1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
use rustc_ast::ptr::P;
use rustc_ast::*;
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_hir as hir;
use rustc_hir::def::Res;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::Ident;
use rustc_span::Span;

use super::errors::{
    ArbitraryExpressionInPattern, ExtraDoubleDot, MisplacedDoubleDot, SubTupleBinding,
};
use super::{ImplTraitContext, LoweringContext, ParamMode, ResolverAstLoweringExt};
use crate::ImplTraitPosition;

impl<'a, 'hir> LoweringContext<'a, 'hir> {
    pub(crate) fn lower_pat(&mut self, pattern: &Pat) -> &'hir hir::Pat<'hir> {
        self.arena.alloc(self.lower_pat_mut(pattern))
    }

    fn lower_pat_mut(&mut self, mut pattern: &Pat) -> hir::Pat<'hir> {
        ensure_sufficient_stack(|| {
            // loop here to avoid recursion
            let node = loop {
                match &pattern.kind {
                    PatKind::Wild => break hir::PatKind::Wild,
                    PatKind::Never => break hir::PatKind::Never,
                    PatKind::Ident(binding_mode, ident, sub) => {
                        let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(s));
                        break self.lower_pat_ident(pattern, *binding_mode, *ident, lower_sub);
                    }
                    PatKind::Lit(e) => {
                        break hir::PatKind::Lit(self.lower_expr_within_pat(e, false));
                    }
                    PatKind::TupleStruct(qself, path, pats) => {
                        let qpath = self.lower_qpath(
                            pattern.id,
                            qself,
                            path,
                            ParamMode::Optional,
                            ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                            None,
                        );
                        let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
                        break hir::PatKind::TupleStruct(qpath, pats, ddpos);
                    }
                    PatKind::Or(pats) => {
                        break hir::PatKind::Or(
                            self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat_mut(x))),
                        );
                    }
                    PatKind::Path(qself, path) => {
                        let qpath = self.lower_qpath(
                            pattern.id,
                            qself,
                            path,
                            ParamMode::Optional,
                            ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                            None,
                        );
                        break hir::PatKind::Path(qpath);
                    }
                    PatKind::Struct(qself, path, fields, etc) => {
                        let qpath = self.lower_qpath(
                            pattern.id,
                            qself,
                            path,
                            ParamMode::Optional,
                            ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                            None,
                        );

                        let fs = self.arena.alloc_from_iter(fields.iter().map(|f| {
                            let hir_id = self.lower_node_id(f.id);
                            self.lower_attrs(hir_id, &f.attrs);

                            hir::PatField {
                                hir_id,
                                ident: self.lower_ident(f.ident),
                                pat: self.lower_pat(&f.pat),
                                is_shorthand: f.is_shorthand,
                                span: self.lower_span(f.span),
                            }
                        }));
                        break hir::PatKind::Struct(qpath, fs, *etc == ast::PatFieldsRest::Rest);
                    }
                    PatKind::Tuple(pats) => {
                        let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
                        break hir::PatKind::Tuple(pats, ddpos);
                    }
                    PatKind::Box(inner) => {
                        break hir::PatKind::Box(self.lower_pat(inner));
                    }
                    PatKind::Deref(inner) => {
                        break hir::PatKind::Deref(self.lower_pat(inner));
                    }
                    PatKind::Ref(inner, mutbl) => {
                        break hir::PatKind::Ref(self.lower_pat(inner), *mutbl);
                    }
                    PatKind::Range(e1, e2, Spanned { node: end, .. }) => {
                        break hir::PatKind::Range(
                            e1.as_deref().map(|e| self.lower_expr_within_pat(e, true)),
                            e2.as_deref().map(|e| self.lower_expr_within_pat(e, true)),
                            self.lower_range_end(end, e2.is_some()),
                        );
                    }
                    PatKind::Slice(pats) => break self.lower_pat_slice(pats),
                    PatKind::Rest => {
                        // If we reach here the `..` pattern is not semantically allowed.
                        break self.ban_illegal_rest_pat(pattern.span);
                    }
                    // return inner to be processed in next loop
                    PatKind::Paren(inner) => pattern = inner,
                    PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", pattern.span),
                    PatKind::Err(guar) => break hir::PatKind::Err(*guar),
                }
            };

            self.pat_with_node_id_of(pattern, node)
        })
    }

    fn lower_pat_tuple(
        &mut self,
        pats: &[P<Pat>],
        ctx: &str,
    ) -> (&'hir [hir::Pat<'hir>], hir::DotDotPos) {
        let mut elems = Vec::with_capacity(pats.len());
        let mut rest = None;

        let mut iter = pats.iter().enumerate();
        for (idx, pat) in iter.by_ref() {
            // Interpret the first `..` pattern as a sub-tuple pattern.
            // Note that unlike for slice patterns,
            // where `xs @ ..` is a legal sub-slice pattern,
            // it is not a legal sub-tuple pattern.
            match &pat.kind {
                // Found a sub-tuple rest pattern
                PatKind::Rest => {
                    rest = Some((idx, pat.span));
                    break;
                }
                // Found a sub-tuple pattern `$binding_mode $ident @ ..`.
                // This is not allowed as a sub-tuple pattern
                PatKind::Ident(_, ident, Some(sub)) if sub.is_rest() => {
                    let sp = pat.span;
                    self.dcx().emit_err(SubTupleBinding {
                        span: sp,
                        ident_name: ident.name,
                        ident: *ident,
                        ctx,
                    });
                }
                _ => {}
            }

            // It was not a sub-tuple pattern so lower it normally.
            elems.push(self.lower_pat_mut(pat));
        }

        for (_, pat) in iter {
            // There was a previous sub-tuple pattern; make sure we don't allow more...
            if pat.is_rest() {
                // ...but there was one again, so error.
                self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
            } else {
                elems.push(self.lower_pat_mut(pat));
            }
        }

        (self.arena.alloc_from_iter(elems), hir::DotDotPos::new(rest.map(|(ddpos, _)| ddpos)))
    }

    /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
    /// `hir::PatKind::Slice(before, slice, after)`.
    ///
    /// When encountering `($binding_mode $ident @)? ..` (`slice`),
    /// this is interpreted as a sub-slice pattern semantically.
    /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
    fn lower_pat_slice(&mut self, pats: &[P<Pat>]) -> hir::PatKind<'hir> {
        let mut before = Vec::new();
        let mut after = Vec::new();
        let mut slice = None;
        let mut prev_rest_span = None;

        // Lowers `$bm $ident @ ..` to `$bm $ident @ _`.
        let lower_rest_sub = |this: &mut Self, pat, &ann, &ident, sub| {
            let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
            let node = this.lower_pat_ident(pat, ann, ident, lower_sub);
            this.pat_with_node_id_of(pat, node)
        };

        let mut iter = pats.iter();
        // Lower all the patterns until the first occurrence of a sub-slice pattern.
        for pat in iter.by_ref() {
            match &pat.kind {
                // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
                PatKind::Rest => {
                    prev_rest_span = Some(pat.span);
                    slice = Some(self.pat_wild_with_node_id_of(pat));
                    break;
                }
                // Found a sub-slice pattern `$binding_mode $ident @ ..`.
                // Record, lower it to `$binding_mode $ident @ _`, and stop here.
                PatKind::Ident(ann, ident, Some(sub)) if sub.is_rest() => {
                    prev_rest_span = Some(sub.span);
                    slice = Some(self.arena.alloc(lower_rest_sub(self, pat, ann, ident, sub)));
                    break;
                }
                // It was not a subslice pattern so lower it normally.
                _ => before.push(self.lower_pat_mut(pat)),
            }
        }

        // Lower all the patterns after the first sub-slice pattern.
        for pat in iter {
            // There was a previous subslice pattern; make sure we don't allow more.
            let rest_span = match &pat.kind {
                PatKind::Rest => Some(pat.span),
                PatKind::Ident(ann, ident, Some(sub)) if sub.is_rest() => {
                    // #69103: Lower into `binding @ _` as above to avoid ICEs.
                    after.push(lower_rest_sub(self, pat, ann, ident, sub));
                    Some(sub.span)
                }
                _ => None,
            };
            if let Some(rest_span) = rest_span {
                // We have e.g., `[a, .., b, ..]`. That's no good, error!
                self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
            } else {
                // Lower the pattern normally.
                after.push(self.lower_pat_mut(pat));
            }
        }

        hir::PatKind::Slice(
            self.arena.alloc_from_iter(before),
            slice,
            self.arena.alloc_from_iter(after),
        )
    }

    fn lower_pat_ident(
        &mut self,
        p: &Pat,
        annotation: BindingMode,
        ident: Ident,
        lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
    ) -> hir::PatKind<'hir> {
        match self.resolver.get_partial_res(p.id).map(|d| d.expect_full_res()) {
            // `None` can occur in body-less function signatures
            res @ (None | Some(Res::Local(_))) => {
                let canonical_id = match res {
                    Some(Res::Local(id)) => id,
                    _ => p.id,
                };

                hir::PatKind::Binding(
                    annotation,
                    self.lower_node_id(canonical_id),
                    self.lower_ident(ident),
                    lower_sub(self),
                )
            }
            Some(res) => {
                let hir_id = self.next_id();
                let res = self.lower_res(res);
                hir::PatKind::Path(hir::QPath::Resolved(
                    None,
                    self.arena.alloc(hir::Path {
                        span: self.lower_span(ident.span),
                        res,
                        segments: arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
                    }),
            ))
            }
        }
    }

    fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
        self.arena.alloc(self.pat_with_node_id_of(p, hir::PatKind::Wild))
    }

    /// Construct a `Pat` with the `HirId` of `p.id` lowered.
    fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
        hir::Pat {
            hir_id: self.lower_node_id(p.id),
            kind,
            span: self.lower_span(p.span),
            default_binding_modes: true,
        }
    }

    /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
    pub(crate) fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
        self.dcx().emit_err(ExtraDoubleDot { span: sp, prev_span: prev_sp, ctx });
    }

    /// Used to ban the `..` pattern in places it shouldn't be semantically.
    fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
        self.dcx().emit_err(MisplacedDoubleDot { span: sp });

        // We're not in a list context so `..` can be reasonably treated
        // as `_` because it should always be valid and roughly matches the
        // intent of `..` (notice that the rest of a single slot is that slot).
        hir::PatKind::Wild
    }

    fn lower_range_end(&mut self, e: &RangeEnd, has_end: bool) -> hir::RangeEnd {
        match *e {
            RangeEnd::Excluded if has_end => hir::RangeEnd::Excluded,
            // No end; so `X..` behaves like `RangeFrom`.
            RangeEnd::Excluded | RangeEnd::Included(_) => hir::RangeEnd::Included,
        }
    }

    /// Matches `'-' lit | lit (cf. parser::Parser::parse_literal_maybe_minus)`,
    /// or paths for ranges.
    //
    // FIXME: do we want to allow `expr -> pattern` conversion to create path expressions?
    // That means making this work:
    //
    // ```rust,ignore (FIXME)
    // struct S;
    // macro_rules! m {
    //     ($a:expr) => {
    //         let $a = S;
    //     }
    // }
    // m!(S);
    // ```
    fn lower_expr_within_pat(&mut self, expr: &Expr, allow_paths: bool) -> &'hir hir::Expr<'hir> {
        match &expr.kind {
            ExprKind::Lit(..)
            | ExprKind::ConstBlock(..)
            | ExprKind::IncludedBytes(..)
            | ExprKind::Err(_)
            | ExprKind::Dummy => {}
            ExprKind::Path(..) if allow_paths => {}
            ExprKind::Unary(UnOp::Neg, inner) if matches!(inner.kind, ExprKind::Lit(_)) => {}
            _ => {
                let pattern_from_macro = expr.is_approximately_pattern();
                let guar = self.dcx().emit_err(ArbitraryExpressionInPattern {
                    span: expr.span,
                    pattern_from_macro_note: pattern_from_macro,
                });
                return self.arena.alloc(self.expr_err(expr.span, guar));
            }
        }
        self.lower_expr(expr)
    }
}