3 use rustc::ty::{self, Ty, TyCtxt};
5 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
6 use rustc_infer::traits::predicate_for_trait_def;
7 use rustc_infer::traits::{self, ObligationCause, PredicateObligation};
9 use rustc_index::vec::Idx;
15 use super::{FieldPat, Pat, PatCtxt, PatKind};
17 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
18 /// Converts an evaluated constant to a pattern (if possible).
19 /// This means aggregate values (like structs and enums) are converted
20 /// to a pattern that matches the value (as if you'd compared via structural equality).
21 pub(super) fn const_to_pat(
23 cv: &'tcx ty::Const<'tcx>,
27 debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
28 debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
30 self.tcx.infer_ctxt().enter(|infcx| {
31 let mut convert = ConstToPat::new(self, id, span, infcx);
37 struct ConstToPat<'a, 'tcx> {
40 param_env: ty::ParamEnv<'tcx>,
42 // This tracks if we signal some hard error for a given const value, so that
43 // we will not subsequently issue an irrelevant lint for the same const
45 saw_const_match_error: Cell<bool>,
47 // inference context used for checking `T: Structural` bounds.
48 infcx: InferCtxt<'a, 'tcx>,
50 include_lint_checks: bool,
53 impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
55 pat_ctxt: &PatCtxt<'_, 'tcx>,
58 infcx: InferCtxt<'a, 'tcx>,
64 param_env: pat_ctxt.param_env,
65 include_lint_checks: pat_ctxt.include_lint_checks,
66 saw_const_match_error: Cell::new(false),
70 fn tcx(&self) -> TyCtxt<'tcx> {
74 fn search_for_structural_match_violation(
77 ) -> Option<traits::NonStructuralMatchTy<'tcx>> {
78 traits::search_for_structural_match_violation(self.id, self.span, self.tcx(), ty)
81 fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
82 traits::type_marked_structural(self.id, self.span, &self.infcx, ty)
85 fn to_pat(&mut self, cv: &'tcx ty::Const<'tcx>) -> Pat<'tcx> {
86 // This method is just a wrapper handling a validity check; the heavy lifting is
87 // performed by the recursive `recur` method, which is not meant to be
88 // invoked except by this method.
90 // once indirect_structural_match is a full fledged error, this
91 // level of indirection can be eliminated
93 let inlined_const_as_pat = self.recur(cv);
95 if self.include_lint_checks && !self.saw_const_match_error.get() {
96 // If we were able to successfully convert the const to some pat,
97 // double-check that all types in the const implement `Structural`.
99 let structural = self.search_for_structural_match_violation(cv.ty);
101 "search_for_structural_match_violation cv.ty: {:?} returned: {:?}",
104 if let Some(non_sm_ty) = structural {
105 let adt_def = match non_sm_ty {
106 traits::NonStructuralMatchTy::Adt(adt_def) => adt_def,
107 traits::NonStructuralMatchTy::Param => {
108 bug!("use of constant whose type is a parameter inside a pattern")
111 let path = self.tcx().def_path_str(adt_def.did);
113 let make_msg = || -> String {
115 "to use a constant of type `{}` in a pattern, \
116 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
121 // double-check there even *is* a semantic `PartialEq` to dispatch to.
123 // (If there isn't, then we can safely issue a hard
124 // error, because that's never worked, due to compiler
125 // using `PartialEq::eq` in this scenario in the past.)
127 // Note: To fix rust-lang/rust#65466, one could lift this check
128 // *before* any structural-match checking, and unconditionally error
129 // if `PartialEq` is not implemented. However, that breaks stable
130 // code at the moment, because types like `for <'a> fn(&'a ())` do
131 // not *yet* implement `PartialEq`. So for now we leave this here.
132 let ty_is_partial_eq: bool = {
133 let partial_eq_trait_id = self.tcx().lang_items().eq_trait().unwrap();
134 let obligation: PredicateObligation<'_> = predicate_for_trait_def(
137 ObligationCause::misc(self.span, self.id),
143 // FIXME: should this call a `predicate_must_hold` variant instead?
144 self.infcx.predicate_may_hold(&obligation)
147 if !ty_is_partial_eq {
148 // span_fatal avoids ICE from resolution of non-existent method (rare case).
149 self.tcx().sess.span_fatal(self.span, &make_msg());
151 self.tcx().struct_span_lint_hir(
152 lint::builtin::INDIRECT_STRUCTURAL_MATCH,
155 |lint| lint.build(&make_msg()).emit(),
164 // Recursive helper for `to_pat`; invoke that (instead of calling this directly).
165 fn recur(&self, cv: &'tcx ty::Const<'tcx>) -> Pat<'tcx> {
167 let span = self.span;
168 let tcx = self.tcx();
169 let param_env = self.param_env;
171 let field_pats = |vals: &[&'tcx ty::Const<'tcx>]| {
175 let field = Field::new(idx);
176 FieldPat { field, pattern: self.recur(val) }
181 let kind = match cv.ty.kind {
183 tcx.struct_span_lint_hir(
184 ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
187 |lint| lint.build("floating-point types cannot be used in patterns").emit(),
189 PatKind::Constant { value: cv }
191 ty::Adt(adt_def, _) if adt_def.is_union() => {
192 // Matching on union fields is unsafe, we can't hide it in constants
193 self.saw_const_match_error.set(true);
194 tcx.sess.span_err(span, "cannot use unions in constant patterns");
197 // keep old code until future-compat upgraded to errors.
198 ty::Adt(adt_def, _) if !self.type_marked_structural(cv.ty) => {
199 debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, cv.ty);
200 let path = tcx.def_path_str(adt_def.did);
202 "to use a constant of type `{}` in a pattern, \
203 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
206 self.saw_const_match_error.set(true);
207 tcx.sess.span_err(span, &msg);
210 // keep old code until future-compat upgraded to errors.
211 ty::Ref(_, adt_ty @ ty::TyS { kind: ty::Adt(_, _), .. }, _)
212 if !self.type_marked_structural(adt_ty) =>
215 if let ty::Adt(adt_def, _) = adt_ty.kind { adt_def } else { unreachable!() };
218 "adt_def {:?} has !type_marked_structural for adt_ty: {:?}",
222 // HACK(estebank): Side-step ICE #53708, but anything other than erroring here
223 // would be wrong. Returnging `PatKind::Wild` is not technically correct.
224 let path = tcx.def_path_str(adt_def.did);
226 "to use a constant of type `{}` in a pattern, \
227 `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
230 self.saw_const_match_error.set(true);
231 tcx.sess.span_err(span, &msg);
234 ty::Adt(adt_def, substs) if adt_def.is_enum() => {
235 let destructured = tcx.destructure_const(param_env.and(cv));
239 variant_index: destructured.variant,
240 subpatterns: field_pats(destructured.fields),
244 let destructured = tcx.destructure_const(param_env.and(cv));
245 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
248 let destructured = tcx.destructure_const(param_env.and(cv));
249 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
251 ty::Array(..) => PatKind::Array {
253 .destructure_const(param_env.and(cv))
256 .map(|val| self.recur(val))
261 _ => PatKind::Constant { value: cv },
264 Pat { span, ty: cv.ty, kind: Box::new(kind) }