rustc_mir_build/thir/pattern/
const_to_pat.rs

1use core::ops::ControlFlow;
2
3use rustc_abi::{FieldIdx, VariantIdx};
4use rustc_apfloat::Float;
5use rustc_data_structures::fx::FxHashSet;
6use rustc_errors::Diag;
7use rustc_hir as hir;
8use rustc_index::Idx;
9use rustc_infer::infer::TyCtxtInferExt;
10use rustc_infer::traits::Obligation;
11use rustc_middle::mir::interpret::ErrorHandled;
12use rustc_middle::thir::{FieldPat, Pat, PatKind};
13use rustc_middle::ty::{
14    self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitableExt, TypeVisitor, ValTree,
15};
16use rustc_middle::{mir, span_bug};
17use rustc_span::def_id::DefId;
18use rustc_span::{DUMMY_SP, Span, sym};
19use rustc_trait_selection::traits::ObligationCause;
20use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
21use tracing::{debug, instrument, trace};
22
23use super::PatCtxt;
24use crate::errors::{
25    ConstPatternDependsOnGenericParameter, CouldNotEvalConstPattern, InvalidPattern, NaNPattern,
26    PointerPattern, TypeNotPartialEq, TypeNotStructural, UnionPattern, UnsizedPattern,
27};
28
29impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
30    /// Converts a constant to a pattern (if possible).
31    /// This means aggregate values (like structs and enums) are converted
32    /// to a pattern that matches the value (as if you'd compared via structural equality).
33    ///
34    /// Only type system constants are supported, as we are using valtrees
35    /// as an intermediate step. Unfortunately those don't carry a type
36    /// so we have to carry one ourselves.
37    #[instrument(level = "debug", skip(self), ret)]
38    pub(super) fn const_to_pat(
39        &self,
40        c: ty::Const<'tcx>,
41        ty: Ty<'tcx>,
42        id: hir::HirId,
43        span: Span,
44    ) -> Box<Pat<'tcx>> {
45        let mut convert = ConstToPat::new(self, id, span, c);
46
47        match c.kind() {
48            ty::ConstKind::Unevaluated(uv) => convert.unevaluated_to_pat(uv, ty),
49            ty::ConstKind::Value(cv) => convert.valtree_to_pat(cv.valtree, cv.ty),
50            _ => span_bug!(span, "Invalid `ConstKind` for `const_to_pat`: {:?}", c),
51        }
52    }
53}
54
55struct ConstToPat<'tcx> {
56    tcx: TyCtxt<'tcx>,
57    typing_env: ty::TypingEnv<'tcx>,
58    span: Span,
59    id: hir::HirId,
60
61    c: ty::Const<'tcx>,
62}
63
64impl<'tcx> ConstToPat<'tcx> {
65    fn new(pat_ctxt: &PatCtxt<'_, 'tcx>, id: hir::HirId, span: Span, c: ty::Const<'tcx>) -> Self {
66        trace!(?pat_ctxt.typeck_results.hir_owner);
67        ConstToPat { tcx: pat_ctxt.tcx, typing_env: pat_ctxt.typing_env, span, id, c }
68    }
69
70    fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
71        ty.is_structural_eq_shallow(self.tcx)
72    }
73
74    /// We errored. Signal that in the pattern, so that follow up errors can be silenced.
75    fn mk_err(&self, mut err: Diag<'_>, ty: Ty<'tcx>) -> Box<Pat<'tcx>> {
76        if let ty::ConstKind::Unevaluated(uv) = self.c.kind() {
77            let def_kind = self.tcx.def_kind(uv.def);
78            if let hir::def::DefKind::AssocConst = def_kind
79                && let Some(def_id) = uv.def.as_local()
80            {
81                // Include the container item in the output.
82                err.span_label(self.tcx.def_span(self.tcx.local_parent(def_id)), "");
83            }
84            if let hir::def::DefKind::Const | hir::def::DefKind::AssocConst = def_kind {
85                err.span_label(
86                    self.tcx.def_span(uv.def),
87                    crate::fluent_generated::mir_build_const_defined_here,
88                );
89            }
90        }
91        Box::new(Pat { span: self.span, ty, kind: PatKind::Error(err.emit()) })
92    }
93
94    fn unevaluated_to_pat(
95        &mut self,
96        uv: ty::UnevaluatedConst<'tcx>,
97        ty: Ty<'tcx>,
98    ) -> Box<Pat<'tcx>> {
99        // It's not *technically* correct to be revealing opaque types here as borrowcheck has
100        // not run yet. However, CTFE itself uses `TypingMode::PostAnalysis` unconditionally even
101        // during typeck and not doing so has a lot of (undesirable) fallout (#101478, #119821).
102        // As a result we always use a revealed env when resolving the instance to evaluate.
103        //
104        // FIXME: `const_eval_resolve_for_typeck` should probably just modify the env itself
105        // instead of having this logic here
106        let typing_env =
107            self.tcx.erase_regions(self.typing_env).with_post_analysis_normalized(self.tcx);
108        let uv = self.tcx.erase_regions(uv);
109
110        // try to resolve e.g. associated constants to their definition on an impl, and then
111        // evaluate the const.
112        let valtree = match self.tcx.const_eval_resolve_for_typeck(typing_env, uv, self.span) {
113            Ok(Ok(c)) => c,
114            Err(ErrorHandled::Reported(_, _)) => {
115                // Let's tell the use where this failing const occurs.
116                let mut err =
117                    self.tcx.dcx().create_err(CouldNotEvalConstPattern { span: self.span });
118                // We've emitted an error on the original const, it would be redundant to complain
119                // on its use as well.
120                if let ty::ConstKind::Unevaluated(uv) = self.c.kind()
121                    && let hir::def::DefKind::Const | hir::def::DefKind::AssocConst =
122                        self.tcx.def_kind(uv.def)
123                {
124                    err.downgrade_to_delayed_bug();
125                }
126                return self.mk_err(err, ty);
127            }
128            Err(ErrorHandled::TooGeneric(_)) => {
129                let mut e = self
130                    .tcx
131                    .dcx()
132                    .create_err(ConstPatternDependsOnGenericParameter { span: self.span });
133                for arg in uv.args {
134                    if let ty::GenericArgKind::Type(ty) = arg.kind()
135                        && let ty::Param(param_ty) = ty.kind()
136                    {
137                        let def_id = self.tcx.hir_enclosing_body_owner(self.id);
138                        let generics = self.tcx.generics_of(def_id);
139                        let param = generics.type_param(*param_ty, self.tcx);
140                        let span = self.tcx.def_span(param.def_id);
141                        e.span_label(span, "constant depends on this generic parameter");
142                        if let Some(ident) = self.tcx.def_ident_span(def_id)
143                            && self.tcx.sess.source_map().is_multiline(ident.between(span))
144                        {
145                            // Display the `fn` name as well in the diagnostic, as the generic isn't
146                            // in the same line and it could be confusing otherwise.
147                            e.span_label(ident, "");
148                        }
149                    }
150                }
151                return self.mk_err(e, ty);
152            }
153            Ok(Err(bad_ty)) => {
154                // The pattern cannot be turned into a valtree.
155                let e = match bad_ty.kind() {
156                    ty::Adt(def, ..) => {
157                        assert!(def.is_union());
158                        self.tcx.dcx().create_err(UnionPattern { span: self.span })
159                    }
160                    ty::FnPtr(..) | ty::RawPtr(..) => {
161                        self.tcx.dcx().create_err(PointerPattern { span: self.span })
162                    }
163                    _ => self.tcx.dcx().create_err(InvalidPattern {
164                        span: self.span,
165                        non_sm_ty: bad_ty,
166                        prefix: bad_ty.prefix_string(self.tcx).to_string(),
167                    }),
168                };
169                return self.mk_err(e, ty);
170            }
171        };
172
173        // Convert the valtree to a const.
174        let inlined_const_as_pat = self.valtree_to_pat(valtree, ty);
175
176        if !inlined_const_as_pat.references_error() {
177            // Always check for `PartialEq` if we had no other errors yet.
178            if !type_has_partial_eq_impl(self.tcx, typing_env, ty).has_impl {
179                let mut err = self.tcx.dcx().create_err(TypeNotPartialEq { span: self.span, ty });
180                extend_type_not_partial_eq(self.tcx, typing_env, ty, &mut err);
181                return self.mk_err(err, ty);
182            }
183        }
184
185        // Wrap the pattern in a marker node to indicate that it is the result of lowering a
186        // constant. This is used for diagnostics, and for unsafety checking of inline const blocks.
187        let kind = PatKind::ExpandedConstant { subpattern: inlined_const_as_pat, def_id: uv.def };
188        Box::new(Pat { kind, ty, span: self.span })
189    }
190
191    fn field_pats(
192        &self,
193        vals: impl Iterator<Item = (ValTree<'tcx>, Ty<'tcx>)>,
194    ) -> Vec<FieldPat<'tcx>> {
195        vals.enumerate()
196            .map(|(idx, (val, ty))| {
197                let field = FieldIdx::new(idx);
198                // Patterns can only use monomorphic types.
199                let ty = self.tcx.normalize_erasing_regions(self.typing_env, ty);
200                FieldPat { field, pattern: *self.valtree_to_pat(val, ty) }
201            })
202            .collect()
203    }
204
205    // Recursive helper for `to_pat`; invoke that (instead of calling this directly).
206    // FIXME(valtrees): Accept `ty::Value` instead of `Ty` and `ty::ValTree` separately.
207    #[instrument(skip(self), level = "debug")]
208    fn valtree_to_pat(&self, cv: ValTree<'tcx>, ty: Ty<'tcx>) -> Box<Pat<'tcx>> {
209        let span = self.span;
210        let tcx = self.tcx;
211        let kind = match ty.kind() {
212            ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
213                // Extremely important check for all ADTs! Make sure they opted-in to be used in
214                // patterns.
215                debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, ty);
216                let PartialEqImplStatus {
217                    is_derived, structural_partial_eq, non_blanket_impl, ..
218                } = type_has_partial_eq_impl(self.tcx, self.typing_env, ty);
219                let (manual_partialeq_impl_span, manual_partialeq_impl_note) =
220                    match (structural_partial_eq, non_blanket_impl) {
221                        (true, _) => (None, false),
222                        (_, Some(def_id)) if def_id.is_local() && !is_derived => {
223                            (Some(tcx.def_span(def_id)), false)
224                        }
225                        _ => (None, true),
226                    };
227                let ty_def_span = tcx.def_span(adt_def.did());
228                let err = TypeNotStructural {
229                    span,
230                    ty,
231                    ty_def_span,
232                    manual_partialeq_impl_span,
233                    manual_partialeq_impl_note,
234                };
235                return self.mk_err(tcx.dcx().create_err(err), ty);
236            }
237            ty::Adt(adt_def, args) if adt_def.is_enum() => {
238                let (&variant_index, fields) = cv.unwrap_branch().split_first().unwrap();
239                let variant_index = VariantIdx::from_u32(variant_index.unwrap_leaf().to_u32());
240                PatKind::Variant {
241                    adt_def: *adt_def,
242                    args,
243                    variant_index,
244                    subpatterns: self.field_pats(
245                        fields.iter().copied().zip(
246                            adt_def.variants()[variant_index]
247                                .fields
248                                .iter()
249                                .map(|field| field.ty(tcx, args)),
250                        ),
251                    ),
252                }
253            }
254            ty::Adt(def, args) => {
255                assert!(!def.is_union()); // Valtree construction would never succeed for unions.
256                PatKind::Leaf {
257                    subpatterns: self.field_pats(cv.unwrap_branch().iter().copied().zip(
258                        def.non_enum_variant().fields.iter().map(|field| field.ty(tcx, args)),
259                    )),
260                }
261            }
262            ty::Tuple(fields) => PatKind::Leaf {
263                subpatterns: self.field_pats(cv.unwrap_branch().iter().copied().zip(fields.iter())),
264            },
265            ty::Slice(elem_ty) => PatKind::Slice {
266                prefix: cv
267                    .unwrap_branch()
268                    .iter()
269                    .map(|val| *self.valtree_to_pat(*val, *elem_ty))
270                    .collect(),
271                slice: None,
272                suffix: Box::new([]),
273            },
274            ty::Array(elem_ty, _) => PatKind::Array {
275                prefix: cv
276                    .unwrap_branch()
277                    .iter()
278                    .map(|val| *self.valtree_to_pat(*val, *elem_ty))
279                    .collect(),
280                slice: None,
281                suffix: Box::new([]),
282            },
283            ty::Str => {
284                // String literal patterns may have type `str` if `deref_patterns` is enabled, in
285                // order to allow `deref!("..."): String`. Since we need a `&str` for the comparison
286                // when lowering to MIR in `Builder::perform_test`, treat the constant as a `&str`.
287                // This works because `str` and `&str` have the same valtree representation.
288                let ref_str_ty = Ty::new_imm_ref(tcx, tcx.lifetimes.re_erased, ty);
289                PatKind::Constant {
290                    value: mir::Const::Ty(ref_str_ty, ty::Const::new_value(tcx, cv, ref_str_ty)),
291                }
292            }
293            ty::Ref(_, pointee_ty, ..) => match *pointee_ty.kind() {
294                // `&str` is represented as a valtree, let's keep using this
295                // optimization for now.
296                ty::Str => PatKind::Constant {
297                    value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
298                },
299                // All other references are converted into deref patterns and then recursively
300                // convert the dereferenced constant to a pattern that is the sub-pattern of the
301                // deref pattern.
302                _ => {
303                    if !pointee_ty.is_sized(tcx, self.typing_env) && !pointee_ty.is_slice() {
304                        return self.mk_err(
305                            tcx.dcx().create_err(UnsizedPattern { span, non_sm_ty: *pointee_ty }),
306                            ty,
307                        );
308                    } else {
309                        // References have the same valtree representation as their pointee.
310                        PatKind::Deref { subpattern: self.valtree_to_pat(cv, *pointee_ty) }
311                    }
312                }
313            },
314            ty::Float(flt) => {
315                let v = cv.unwrap_leaf();
316                let is_nan = match flt {
317                    ty::FloatTy::F16 => v.to_f16().is_nan(),
318                    ty::FloatTy::F32 => v.to_f32().is_nan(),
319                    ty::FloatTy::F64 => v.to_f64().is_nan(),
320                    ty::FloatTy::F128 => v.to_f128().is_nan(),
321                };
322                if is_nan {
323                    // NaNs are not ever equal to anything so they make no sense as patterns.
324                    // Also see <https://github.com/rust-lang/rfcs/pull/3535>.
325                    return self.mk_err(tcx.dcx().create_err(NaNPattern { span }), ty);
326                } else {
327                    PatKind::Constant {
328                        value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
329                    }
330                }
331            }
332            ty::Pat(..) | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::RawPtr(..) => {
333                // The raw pointers we see here have been "vetted" by valtree construction to be
334                // just integers, so we simply allow them.
335                PatKind::Constant { value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)) }
336            }
337            ty::FnPtr(..) => {
338                unreachable!(
339                    "Valtree construction would never succeed for FnPtr, so this is unreachable."
340                )
341            }
342            _ => {
343                let err = InvalidPattern {
344                    span,
345                    non_sm_ty: ty,
346                    prefix: ty.prefix_string(tcx).to_string(),
347                };
348                return self.mk_err(tcx.dcx().create_err(err), ty);
349            }
350        };
351
352        Box::new(Pat { span, ty, kind })
353    }
354}
355
356/// Given a type with type parameters, visit every ADT looking for types that need to
357/// `#[derive(PartialEq)]` for it to be a structural type.
358fn extend_type_not_partial_eq<'tcx>(
359    tcx: TyCtxt<'tcx>,
360    typing_env: ty::TypingEnv<'tcx>,
361    ty: Ty<'tcx>,
362    err: &mut Diag<'_>,
363) {
364    /// Collect all types that need to be `StructuralPartialEq`.
365    struct UsedParamsNeedInstantiationVisitor<'tcx> {
366        tcx: TyCtxt<'tcx>,
367        typing_env: ty::TypingEnv<'tcx>,
368        /// The user has written `impl PartialEq for Ty` which means it's non-structural.
369        adts_with_manual_partialeq: FxHashSet<Span>,
370        /// The type has no `PartialEq` implementation, neither manual or derived.
371        adts_without_partialeq: FxHashSet<Span>,
372        /// The user has written `impl PartialEq for Ty` which means it's non-structural,
373        /// but we don't have a span to point at, so we'll just add them as a `note`.
374        manual: FxHashSet<Ty<'tcx>>,
375        /// The type has no `PartialEq` implementation, neither manual or derived, but
376        /// we don't have a span to point at, so we'll just add them as a `note`.
377        without: FxHashSet<Ty<'tcx>>,
378    }
379
380    impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for UsedParamsNeedInstantiationVisitor<'tcx> {
381        type Result = ControlFlow<()>;
382        fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
383            match ty.kind() {
384                ty::Dynamic(..) => return ControlFlow::Break(()),
385                // Unsafe binders never implement `PartialEq`, so avoid walking into them
386                // which would require instantiating its binder with placeholders too.
387                ty::UnsafeBinder(..) => return ControlFlow::Break(()),
388                ty::FnPtr(..) => return ControlFlow::Continue(()),
389                ty::Adt(def, _args) => {
390                    let ty_def_id = def.did();
391                    let ty_def_span = self.tcx.def_span(ty_def_id);
392                    let PartialEqImplStatus {
393                        has_impl,
394                        is_derived,
395                        structural_partial_eq,
396                        non_blanket_impl,
397                    } = type_has_partial_eq_impl(self.tcx, self.typing_env, ty);
398                    match (has_impl, is_derived, structural_partial_eq, non_blanket_impl) {
399                        (_, _, true, _) => {}
400                        (true, false, _, Some(def_id)) if def_id.is_local() => {
401                            self.adts_with_manual_partialeq.insert(self.tcx.def_span(def_id));
402                        }
403                        (true, false, _, _) if ty_def_id.is_local() => {
404                            self.adts_with_manual_partialeq.insert(ty_def_span);
405                        }
406                        (false, _, _, _) if ty_def_id.is_local() => {
407                            self.adts_without_partialeq.insert(ty_def_span);
408                        }
409                        (true, false, _, _) => {
410                            self.manual.insert(ty);
411                        }
412                        (false, _, _, _) => {
413                            self.without.insert(ty);
414                        }
415                        _ => {}
416                    };
417                    ty.super_visit_with(self)
418                }
419                _ => ty.super_visit_with(self),
420            }
421        }
422    }
423    let mut v = UsedParamsNeedInstantiationVisitor {
424        tcx,
425        typing_env,
426        adts_with_manual_partialeq: FxHashSet::default(),
427        adts_without_partialeq: FxHashSet::default(),
428        manual: FxHashSet::default(),
429        without: FxHashSet::default(),
430    };
431    if v.visit_ty(ty).is_break() {
432        return;
433    }
434    #[allow(rustc::potential_query_instability)] // Span labels will be sorted by the rendering
435    for span in v.adts_with_manual_partialeq {
436        err.span_note(span, "the `PartialEq` trait must be derived, manual `impl`s are not sufficient; see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details");
437    }
438    #[allow(rustc::potential_query_instability)] // Span labels will be sorted by the rendering
439    for span in v.adts_without_partialeq {
440        err.span_label(
441            span,
442            "must be annotated with `#[derive(PartialEq)]` to be usable in patterns",
443        );
444    }
445    #[allow(rustc::potential_query_instability)]
446    let mut manual: Vec<_> = v.manual.into_iter().map(|t| t.to_string()).collect();
447    manual.sort();
448    for ty in manual {
449        err.note(format!(
450            "`{ty}` must be annotated with `#[derive(PartialEq)]` to be usable in patterns, manual `impl`s are not sufficient; see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details"
451        ));
452    }
453    #[allow(rustc::potential_query_instability)]
454    let mut without: Vec<_> = v.without.into_iter().map(|t| t.to_string()).collect();
455    without.sort();
456    for ty in without {
457        err.note(format!(
458            "`{ty}` must be annotated with `#[derive(PartialEq)]` to be usable in patterns"
459        ));
460    }
461}
462
463#[derive(Debug)]
464struct PartialEqImplStatus {
465    has_impl: bool,
466    is_derived: bool,
467    structural_partial_eq: bool,
468    non_blanket_impl: Option<DefId>,
469}
470
471#[instrument(level = "trace", skip(tcx), ret)]
472fn type_has_partial_eq_impl<'tcx>(
473    tcx: TyCtxt<'tcx>,
474    typing_env: ty::TypingEnv<'tcx>,
475    ty: Ty<'tcx>,
476) -> PartialEqImplStatus {
477    let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
478    // double-check there even *is* a semantic `PartialEq` to dispatch to.
479    //
480    // (If there isn't, then we can safely issue a hard
481    // error, because that's never worked, due to compiler
482    // using `PartialEq::eq` in this scenario in the past.)
483    let partial_eq_trait_id = tcx.require_lang_item(hir::LangItem::PartialEq, DUMMY_SP);
484    let structural_partial_eq_trait_id =
485        tcx.require_lang_item(hir::LangItem::StructuralPeq, DUMMY_SP);
486
487    let partial_eq_obligation = Obligation::new(
488        tcx,
489        ObligationCause::dummy(),
490        param_env,
491        ty::TraitRef::new(tcx, partial_eq_trait_id, [ty, ty]),
492    );
493
494    let mut automatically_derived = false;
495    let mut structural_peq = false;
496    let mut impl_def_id = None;
497    for def_id in tcx.non_blanket_impls_for_ty(partial_eq_trait_id, ty) {
498        automatically_derived = tcx.has_attr(def_id, sym::automatically_derived);
499        impl_def_id = Some(def_id);
500    }
501    for _ in tcx.non_blanket_impls_for_ty(structural_partial_eq_trait_id, ty) {
502        structural_peq = true;
503    }
504    // This *could* accept a type that isn't actually `PartialEq`, because region bounds get
505    // ignored. However that should be pretty much impossible since consts that do not depend on
506    // generics can only mention the `'static` lifetime, and how would one have a type that's
507    // `PartialEq` for some lifetime but *not* for `'static`? If this ever becomes a problem
508    // we'll need to leave some sort of trace of this requirement in the MIR so that borrowck
509    // can ensure that the type really implements `PartialEq`.
510    // We also do *not* require `const PartialEq`, not even in `const fn`. This violates the model
511    // that patterns can only do things that the code could also do without patterns, but it is
512    // needed for backwards compatibility. The actual pattern matching compares primitive values,
513    // `PartialEq::eq` never gets invoked, so there's no risk of us running non-const code.
514    PartialEqImplStatus {
515        has_impl: infcx.predicate_must_hold_modulo_regions(&partial_eq_obligation),
516        is_derived: automatically_derived,
517        structural_partial_eq: structural_peq,
518        non_blanket_impl: impl_def_id,
519    }
520}
rustc_mir_build/thir/pattern/const_to_pat.rs

rustc_mir_build/thir/pattern/
const_to_pat.rs
