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, 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)))
125 crate struct HygieneData {
126 /// Each expansion should have an associated expansion data, but sometimes there's a delay
127 /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
128 /// first and then resolved later), so we use an `Option` here.
129 expn_data: Vec<Option<ExpnData>>,
130 syntax_context_data: Vec<SyntaxContextData>,
131 syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
135 crate fn new(edition: Edition) -> Self {
137 expn_data: vec![Some(ExpnData::default(ExpnKind::Root, DUMMY_SP, edition))],
138 syntax_context_data: vec![SyntaxContextData {
139 outer_expn: ExpnId::root(),
140 outer_transparency: Transparency::Opaque,
141 parent: SyntaxContext(0),
142 opaque: SyntaxContext(0),
143 opaque_and_semitransparent: SyntaxContext(0),
144 dollar_crate_name: kw::DollarCrate,
146 syntax_context_map: FxHashMap::default(),
150 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
151 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
154 fn fresh_expn(&mut self, expn_data: Option<ExpnData>) -> ExpnId {
155 self.expn_data.push(expn_data);
156 ExpnId(self.expn_data.len() as u32 - 1)
159 fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
160 self.expn_data[expn_id.0 as usize].as_ref()
161 .expect("no expansion data for an expansion ID")
164 fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
165 while expn_id != ancestor {
166 if expn_id == ExpnId::root() {
169 expn_id = self.expn_data(expn_id).parent;
174 fn modern(&self, ctxt: SyntaxContext) -> SyntaxContext {
175 self.syntax_context_data[ctxt.0 as usize].opaque
178 fn modern_and_legacy(&self, ctxt: SyntaxContext) -> SyntaxContext {
179 self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
182 fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
183 self.syntax_context_data[ctxt.0 as usize].outer_expn
186 fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
187 let data = &self.syntax_context_data[ctxt.0 as usize];
188 (data.outer_expn, data.outer_transparency)
191 fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
192 self.syntax_context_data[ctxt.0 as usize].parent
195 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
196 let outer_mark = self.outer_mark(*ctxt);
197 *ctxt = self.parent_ctxt(*ctxt);
201 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
202 let mut marks = Vec::new();
203 while ctxt != SyntaxContext::root() {
204 marks.push(self.outer_mark(ctxt));
205 ctxt = self.parent_ctxt(ctxt);
211 fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
212 while span.from_expansion() && span.ctxt() != to {
213 span = self.expn_data(self.outer_expn(span.ctxt())).call_site;
218 fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
219 let mut scope = None;
220 while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
221 scope = Some(self.remove_mark(ctxt).0);
227 &mut self, ctxt: SyntaxContext, expn_id: ExpnId, transparency: Transparency
229 assert_ne!(expn_id, ExpnId::root());
230 if transparency == Transparency::Opaque {
231 return self.apply_mark_internal(ctxt, expn_id, transparency);
234 let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
235 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
236 self.modern(call_site_ctxt)
238 self.modern_and_legacy(call_site_ctxt)
241 if call_site_ctxt == SyntaxContext::root() {
242 return self.apply_mark_internal(ctxt, expn_id, transparency);
245 // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
246 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
248 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
249 // at their invocation. That is, we pretend that the macros 1.0 definition
250 // was defined at its invocation (i.e., inside the macros 2.0 definition)
251 // so that the macros 2.0 definition remains hygienic.
253 // See the example at `test/ui/hygiene/legacy_interaction.rs`.
254 for (expn_id, transparency) in self.marks(ctxt) {
255 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
257 self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
260 fn apply_mark_internal(
261 &mut self, ctxt: SyntaxContext, expn_id: ExpnId, transparency: Transparency
263 let syntax_context_data = &mut self.syntax_context_data;
264 let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
265 let mut opaque_and_semitransparent =
266 syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
268 if transparency >= Transparency::Opaque {
270 opaque = *self.syntax_context_map.entry((parent, expn_id, transparency))
272 let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
273 syntax_context_data.push(SyntaxContextData {
275 outer_transparency: transparency,
278 opaque_and_semitransparent: new_opaque,
279 dollar_crate_name: kw::DollarCrate,
285 if transparency >= Transparency::SemiTransparent {
286 let parent = opaque_and_semitransparent;
287 opaque_and_semitransparent =
288 *self.syntax_context_map.entry((parent, expn_id, transparency))
290 let new_opaque_and_semitransparent =
291 SyntaxContext(syntax_context_data.len() as u32);
292 syntax_context_data.push(SyntaxContextData {
294 outer_transparency: transparency,
297 opaque_and_semitransparent: new_opaque_and_semitransparent,
298 dollar_crate_name: kw::DollarCrate,
300 new_opaque_and_semitransparent
305 *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
306 let new_opaque_and_semitransparent_and_transparent =
307 SyntaxContext(syntax_context_data.len() as u32);
308 syntax_context_data.push(SyntaxContextData {
310 outer_transparency: transparency,
313 opaque_and_semitransparent,
314 dollar_crate_name: kw::DollarCrate,
316 new_opaque_and_semitransparent_and_transparent
321 pub fn clear_syntax_context_map() {
322 HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
325 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
326 HygieneData::with(|data| data.walk_chain(span, to))
329 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
330 // The new contexts that need updating are at the end of the list and have `$crate` as a name.
331 let (len, to_update) = HygieneData::with(|data| (
332 data.syntax_context_data.len(),
333 data.syntax_context_data.iter().rev()
334 .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate).count()
336 // The callback must be called from outside of the `HygieneData` lock,
337 // since it will try to acquire it too.
338 let range_to_update = len - to_update .. len;
340 range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
341 HygieneData::with(|data| range_to_update.zip(names.into_iter()).for_each(|(idx, name)| {
342 data.syntax_context_data[idx].dollar_crate_name = name;
348 pub const fn root() -> Self {
353 crate fn as_u32(self) -> u32 {
358 crate fn from_u32(raw: u32) -> SyntaxContext {
362 /// Extend a syntax context with a given expansion and transparency.
363 crate fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
364 HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
367 /// Pulls a single mark off of the syntax context. This effectively moves the
368 /// context up one macro definition level. That is, if we have a nested macro
369 /// definition as follows:
379 /// and we have a SyntaxContext that is referring to something declared by an invocation
380 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
381 /// invocation of f that created g1.
382 /// Returns the mark that was removed.
383 pub fn remove_mark(&mut self) -> ExpnId {
384 HygieneData::with(|data| data.remove_mark(self).0)
387 pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
388 HygieneData::with(|data| data.marks(self))
391 /// Adjust this context for resolution in a scope created by the given expansion.
392 /// For example, consider the following three resolutions of `f`:
395 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
397 /// macro m($f:ident) {
399 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
400 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
402 /// foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
403 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
404 /// //| and it resolves to `::foo::f`.
405 /// bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
406 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
407 /// //| and it resolves to `::bar::f`.
408 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
409 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
410 /// //| and it resolves to `::bar::$f`.
413 /// This returns the expansion whose definition scope we use to privacy check the resolution,
414 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
415 pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
416 HygieneData::with(|data| data.adjust(self, expn_id))
419 /// Like `SyntaxContext::adjust`, but also modernizes `self`.
420 pub fn modernize_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
421 HygieneData::with(|data| {
422 *self = data.modern(*self);
423 data.adjust(self, expn_id)
427 /// Adjust this context for resolution in a scope created by the given expansion
428 /// via a glob import with the given `SyntaxContext`.
433 /// macro m($i:ident) {
435 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
436 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
439 /// macro n($j:ident) {
441 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
442 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
443 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
444 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
445 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
446 /// //^ This cannot be glob-adjusted, so this is a resolution error.
450 /// This returns `None` if the context cannot be glob-adjusted.
451 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
452 pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
453 HygieneData::with(|data| {
454 let mut scope = None;
455 let mut glob_ctxt = data.modern(glob_span.ctxt());
456 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
457 scope = Some(data.remove_mark(&mut glob_ctxt).0);
458 if data.remove_mark(self).0 != scope.unwrap() {
462 if data.adjust(self, expn_id).is_some() {
469 /// Undo `glob_adjust` if possible:
472 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
473 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
476 pub fn reverse_glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span)
477 -> Option<Option<ExpnId>> {
478 HygieneData::with(|data| {
479 if data.adjust(self, expn_id).is_some() {
483 let mut glob_ctxt = data.modern(glob_span.ctxt());
484 let mut marks = Vec::new();
485 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
486 marks.push(data.remove_mark(&mut glob_ctxt));
489 let scope = marks.last().map(|mark| mark.0);
490 while let Some((expn_id, transparency)) = marks.pop() {
491 *self = data.apply_mark(*self, expn_id, transparency);
497 pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
498 HygieneData::with(|data| {
499 let mut self_modern = data.modern(self);
500 data.adjust(&mut self_modern, expn_id);
501 self_modern == data.modern(other)
506 pub fn modern(self) -> SyntaxContext {
507 HygieneData::with(|data| data.modern(self))
511 pub fn modern_and_legacy(self) -> SyntaxContext {
512 HygieneData::with(|data| data.modern_and_legacy(self))
516 pub fn outer_expn(self) -> ExpnId {
517 HygieneData::with(|data| data.outer_expn(self))
520 /// `ctxt.outer_expn_data()` is equivalent to but faster than
521 /// `ctxt.outer_expn().expn_data()`.
523 pub fn outer_expn_data(self) -> ExpnData {
524 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
528 pub fn outer_mark_with_data(self) -> (ExpnId, Transparency, ExpnData) {
529 HygieneData::with(|data| {
530 let (expn_id, transparency) = data.outer_mark(self);
531 (expn_id, transparency, data.expn_data(expn_id).clone())
535 pub fn dollar_crate_name(self) -> Symbol {
536 HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
540 impl fmt::Debug for SyntaxContext {
541 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
542 write!(f, "#{}", self.0)
547 /// Creates a fresh expansion with given properties.
548 /// Expansions are normally created by macros, but in some cases expansions are created for
549 /// other compiler-generated code to set per-span properties like allowed unstable features.
550 /// The returned span belongs to the created expansion and has the new properties,
551 /// but its location is inherited from the current span.
552 pub fn fresh_expansion(self, expn_data: ExpnData) -> Span {
553 self.fresh_expansion_with_transparency(expn_data, Transparency::Transparent)
556 pub fn fresh_expansion_with_transparency(
557 self, expn_data: ExpnData, transparency: Transparency
559 HygieneData::with(|data| {
560 let expn_id = data.fresh_expn(Some(expn_data));
561 self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
566 /// A subset of properties from both macro definition and macro call available through global data.
567 /// Avoid using this if you have access to the original definition or call structures.
568 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
569 pub struct ExpnData {
570 // --- The part unique to each expansion.
571 /// The kind of this expansion - macro or compiler desugaring.
573 /// The expansion that produced this expansion.
575 /// The location of the actual macro invocation or syntax sugar , e.g.
576 /// `let x = foo!();` or `if let Some(y) = x {}`
578 /// This may recursively refer to other macro invocations, e.g., if
579 /// `foo!()` invoked `bar!()` internally, and there was an
580 /// expression inside `bar!`; the call_site of the expression in
581 /// the expansion would point to the `bar!` invocation; that
582 /// call_site span would have its own ExpnData, with the call_site
583 /// pointing to the `foo!` invocation.
586 // --- The part specific to the macro/desugaring definition.
587 // --- It may be reasonable to share this part between expansions with the same definition,
588 // --- but such sharing is known to bring some minor inconveniences without also bringing
589 // --- noticeable perf improvements (PR #62898).
590 /// The span of the macro definition (possibly dummy).
591 /// This span serves only informational purpose and is not used for resolution.
593 /// List of #[unstable]/feature-gated features that the macro is allowed to use
594 /// internally without forcing the whole crate to opt-in
596 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
597 /// Whether the macro is allowed to use `unsafe` internally
598 /// even if the user crate has `#![forbid(unsafe_code)]`.
599 pub allow_internal_unsafe: bool,
600 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
601 /// for a given macro.
602 pub local_inner_macros: bool,
603 /// Edition of the crate in which the macro is defined.
604 pub edition: Edition,
608 /// Constructs expansion data with default properties.
609 pub fn default(kind: ExpnKind, call_site: Span, edition: Edition) -> ExpnData {
612 parent: ExpnId::root(),
615 allow_internal_unstable: None,
616 allow_internal_unsafe: false,
617 local_inner_macros: false,
622 pub fn allow_unstable(kind: ExpnKind, call_site: Span, edition: Edition,
623 allow_internal_unstable: Lrc<[Symbol]>) -> ExpnData {
625 allow_internal_unstable: Some(allow_internal_unstable),
626 ..ExpnData::default(kind, call_site, edition)
631 pub fn is_root(&self) -> bool {
632 if let ExpnKind::Root = self.kind { true } else { false }
637 #[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
639 /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
641 /// Expansion produced by a macro.
642 Macro(MacroKind, Symbol),
643 /// Transform done by the compiler on the AST.
645 /// Desugaring done by the compiler during HIR lowering.
646 Desugaring(DesugaringKind)
650 pub fn descr(&self) -> Symbol {
652 ExpnKind::Root => kw::PathRoot,
653 ExpnKind::Macro(_, descr) => descr,
654 ExpnKind::AstPass(kind) => Symbol::intern(kind.descr()),
655 ExpnKind::Desugaring(kind) => Symbol::intern(kind.descr()),
660 /// The kind of macro invocation or definition.
661 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
663 /// A bang macro `foo!()`.
665 /// An attribute macro `#[foo]`.
667 /// A derive macro `#[derive(Foo)]`
672 pub fn descr(self) -> &'static str {
674 MacroKind::Bang => "macro",
675 MacroKind::Attr => "attribute macro",
676 MacroKind::Derive => "derive macro",
680 pub fn article(self) -> &'static str {
682 MacroKind::Attr => "an",
688 /// The kind of AST transform.
689 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable)]
698 fn descr(self) -> &'static str {
700 AstPass::StdImports => "standard library imports",
701 AstPass::TestHarness => "test harness",
702 AstPass::ProcMacroHarness => "proc macro harness",
703 AstPass::PluginMacroDefs => "plugin macro definitions",
708 /// The kind of compiler desugaring.
709 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable)]
710 pub enum DesugaringKind {
711 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
712 /// However, we do not want to blame `c` for unreachability but rather say that `i`
713 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
714 /// This also applies to `while` loops.
718 /// Desugaring of an `impl Trait` in return type position
719 /// to an `type Foo = impl Trait;` and replacing the
720 /// `impl Trait` with `Foo`.
727 impl DesugaringKind {
728 /// The description wording should combine well with "desugaring of {}".
729 fn descr(self) -> &'static str {
731 DesugaringKind::CondTemporary => "`if` or `while` condition",
732 DesugaringKind::Async => "`async` block or function",
733 DesugaringKind::Await => "`await` expression",
734 DesugaringKind::QuestionMark => "operator `?`",
735 DesugaringKind::TryBlock => "`try` block",
736 DesugaringKind::OpaqueTy => "`impl Trait`",
737 DesugaringKind::ForLoop => "`for` loop",
742 impl Encodable for ExpnId {
743 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
744 Ok(()) // FIXME(jseyfried) intercrate hygiene
748 impl Decodable for ExpnId {
749 fn decode<D: Decoder>(_: &mut D) -> Result<Self, D::Error> {
750 Ok(ExpnId::root()) // FIXME(jseyfried) intercrate hygiene