1 use super::{ImplTraitContext, LoweringContext, ParamMode};
5 use rustc_data_structures::stack::ensure_sufficient_stack;
6 use rustc_errors::Applicability;
8 use rustc_hir::def::Res;
9 use rustc_span::symbol::Ident;
10 use rustc_span::{source_map::Spanned, Span};
12 impl<'a, 'hir> LoweringContext<'a, 'hir> {
13 crate fn lower_pat(&mut self, mut pattern: &Pat) -> &'hir hir::Pat<'hir> {
14 ensure_sufficient_stack(|| {
15 // loop here to avoid recursion
18 PatKind::Wild => break hir::PatKind::Wild,
19 PatKind::Ident(ref binding_mode, ident, ref sub) => {
20 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
21 break self.lower_pat_ident(pattern, binding_mode, ident, lower_sub);
23 PatKind::Lit(ref e) => break hir::PatKind::Lit(self.lower_expr(e)),
24 PatKind::TupleStruct(ref path, ref pats) => {
25 let qpath = self.lower_qpath(
30 ImplTraitContext::disallowed(),
32 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
33 break hir::PatKind::TupleStruct(qpath, pats, ddpos);
35 PatKind::Or(ref pats) => {
36 break hir::PatKind::Or(
37 self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))),
40 PatKind::Path(ref qself, ref path) => {
41 let qpath = self.lower_qpath(
46 ImplTraitContext::disallowed(),
48 break hir::PatKind::Path(qpath);
50 PatKind::Struct(ref path, ref fields, etc) => {
51 let qpath = self.lower_qpath(
56 ImplTraitContext::disallowed(),
59 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
60 hir_id: self.next_id(),
62 pat: self.lower_pat(&f.pat),
63 is_shorthand: f.is_shorthand,
66 break hir::PatKind::Struct(qpath, fs, etc);
68 PatKind::Tuple(ref pats) => {
69 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
70 break hir::PatKind::Tuple(pats, ddpos);
72 PatKind::Box(ref inner) => {
73 break hir::PatKind::Box(self.lower_pat(inner));
75 PatKind::Ref(ref inner, mutbl) => {
76 break hir::PatKind::Ref(self.lower_pat(inner), mutbl);
78 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => {
79 break hir::PatKind::Range(
80 e1.as_deref().map(|e| self.lower_expr(e)),
81 e2.as_deref().map(|e| self.lower_expr(e)),
82 self.lower_range_end(end, e2.is_some()),
85 PatKind::Slice(ref pats) => break self.lower_pat_slice(pats),
87 // If we reach here the `..` pattern is not semantically allowed.
88 break self.ban_illegal_rest_pat(pattern.span);
90 // return inner to be processed in next loop
91 PatKind::Paren(ref inner) => pattern = inner,
92 PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", pattern.span),
96 self.pat_with_node_id_of(pattern, node)
104 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
105 let mut elems = Vec::with_capacity(pats.len());
108 let mut iter = pats.iter().enumerate();
109 for (idx, pat) in iter.by_ref() {
110 // Interpret the first `..` pattern as a sub-tuple pattern.
111 // Note that unlike for slice patterns,
112 // where `xs @ ..` is a legal sub-slice pattern,
113 // it is not a legal sub-tuple pattern.
115 // Found a sub-tuple rest pattern
117 rest = Some((idx, pat.span));
120 // Found a sub-tuple pattern `$binding_mode $ident @ ..`.
121 // This is not allowed as a sub-tuple pattern
122 PatKind::Ident(ref _bm, ident, Some(ref sub)) if sub.is_rest() => {
127 &format!("`{} @` is not allowed in a {}", ident.name, ctx),
129 .span_label(sp, "this is only allowed in slice patterns")
130 .help("remove this and bind each tuple field independently")
131 .span_suggestion_verbose(
133 &format!("if you don't need to use the contents of {}, discard the tuple's remaining fields", ident),
135 Applicability::MaybeIncorrect,
142 // It was not a sub-tuple pattern so lower it normally.
143 elems.push(self.lower_pat(pat));
146 for (_, pat) in iter {
147 // There was a previous sub-tuple pattern; make sure we don't allow more...
149 // ...but there was one again, so error.
150 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
152 elems.push(self.lower_pat(pat));
156 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
159 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
160 /// `hir::PatKind::Slice(before, slice, after)`.
162 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
163 /// this is interpreted as a sub-slice pattern semantically.
164 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
165 fn lower_pat_slice(&mut self, pats: &[P<Pat>]) -> hir::PatKind<'hir> {
166 let mut before = Vec::new();
167 let mut after = Vec::new();
168 let mut slice = None;
169 let mut prev_rest_span = None;
171 // Lowers `$bm $ident @ ..` to `$bm $ident @ _`.
172 let lower_rest_sub = |this: &mut Self, pat, bm, ident, sub| {
173 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
174 let node = this.lower_pat_ident(pat, bm, ident, lower_sub);
175 this.pat_with_node_id_of(pat, node)
178 let mut iter = pats.iter();
179 // Lower all the patterns until the first occurrence of a sub-slice pattern.
180 for pat in iter.by_ref() {
182 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
184 prev_rest_span = Some(pat.span);
185 slice = Some(self.pat_wild_with_node_id_of(pat));
188 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
189 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
190 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
191 prev_rest_span = Some(sub.span);
192 slice = Some(lower_rest_sub(self, pat, bm, ident, sub));
195 // It was not a subslice pattern so lower it normally.
196 _ => before.push(self.lower_pat(pat)),
200 // Lower all the patterns after the first sub-slice pattern.
202 // There was a previous subslice pattern; make sure we don't allow more.
203 let rest_span = match pat.kind {
204 PatKind::Rest => Some(pat.span),
205 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
206 // #69103: Lower into `binding @ _` as above to avoid ICEs.
207 after.push(lower_rest_sub(self, pat, bm, ident, sub));
212 if let Some(rest_span) = rest_span {
213 // We have e.g., `[a, .., b, ..]`. That's no good, error!
214 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
216 // Lower the pattern normally.
217 after.push(self.lower_pat(pat));
222 self.arena.alloc_from_iter(before),
224 self.arena.alloc_from_iter(after),
231 binding_mode: &BindingMode,
233 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
234 ) -> hir::PatKind<'hir> {
235 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
236 // `None` can occur in body-less function signatures
237 res @ (None | Some(Res::Local(_))) => {
238 let canonical_id = match res {
239 Some(Res::Local(id)) => id,
243 hir::PatKind::Binding(
244 self.lower_binding_mode(binding_mode),
245 self.lower_node_id(canonical_id),
250 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
252 self.arena.alloc(hir::Path {
254 res: self.lower_res(res),
255 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
261 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
263 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
264 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
265 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
266 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
270 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
271 self.pat_with_node_id_of(p, hir::PatKind::Wild)
274 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
275 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
276 self.arena.alloc(hir::Pat {
277 hir_id: self.lower_node_id(p.id),
280 default_binding_modes: true,
284 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
285 crate fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
287 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
288 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
289 .span_label(prev_sp, "previously used here")
293 /// Used to ban the `..` pattern in places it shouldn't be semantically.
294 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
296 .struct_span_err(sp, "`..` patterns are not allowed here")
297 .note("only allowed in tuple, tuple struct, and slice patterns")
300 // We're not in a list context so `..` can be reasonably treated
301 // as `_` because it should always be valid and roughly matches the
302 // intent of `..` (notice that the rest of a single slot is that slot).
306 fn lower_range_end(&mut self, e: &RangeEnd, has_end: bool) -> hir::RangeEnd {
308 RangeEnd::Excluded if has_end => hir::RangeEnd::Excluded,
309 // No end; so `X..` behaves like `RangeFrom`.
310 RangeEnd::Excluded | RangeEnd::Included(_) => hir::RangeEnd::Included,