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 `$crate` with this context would resolve.
53 dollar_crate_name: Symbol,
56 /// A unique ID associated with a macro invocation and expansion.
57 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
58 pub struct ExpnId(u32);
60 /// A property of a macro expansion that determines how identifiers
61 /// produced by that expansion are resolved.
62 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug, RustcEncodable, RustcDecodable)]
63 #[derive(HashStable_Generic)]
64 pub enum Transparency {
65 /// Identifier produced by a transparent expansion is always resolved at call-site.
66 /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
68 /// Identifier produced by a semi-transparent expansion may be resolved
69 /// either at call-site or at definition-site.
70 /// If it's a local variable, label or `$crate` then it's resolved at def-site.
71 /// Otherwise it's resolved at call-site.
72 /// `macro_rules` macros behave like this, built-in macros currently behave like this too,
73 /// but that's an implementation detail.
75 /// Identifier produced by an opaque expansion is always resolved at definition-site.
76 /// Def-site spans in procedural macros, identifiers from `macro` by default use this.
81 pub fn fresh(expn_data: Option<ExpnData>) -> Self {
82 HygieneData::with(|data| data.fresh_expn(expn_data))
85 /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
87 pub fn root() -> Self {
92 pub fn as_u32(self) -> u32 {
97 pub fn from_u32(raw: u32) -> ExpnId {
102 pub fn expn_data(self) -> ExpnData {
103 HygieneData::with(|data| data.expn_data(self).clone())
107 pub fn set_expn_data(self, expn_data: ExpnData) {
108 HygieneData::with(|data| {
109 let old_expn_data = &mut data.expn_data[self.0 as usize];
110 assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
111 *old_expn_data = Some(expn_data);
115 pub fn is_descendant_of(self, ancestor: ExpnId) -> bool {
116 HygieneData::with(|data| data.is_descendant_of(self, ancestor))
119 /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
120 /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
121 pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
122 HygieneData::with(|data| data.is_descendant_of(self, data.outer_expn(ctxt)))
125 /// Returns span for the macro which originally caused this expansion to happen.
127 /// Stops backtracing at include! boundary.
128 pub fn expansion_cause(mut self) -> Option<Span> {
129 let mut last_macro = None;
131 let expn_data = self.expn_data();
132 // Stop going up the backtrace once include! is encountered
133 if expn_data.is_root()
134 || expn_data.kind == ExpnKind::Macro(MacroKind::Bang, sym::include)
138 self = expn_data.call_site.ctxt().outer_expn();
139 last_macro = Some(expn_data.call_site);
146 crate struct HygieneData {
147 /// Each expansion should have an associated expansion data, but sometimes there's a delay
148 /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
149 /// first and then resolved later), so we use an `Option` here.
150 expn_data: Vec<Option<ExpnData>>,
151 syntax_context_data: Vec<SyntaxContextData>,
152 syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
156 crate fn new(edition: Edition) -> Self {
158 expn_data: vec![Some(ExpnData::default(ExpnKind::Root, DUMMY_SP, edition))],
159 syntax_context_data: vec![SyntaxContextData {
160 outer_expn: ExpnId::root(),
161 outer_transparency: Transparency::Opaque,
162 parent: SyntaxContext(0),
163 opaque: SyntaxContext(0),
164 opaque_and_semitransparent: SyntaxContext(0),
165 dollar_crate_name: kw::DollarCrate,
167 syntax_context_map: FxHashMap::default(),
171 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
172 GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut()))
175 fn fresh_expn(&mut self, expn_data: Option<ExpnData>) -> ExpnId {
176 self.expn_data.push(expn_data);
177 ExpnId(self.expn_data.len() as u32 - 1)
180 fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
181 self.expn_data[expn_id.0 as usize].as_ref().expect("no expansion data for an expansion ID")
184 fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
185 while expn_id != ancestor {
186 if expn_id == ExpnId::root() {
189 expn_id = self.expn_data(expn_id).parent;
194 fn normalize_to_macros_2_0(&self, ctxt: SyntaxContext) -> SyntaxContext {
195 self.syntax_context_data[ctxt.0 as usize].opaque
198 fn normalize_to_macro_rules(&self, ctxt: SyntaxContext) -> SyntaxContext {
199 self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
202 fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
203 self.syntax_context_data[ctxt.0 as usize].outer_expn
206 fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
207 let data = &self.syntax_context_data[ctxt.0 as usize];
208 (data.outer_expn, data.outer_transparency)
211 fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
212 self.syntax_context_data[ctxt.0 as usize].parent
215 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
216 let outer_mark = self.outer_mark(*ctxt);
217 *ctxt = self.parent_ctxt(*ctxt);
221 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
222 let mut marks = Vec::new();
223 while ctxt != SyntaxContext::root() {
224 marks.push(self.outer_mark(ctxt));
225 ctxt = self.parent_ctxt(ctxt);
231 fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
232 while span.from_expansion() && span.ctxt() != to {
233 span = self.expn_data(self.outer_expn(span.ctxt())).call_site;
238 fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
239 let mut scope = None;
240 while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
241 scope = Some(self.remove_mark(ctxt).0);
250 transparency: Transparency,
252 assert_ne!(expn_id, ExpnId::root());
253 if transparency == Transparency::Opaque {
254 return self.apply_mark_internal(ctxt, expn_id, transparency);
257 let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
258 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
259 self.normalize_to_macros_2_0(call_site_ctxt)
261 self.normalize_to_macro_rules(call_site_ctxt)
264 if call_site_ctxt == SyntaxContext::root() {
265 return self.apply_mark_internal(ctxt, expn_id, transparency);
268 // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
269 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
271 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
272 // at their invocation. That is, we pretend that the macros 1.0 definition
273 // was defined at its invocation (i.e., inside the macros 2.0 definition)
274 // so that the macros 2.0 definition remains hygienic.
276 // See the example at `test/ui/hygiene/legacy_interaction.rs`.
277 for (expn_id, transparency) in self.marks(ctxt) {
278 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
280 self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
283 fn apply_mark_internal(
287 transparency: Transparency,
289 let syntax_context_data = &mut self.syntax_context_data;
290 let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
291 let mut opaque_and_semitransparent =
292 syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
294 if transparency >= Transparency::Opaque {
298 .entry((parent, expn_id, transparency))
300 let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
301 syntax_context_data.push(SyntaxContextData {
303 outer_transparency: transparency,
306 opaque_and_semitransparent: new_opaque,
307 dollar_crate_name: kw::DollarCrate,
313 if transparency >= Transparency::SemiTransparent {
314 let parent = opaque_and_semitransparent;
315 opaque_and_semitransparent = *self
317 .entry((parent, expn_id, transparency))
319 let new_opaque_and_semitransparent =
320 SyntaxContext(syntax_context_data.len() as u32);
321 syntax_context_data.push(SyntaxContextData {
323 outer_transparency: transparency,
326 opaque_and_semitransparent: new_opaque_and_semitransparent,
327 dollar_crate_name: kw::DollarCrate,
329 new_opaque_and_semitransparent
334 *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
335 let new_opaque_and_semitransparent_and_transparent =
336 SyntaxContext(syntax_context_data.len() as u32);
337 syntax_context_data.push(SyntaxContextData {
339 outer_transparency: transparency,
342 opaque_and_semitransparent,
343 dollar_crate_name: kw::DollarCrate,
345 new_opaque_and_semitransparent_and_transparent
350 pub fn clear_syntax_context_map() {
351 HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
354 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
355 HygieneData::with(|data| data.walk_chain(span, to))
358 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
359 // The new contexts that need updating are at the end of the list and have `$crate` as a name.
360 let (len, to_update) = HygieneData::with(|data| {
362 data.syntax_context_data.len(),
363 data.syntax_context_data
366 .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate)
370 // The callback must be called from outside of the `HygieneData` lock,
371 // since it will try to acquire it too.
372 let range_to_update = len - to_update..len;
374 range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
375 HygieneData::with(|data| {
376 range_to_update.zip(names.into_iter()).for_each(|(idx, name)| {
377 data.syntax_context_data[idx].dollar_crate_name = name;
382 pub fn debug_hygiene_data(verbose: bool) -> String {
383 HygieneData::with(|data| {
385 format!("{:#?}", data)
387 let mut s = String::from("");
388 s.push_str("Expansions:");
389 data.expn_data.iter().enumerate().for_each(|(id, expn_info)| {
390 let expn_info = expn_info.as_ref().expect("no expansion data for an expansion ID");
392 "\n{}: parent: {:?}, call_site_ctxt: {:?}, kind: {:?}",
395 expn_info.call_site.ctxt(),
399 s.push_str("\n\nSyntaxContexts:");
400 data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
402 "\n#{}: parent: {:?}, outer_mark: ({:?}, {:?})",
403 id, ctxt.parent, ctxt.outer_expn, ctxt.outer_transparency,
413 pub const fn root() -> Self {
418 crate fn as_u32(self) -> u32 {
423 crate fn from_u32(raw: u32) -> SyntaxContext {
427 /// Extend a syntax context with a given expansion and transparency.
428 crate fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
429 HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
432 /// Pulls a single mark off of the syntax context. This effectively moves the
433 /// context up one macro definition level. That is, if we have a nested macro
434 /// definition as follows:
444 /// and we have a SyntaxContext that is referring to something declared by an invocation
445 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
446 /// invocation of f that created g1.
447 /// Returns the mark that was removed.
448 pub fn remove_mark(&mut self) -> ExpnId {
449 HygieneData::with(|data| data.remove_mark(self).0)
452 pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
453 HygieneData::with(|data| data.marks(self))
456 /// Adjust this context for resolution in a scope created by the given expansion.
457 /// For example, consider the following three resolutions of `f`:
460 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
462 /// macro m($f:ident) {
464 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
465 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
467 /// foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
468 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
469 /// //| and it resolves to `::foo::f`.
470 /// bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
471 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
472 /// //| and it resolves to `::bar::f`.
473 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
474 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
475 /// //| and it resolves to `::bar::$f`.
478 /// This returns the expansion whose definition scope we use to privacy check the resolution,
479 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
480 pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
481 HygieneData::with(|data| data.adjust(self, expn_id))
484 /// Like `SyntaxContext::adjust`, but also normalizes `self` to macros 2.0.
485 pub fn normalize_to_macros_2_0_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
486 HygieneData::with(|data| {
487 *self = data.normalize_to_macros_2_0(*self);
488 data.adjust(self, expn_id)
492 /// Adjust this context for resolution in a scope created by the given expansion
493 /// via a glob import with the given `SyntaxContext`.
498 /// macro m($i:ident) {
500 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
501 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
504 /// macro n($j:ident) {
506 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
507 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
508 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
509 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
510 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
511 /// //^ This cannot be glob-adjusted, so this is a resolution error.
515 /// This returns `None` if the context cannot be glob-adjusted.
516 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
517 pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
518 HygieneData::with(|data| {
519 let mut scope = None;
520 let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
521 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
522 scope = Some(data.remove_mark(&mut glob_ctxt).0);
523 if data.remove_mark(self).0 != scope.unwrap() {
527 if data.adjust(self, expn_id).is_some() {
534 /// Undo `glob_adjust` if possible:
537 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
538 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
541 pub fn reverse_glob_adjust(
545 ) -> Option<Option<ExpnId>> {
546 HygieneData::with(|data| {
547 if data.adjust(self, expn_id).is_some() {
551 let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
552 let mut marks = Vec::new();
553 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
554 marks.push(data.remove_mark(&mut glob_ctxt));
557 let scope = marks.last().map(|mark| mark.0);
558 while let Some((expn_id, transparency)) = marks.pop() {
559 *self = data.apply_mark(*self, expn_id, transparency);
565 pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
566 HygieneData::with(|data| {
567 let mut self_normalized = data.normalize_to_macros_2_0(self);
568 data.adjust(&mut self_normalized, expn_id);
569 self_normalized == data.normalize_to_macros_2_0(other)
574 pub fn normalize_to_macros_2_0(self) -> SyntaxContext {
575 HygieneData::with(|data| data.normalize_to_macros_2_0(self))
579 pub fn normalize_to_macro_rules(self) -> SyntaxContext {
580 HygieneData::with(|data| data.normalize_to_macro_rules(self))
584 pub fn outer_expn(self) -> ExpnId {
585 HygieneData::with(|data| data.outer_expn(self))
588 /// `ctxt.outer_expn_data()` is equivalent to but faster than
589 /// `ctxt.outer_expn().expn_data()`.
591 pub fn outer_expn_data(self) -> ExpnData {
592 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
596 pub fn outer_mark_with_data(self) -> (ExpnId, Transparency, ExpnData) {
597 HygieneData::with(|data| {
598 let (expn_id, transparency) = data.outer_mark(self);
599 (expn_id, transparency, data.expn_data(expn_id).clone())
603 pub fn dollar_crate_name(self) -> Symbol {
604 HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
608 impl fmt::Debug for SyntaxContext {
609 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
610 write!(f, "#{}", self.0)
615 /// Creates a fresh expansion with given properties.
616 /// Expansions are normally created by macros, but in some cases expansions are created for
617 /// other compiler-generated code to set per-span properties like allowed unstable features.
618 /// The returned span belongs to the created expansion and has the new properties,
619 /// but its location is inherited from the current span.
620 pub fn fresh_expansion(self, expn_data: ExpnData) -> Span {
621 self.fresh_expansion_with_transparency(expn_data, Transparency::Transparent)
624 pub fn fresh_expansion_with_transparency(
627 transparency: Transparency,
629 HygieneData::with(|data| {
630 let expn_id = data.fresh_expn(Some(expn_data));
631 self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
636 /// A subset of properties from both macro definition and macro call available through global data.
637 /// Avoid using this if you have access to the original definition or call structures.
638 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
639 pub struct ExpnData {
640 // --- The part unique to each expansion.
641 /// The kind of this expansion - macro or compiler desugaring.
643 /// The expansion that produced this expansion.
644 #[stable_hasher(ignore)]
646 /// The location of the actual macro invocation or syntax sugar , e.g.
647 /// `let x = foo!();` or `if let Some(y) = x {}`
649 /// This may recursively refer to other macro invocations, e.g., if
650 /// `foo!()` invoked `bar!()` internally, and there was an
651 /// expression inside `bar!`; the call_site of the expression in
652 /// the expansion would point to the `bar!` invocation; that
653 /// call_site span would have its own ExpnData, with the call_site
654 /// pointing to the `foo!` invocation.
657 // --- The part specific to the macro/desugaring definition.
658 // --- It may be reasonable to share this part between expansions with the same definition,
659 // --- but such sharing is known to bring some minor inconveniences without also bringing
660 // --- noticeable perf improvements (PR #62898).
661 /// The span of the macro definition (possibly dummy).
662 /// This span serves only informational purpose and is not used for resolution.
664 /// List of `#[unstable]`/feature-gated features that the macro is allowed to use
665 /// internally without forcing the whole crate to opt-in
667 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
668 /// Whether the macro is allowed to use `unsafe` internally
669 /// even if the user crate has `#![forbid(unsafe_code)]`.
670 pub allow_internal_unsafe: bool,
671 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
672 /// for a given macro.
673 pub local_inner_macros: bool,
674 /// Edition of the crate in which the macro is defined.
675 pub edition: Edition,
679 /// Constructs expansion data with default properties.
680 pub fn default(kind: ExpnKind, call_site: Span, edition: Edition) -> ExpnData {
683 parent: ExpnId::root(),
686 allow_internal_unstable: None,
687 allow_internal_unsafe: false,
688 local_inner_macros: false,
693 pub fn allow_unstable(
697 allow_internal_unstable: Lrc<[Symbol]>,
700 allow_internal_unstable: Some(allow_internal_unstable),
701 ..ExpnData::default(kind, call_site, edition)
706 pub fn is_root(&self) -> bool {
707 if let ExpnKind::Root = self.kind { true } else { false }
712 #[derive(Clone, Debug, PartialEq, RustcEncodable, RustcDecodable, HashStable_Generic)]
714 /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
716 /// Expansion produced by a macro.
717 Macro(MacroKind, Symbol),
718 /// Transform done by the compiler on the AST.
720 /// Desugaring done by the compiler during HIR lowering.
721 Desugaring(DesugaringKind),
725 pub fn descr(&self) -> String {
727 ExpnKind::Root => kw::PathRoot.to_string(),
728 ExpnKind::Macro(macro_kind, name) => match macro_kind {
729 MacroKind::Bang => format!("{}!", name),
730 MacroKind::Attr => format!("#[{}]", name),
731 MacroKind::Derive => format!("#[derive({})]", name),
733 ExpnKind::AstPass(kind) => kind.descr().to_string(),
734 ExpnKind::Desugaring(kind) => format!("desugaring of {}", kind.descr()),
739 /// The kind of macro invocation or definition.
740 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
741 #[derive(HashStable_Generic)]
743 /// A bang macro `foo!()`.
745 /// An attribute macro `#[foo]`.
747 /// A derive macro `#[derive(Foo)]`
752 pub fn descr(self) -> &'static str {
754 MacroKind::Bang => "macro",
755 MacroKind::Attr => "attribute macro",
756 MacroKind::Derive => "derive macro",
760 pub fn descr_expected(self) -> &'static str {
762 MacroKind::Attr => "attribute",
767 pub fn article(self) -> &'static str {
769 MacroKind::Attr => "an",
775 /// The kind of AST transform.
776 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
784 fn descr(self) -> &'static str {
786 AstPass::StdImports => "standard library imports",
787 AstPass::TestHarness => "test harness",
788 AstPass::ProcMacroHarness => "proc macro harness",
793 /// The kind of compiler desugaring.
794 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
795 pub enum DesugaringKind {
796 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
797 /// However, we do not want to blame `c` for unreachability but rather say that `i`
798 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
799 /// This also applies to `while` loops.
803 /// Desugaring of an `impl Trait` in return type position
804 /// to an `type Foo = impl Trait;` and replacing the
805 /// `impl Trait` with `Foo`.
812 impl DesugaringKind {
813 /// The description wording should combine well with "desugaring of {}".
814 fn descr(self) -> &'static str {
816 DesugaringKind::CondTemporary => "`if` or `while` condition",
817 DesugaringKind::Async => "`async` block or function",
818 DesugaringKind::Await => "`await` expression",
819 DesugaringKind::QuestionMark => "operator `?`",
820 DesugaringKind::TryBlock => "`try` block",
821 DesugaringKind::OpaqueTy => "`impl Trait`",
822 DesugaringKind::ForLoop => "`for` loop",
827 impl Encodable for ExpnId {
828 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
829 Ok(()) // FIXME(jseyfried) intercrate hygiene
833 impl Decodable for ExpnId {
834 fn decode<D: Decoder>(_: &mut D) -> Result<Self, D::Error> {
835 Ok(ExpnId::root()) // FIXME(jseyfried) intercrate hygiene