| {
609 let expn_id = data.fresh_expn(Some(expn_data));
610 self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
615 /// A subset of properties from both macro definition and macro call available through global data.
616 /// Avoid using this if you have access to the original definition or call structures.
617 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
618 pub struct ExpnData {
619 // --- The part unique to each expansion.
620 /// The kind of this expansion - macro or compiler desugaring.
622 /// The expansion that produced this expansion.
624 /// The location of the actual macro invocation or syntax sugar , e.g.
625 /// `let x = foo!();` or `if let Some(y) = x {}`
627 /// This may recursively refer to other macro invocations, e.g., if
628 /// `foo!()` invoked `bar!()` internally, and there was an
629 /// expression inside `bar!`; the call_site of the expression in
630 /// the expansion would point to the `bar!` invocation; that
631 /// call_site span would have its own ExpnData, with the call_site
632 /// pointing to the `foo!` invocation.
635 // --- The part specific to the macro/desugaring definition.
636 // --- It may be reasonable to share this part between expansions with the same definition,
637 // --- but such sharing is known to bring some minor inconveniences without also bringing
638 // --- noticeable perf improvements (PR #62898).
639 /// The span of the macro definition (possibly dummy).
640 /// This span serves only informational purpose and is not used for resolution.
642 /// List of #[unstable]/feature-gated features that the macro is allowed to use
643 /// internally without forcing the whole crate to opt-in
645 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
646 /// Whether the macro is allowed to use `unsafe` internally
647 /// even if the user crate has `#![forbid(unsafe_code)]`.
648 pub allow_internal_unsafe: bool,
649 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
650 /// for a given macro.
651 pub local_inner_macros: bool,
652 /// Edition of the crate in which the macro is defined.
653 pub edition: Edition,
657 /// Constructs expansion data with default properties.
658 pub fn default(kind: ExpnKind, call_site: Span, edition: Edition) -> ExpnData {
661 parent: ExpnId::root(),
664 allow_internal_unstable: None,
665 allow_internal_unsafe: false,
666 local_inner_macros: false,
671 pub fn allow_unstable(kind: ExpnKind, call_site: Span, edition: Edition,
672 allow_internal_unstable: Lrc<[Symbol]>) -> ExpnData {
674 allow_internal_unstable: Some(allow_internal_unstable),
675 ..ExpnData::default(kind, call_site, edition)
680 pub fn is_root(&self) -> bool {
681 if let ExpnKind::Root = self.kind { true } else { false }
686 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
688 /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
690 /// Expansion produced by a macro.
691 Macro(MacroKind, Symbol),
692 /// Transform done by the compiler on the AST.
694 /// Desugaring done by the compiler during HIR lowering.
695 Desugaring(DesugaringKind)
699 pub fn descr(&self) -> Symbol {
701 ExpnKind::Root => kw::PathRoot,
702 ExpnKind::Macro(_, descr) => descr,
703 ExpnKind::AstPass(kind) => Symbol::intern(kind.descr()),
704 ExpnKind::Desugaring(kind) => Symbol::intern(kind.descr()),
709 /// The kind of macro invocation or definition.
710 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
712 /// A bang macro `foo!()`.
714 /// An attribute macro `#[foo]`.
716 /// A derive macro `#[derive(Foo)]`
721 pub fn descr(self) -> &'static str {
723 MacroKind::Bang => "macro",
724 MacroKind::Attr => "attribute macro",
725 MacroKind::Derive => "derive macro",
729 pub fn descr_expected(self) -> &'static str {
731 MacroKind::Attr => "attribute",
736 pub fn article(self) -> &'static str {
738 MacroKind::Attr => "an",
744 /// The kind of AST transform.
745 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable)]
754 fn descr(self) -> &'static str {
756 AstPass::StdImports => "standard library imports",
757 AstPass::TestHarness => "test harness",
758 AstPass::ProcMacroHarness => "proc macro harness",
759 AstPass::PluginMacroDefs => "plugin macro definitions",
764 /// The kind of compiler desugaring.
765 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable)]
766 pub enum DesugaringKind {
767 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
768 /// However, we do not want to blame `c` for unreachability but rather say that `i`
769 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
770 /// This also applies to `while` loops.
774 /// Desugaring of an `impl Trait` in return type position
775 /// to an `type Foo = impl Trait;` and replacing the
776 /// `impl Trait` with `Foo`.
783 impl DesugaringKind {
784 /// The description wording should combine well with "desugaring of {}".
785 fn descr(self) -> &'static str {
787 DesugaringKind::CondTemporary => "`if` or `while` condition",
788 DesugaringKind::Async => "`async` block or function",
789 DesugaringKind::Await => "`await` expression",
790 DesugaringKind::QuestionMark => "operator `?`",
791 DesugaringKind::TryBlock => "`try` block",
792 DesugaringKind::OpaqueTy => "`impl Trait`",
793 DesugaringKind::ForLoop => "`for` loop",
798 impl Encodable for ExpnId {
799 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
800 Ok(()) // FIXME(jseyfried) intercrate hygiene
804 impl Decodable for ExpnId {
805 fn decode<D: Decoder>(_: &mut D) -> Result<Self, D::Error> {
806 Ok(ExpnId::root()) // FIXME(jseyfried) intercrate hygiene