3 use rustc::ty::{self, Ty, TyCtxt};
5 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
6 use rustc_trait_selection::traits::predicate_for_trait_def;
7 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
8 use rustc_trait_selection::traits::{self, ObligationCause, PredicateObligation};
10 use rustc_index::vec::Idx;
16 use super::{FieldPat, Pat, PatCtxt, PatKind};
18 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
19 /// Converts an evaluated constant to a pattern (if possible).
20 /// This means aggregate values (like structs and enums) are converted
21 /// to a pattern that matches the value (as if you'd compared via structural equality).
22 pub(super) fn const_to_pat(
24 cv: &'tcx ty::Const<'tcx>,
28 debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
29 debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
31 self.tcx.infer_ctxt().enter(|infcx| {
32 let mut convert = ConstToPat::new(self, id, span, infcx);
38 struct ConstToPat<'a, 'tcx> {
41 param_env: ty::ParamEnv<'tcx>,
43 // This tracks if we signal some hard error for a given const value, so that
44 // we will not subsequently issue an irrelevant lint for the same const
46 saw_const_match_error: Cell<bool>,
48 // inference context used for checking `T: Structural` bounds.
49 infcx: InferCtxt<'a, 'tcx>,
51 include_lint_checks: bool,
54 impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
56 pat_ctxt: &PatCtxt<'_, 'tcx>,
59 infcx: InferCtxt<'a, 'tcx>,
65 param_env: pat_ctxt.param_env,
66 include_lint_checks: pat_ctxt.include_lint_checks,
67 saw_const_match_error: Cell::new(false),
71 fn tcx(&self) -> TyCtxt<'tcx> {
75 fn search_for_structural_match_violation(
78 ) -> Option<traits::NonStructuralMatchTy<'tcx>> {
79 traits::search_for_structural_match_violation(self.id, self.span, self.tcx(), ty)
82 fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
83 traits::type_marked_structural(self.id, self.span, &self.infcx, ty)
86 fn to_pat(&mut self, cv: &'tcx ty::Const<'tcx>) -> Pat<'tcx> {
87 // This method is just a wrapper handling a validity check; the heavy lifting is
88 // performed by the recursive `recur` method, which is not meant to be
89 // invoked except by this method.
91 // once indirect_structural_match is a full fledged error, this
92 // level of indirection can be eliminated
94 let inlined_const_as_pat = self.recur(cv);
96 if self.include_lint_checks && !self.saw_const_match_error.get() {
97 // If we were able to successfully convert the const to some pat,
98 // double-check that all types in the const implement `Structural`.
100 let structural = self.search_for_structural_match_violation(cv.ty);
102 "search_for_structural_match_violation cv.ty: {:?} returned: {:?}",
105 if let Some(non_sm_ty) = structural {
106 let adt_def = match non_sm_ty {
107 traits::NonStructuralMatchTy::Adt(adt_def) => adt_def,
108 traits::NonStructuralMatchTy::Param => {
109 bug!("use of constant whose type is a parameter inside a pattern")
112 let path = self.tcx().def_path_str(adt_def.did);
114 let make_msg = || -> String {
116 "to use a constant of type `{}` in a pattern, \
117 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
122 // double-check there even *is* a semantic `PartialEq` to dispatch to.
124 // (If there isn't, then we can safely issue a hard
125 // error, because that's never worked, due to compiler
126 // using `PartialEq::eq` in this scenario in the past.)
128 // Note: To fix rust-lang/rust#65466, one could lift this check
129 // *before* any structural-match checking, and unconditionally error
130 // if `PartialEq` is not implemented. However, that breaks stable
131 // code at the moment, because types like `for <'a> fn(&'a ())` do
132 // not *yet* implement `PartialEq`. So for now we leave this here.
133 let ty_is_partial_eq: bool = {
134 let partial_eq_trait_id = self.tcx().lang_items().eq_trait().unwrap();
135 let obligation: PredicateObligation<'_> = predicate_for_trait_def(
138 ObligationCause::misc(self.span, self.id),
144 // FIXME: should this call a `predicate_must_hold` variant instead?
145 self.infcx.predicate_may_hold(&obligation)
148 if !ty_is_partial_eq {
149 // span_fatal avoids ICE from resolution of non-existent method (rare case).
150 self.tcx().sess.span_fatal(self.span, &make_msg());
152 self.tcx().struct_span_lint_hir(
153 lint::builtin::INDIRECT_STRUCTURAL_MATCH,
156 |lint| lint.build(&make_msg()).emit(),
165 // Recursive helper for `to_pat`; invoke that (instead of calling this directly).
166 fn recur(&self, cv: &'tcx ty::Const<'tcx>) -> Pat<'tcx> {
168 let span = self.span;
169 let tcx = self.tcx();
170 let param_env = self.param_env;
172 let field_pats = |vals: &[&'tcx ty::Const<'tcx>]| {
176 let field = Field::new(idx);
177 FieldPat { field, pattern: self.recur(val) }
182 let kind = match cv.ty.kind {
184 tcx.struct_span_lint_hir(
185 ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
188 |lint| lint.build("floating-point types cannot be used in patterns").emit(),
190 PatKind::Constant { value: cv }
192 ty::Adt(adt_def, _) if adt_def.is_union() => {
193 // Matching on union fields is unsafe, we can't hide it in constants
194 self.saw_const_match_error.set(true);
195 tcx.sess.span_err(span, "cannot use unions in constant patterns");
198 // keep old code until future-compat upgraded to errors.
199 ty::Adt(adt_def, _) if !self.type_marked_structural(cv.ty) => {
200 debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, cv.ty);
201 let path = tcx.def_path_str(adt_def.did);
203 "to use a constant of type `{}` in a pattern, \
204 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
207 self.saw_const_match_error.set(true);
208 tcx.sess.span_err(span, &msg);
211 // keep old code until future-compat upgraded to errors.
212 ty::Ref(_, adt_ty @ ty::TyS { kind: ty::Adt(_, _), .. }, _)
213 if !self.type_marked_structural(adt_ty) =>
216 if let ty::Adt(adt_def, _) = adt_ty.kind { adt_def } else { unreachable!() };
219 "adt_def {:?} has !type_marked_structural for adt_ty: {:?}",
223 // HACK(estebank): Side-step ICE #53708, but anything other than erroring here
224 // would be wrong. Returnging `PatKind::Wild` is not technically correct.
225 let path = tcx.def_path_str(adt_def.did);
227 "to use a constant of type `{}` in a pattern, \
228 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
231 self.saw_const_match_error.set(true);
232 tcx.sess.span_err(span, &msg);
235 ty::Adt(adt_def, substs) if adt_def.is_enum() => {
236 let destructured = tcx.destructure_const(param_env.and(cv));
240 variant_index: destructured.variant,
241 subpatterns: field_pats(destructured.fields),
245 let destructured = tcx.destructure_const(param_env.and(cv));
246 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
249 let destructured = tcx.destructure_const(param_env.and(cv));
250 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
252 ty::Array(..) => PatKind::Array {
254 .destructure_const(param_env.and(cv))
257 .map(|val| self.recur(val))
262 _ => PatKind::Constant { value: cv },
265 Pat { span, ty: cv.ty, kind: Box::new(kind) }