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
use rustc_middle::mir::*;
use rustc_middle::thir::{self, *};
use rustc_middle::ty::{self, Ty, TypeVisitableExt};

use crate::build::expr::as_place::{PlaceBase, PlaceBuilder};
use crate::build::matches::{FlatPat, MatchPairTree, TestCase};
use crate::build::Builder;

impl<'a, 'tcx> Builder<'a, 'tcx> {
    /// Builds and returns [`MatchPairTree`] subtrees, one for each pattern in
    /// `subpatterns`, representing the fields of a [`PatKind::Variant`] or
    /// [`PatKind::Leaf`].
    ///
    /// Used internally by [`MatchPairTree::for_pattern`].
    fn field_match_pairs<'pat>(
        &mut self,
        place: PlaceBuilder<'tcx>,
        subpatterns: &'pat [FieldPat<'tcx>],
    ) -> Vec<MatchPairTree<'pat, 'tcx>> {
        subpatterns
            .iter()
            .map(|fieldpat| {
                let place =
                    place.clone_project(PlaceElem::Field(fieldpat.field, fieldpat.pattern.ty));
                MatchPairTree::for_pattern(place, &fieldpat.pattern, self)
            })
            .collect()
    }

    /// Builds [`MatchPairTree`] subtrees for the prefix/middle/suffix parts of an
    /// array pattern or slice pattern, and adds those trees to `match_pairs`.
    ///
    /// Used internally by [`MatchPairTree::for_pattern`].
    fn prefix_slice_suffix<'pat>(
        &mut self,
        match_pairs: &mut Vec<MatchPairTree<'pat, 'tcx>>,
        place: &PlaceBuilder<'tcx>,
        prefix: &'pat [Box<Pat<'tcx>>],
        opt_slice: &'pat Option<Box<Pat<'tcx>>>,
        suffix: &'pat [Box<Pat<'tcx>>],
    ) {
        let tcx = self.tcx;
        let (min_length, exact_size) = if let Some(place_resolved) = place.try_to_place(self) {
            match place_resolved.ty(&self.local_decls, tcx).ty.kind() {
                ty::Array(_, length) => (length.eval_target_usize(tcx, self.param_env), true),
                _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
            }
        } else {
            ((prefix.len() + suffix.len()).try_into().unwrap(), false)
        };

        match_pairs.extend(prefix.iter().enumerate().map(|(idx, subpattern)| {
            let elem =
                ProjectionElem::ConstantIndex { offset: idx as u64, min_length, from_end: false };
            MatchPairTree::for_pattern(place.clone_project(elem), subpattern, self)
        }));

        if let Some(subslice_pat) = opt_slice {
            let suffix_len = suffix.len() as u64;
            let subslice = place.clone_project(PlaceElem::Subslice {
                from: prefix.len() as u64,
                to: if exact_size { min_length - suffix_len } else { suffix_len },
                from_end: !exact_size,
            });
            match_pairs.push(MatchPairTree::for_pattern(subslice, subslice_pat, self));
        }

        match_pairs.extend(suffix.iter().rev().enumerate().map(|(idx, subpattern)| {
            let end_offset = (idx + 1) as u64;
            let elem = ProjectionElem::ConstantIndex {
                offset: if exact_size { min_length - end_offset } else { end_offset },
                min_length,
                from_end: !exact_size,
            };
            let place = place.clone_project(elem);
            MatchPairTree::for_pattern(place, subpattern, self)
        }));
    }
}

impl<'pat, 'tcx> MatchPairTree<'pat, 'tcx> {
    /// Recursively builds a match pair tree for the given pattern and its
    /// subpatterns.
    pub(in crate::build) fn for_pattern(
        mut place_builder: PlaceBuilder<'tcx>,
        pattern: &'pat Pat<'tcx>,
        cx: &mut Builder<'_, 'tcx>,
    ) -> MatchPairTree<'pat, 'tcx> {
        // Force the place type to the pattern's type.
        // FIXME(oli-obk): can we use this to simplify slice/array pattern hacks?
        if let Some(resolved) = place_builder.resolve_upvar(cx) {
            place_builder = resolved;
        }

        // Only add the OpaqueCast projection if the given place is an opaque type and the
        // expected type from the pattern is not.
        let may_need_cast = match place_builder.base() {
            PlaceBase::Local(local) => {
                let ty =
                    Place::ty_from(local, place_builder.projection(), &cx.local_decls, cx.tcx).ty;
                ty != pattern.ty && ty.has_opaque_types()
            }
            _ => true,
        };
        if may_need_cast {
            place_builder = place_builder.project(ProjectionElem::OpaqueCast(pattern.ty));
        }

        let place = place_builder.try_to_place(cx);
        let default_irrefutable = || TestCase::Irrefutable { binding: None, ascription: None };
        let mut subpairs = Vec::new();
        let test_case = match pattern.kind {
            PatKind::Wild | PatKind::Error(_) => default_irrefutable(),

            PatKind::Or { ref pats } => TestCase::Or {
                pats: pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect(),
            },

            PatKind::Range(ref range) => {
                if range.is_full_range(cx.tcx) == Some(true) {
                    default_irrefutable()
                } else {
                    TestCase::Range(range)
                }
            }

            PatKind::Constant { value } => TestCase::Constant { value },

            PatKind::AscribeUserType {
                ascription: thir::Ascription { ref annotation, variance },
                ref subpattern,
                ..
            } => {
                // Apply the type ascription to the value at `match_pair.place`
                let ascription = place.map(|source| super::Ascription {
                    annotation: annotation.clone(),
                    source,
                    variance,
                });

                subpairs.push(MatchPairTree::for_pattern(place_builder, subpattern, cx));
                TestCase::Irrefutable { ascription, binding: None }
            }

            PatKind::Binding { mode, var, ref subpattern, .. } => {
                let binding = place.map(|source| super::Binding {
                    span: pattern.span,
                    source,
                    var_id: var,
                    binding_mode: mode,
                });

                if let Some(subpattern) = subpattern.as_ref() {
                    // this is the `x @ P` case; have to keep matching against `P` now
                    subpairs.push(MatchPairTree::for_pattern(place_builder, subpattern, cx));
                }
                TestCase::Irrefutable { ascription: None, binding }
            }

            PatKind::InlineConstant { subpattern: ref pattern, def, .. } => {
                // Apply a type ascription for the inline constant to the value at `match_pair.place`
                let ascription = place.map(|source| {
                    let span = pattern.span;
                    let parent_id = cx.tcx.typeck_root_def_id(cx.def_id.to_def_id());
                    let args = ty::InlineConstArgs::new(
                        cx.tcx,
                        ty::InlineConstArgsParts {
                            parent_args: ty::GenericArgs::identity_for_item(cx.tcx, parent_id),
                            ty: cx.infcx.next_ty_var(span),
                        },
                    )
                    .args;
                    let user_ty = cx.infcx.canonicalize_user_type_annotation(ty::UserType::TypeOf(
                        def.to_def_id(),
                        ty::UserArgs { args, user_self_ty: None },
                    ));
                    let annotation = ty::CanonicalUserTypeAnnotation {
                        inferred_ty: pattern.ty,
                        span,
                        user_ty: Box::new(user_ty),
                    };
                    super::Ascription { annotation, source, variance: ty::Contravariant }
                });

                subpairs.push(MatchPairTree::for_pattern(place_builder, pattern, cx));
                TestCase::Irrefutable { ascription, binding: None }
            }

            PatKind::Array { ref prefix, ref slice, ref suffix } => {
                cx.prefix_slice_suffix(&mut subpairs, &place_builder, prefix, slice, suffix);
                default_irrefutable()
            }
            PatKind::Slice { ref prefix, ref slice, ref suffix } => {
                cx.prefix_slice_suffix(&mut subpairs, &place_builder, prefix, slice, suffix);

                if prefix.is_empty() && slice.is_some() && suffix.is_empty() {
                    default_irrefutable()
                } else {
                    TestCase::Slice {
                        len: prefix.len() + suffix.len(),
                        variable_length: slice.is_some(),
                    }
                }
            }

            PatKind::Variant { adt_def, variant_index, args, ref subpatterns } => {
                let downcast_place = place_builder.downcast(adt_def, variant_index); // `(x as Variant)`
                subpairs = cx.field_match_pairs(downcast_place, subpatterns);

                let irrefutable = adt_def.variants().iter_enumerated().all(|(i, v)| {
                    i == variant_index
                        || !v
                            .inhabited_predicate(cx.tcx, adt_def)
                            .instantiate(cx.tcx, args)
                            .apply_ignore_module(cx.tcx, cx.param_env)
                }) && (adt_def.did().is_local()
                    || !adt_def.is_variant_list_non_exhaustive());
                if irrefutable {
                    default_irrefutable()
                } else {
                    TestCase::Variant { adt_def, variant_index }
                }
            }

            PatKind::Leaf { ref subpatterns } => {
                subpairs = cx.field_match_pairs(place_builder, subpatterns);
                default_irrefutable()
            }

            PatKind::Deref { ref subpattern } => {
                subpairs.push(MatchPairTree::for_pattern(place_builder.deref(), subpattern, cx));
                default_irrefutable()
            }

            PatKind::DerefPattern { ref subpattern, mutability } => {
                // Create a new temporary for each deref pattern.
                // FIXME(deref_patterns): dedup temporaries to avoid multiple `deref()` calls?
                let temp = cx.temp(
                    Ty::new_ref(cx.tcx, cx.tcx.lifetimes.re_erased, subpattern.ty, mutability),
                    pattern.span,
                );
                subpairs.push(MatchPairTree::for_pattern(
                    PlaceBuilder::from(temp).deref(),
                    subpattern,
                    cx,
                ));
                TestCase::Deref { temp, mutability }
            }

            PatKind::Never => TestCase::Never,
        };

        MatchPairTree { place, test_case, subpairs, pattern }
    }
}