compiler/rustc_const_eval/src/util/call_kind.rs

   1 //! Common logic for borrowck use-after-move errors when moved into a `fn(self)`,
   2 //! as well as errors when attempting to call a non-const function in a const
   3 //! context.
   4
   5 use rustc_hir::def_id::DefId;
   6 use rustc_hir::lang_items::LangItemGroup;
   7 use rustc_middle::ty::subst::SubstsRef;
   8 use rustc_middle::ty::{self, AssocItemContainer, DefIdTree, Instance, ParamEnv, Ty, TyCtxt};
   9 use rustc_span::symbol::Ident;
  10 use rustc_span::{sym, DesugaringKind, Span};
  11
  12 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
  13 pub enum CallDesugaringKind {
  14     /// for _ in x {} calls x.into_iter()
  15     ForLoopIntoIter,
  16     /// x? calls x.branch()
  17     QuestionBranch,
  18     /// x? calls type_of(x)::from_residual()
  19     QuestionFromResidual,
  20     /// try { ..; x } calls type_of(x)::from_output(x)
  21     TryBlockFromOutput,
  22 }
  23
  24 impl CallDesugaringKind {
  25     pub fn trait_def_id(self, tcx: TyCtxt<'_>) -> DefId {
  26         match self {
  27             Self::ForLoopIntoIter => tcx.get_diagnostic_item(sym::IntoIterator).unwrap(),
  28             Self::QuestionBranch | Self::TryBlockFromOutput => {
  29                 tcx.lang_items().try_trait().unwrap()
  30             }
  31             Self::QuestionFromResidual => tcx.get_diagnostic_item(sym::FromResidual).unwrap(),
  32         }
  33     }
  34 }
  35
  36 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
  37 pub enum CallKind<'tcx> {
  38     /// A normal method call of the form `receiver.foo(a, b, c)`
  39     Normal {
  40         self_arg: Option<Ident>,
  41         desugaring: Option<(CallDesugaringKind, Ty<'tcx>)>,
  42         /// Whether the self type of the method call has an `.as_ref()` method.
  43         /// Used for better diagnostics.
  44         is_option_or_result: bool,
  45     },
  46     /// A call to `Fn(..)::call(..)`, desugared from `my_closure(a, b, c)`
  47     FnCall { fn_trait_id: DefId, self_ty: Ty<'tcx> },
  48     /// A call to an operator trait, desugared from operator syntax (e.g. `a << b`)
  49     Operator { self_arg: Option<Ident>, trait_id: DefId, self_ty: Ty<'tcx> },
  50     DerefCoercion {
  51         /// The `Span` of the `Target` associated type
  52         /// in the `Deref` impl we are using.
  53         deref_target: Span,
  54         /// The type `T::Deref` we are dereferencing to
  55         deref_target_ty: Ty<'tcx>,
  56         self_ty: Ty<'tcx>,
  57     },
  58 }
  59
  60 pub fn call_kind<'tcx>(
  61     tcx: TyCtxt<'tcx>,
  62     param_env: ParamEnv<'tcx>,
  63     method_did: DefId,
  64     method_substs: SubstsRef<'tcx>,
  65     fn_call_span: Span,
  66     from_hir_call: bool,
  67     self_arg: Option<Ident>,
  68 ) -> CallKind<'tcx> {
  69     let parent = tcx.opt_associated_item(method_did).and_then(|assoc| match assoc.container {
  70         AssocItemContainer::ImplContainer(impl_did) => tcx.trait_id_of_impl(impl_did),
  71         AssocItemContainer::TraitContainer(trait_did) => Some(trait_did),
  72     });
  73
  74     let fn_call = parent
  75         .and_then(|p| tcx.lang_items().group(LangItemGroup::Fn).iter().find(|did| **did == p));
  76
  77     let operator = (!from_hir_call)
  78         .then(|| parent)
  79         .flatten()
  80         .and_then(|p| tcx.lang_items().group(LangItemGroup::Op).iter().find(|did| **did == p));
  81
  82     let is_deref = !from_hir_call && tcx.is_diagnostic_item(sym::deref_method, method_did);
  83
  84     // Check for a 'special' use of 'self' -
  85     // an FnOnce call, an operator (e.g. `<<`), or a
  86     // deref coercion.
  87     let kind = if let Some(&trait_id) = fn_call {
  88         Some(CallKind::FnCall { fn_trait_id: trait_id, self_ty: method_substs.type_at(0) })
  89     } else if let Some(&trait_id) = operator {
  90         Some(CallKind::Operator { self_arg, trait_id, self_ty: method_substs.type_at(0) })
  91     } else if is_deref {
  92         let deref_target = tcx.get_diagnostic_item(sym::deref_target).and_then(|deref_target| {
  93             Instance::resolve(tcx, param_env, deref_target, method_substs).transpose()
  94         });
  95         if let Some(Ok(instance)) = deref_target {
  96             let deref_target_ty = instance.ty(tcx, param_env);
  97             Some(CallKind::DerefCoercion {
  98                 deref_target: tcx.def_span(instance.def_id()),
  99                 deref_target_ty,
 100                 self_ty: method_substs.type_at(0),
 101             })
 102         } else {
 103             None
 104         }
 105     } else {
 106         None
 107     };
 108
 109     kind.unwrap_or_else(|| {
 110         // This isn't a 'special' use of `self`
 111         debug!(?method_did, ?fn_call_span);
 112         let desugaring = if Some(method_did) == tcx.lang_items().into_iter_fn()
 113             && fn_call_span.desugaring_kind() == Some(DesugaringKind::ForLoop)
 114         {
 115             Some((CallDesugaringKind::ForLoopIntoIter, method_substs.type_at(0)))
 116         } else if fn_call_span.desugaring_kind() == Some(DesugaringKind::QuestionMark) {
 117             if Some(method_did) == tcx.lang_items().branch_fn() {
 118                 Some((CallDesugaringKind::QuestionBranch, method_substs.type_at(0)))
 119             } else if Some(method_did) == tcx.lang_items().from_residual_fn() {
 120                 Some((CallDesugaringKind::QuestionFromResidual, method_substs.type_at(0)))
 121             } else {
 122                 None
 123             }
 124         } else if Some(method_did) == tcx.lang_items().from_output_fn()
 125             && fn_call_span.desugaring_kind() == Some(DesugaringKind::TryBlock)
 126         {
 127             Some((CallDesugaringKind::TryBlockFromOutput, method_substs.type_at(0)))
 128         } else {
 129             None
 130         };
 131         let parent_did = tcx.parent(method_did);
 132         let parent_self_ty = (tcx.def_kind(parent_did) == rustc_hir::def::DefKind::Impl)
 133             .then_some(parent_did)
 134             .and_then(|did| match tcx.type_of(did).kind() {
 135                 ty::Adt(def, ..) => Some(def.did()),
 136                 _ => None,
 137             });
 138         let is_option_or_result = parent_self_ty.map_or(false, |def_id| {
 139             matches!(tcx.get_diagnostic_name(def_id), Some(sym::Option | sym::Result))
 140         });
 141         CallKind::Normal { self_arg, desugaring, is_option_or_result }
 142     })
 143 }