compiler/rustc_hir_analysis/src/autoderef.rs

   1 use crate::errors::AutoDerefReachedRecursionLimit;
   2 use crate::traits::query::evaluate_obligation::InferCtxtExt;
   3 use crate::traits::NormalizeExt;
   4 use crate::traits::{self, TraitEngine, TraitEngineExt};
   5 use rustc_infer::infer::InferCtxt;
   6 use rustc_middle::ty::TypeVisitable;
   7 use rustc_middle::ty::{self, Ty, TyCtxt};
   8 use rustc_session::Limit;
   9 use rustc_span::def_id::LocalDefId;
  10 use rustc_span::def_id::LOCAL_CRATE;
  11 use rustc_span::Span;
  12
  13 #[derive(Copy, Clone, Debug)]
  14 pub enum AutoderefKind {
  15     Builtin,
  16     Overloaded,
  17 }
  18
  19 struct AutoderefSnapshot<'tcx> {
  20     at_start: bool,
  21     reached_recursion_limit: bool,
  22     steps: Vec<(Ty<'tcx>, AutoderefKind)>,
  23     cur_ty: Ty<'tcx>,
  24     obligations: Vec<traits::PredicateObligation<'tcx>>,
  25 }
  26
  27 pub struct Autoderef<'a, 'tcx> {
  28     // Meta infos:
  29     infcx: &'a InferCtxt<'tcx>,
  30     span: Span,
  31     body_id: LocalDefId,
  32     param_env: ty::ParamEnv<'tcx>,
  33
  34     // Current state:
  35     state: AutoderefSnapshot<'tcx>,
  36
  37     // Configurations:
  38     include_raw_pointers: bool,
  39     silence_errors: bool,
  40 }
  41
  42 impl<'a, 'tcx> Iterator for Autoderef<'a, 'tcx> {
  43     type Item = (Ty<'tcx>, usize);
  44
  45     fn next(&mut self) -> Option<Self::Item> {
  46         let tcx = self.infcx.tcx;
  47
  48         debug!("autoderef: steps={:?}, cur_ty={:?}", self.state.steps, self.state.cur_ty);
  49         if self.state.at_start {
  50             self.state.at_start = false;
  51             debug!("autoderef stage #0 is {:?}", self.state.cur_ty);
  52             return Some((self.state.cur_ty, 0));
  53         }
  54
  55         // If we have reached the recursion limit, error gracefully.
  56         if !tcx.recursion_limit().value_within_limit(self.state.steps.len()) {
  57             if !self.silence_errors {
  58                 report_autoderef_recursion_limit_error(tcx, self.span, self.state.cur_ty);
  59             }
  60             self.state.reached_recursion_limit = true;
  61             return None;
  62         }
  63
  64         if self.state.cur_ty.is_ty_var() {
  65             return None;
  66         }
  67
  68         // Otherwise, deref if type is derefable:
  69         let (kind, new_ty) =
  70             if let Some(mt) = self.state.cur_ty.builtin_deref(self.include_raw_pointers) {
  71                 (AutoderefKind::Builtin, mt.ty)
  72             } else if let Some(ty) = self.overloaded_deref_ty(self.state.cur_ty) {
  73                 (AutoderefKind::Overloaded, ty)
  74             } else {
  75                 return None;
  76             };
  77
  78         if new_ty.references_error() {
  79             return None;
  80         }
  81
  82         self.state.steps.push((self.state.cur_ty, kind));
  83         debug!(
  84             "autoderef stage #{:?} is {:?} from {:?}",
  85             self.step_count(),
  86             new_ty,
  87             (self.state.cur_ty, kind)
  88         );
  89         self.state.cur_ty = new_ty;
  90
  91         Some((self.state.cur_ty, self.step_count()))
  92     }
  93 }
  94
  95 impl<'a, 'tcx> Autoderef<'a, 'tcx> {
  96     pub fn new(
  97         infcx: &'a InferCtxt<'tcx>,
  98         param_env: ty::ParamEnv<'tcx>,
  99         body_def_id: LocalDefId,
 100         span: Span,
 101         base_ty: Ty<'tcx>,
 102     ) -> Autoderef<'a, 'tcx> {
 103         Autoderef {
 104             infcx,
 105             span,
 106             body_id: body_def_id,
 107             param_env,
 108             state: AutoderefSnapshot {
 109                 steps: vec![],
 110                 cur_ty: infcx.resolve_vars_if_possible(base_ty),
 111                 obligations: vec![],
 112                 at_start: true,
 113                 reached_recursion_limit: false,
 114             },
 115             include_raw_pointers: false,
 116             silence_errors: false,
 117         }
 118     }
 119
 120     fn overloaded_deref_ty(&mut self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
 121         debug!("overloaded_deref_ty({:?})", ty);
 122
 123         let tcx = self.infcx.tcx;
 124
 125         // <ty as Deref>
 126         let trait_ref = tcx.mk_trait_ref(tcx.lang_items().deref_trait()?, [ty]);
 127
 128         let cause = traits::ObligationCause::misc(self.span, self.body_id);
 129
 130         let obligation = traits::Obligation::new(
 131             tcx,
 132             cause.clone(),
 133             self.param_env,
 134             ty::Binder::dummy(trait_ref),
 135         );
 136         if !self.infcx.predicate_may_hold(&obligation) {
 137             debug!("overloaded_deref_ty: cannot match obligation");
 138             return None;
 139         }
 140
 141         let normalized_ty = self
 142             .infcx
 143             .at(&cause, self.param_env)
 144             .normalize(tcx.mk_projection(tcx.lang_items().deref_target()?, trait_ref.substs));
 145         let mut fulfillcx = <dyn TraitEngine<'tcx>>::new_in_snapshot(tcx);
 146         let normalized_ty =
 147             normalized_ty.into_value_registering_obligations(self.infcx, &mut *fulfillcx);
 148         let errors = fulfillcx.select_where_possible(&self.infcx);
 149         if !errors.is_empty() {
 150             // This shouldn't happen, except for evaluate/fulfill mismatches,
 151             // but that's not a reason for an ICE (`predicate_may_hold` is conservative
 152             // by design).
 153             debug!("overloaded_deref_ty: encountered errors {:?} while fulfilling", errors);
 154             return None;
 155         }
 156         let obligations = fulfillcx.pending_obligations();
 157         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
 158         self.state.obligations.extend(obligations);
 159
 160         Some(self.infcx.resolve_vars_if_possible(normalized_ty))
 161     }
 162
 163     /// Returns the final type we ended up with, which may be an inference
 164     /// variable (we will resolve it first, if we want).
 165     pub fn final_ty(&self, resolve: bool) -> Ty<'tcx> {
 166         if resolve {
 167             self.infcx.resolve_vars_if_possible(self.state.cur_ty)
 168         } else {
 169             self.state.cur_ty
 170         }
 171     }
 172
 173     pub fn step_count(&self) -> usize {
 174         self.state.steps.len()
 175     }
 176
 177     pub fn into_obligations(self) -> Vec<traits::PredicateObligation<'tcx>> {
 178         self.state.obligations
 179     }
 180
 181     pub fn current_obligations(&self) -> Vec<traits::PredicateObligation<'tcx>> {
 182         self.state.obligations.clone()
 183     }
 184
 185     pub fn steps(&self) -> &[(Ty<'tcx>, AutoderefKind)] {
 186         &self.state.steps
 187     }
 188
 189     pub fn span(&self) -> Span {
 190         self.span
 191     }
 192
 193     pub fn reached_recursion_limit(&self) -> bool {
 194         self.state.reached_recursion_limit
 195     }
 196
 197     /// also dereference through raw pointer types
 198     /// e.g., assuming ptr_to_Foo is the type `*const Foo`
 199     /// fcx.autoderef(span, ptr_to_Foo)  => [*const Foo]
 200     /// fcx.autoderef(span, ptr_to_Foo).include_raw_ptrs() => [*const Foo, Foo]
 201     pub fn include_raw_pointers(mut self) -> Self {
 202         self.include_raw_pointers = true;
 203         self
 204     }
 205
 206     pub fn silence_errors(mut self) -> Self {
 207         self.silence_errors = true;
 208         self
 209     }
 210 }
 211
 212 pub fn report_autoderef_recursion_limit_error<'tcx>(tcx: TyCtxt<'tcx>, span: Span, ty: Ty<'tcx>) {
 213     // We've reached the recursion limit, error gracefully.
 214     let suggested_limit = match tcx.recursion_limit() {
 215         Limit(0) => Limit(2),
 216         limit => limit * 2,
 217     };
 218     tcx.sess.emit_err(AutoDerefReachedRecursionLimit {
 219         span,
 220         ty,
 221         suggested_limit,
 222         crate_name: tcx.crate_name(LOCAL_CRATE),
 223     });
 224 }