src/librustc_mir_build/hair/pattern/const_to_pat.rs

   1 use rustc::lint;
   2 use rustc::mir::Field;
   3 use rustc::ty::{self, Ty, TyCtxt};
   4 use rustc_hir as hir;
   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};
   9
  10 use rustc_index::vec::Idx;
  11
  12 use rustc_span::Span;
  13
  14 use std::cell::Cell;
  15
  16 use super::{FieldPat, Pat, PatCtxt, PatKind};
  17
  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(
  23         &self,
  24         cv: &'tcx ty::Const<'tcx>,
  25         id: hir::HirId,
  26         span: Span,
  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)
  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(&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.
  90         //
  91         // once indirect_structural_match is a full fledged error, this
  92         // level of indirection can be eliminated
  93
  94         let inlined_const_as_pat = self.recur(cv);
  95
  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`.
  99
 100             let structural = self.search_for_structural_match_violation(cv.ty);
 101             debug!(
 102                 "search_for_structural_match_violation cv.ty: {:?} returned: {:?}",
 103                 cv.ty, structural
 104             );
 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")
 110                     }
 111                 };
 112                 let path = self.tcx().def_path_str(adt_def.did);
 113
 114                 let make_msg = || -> String {
 115                     format!(
 116                         "to use a constant of type `{}` in a pattern, \
 117                          `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 118                         path, path,
 119                     )
 120                 };
 121
 122                 // double-check there even *is* a semantic `PartialEq` to dispatch to.
 123                 //
 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.)
 127                 //
 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(
 136                         self.tcx(),
 137                         self.param_env,
 138                         ObligationCause::misc(self.span, self.id),
 139                         partial_eq_trait_id,
 140                         0,
 141                         cv.ty,
 142                         &[],
 143                     );
 144                     // FIXME: should this call a `predicate_must_hold` variant instead?
 145                     self.infcx.predicate_may_hold(&obligation)
 146                 };
 147
 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());
 151                 } else {
 152                     self.tcx().struct_span_lint_hir(
 153                         lint::builtin::INDIRECT_STRUCTURAL_MATCH,
 154                         self.id,
 155                         self.span,
 156                         |lint| lint.build(&make_msg()).emit(),
 157                     );
 158                 }
 159             }
 160         }
 161
 162         inlined_const_as_pat
 163     }
 164
 165     // Recursive helper for `to_pat`; invoke that (instead of calling this directly).
 166     fn recur(&self, cv: &'tcx ty::Const<'tcx>) -> Pat<'tcx> {
 167         let id = self.id;
 168         let span = self.span;
 169         let tcx = self.tcx();
 170         let param_env = self.param_env;
 171
 172         let field_pats = |vals: &[&'tcx ty::Const<'tcx>]| {
 173             vals.iter()
 174                 .enumerate()
 175                 .map(|(idx, val)| {
 176                     let field = Field::new(idx);
 177                     FieldPat { field, pattern: self.recur(val) }
 178                 })
 179                 .collect()
 180         };
 181
 182         let kind = match cv.ty.kind {
 183             ty::Float(_) => {
 184                 tcx.struct_span_lint_hir(
 185                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 186                     id,
 187                     span,
 188                     |lint| lint.build("floating-point types cannot be used in patterns").emit(),
 189                 );
 190                 PatKind::Constant { value: cv }
 191             }
 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");
 196                 PatKind::Wild
 197             }
 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);
 202                 let msg = format!(
 203                     "to use a constant of type `{}` in a pattern, \
 204                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 205                     path, path,
 206                 );
 207                 self.saw_const_match_error.set(true);
 208                 tcx.sess.span_err(span, &msg);
 209                 PatKind::Wild
 210             }
 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) =>
 214             {
 215                 let adt_def =
 216                     if let ty::Adt(adt_def, _) = adt_ty.kind { adt_def } else { unreachable!() };
 217
 218                 debug!(
 219                     "adt_def {:?} has !type_marked_structural for adt_ty: {:?}",
 220                     adt_def, adt_ty
 221                 );
 222
 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);
 226                 let msg = format!(
 227                     "to use a constant of type `{}` in a pattern, \
 228                      `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 229                     path, path,
 230                 );
 231                 self.saw_const_match_error.set(true);
 232                 tcx.sess.span_err(span, &msg);
 233                 PatKind::Wild
 234             }
 235             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 236                 let destructured = tcx.destructure_const(param_env.and(cv));
 237                 PatKind::Variant {
 238                     adt_def,
 239                     substs,
 240                     variant_index: destructured.variant,
 241                     subpatterns: field_pats(destructured.fields),
 242                 }
 243             }
 244             ty::Adt(_, _) => {
 245                 let destructured = tcx.destructure_const(param_env.and(cv));
 246                 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
 247             }
 248             ty::Tuple(_) => {
 249                 let destructured = tcx.destructure_const(param_env.and(cv));
 250                 PatKind::Leaf { subpatterns: field_pats(destructured.fields) }
 251             }
 252             ty::Array(..) => PatKind::Array {
 253                 prefix: tcx
 254                     .destructure_const(param_env.and(cv))
 255                     .fields
 256                     .iter()
 257                     .map(|val| self.recur(val))
 258                     .collect(),
 259                 slice: None,
 260                 suffix: Vec::new(),
 261             },
 262             _ => PatKind::Constant { value: cv },
 263         };
 264
 265         Pat { span, ty: cv.ty, kind: Box::new(kind) }
 266     }
 267 }