compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

   1 mod _impl;
   2 mod adjust_fulfillment_errors;
   3 mod arg_matrix;
   4 mod checks;
   5 mod suggestions;
   6
   7 pub use _impl::*;
   8 use rustc_errors::ErrorGuaranteed;
   9 pub use suggestions::*;
  10
  11 use crate::coercion::DynamicCoerceMany;
  12 use crate::{Diverges, EnclosingBreakables, Inherited};
  13 use rustc_hir as hir;
  14 use rustc_hir::def_id::{DefId, LocalDefId};
  15 use rustc_hir_analysis::astconv::AstConv;
  16 use rustc_infer::infer;
  17 use rustc_infer::infer::error_reporting::TypeErrCtxt;
  18 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
  19 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
  20 use rustc_middle::ty::subst::GenericArgKind;
  21 use rustc_middle::ty::{self, Const, Ty, TyCtxt, TypeVisitableExt};
  22 use rustc_session::Session;
  23 use rustc_span::symbol::Ident;
  24 use rustc_span::{self, Span, DUMMY_SP};
  25 use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode, ObligationCtxt};
  26
  27 use std::cell::{Cell, RefCell};
  28 use std::ops::Deref;
  29
  30 /// The `FnCtxt` stores type-checking context needed to type-check bodies of
  31 /// functions, closures, and `const`s, including performing type inference
  32 /// with [`InferCtxt`].
  33 ///
  34 /// This is in contrast to [`ItemCtxt`], which is used to type-check item *signatures*
  35 /// and thus does not perform type inference.
  36 ///
  37 /// See [`ItemCtxt`]'s docs for more.
  38 ///
  39 /// [`ItemCtxt`]: rustc_hir_analysis::collect::ItemCtxt
  40 /// [`InferCtxt`]: infer::InferCtxt
  41 pub struct FnCtxt<'a, 'tcx> {
  42     pub(super) body_id: LocalDefId,
  43
  44     /// The parameter environment used for proving trait obligations
  45     /// in this function. This can change when we descend into
  46     /// closures (as they bring new things into scope), hence it is
  47     /// not part of `Inherited` (as of the time of this writing,
  48     /// closures do not yet change the environment, but they will
  49     /// eventually).
  50     pub(super) param_env: ty::ParamEnv<'tcx>,
  51
  52     /// Number of errors that had been reported when we started
  53     /// checking this function. On exit, if we find that *more* errors
  54     /// have been reported, we will skip regionck and other work that
  55     /// expects the types within the function to be consistent.
  56     // FIXME(matthewjasper) This should not exist, and it's not correct
  57     // if type checking is run in parallel.
  58     err_count_on_creation: usize,
  59
  60     /// If `Some`, this stores coercion information for returned
  61     /// expressions. If `None`, this is in a context where return is
  62     /// inappropriate, such as a const expression.
  63     ///
  64     /// This is a `RefCell<DynamicCoerceMany>`, which means that we
  65     /// can track all the return expressions and then use them to
  66     /// compute a useful coercion from the set, similar to a match
  67     /// expression or other branching context. You can use methods
  68     /// like `expected_ty` to access the declared return type (if
  69     /// any).
  70     pub(super) ret_coercion: Option<RefCell<DynamicCoerceMany<'tcx>>>,
  71
  72     /// First span of a return site that we find. Used in error messages.
  73     pub(super) ret_coercion_span: Cell<Option<Span>>,
  74
  75     pub(super) resume_yield_tys: Option<(Ty<'tcx>, Ty<'tcx>)>,
  76
  77     /// Whether the last checked node generates a divergence (e.g.,
  78     /// `return` will set this to `Always`). In general, when entering
  79     /// an expression or other node in the tree, the initial value
  80     /// indicates whether prior parts of the containing expression may
  81     /// have diverged. It is then typically set to `Maybe` (and the
  82     /// old value remembered) for processing the subparts of the
  83     /// current expression. As each subpart is processed, they may set
  84     /// the flag to `Always`, etc. Finally, at the end, we take the
  85     /// result and "union" it with the original value, so that when we
  86     /// return the flag indicates if any subpart of the parent
  87     /// expression (up to and including this part) has diverged. So,
  88     /// if you read it after evaluating a subexpression `X`, the value
  89     /// you get indicates whether any subexpression that was
  90     /// evaluating up to and including `X` diverged.
  91     ///
  92     /// We currently use this flag only for diagnostic purposes:
  93     ///
  94     /// - To warn about unreachable code: if, after processing a
  95     ///   sub-expression but before we have applied the effects of the
  96     ///   current node, we see that the flag is set to `Always`, we
  97     ///   can issue a warning. This corresponds to something like
  98     ///   `foo(return)`; we warn on the `foo()` expression. (We then
  99     ///   update the flag to `WarnedAlways` to suppress duplicate
 100     ///   reports.) Similarly, if we traverse to a fresh statement (or
 101     ///   tail expression) from an `Always` setting, we will issue a
 102     ///   warning. This corresponds to something like `{return;
 103     ///   foo();}` or `{return; 22}`, where we would warn on the
 104     ///   `foo()` or `22`.
 105     ///
 106     /// An expression represents dead code if, after checking it,
 107     /// the diverges flag is set to something other than `Maybe`.
 108     pub(super) diverges: Cell<Diverges>,
 109
 110     pub(super) enclosing_breakables: RefCell<EnclosingBreakables<'tcx>>,
 111
 112     pub(super) inh: &'a Inherited<'tcx>,
 113
 114     pub(super) fallback_has_occurred: Cell<bool>,
 115 }
 116
 117 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 118     pub fn new(
 119         inh: &'a Inherited<'tcx>,
 120         param_env: ty::ParamEnv<'tcx>,
 121         body_id: LocalDefId,
 122     ) -> FnCtxt<'a, 'tcx> {
 123         FnCtxt {
 124             body_id,
 125             param_env,
 126             err_count_on_creation: inh.tcx.sess.err_count(),
 127             ret_coercion: None,
 128             ret_coercion_span: Cell::new(None),
 129             resume_yield_tys: None,
 130             diverges: Cell::new(Diverges::Maybe),
 131             enclosing_breakables: RefCell::new(EnclosingBreakables {
 132                 stack: Vec::new(),
 133                 by_id: Default::default(),
 134             }),
 135             inh,
 136             fallback_has_occurred: Cell::new(false),
 137         }
 138     }
 139
 140     pub fn cause(&self, span: Span, code: ObligationCauseCode<'tcx>) -> ObligationCause<'tcx> {
 141         ObligationCause::new(span, self.body_id, code)
 142     }
 143
 144     pub fn misc(&self, span: Span) -> ObligationCause<'tcx> {
 145         self.cause(span, ObligationCauseCode::MiscObligation)
 146     }
 147
 148     pub fn sess(&self) -> &Session {
 149         &self.tcx.sess
 150     }
 151
 152     /// Creates an `TypeErrCtxt` with a reference to the in-progress
 153     /// `TypeckResults` which is used for diagnostics.
 154     /// Use [`InferCtxt::err_ctxt`] to start one without a `TypeckResults`.
 155     ///
 156     /// [`InferCtxt::err_ctxt`]: infer::InferCtxt::err_ctxt
 157     pub fn err_ctxt(&'a self) -> TypeErrCtxt<'a, 'tcx> {
 158         TypeErrCtxt {
 159             infcx: &self.infcx,
 160             typeck_results: Some(self.typeck_results.borrow()),
 161             fallback_has_occurred: self.fallback_has_occurred.get(),
 162             normalize_fn_sig: Box::new(|fn_sig| {
 163                 if fn_sig.has_escaping_bound_vars() {
 164                     return fn_sig;
 165                 }
 166                 self.probe(|_| {
 167                     let ocx = ObligationCtxt::new_in_snapshot(self);
 168                     let normalized_fn_sig =
 169                         ocx.normalize(&ObligationCause::dummy(), self.param_env, fn_sig);
 170                     if ocx.select_all_or_error().is_empty() {
 171                         let normalized_fn_sig = self.resolve_vars_if_possible(normalized_fn_sig);
 172                         if !normalized_fn_sig.needs_infer() {
 173                             return normalized_fn_sig;
 174                         }
 175                     }
 176                     fn_sig
 177                 })
 178             }),
 179             autoderef_steps: Box::new(|ty| {
 180                 let mut autoderef = self.autoderef(DUMMY_SP, ty).silence_errors();
 181                 let mut steps = vec![];
 182                 while let Some((ty, _)) = autoderef.next() {
 183                     steps.push((ty, autoderef.current_obligations()));
 184                 }
 185                 steps
 186             }),
 187         }
 188     }
 189
 190     pub fn errors_reported_since_creation(&self) -> bool {
 191         self.tcx.sess.err_count() > self.err_count_on_creation
 192     }
 193 }
 194
 195 impl<'a, 'tcx> Deref for FnCtxt<'a, 'tcx> {
 196     type Target = Inherited<'tcx>;
 197     fn deref(&self) -> &Self::Target {
 198         &self.inh
 199     }
 200 }
 201
 202 impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
 203     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 204         self.tcx
 205     }
 206
 207     fn item_def_id(&self) -> DefId {
 208         self.body_id.to_def_id()
 209     }
 210
 211     fn get_type_parameter_bounds(
 212         &self,
 213         _: Span,
 214         def_id: LocalDefId,
 215         _: Ident,
 216     ) -> ty::GenericPredicates<'tcx> {
 217         let tcx = self.tcx;
 218         let item_def_id = tcx.hir().ty_param_owner(def_id);
 219         let generics = tcx.generics_of(item_def_id);
 220         let index = generics.param_def_id_to_index[&def_id.to_def_id()];
 221         ty::GenericPredicates {
 222             parent: None,
 223             predicates: tcx.arena.alloc_from_iter(
 224                 self.param_env.caller_bounds().iter().filter_map(|predicate| {
 225                     match predicate.kind().skip_binder() {
 226                         ty::PredicateKind::Clause(ty::Clause::Trait(data))
 227                             if data.self_ty().is_param(index) =>
 228                         {
 229                             // HACK(eddyb) should get the original `Span`.
 230                             let span = tcx.def_span(def_id);
 231                             Some((predicate, span))
 232                         }
 233                         _ => None,
 234                     }
 235                 }),
 236             ),
 237         }
 238     }
 239
 240     fn re_infer(&self, def: Option<&ty::GenericParamDef>, span: Span) -> Option<ty::Region<'tcx>> {
 241         let v = match def {
 242             Some(def) => infer::EarlyBoundRegion(span, def.name),
 243             None => infer::MiscVariable(span),
 244         };
 245         Some(self.next_region_var(v))
 246     }
 247
 248     fn allow_ty_infer(&self) -> bool {
 249         true
 250     }
 251
 252     fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
 253         if let Some(param) = param {
 254             if let GenericArgKind::Type(ty) = self.var_for_def(span, param).unpack() {
 255                 return ty;
 256             }
 257             unreachable!()
 258         } else {
 259             self.next_ty_var(TypeVariableOrigin {
 260                 kind: TypeVariableOriginKind::TypeInference,
 261                 span,
 262             })
 263         }
 264     }
 265
 266     fn ct_infer(
 267         &self,
 268         ty: Ty<'tcx>,
 269         param: Option<&ty::GenericParamDef>,
 270         span: Span,
 271     ) -> Const<'tcx> {
 272         if let Some(param) = param {
 273             if let GenericArgKind::Const(ct) = self.var_for_def(span, param).unpack() {
 274                 return ct;
 275             }
 276             unreachable!()
 277         } else {
 278             self.next_const_var(
 279                 ty,
 280                 ConstVariableOrigin { kind: ConstVariableOriginKind::ConstInference, span },
 281             )
 282         }
 283     }
 284
 285     fn projected_ty_from_poly_trait_ref(
 286         &self,
 287         span: Span,
 288         item_def_id: DefId,
 289         item_segment: &hir::PathSegment<'_>,
 290         poly_trait_ref: ty::PolyTraitRef<'tcx>,
 291     ) -> Ty<'tcx> {
 292         let trait_ref = self.instantiate_binder_with_fresh_vars(
 293             span,
 294             infer::LateBoundRegionConversionTime::AssocTypeProjection(item_def_id),
 295             poly_trait_ref,
 296         );
 297
 298         let item_substs = self.astconv().create_substs_for_associated_item(
 299             span,
 300             item_def_id,
 301             item_segment,
 302             trait_ref.substs,
 303         );
 304
 305         self.tcx().mk_projection(item_def_id, item_substs)
 306     }
 307
 308     fn probe_adt(&self, span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>> {
 309         match ty.kind() {
 310             ty::Adt(adt_def, _) => Some(*adt_def),
 311             // FIXME(#104767): Should we handle bound regions here?
 312             ty::Alias(ty::Projection, _) if !ty.has_escaping_bound_vars() => {
 313                 self.normalize(span, ty).ty_adt_def()
 314             }
 315             _ => None,
 316         }
 317     }
 318
 319     fn set_tainted_by_errors(&self, e: ErrorGuaranteed) {
 320         self.infcx.set_tainted_by_errors(e)
 321     }
 322
 323     fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span) {
 324         // FIXME: normalization and escaping regions
 325         let ty = if !ty.has_escaping_bound_vars() { self.normalize(span, ty) } else { ty };
 326         self.write_ty(hir_id, ty)
 327     }
 328
 329     fn infcx(&self) -> Option<&infer::InferCtxt<'tcx>> {
 330         Some(&self.infcx)
 331     }
 332 }
 333
 334 /// Represents a user-provided type in the raw form (never normalized).
 335 ///
 336 /// This is a bridge between the interface of `AstConv`, which outputs a raw `Ty`,
 337 /// and the API in this module, which expect `Ty` to be fully normalized.
 338 #[derive(Clone, Copy, Debug)]
 339 pub struct RawTy<'tcx> {
 340     pub raw: Ty<'tcx>,
 341
 342     /// The normalized form of `raw`, stored here for efficiency.
 343     pub normalized: Ty<'tcx>,
 344 }