compiler/rustc_ast_lowering/src/pat.rs

   1 use super::{ImplTraitContext, LoweringContext, ParamMode};
   2
   3 use rustc_ast::ptr::P;
   4 use rustc_ast::*;
   5 use rustc_data_structures::stack::ensure_sufficient_stack;
   6 use rustc_errors::Applicability;
   7 use rustc_hir as hir;
   8 use rustc_hir::def::Res;
   9 use rustc_span::symbol::Ident;
  10 use rustc_span::{source_map::Spanned, Span};
  11
  12 impl<'a, 'hir> LoweringContext<'a, 'hir> {
  13     crate fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
  14         ensure_sufficient_stack(|| {
  15             let node = match p.kind {
  16                 PatKind::Wild => hir::PatKind::Wild,
  17                 PatKind::Ident(ref binding_mode, ident, ref sub) => {
  18                     let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
  19                     let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
  20                     node
  21                 }
  22                 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
  23                 PatKind::TupleStruct(ref path, ref pats) => {
  24                     let qpath = self.lower_qpath(
  25                         p.id,
  26                         &None,
  27                         path,
  28                         ParamMode::Optional,
  29                         ImplTraitContext::disallowed(),
  30                     );
  31                     let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
  32                     hir::PatKind::TupleStruct(qpath, pats, ddpos)
  33                 }
  34                 PatKind::Or(ref pats) => hir::PatKind::Or(
  35                     self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))),
  36                 ),
  37                 PatKind::Path(ref qself, ref path) => {
  38                     let qpath = self.lower_qpath(
  39                         p.id,
  40                         qself,
  41                         path,
  42                         ParamMode::Optional,
  43                         ImplTraitContext::disallowed(),
  44                     );
  45                     hir::PatKind::Path(qpath)
  46                 }
  47                 PatKind::Struct(ref path, ref fields, etc) => {
  48                     let qpath = self.lower_qpath(
  49                         p.id,
  50                         &None,
  51                         path,
  52                         ParamMode::Optional,
  53                         ImplTraitContext::disallowed(),
  54                     );
  55
  56                     let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
  57                         hir_id: self.next_id(),
  58                         ident: f.ident,
  59                         pat: self.lower_pat(&f.pat),
  60                         is_shorthand: f.is_shorthand,
  61                         span: f.span,
  62                     }));
  63                     hir::PatKind::Struct(qpath, fs, etc)
  64                 }
  65                 PatKind::Tuple(ref pats) => {
  66                     let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
  67                     hir::PatKind::Tuple(pats, ddpos)
  68                 }
  69                 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
  70                 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
  71                 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => {
  72                     hir::PatKind::Range(
  73                         e1.as_deref().map(|e| self.lower_expr(e)),
  74                         e2.as_deref().map(|e| self.lower_expr(e)),
  75                         self.lower_range_end(end, e2.is_some()),
  76                     )
  77                 }
  78                 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
  79                 PatKind::Rest => {
  80                     // If we reach here the `..` pattern is not semantically allowed.
  81                     self.ban_illegal_rest_pat(p.span)
  82                 }
  83                 // FIXME: consider not using recursion to lower this.
  84                 PatKind::Paren(ref inner) => return self.lower_pat(inner),
  85                 PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", p.span),
  86             };
  87
  88             self.pat_with_node_id_of(p, node)
  89         })
  90     }
  91
  92     fn lower_pat_tuple(
  93         &mut self,
  94         pats: &[P<Pat>],
  95         ctx: &str,
  96     ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
  97         let mut elems = Vec::with_capacity(pats.len());
  98         let mut rest = None;
  99
 100         let mut iter = pats.iter().enumerate();
 101         for (idx, pat) in iter.by_ref() {
 102             // Interpret the first `..` pattern as a sub-tuple pattern.
 103             // Note that unlike for slice patterns,
 104             // where `xs @ ..` is a legal sub-slice pattern,
 105             // it is not a legal sub-tuple pattern.
 106             match pat.kind {
 107                 // Found a sub-tuple rest pattern
 108                 PatKind::Rest => {
 109                     rest = Some((idx, pat.span));
 110                     break;
 111                 }
 112                 // Found a sub-tuple pattern `$binding_mode $ident @ ..`.
 113                 // This is not allowed as a sub-tuple pattern
 114                 PatKind::Ident(ref _bm, ident, Some(ref sub)) if sub.is_rest() => {
 115                     let sp = pat.span;
 116                     self.diagnostic()
 117                         .struct_span_err(
 118                             sp,
 119                             &format!("`{} @` is not allowed in a {}", ident.name, ctx),
 120                         )
 121                         .span_label(sp, "this is only allowed in slice patterns")
 122                         .help("remove this and bind each tuple field independently")
 123                         .span_suggestion_verbose(
 124                             sp,
 125                             &format!("if you don't need to use the contents of {}, discard the tuple's remaining fields", ident),
 126                             "..".to_string(),
 127                             Applicability::MaybeIncorrect,
 128                         )
 129                         .emit();
 130                 }
 131                 _ => {}
 132             }
 133
 134             // It was not a sub-tuple pattern so lower it normally.
 135             elems.push(self.lower_pat(pat));
 136         }
 137
 138         for (_, pat) in iter {
 139             // There was a previous sub-tuple pattern; make sure we don't allow more...
 140             if pat.is_rest() {
 141                 // ...but there was one again, so error.
 142                 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
 143             } else {
 144                 elems.push(self.lower_pat(pat));
 145             }
 146         }
 147
 148         (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
 149     }
 150
 151     /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
 152     /// `hir::PatKind::Slice(before, slice, after)`.
 153     ///
 154     /// When encountering `($binding_mode $ident @)? ..` (`slice`),
 155     /// this is interpreted as a sub-slice pattern semantically.
 156     /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
 157     fn lower_pat_slice(&mut self, pats: &[P<Pat>]) -> hir::PatKind<'hir> {
 158         let mut before = Vec::new();
 159         let mut after = Vec::new();
 160         let mut slice = None;
 161         let mut prev_rest_span = None;
 162
 163         // Lowers `$bm $ident @ ..` to `$bm $ident @ _`.
 164         let lower_rest_sub = |this: &mut Self, pat, bm, ident, sub| {
 165             let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
 166             let node = this.lower_pat_ident(pat, bm, ident, lower_sub);
 167             this.pat_with_node_id_of(pat, node)
 168         };
 169
 170         let mut iter = pats.iter();
 171         // Lower all the patterns until the first occurrence of a sub-slice pattern.
 172         for pat in iter.by_ref() {
 173             match pat.kind {
 174                 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
 175                 PatKind::Rest => {
 176                     prev_rest_span = Some(pat.span);
 177                     slice = Some(self.pat_wild_with_node_id_of(pat));
 178                     break;
 179                 }
 180                 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
 181                 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
 182                 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
 183                     prev_rest_span = Some(sub.span);
 184                     slice = Some(lower_rest_sub(self, pat, bm, ident, sub));
 185                     break;
 186                 }
 187                 // It was not a subslice pattern so lower it normally.
 188                 _ => before.push(self.lower_pat(pat)),
 189             }
 190         }
 191
 192         // Lower all the patterns after the first sub-slice pattern.
 193         for pat in iter {
 194             // There was a previous subslice pattern; make sure we don't allow more.
 195             let rest_span = match pat.kind {
 196                 PatKind::Rest => Some(pat.span),
 197                 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
 198                     // #69103: Lower into `binding @ _` as above to avoid ICEs.
 199                     after.push(lower_rest_sub(self, pat, bm, ident, sub));
 200                     Some(sub.span)
 201                 }
 202                 _ => None,
 203             };
 204             if let Some(rest_span) = rest_span {
 205                 // We have e.g., `[a, .., b, ..]`. That's no good, error!
 206                 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
 207             } else {
 208                 // Lower the pattern normally.
 209                 after.push(self.lower_pat(pat));
 210             }
 211         }
 212
 213         hir::PatKind::Slice(
 214             self.arena.alloc_from_iter(before),
 215             slice,
 216             self.arena.alloc_from_iter(after),
 217         )
 218     }
 219
 220     fn lower_pat_ident(
 221         &mut self,
 222         p: &Pat,
 223         binding_mode: &BindingMode,
 224         ident: Ident,
 225         lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
 226     ) -> hir::PatKind<'hir> {
 227         match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
 228             // `None` can occur in body-less function signatures
 229             res @ (None | Some(Res::Local(_))) => {
 230                 let canonical_id = match res {
 231                     Some(Res::Local(id)) => id,
 232                     _ => p.id,
 233                 };
 234
 235                 hir::PatKind::Binding(
 236                     self.lower_binding_mode(binding_mode),
 237                     self.lower_node_id(canonical_id),
 238                     ident,
 239                     lower_sub(self),
 240                 )
 241             }
 242             Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
 243                 None,
 244                 self.arena.alloc(hir::Path {
 245                     span: ident.span,
 246                     res: self.lower_res(res),
 247                     segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
 248                 }),
 249             )),
 250         }
 251     }
 252
 253     fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
 254         match *b {
 255             BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
 256             BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
 257             BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
 258             BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
 259         }
 260     }
 261
 262     fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
 263         self.pat_with_node_id_of(p, hir::PatKind::Wild)
 264     }
 265
 266     /// Construct a `Pat` with the `HirId` of `p.id` lowered.
 267     fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
 268         self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
 269     }
 270
 271     /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
 272     fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
 273         self.diagnostic()
 274             .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
 275             .span_label(sp, &format!("can only be used once per {} pattern", ctx))
 276             .span_label(prev_sp, "previously used here")
 277             .emit();
 278     }
 279
 280     /// Used to ban the `..` pattern in places it shouldn't be semantically.
 281     fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
 282         self.diagnostic()
 283             .struct_span_err(sp, "`..` patterns are not allowed here")
 284             .note("only allowed in tuple, tuple struct, and slice patterns")
 285             .emit();
 286
 287         // We're not in a list context so `..` can be reasonably treated
 288         // as `_` because it should always be valid and roughly matches the
 289         // intent of `..` (notice that the rest of a single slot is that slot).
 290         hir::PatKind::Wild
 291     }
 292
 293     fn lower_range_end(&mut self, e: &RangeEnd, has_end: bool) -> hir::RangeEnd {
 294         match *e {
 295             RangeEnd::Excluded if has_end => hir::RangeEnd::Excluded,
 296             // No end; so `X..` behaves like `RangeFrom`.
 297             RangeEnd::Excluded | RangeEnd::Included(_) => hir::RangeEnd::Included,
 298         }
 299     }
 300 }