1 //! Machinery for hygienic macros.
3 //! Inspired by Matthew Flatt et al., “Macros That Work Together: Compile-Time Bindings, Partial
4 //! Expansion, and Definition Contexts,” *Journal of Functional Programming* 22, no. 2
5 //! (March 1, 2012): 181–216, <https://doi.org/10.1017/S0956796812000093>.
7 // Hygiene data is stored in a global variable and accessed via TLS, which
8 // means that accesses are somewhat expensive. (`HygieneData::with`
9 // encapsulates a single access.) Therefore, on hot code paths it is worth
10 // ensuring that multiple HygieneData accesses are combined into a single
11 // `HygieneData::with`.
13 // This explains why `HygieneData`, `SyntaxContext` and `ExpnId` have interfaces
14 // with a certain amount of redundancy in them. For example,
15 // `SyntaxContext::outer_expn_data` combines `SyntaxContext::outer` and
16 // `ExpnId::expn_data` so that two `HygieneData` accesses can be performed within
17 // a single `HygieneData::with` call.
19 // It also explains why many functions appear in `HygieneData` and again in
20 // `SyntaxContext` or `ExpnId`. For example, `HygieneData::outer` and
21 // `SyntaxContext::outer` do the same thing, but the former is for use within a
22 // `HygieneData::with` call while the latter is for use outside such a call.
23 // When modifying this file it is important to understand this distinction,
24 // because getting it wrong can lead to nested `HygieneData::with` calls that
25 // trigger runtime aborts. (Fortunately these are obvious and easy to fix.)
27 use crate::def_id::{DefId, CRATE_DEF_INDEX};
28 use crate::edition::Edition;
29 use crate::symbol::{kw, sym, Symbol};
30 use crate::SESSION_GLOBALS;
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(
162 Some(DefId::local(CRATE_DEF_INDEX)),
164 syntax_context_data: vec![SyntaxContextData {
165 outer_expn: ExpnId::root(),
166 outer_transparency: Transparency::Opaque,
167 parent: SyntaxContext(0),
168 opaque: SyntaxContext(0),
169 opaque_and_semitransparent: SyntaxContext(0),
170 dollar_crate_name: kw::DollarCrate,
172 syntax_context_map: FxHashMap::default(),
176 fn with<T, F: FnOnce(&mut HygieneData) -> T>(f: F) -> T {
177 SESSION_GLOBALS.with(|session_globals| f(&mut *session_globals.hygiene_data.borrow_mut()))
180 fn fresh_expn(&mut self, expn_data: Option<ExpnData>) -> ExpnId {
181 self.expn_data.push(expn_data);
182 ExpnId(self.expn_data.len() as u32 - 1)
185 fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
186 self.expn_data[expn_id.0 as usize].as_ref().expect("no expansion data for an expansion ID")
189 fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
190 while expn_id != ancestor {
191 if expn_id == ExpnId::root() {
194 expn_id = self.expn_data(expn_id).parent;
199 fn normalize_to_macros_2_0(&self, ctxt: SyntaxContext) -> SyntaxContext {
200 self.syntax_context_data[ctxt.0 as usize].opaque
203 fn normalize_to_macro_rules(&self, ctxt: SyntaxContext) -> SyntaxContext {
204 self.syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent
207 fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
208 self.syntax_context_data[ctxt.0 as usize].outer_expn
211 fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
212 let data = &self.syntax_context_data[ctxt.0 as usize];
213 (data.outer_expn, data.outer_transparency)
216 fn parent_ctxt(&self, ctxt: SyntaxContext) -> SyntaxContext {
217 self.syntax_context_data[ctxt.0 as usize].parent
220 fn remove_mark(&self, ctxt: &mut SyntaxContext) -> (ExpnId, Transparency) {
221 let outer_mark = self.outer_mark(*ctxt);
222 *ctxt = self.parent_ctxt(*ctxt);
226 fn marks(&self, mut ctxt: SyntaxContext) -> Vec<(ExpnId, Transparency)> {
227 let mut marks = Vec::new();
228 while ctxt != SyntaxContext::root() {
229 marks.push(self.outer_mark(ctxt));
230 ctxt = self.parent_ctxt(ctxt);
236 fn walk_chain(&self, mut span: Span, to: SyntaxContext) -> Span {
237 while span.from_expansion() && span.ctxt() != to {
238 span = self.expn_data(self.outer_expn(span.ctxt())).call_site;
243 fn adjust(&self, ctxt: &mut SyntaxContext, expn_id: ExpnId) -> Option<ExpnId> {
244 let mut scope = None;
245 while !self.is_descendant_of(expn_id, self.outer_expn(*ctxt)) {
246 scope = Some(self.remove_mark(ctxt).0);
255 transparency: Transparency,
257 assert_ne!(expn_id, ExpnId::root());
258 if transparency == Transparency::Opaque {
259 return self.apply_mark_internal(ctxt, expn_id, transparency);
262 let call_site_ctxt = self.expn_data(expn_id).call_site.ctxt();
263 let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
264 self.normalize_to_macros_2_0(call_site_ctxt)
266 self.normalize_to_macro_rules(call_site_ctxt)
269 if call_site_ctxt == SyntaxContext::root() {
270 return self.apply_mark_internal(ctxt, expn_id, transparency);
273 // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
274 // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
276 // In this case, the tokens from the macros 1.0 definition inherit the hygiene
277 // at their invocation. That is, we pretend that the macros 1.0 definition
278 // was defined at its invocation (i.e., inside the macros 2.0 definition)
279 // so that the macros 2.0 definition remains hygienic.
281 // See the example at `test/ui/hygiene/legacy_interaction.rs`.
282 for (expn_id, transparency) in self.marks(ctxt) {
283 call_site_ctxt = self.apply_mark_internal(call_site_ctxt, expn_id, transparency);
285 self.apply_mark_internal(call_site_ctxt, expn_id, transparency)
288 fn apply_mark_internal(
292 transparency: Transparency,
294 let syntax_context_data = &mut self.syntax_context_data;
295 let mut opaque = syntax_context_data[ctxt.0 as usize].opaque;
296 let mut opaque_and_semitransparent =
297 syntax_context_data[ctxt.0 as usize].opaque_and_semitransparent;
299 if transparency >= Transparency::Opaque {
303 .entry((parent, expn_id, transparency))
305 let new_opaque = SyntaxContext(syntax_context_data.len() as u32);
306 syntax_context_data.push(SyntaxContextData {
308 outer_transparency: transparency,
311 opaque_and_semitransparent: new_opaque,
312 dollar_crate_name: kw::DollarCrate,
318 if transparency >= Transparency::SemiTransparent {
319 let parent = opaque_and_semitransparent;
320 opaque_and_semitransparent = *self
322 .entry((parent, expn_id, transparency))
324 let new_opaque_and_semitransparent =
325 SyntaxContext(syntax_context_data.len() as u32);
326 syntax_context_data.push(SyntaxContextData {
328 outer_transparency: transparency,
331 opaque_and_semitransparent: new_opaque_and_semitransparent,
332 dollar_crate_name: kw::DollarCrate,
334 new_opaque_and_semitransparent
339 *self.syntax_context_map.entry((parent, expn_id, transparency)).or_insert_with(|| {
340 let new_opaque_and_semitransparent_and_transparent =
341 SyntaxContext(syntax_context_data.len() as u32);
342 syntax_context_data.push(SyntaxContextData {
344 outer_transparency: transparency,
347 opaque_and_semitransparent,
348 dollar_crate_name: kw::DollarCrate,
350 new_opaque_and_semitransparent_and_transparent
355 pub fn clear_syntax_context_map() {
356 HygieneData::with(|data| data.syntax_context_map = FxHashMap::default());
359 pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
360 HygieneData::with(|data| data.walk_chain(span, to))
363 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {
364 // The new contexts that need updating are at the end of the list and have `$crate` as a name.
365 let (len, to_update) = HygieneData::with(|data| {
367 data.syntax_context_data.len(),
368 data.syntax_context_data
371 .take_while(|scdata| scdata.dollar_crate_name == kw::DollarCrate)
375 // The callback must be called from outside of the `HygieneData` lock,
376 // since it will try to acquire it too.
377 let range_to_update = len - to_update..len;
379 range_to_update.clone().map(|idx| get_name(SyntaxContext::from_u32(idx as u32))).collect();
380 HygieneData::with(|data| {
381 range_to_update.zip(names.into_iter()).for_each(|(idx, name)| {
382 data.syntax_context_data[idx].dollar_crate_name = name;
387 pub fn debug_hygiene_data(verbose: bool) -> String {
388 HygieneData::with(|data| {
390 format!("{:#?}", data)
392 let mut s = String::from("");
393 s.push_str("Expansions:");
394 data.expn_data.iter().enumerate().for_each(|(id, expn_info)| {
395 let expn_info = expn_info.as_ref().expect("no expansion data for an expansion ID");
397 "\n{}: parent: {:?}, call_site_ctxt: {:?}, def_site_ctxt: {:?}, kind: {:?}",
400 expn_info.call_site.ctxt(),
401 expn_info.def_site.ctxt(),
405 s.push_str("\n\nSyntaxContexts:");
406 data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
408 "\n#{}: parent: {:?}, outer_mark: ({:?}, {:?})",
409 id, ctxt.parent, ctxt.outer_expn, ctxt.outer_transparency,
419 pub const fn root() -> Self {
424 crate fn as_u32(self) -> u32 {
429 crate fn from_u32(raw: u32) -> SyntaxContext {
433 /// Extend a syntax context with a given expansion and transparency.
434 crate fn apply_mark(self, expn_id: ExpnId, transparency: Transparency) -> SyntaxContext {
435 HygieneData::with(|data| data.apply_mark(self, expn_id, transparency))
438 /// Pulls a single mark off of the syntax context. This effectively moves the
439 /// context up one macro definition level. That is, if we have a nested macro
440 /// definition as follows:
450 /// and we have a SyntaxContext that is referring to something declared by an invocation
451 /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the
452 /// invocation of f that created g1.
453 /// Returns the mark that was removed.
454 pub fn remove_mark(&mut self) -> ExpnId {
455 HygieneData::with(|data| data.remove_mark(self).0)
458 pub fn marks(self) -> Vec<(ExpnId, Transparency)> {
459 HygieneData::with(|data| data.marks(self))
462 /// Adjust this context for resolution in a scope created by the given expansion.
463 /// For example, consider the following three resolutions of `f`:
466 /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty.
468 /// macro m($f:ident) {
470 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
471 /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty.
473 /// foo::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
474 /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`,
475 /// //| and it resolves to `::foo::f`.
476 /// bar::f(); // `f`'s `SyntaxContext` has a single `ExpnId` from `m`
477 /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`,
478 /// //| and it resolves to `::bar::f`.
479 /// bar::$f(); // `f`'s `SyntaxContext` is empty.
480 /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`,
481 /// //| and it resolves to `::bar::$f`.
484 /// This returns the expansion whose definition scope we use to privacy check the resolution,
485 /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope).
486 pub fn adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
487 HygieneData::with(|data| data.adjust(self, expn_id))
490 /// Like `SyntaxContext::adjust`, but also normalizes `self` to macros 2.0.
491 pub fn normalize_to_macros_2_0_and_adjust(&mut self, expn_id: ExpnId) -> Option<ExpnId> {
492 HygieneData::with(|data| {
493 *self = data.normalize_to_macros_2_0(*self);
494 data.adjust(self, expn_id)
498 /// Adjust this context for resolution in a scope created by the given expansion
499 /// via a glob import with the given `SyntaxContext`.
504 /// macro m($i:ident) {
506 /// pub fn f() {} // `f`'s `SyntaxContext` has a single `ExpnId` from `m`.
507 /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty.
510 /// macro n($j:ident) {
512 /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n`
513 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`.
514 /// $i(); // `$i`'s `SyntaxContext` has a mark from `n`
515 /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`.
516 /// $j(); // `$j`'s `SyntaxContext` has a mark from `m`
517 /// //^ This cannot be glob-adjusted, so this is a resolution error.
521 /// This returns `None` if the context cannot be glob-adjusted.
522 /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details).
523 pub fn glob_adjust(&mut self, expn_id: ExpnId, glob_span: Span) -> Option<Option<ExpnId>> {
524 HygieneData::with(|data| {
525 let mut scope = None;
526 let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
527 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
528 scope = Some(data.remove_mark(&mut glob_ctxt).0);
529 if data.remove_mark(self).0 != scope.unwrap() {
533 if data.adjust(self, expn_id).is_some() {
540 /// Undo `glob_adjust` if possible:
543 /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) {
544 /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope));
547 pub fn reverse_glob_adjust(
551 ) -> Option<Option<ExpnId>> {
552 HygieneData::with(|data| {
553 if data.adjust(self, expn_id).is_some() {
557 let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
558 let mut marks = Vec::new();
559 while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {
560 marks.push(data.remove_mark(&mut glob_ctxt));
563 let scope = marks.last().map(|mark| mark.0);
564 while let Some((expn_id, transparency)) = marks.pop() {
565 *self = data.apply_mark(*self, expn_id, transparency);
571 pub fn hygienic_eq(self, other: SyntaxContext, expn_id: ExpnId) -> bool {
572 HygieneData::with(|data| {
573 let mut self_normalized = data.normalize_to_macros_2_0(self);
574 data.adjust(&mut self_normalized, expn_id);
575 self_normalized == data.normalize_to_macros_2_0(other)
580 pub fn normalize_to_macros_2_0(self) -> SyntaxContext {
581 HygieneData::with(|data| data.normalize_to_macros_2_0(self))
585 pub fn normalize_to_macro_rules(self) -> SyntaxContext {
586 HygieneData::with(|data| data.normalize_to_macro_rules(self))
590 pub fn outer_expn(self) -> ExpnId {
591 HygieneData::with(|data| data.outer_expn(self))
594 /// `ctxt.outer_expn_data()` is equivalent to but faster than
595 /// `ctxt.outer_expn().expn_data()`.
597 pub fn outer_expn_data(self) -> ExpnData {
598 HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
602 pub fn outer_mark_with_data(self) -> (ExpnId, Transparency, ExpnData) {
603 HygieneData::with(|data| {
604 let (expn_id, transparency) = data.outer_mark(self);
605 (expn_id, transparency, data.expn_data(expn_id).clone())
609 pub fn dollar_crate_name(self) -> Symbol {
610 HygieneData::with(|data| data.syntax_context_data[self.0 as usize].dollar_crate_name)
614 impl fmt::Debug for SyntaxContext {
615 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
616 write!(f, "#{}", self.0)
621 /// Creates a fresh expansion with given properties.
622 /// Expansions are normally created by macros, but in some cases expansions are created for
623 /// other compiler-generated code to set per-span properties like allowed unstable features.
624 /// The returned span belongs to the created expansion and has the new properties,
625 /// but its location is inherited from the current span.
626 pub fn fresh_expansion(self, expn_data: ExpnData) -> Span {
627 self.fresh_expansion_with_transparency(expn_data, Transparency::Transparent)
630 pub fn fresh_expansion_with_transparency(
633 transparency: Transparency,
635 HygieneData::with(|data| {
636 let expn_id = data.fresh_expn(Some(expn_data));
637 self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
642 /// A subset of properties from both macro definition and macro call available through global data.
643 /// Avoid using this if you have access to the original definition or call structures.
644 #[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
645 pub struct ExpnData {
646 // --- The part unique to each expansion.
647 /// The kind of this expansion - macro or compiler desugaring.
649 /// The expansion that produced this expansion.
650 #[stable_hasher(ignore)]
652 /// The location of the actual macro invocation or syntax sugar , e.g.
653 /// `let x = foo!();` or `if let Some(y) = x {}`
655 /// This may recursively refer to other macro invocations, e.g., if
656 /// `foo!()` invoked `bar!()` internally, and there was an
657 /// expression inside `bar!`; the call_site of the expression in
658 /// the expansion would point to the `bar!` invocation; that
659 /// call_site span would have its own ExpnData, with the call_site
660 /// pointing to the `foo!` invocation.
663 // --- The part specific to the macro/desugaring definition.
664 // --- It may be reasonable to share this part between expansions with the same definition,
665 // --- but such sharing is known to bring some minor inconveniences without also bringing
666 // --- noticeable perf improvements (PR #62898).
667 /// The span of the macro definition (possibly dummy).
668 /// This span serves only informational purpose and is not used for resolution.
670 /// List of `#[unstable]`/feature-gated features that the macro is allowed to use
671 /// internally without forcing the whole crate to opt-in
673 pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
674 /// Whether the macro is allowed to use `unsafe` internally
675 /// even if the user crate has `#![forbid(unsafe_code)]`.
676 pub allow_internal_unsafe: bool,
677 /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
678 /// for a given macro.
679 pub local_inner_macros: bool,
680 /// Edition of the crate in which the macro is defined.
681 pub edition: Edition,
682 /// The `DefId` of the macro being invoked,
683 /// if this `ExpnData` corresponds to a macro invocation
684 pub macro_def_id: Option<DefId>,
688 /// Constructs expansion data with default properties.
693 macro_def_id: Option<DefId>,
697 parent: ExpnId::root(),
700 allow_internal_unstable: None,
701 allow_internal_unsafe: false,
702 local_inner_macros: false,
708 pub fn allow_unstable(
712 allow_internal_unstable: Lrc<[Symbol]>,
713 macro_def_id: Option<DefId>,
716 allow_internal_unstable: Some(allow_internal_unstable),
717 ..ExpnData::default(kind, call_site, edition, macro_def_id)
722 pub fn is_root(&self) -> bool {
723 if let ExpnKind::Root = self.kind { true } else { false }
728 #[derive(Clone, Debug, PartialEq, RustcEncodable, RustcDecodable, HashStable_Generic)]
730 /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind.
732 /// Expansion produced by a macro.
733 Macro(MacroKind, Symbol),
734 /// Transform done by the compiler on the AST.
736 /// Desugaring done by the compiler during HIR lowering.
737 Desugaring(DesugaringKind),
741 pub fn descr(&self) -> String {
743 ExpnKind::Root => kw::PathRoot.to_string(),
744 ExpnKind::Macro(macro_kind, name) => match macro_kind {
745 MacroKind::Bang => format!("{}!", name),
746 MacroKind::Attr => format!("#[{}]", name),
747 MacroKind::Derive => format!("#[derive({})]", name),
749 ExpnKind::AstPass(kind) => kind.descr().to_string(),
750 ExpnKind::Desugaring(kind) => format!("desugaring of {}", kind.descr()),
755 /// The kind of macro invocation or definition.
756 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
757 #[derive(HashStable_Generic)]
759 /// A bang macro `foo!()`.
761 /// An attribute macro `#[foo]`.
763 /// A derive macro `#[derive(Foo)]`
768 pub fn descr(self) -> &'static str {
770 MacroKind::Bang => "macro",
771 MacroKind::Attr => "attribute macro",
772 MacroKind::Derive => "derive macro",
776 pub fn descr_expected(self) -> &'static str {
778 MacroKind::Attr => "attribute",
783 pub fn article(self) -> &'static str {
785 MacroKind::Attr => "an",
791 /// The kind of AST transform.
792 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
800 fn descr(self) -> &'static str {
802 AstPass::StdImports => "standard library imports",
803 AstPass::TestHarness => "test harness",
804 AstPass::ProcMacroHarness => "proc macro harness",
809 /// The kind of compiler desugaring.
810 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
811 pub enum DesugaringKind {
812 /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`.
813 /// However, we do not want to blame `c` for unreachability but rather say that `i`
814 /// is unreachable. This desugaring kind allows us to avoid blaming `c`.
815 /// This also applies to `while` loops.
819 /// Desugaring of an `impl Trait` in return type position
820 /// to an `type Foo = impl Trait;` and replacing the
821 /// `impl Trait` with `Foo`.
828 /// A location in the desugaring of a `for` loop
829 #[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable_Generic)]
830 pub enum ForLoopLoc {
835 impl DesugaringKind {
836 /// The description wording should combine well with "desugaring of {}".
837 fn descr(self) -> &'static str {
839 DesugaringKind::CondTemporary => "`if` or `while` condition",
840 DesugaringKind::Async => "`async` block or function",
841 DesugaringKind::Await => "`await` expression",
842 DesugaringKind::QuestionMark => "operator `?`",
843 DesugaringKind::TryBlock => "`try` block",
844 DesugaringKind::OpaqueTy => "`impl Trait`",
845 DesugaringKind::ForLoop(_) => "`for` loop",
850 impl Encodable for ExpnId {
851 fn encode<E: Encoder>(&self, _: &mut E) -> Result<(), E::Error> {
852 Ok(()) // FIXME(jseyfried) intercrate hygiene
856 impl Decodable for ExpnId {
857 fn decode<D: Decoder>(_: &mut D) -> Result<Self, D::Error> {
858 Ok(ExpnId::root()) // FIXME(jseyfried) intercrate hygiene