src/librustc_mir_build/hair/pattern/const_to_pat.rs

   1 use rustc_hir as hir;
   2 use rustc_hir::lang_items::EqTraitLangItem;
   3 use rustc_index::vec::Idx;
   4 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
   5 use rustc_middle::mir::Field;
   6 use rustc_middle::ty::{self, Ty, TyCtxt};
   7 use rustc_session::lint;
   8 use rustc_span::Span;
   9 use rustc_trait_selection::traits::predicate_for_trait_def;
  10 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
  11 use rustc_trait_selection::traits::{self, ObligationCause, PredicateObligation};
  12
  13 use std::cell::Cell;
  14
  15 use super::{FieldPat, Pat, PatCtxt, PatKind};
  16
  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(
  22         &self,
  23         cv: &'tcx ty::Const<'tcx>,
  24         id: hir::HirId,
  25         span: Span,
  26         mir_structural_match_violation: bool,
  27     ) -> Pat<'tcx> {
  28         debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
  29         debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
  30
  31         self.tcx.infer_ctxt().enter(|infcx| {
  32             let mut convert = ConstToPat::new(self, id, span, infcx);
  33             convert.to_pat(cv, mir_structural_match_violation)
  34         })
  35     }
  36 }
  37
  38 struct ConstToPat<'a, 'tcx> {
  39     id: hir::HirId,
  40     span: Span,
  41     param_env: ty::ParamEnv<'tcx>,
  42
  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
  45     // value.
  46     saw_const_match_error: Cell<bool>,
  47
  48     // inference context used for checking `T: Structural` bounds.
  49     infcx: InferCtxt<'a, 'tcx>,
  50
  51     include_lint_checks: bool,
  52 }
  53
  54 impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
  55     fn new(
  56         pat_ctxt: &PatCtxt<'_, 'tcx>,
  57         id: hir::HirId,
  58         span: Span,
  59         infcx: InferCtxt<'a, 'tcx>,
  60     ) -> Self {
  61         ConstToPat {
  62             id,
  63             span,
  64             infcx,
  65             param_env: pat_ctxt.param_env,
  66             include_lint_checks: pat_ctxt.include_lint_checks,
  67             saw_const_match_error: Cell::new(false),
  68         }
  69     }
  70
  71     fn tcx(&self) -> TyCtxt<'tcx> {
  72         self.infcx.tcx
  73     }
  74
  75     fn search_for_structural_match_violation(
  76         &self,
  77         ty: Ty<'tcx>,
  78     ) -> Option<traits::NonStructuralMatchTy<'tcx>> {
  79         traits::search_for_structural_match_violation(self.id, self.span, self.tcx(), ty)
  80     }
  81
  82     fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
  83         traits::type_marked_structural(self.id, self.span, &self.infcx, ty)
  84     }
  85
  86     fn to_pat(
  87         &mut self,
  88         cv: &'tcx ty::Const<'tcx>,
  89         mir_structural_match_violation: bool,
  90     ) -> Pat<'tcx> {
  91         // This method is just a wrapper handling a validity check; the heavy lifting is
  92         // performed by the recursive `recur` method, which is not meant to be
  93         // invoked except by this method.
  94         //
  95         // once indirect_structural_match is a full fledged error, this
  96         // level of indirection can be eliminated
  97
  98         let inlined_const_as_pat = self.recur(cv);
  99
 100         if self.include_lint_checks && !self.saw_const_match_error.get() {
 101             // If we were able to successfully convert the const to some pat,
 102             // double-check that all types in the const implement `Structural`.
 103
 104             let structural = self.search_for_structural_match_violation(cv.ty);
 105             debug!(
 106                 "search_for_structural_match_violation cv.ty: {:?} returned: {:?}",
 107                 cv.ty, structural
 108             );
 109
 110             if structural.is_none() && mir_structural_match_violation {
 111                 bug!("MIR const-checker found novel structural match violation");
 112             }
 113
 114             if let Some(non_sm_ty) = structural {
 115                 let msg = match non_sm_ty {
 116                     traits::NonStructuralMatchTy::Adt(adt_def) => {
 117                         let path = self.tcx().def_path_str(adt_def.did);
 118                         format!(
 119                             "to use a constant of type `{}` in a pattern, \
 120                              `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 121                             path, path,
 122                         )
 123                     }
 124                     traits::NonStructuralMatchTy::Dynamic => {
 125                         "trait objects cannot be used in patterns".to_string()
 126                     }
 127                     traits::NonStructuralMatchTy::Opaque => {
 128                         "opaque types cannot be used in patterns".to_string()
 129                     }
 130                     traits::NonStructuralMatchTy::Generator => {
 131                         "generators cannot be used in patterns".to_string()
 132                     }
 133                     traits::NonStructuralMatchTy::Param => {
 134                         bug!("use of a constant whose type is a parameter inside a pattern")
 135                     }
 136                     traits::NonStructuralMatchTy::Projection => {
 137                         bug!("use of a constant whose type is a projection inside a pattern")
 138                     }
 139                     traits::NonStructuralMatchTy::Foreign => {
 140                         bug!("use of a value of a foreign type inside a pattern")
 141                     }
 142                 };
 143
 144                 // double-check there even *is* a semantic `PartialEq` to dispatch to.
 145                 //
 146                 // (If there isn't, then we can safely issue a hard
 147                 // error, because that's never worked, due to compiler
 148                 // using `PartialEq::eq` in this scenario in the past.)
 149                 //
 150                 // Note: To fix rust-lang/rust#65466, one could lift this check
 151                 // *before* any structural-match checking, and unconditionally error
 152                 // if `PartialEq` is not implemented. However, that breaks stable
 153                 // code at the moment, because types like `for <'a> fn(&'a ())` do
 154                 // not *yet* implement `PartialEq`. So for now we leave this here.
 155                 let ty_is_partial_eq: bool = {
 156                     let partial_eq_trait_id =
 157                         self.tcx().require_lang_item(EqTraitLangItem, Some(self.span));
 158                     let obligation: PredicateObligation<'_> = predicate_for_trait_def(
 159                         self.tcx(),
 160                         self.param_env,
 161                         ObligationCause::misc(self.span, self.id),
 162                         partial_eq_trait_id,
 163                         0,
 164                         cv.ty,
 165                         &[],
 166                     );
 167                     // FIXME: should this call a `predicate_must_hold` variant instead?
 168                     self.infcx.predicate_may_hold(&obligation)
 169                 };
 170
 171                 if !ty_is_partial_eq {
 172                     // span_fatal avoids ICE from resolution of non-existent method (rare case).
 173                     self.tcx().sess.span_fatal(self.span, &msg);
 174                 } else if mir_structural_match_violation {
 175                     self.tcx().struct_span_lint_hir(
 176                         lint::builtin::INDIRECT_STRUCTURAL_MATCH,
 177                         self.id,
 178                         self.span,
 179                         |lint| lint.build(&msg).emit(),
 180                     );
 181                 } else {
 182                     debug!(
 183                         "`search_for_structural_match_violation` found one, but `CustomEq` was \
 184                           not in the qualifs for that `const`"
 185                     );
 186                 }
 187             }
 188         }
 189
 190         inlined_const_as_pat
 191     }
 192
 193     // Recursive helper for `to_pat`; invoke that (instead of calling this directly).
 194     fn recur(&self, cv: &'tcx ty::Const<'tcx>) -> Pat<'tcx> {
 195         let id = self.id;
 196         let span = self.span;
 197         let tcx = self.tcx();
 198         let param_env = self.param_env;
 199
 200         let field_pats = |vals: &[&'tcx ty::Const<'tcx>]| {
 201             vals.iter()
 202                 .enumerate()
 203                 .map(|(idx, val)| {
 204                     let field = Field::new(idx);
 205                     FieldPat { field, pattern: self.recur(val) }
 206                 })
 207                 .collect()
 208         };
 209
 210         let kind = match cv.ty.kind {
 211             ty::Float(_) => {
 212                 tcx.struct_span_lint_hir(
 213                     lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 214                     id,
 215                     span,
 216                     |lint| lint.build("floating-point types cannot be used in patterns").emit(),
 217                 );
 218                 PatKind::Constant { value: cv }
 219             }
 220             ty::Adt(adt_def, _) if adt_def.is_union() => {
 221                 // Matching on union fields is unsafe, we can't hide it in constants
 222                 self.saw_const_match_error.set(true);
 223                 tcx.sess.span_err(span, "cannot use unions in constant patterns");
 224                 PatKind::Wild
 225             }
 226             // keep old code until future-compat upgraded to errors.
 227             ty::Adt(adt_def, _) if !self.type_marked_structural(cv.ty) => {
 228                 debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, cv.ty);
 229                 let path = tcx.def_path_str(adt_def.did);
 230                 let msg = format!(
 231                     "to use a constant of type `{}` in a pattern, \
 232                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 233                     path, path,
 234                 );
 235                 self.saw_const_match_error.set(true);
 236                 tcx.sess.span_err(span, &msg);
 237                 PatKind::Wild
 238             }
 239             // keep old code until future-compat upgraded to errors.
 240             ty::Ref(_, adt_ty @ ty::TyS { kind: ty::Adt(_, _), .. }, _)
 241                 if !self.type_marked_structural(adt_ty) =>
 242             {
 243                 let adt_def =
 244                     if let ty::Adt(adt_def, _) = adt_ty.kind { adt_def } else { unreachable!() };
 245
 246                 debug!(
 247                     "adt_def {:?} has !type_marked_structural for adt_ty: {:?}",
 248                     adt_def, adt_ty
 249                 );
 250
 251                 // HACK(estebank): Side-step ICE #53708, but anything other than erroring here
 252                 // would be wrong. Returnging `PatKind::Wild` is not technically correct.
 253                 let path = tcx.def_path_str(adt_def.did);
 254                 let msg = format!(
 255                     "to use a constant of type `{}` in a pattern, \
 256                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 257                     path, path,
 258                 );
 259                 self.saw_const_match_error.set(true);
 260                 tcx.sess.span_err(span, &msg);
 261                 PatKind::Wild
 262             }
 263             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 264                 let destructured = tcx.destructure_const(param_env.and(cv));
 265                 PatKind::Variant {
 266                     adt_def,
 267                     substs,
 268                     variant_index: destructured.variant,
 269                     subpatterns: field_pats(destructured.fields),
 270                 }
 271             }
 272             ty::Adt(_, _) => {
 273                 let destructured = tcx.destructure_const(param_env.and(cv));
 274                 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
 275             }
 276             ty::Tuple(_) => {
 277                 let destructured = tcx.destructure_const(param_env.and(cv));
 278                 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
 279             }
 280             ty::Array(..) => PatKind::Array {
 281                 prefix: tcx
 282                     .destructure_const(param_env.and(cv))
 283                     .fields
 284                     .iter()
 285                     .map(|val| self.recur(val))
 286                     .collect(),
 287                 slice: None,
 288                 suffix: Vec::new(),
 289             },
 290             _ => PatKind::Constant { value: cv },
 291         };
 292
 293         Pat { span, ty: cv.ty, kind: Box::new(kind) }
 294     }
 295 }