compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs

   1 use super::{
   2     ObligationCauseCode, OnUnimplementedDirective, OnUnimplementedNote, PredicateObligation,
   3 };
   4 use crate::infer::InferCtxt;
   5 use rustc_hir as hir;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_middle::ty::subst::Subst;
   8 use rustc_middle::ty::{self, GenericParamDefKind};
   9 use rustc_span::symbol::sym;
  10
  11 use super::InferCtxtPrivExt;
  12
  13 crate trait InferCtxtExt<'tcx> {
  14     /*private*/
  15     fn impl_similar_to(
  16         &self,
  17         trait_ref: ty::PolyTraitRef<'tcx>,
  18         obligation: &PredicateObligation<'tcx>,
  19     ) -> Option<DefId>;
  20
  21     /*private*/
  22     fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str>;
  23
  24     fn on_unimplemented_note(
  25         &self,
  26         trait_ref: ty::PolyTraitRef<'tcx>,
  27         obligation: &PredicateObligation<'tcx>,
  28     ) -> OnUnimplementedNote;
  29 }
  30
  31 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
  32     fn impl_similar_to(
  33         &self,
  34         trait_ref: ty::PolyTraitRef<'tcx>,
  35         obligation: &PredicateObligation<'tcx>,
  36     ) -> Option<DefId> {
  37         let tcx = self.tcx;
  38         let param_env = obligation.param_env;
  39         let trait_ref = tcx.erase_late_bound_regions(&trait_ref);
  40         let trait_self_ty = trait_ref.self_ty();
  41
  42         let mut self_match_impls = vec![];
  43         let mut fuzzy_match_impls = vec![];
  44
  45         self.tcx.for_each_relevant_impl(trait_ref.def_id, trait_self_ty, |def_id| {
  46             let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
  47             let impl_trait_ref = tcx.impl_trait_ref(def_id).unwrap().subst(tcx, impl_substs);
  48
  49             let impl_self_ty = impl_trait_ref.self_ty();
  50
  51             if let Ok(..) = self.can_eq(param_env, trait_self_ty, impl_self_ty) {
  52                 self_match_impls.push(def_id);
  53
  54                 if trait_ref
  55                     .substs
  56                     .types()
  57                     .skip(1)
  58                     .zip(impl_trait_ref.substs.types().skip(1))
  59                     .all(|(u, v)| self.fuzzy_match_tys(u, v))
  60                 {
  61                     fuzzy_match_impls.push(def_id);
  62                 }
  63             }
  64         });
  65
  66         let impl_def_id = if self_match_impls.len() == 1 {
  67             self_match_impls[0]
  68         } else if fuzzy_match_impls.len() == 1 {
  69             fuzzy_match_impls[0]
  70         } else {
  71             return None;
  72         };
  73
  74         tcx.has_attr(impl_def_id, sym::rustc_on_unimplemented).then_some(impl_def_id)
  75     }
  76
  77     /// Used to set on_unimplemented's `ItemContext`
  78     /// to be the enclosing (async) block/function/closure
  79     fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str> {
  80         let hir = &self.tcx.hir();
  81         let node = hir.find(hir_id)?;
  82         match &node {
  83             hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) => {
  84                 self.describe_generator(*body_id).or_else(|| {
  85                     Some(match sig.header {
  86                         hir::FnHeader { asyncness: hir::IsAsync::Async, .. } => "an async function",
  87                         _ => "a function",
  88                     })
  89                 })
  90             }
  91             hir::Node::TraitItem(hir::TraitItem {
  92                 kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(body_id)),
  93                 ..
  94             }) => self.describe_generator(*body_id).or_else(|| Some("a trait method")),
  95             hir::Node::ImplItem(hir::ImplItem {
  96                 kind: hir::ImplItemKind::Fn(sig, body_id),
  97                 ..
  98             }) => self.describe_generator(*body_id).or_else(|| {
  99                 Some(match sig.header {
 100                     hir::FnHeader { asyncness: hir::IsAsync::Async, .. } => "an async method",
 101                     _ => "a method",
 102                 })
 103             }),
 104             hir::Node::Expr(hir::Expr {
 105                 kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability),
 106                 ..
 107             }) => self.describe_generator(*body_id).or_else(|| {
 108                 Some(if gen_movability.is_some() { "an async closure" } else { "a closure" })
 109             }),
 110             hir::Node::Expr(hir::Expr { .. }) => {
 111                 let parent_hid = hir.get_parent_node(hir_id);
 112                 if parent_hid != hir_id { self.describe_enclosure(parent_hid) } else { None }
 113             }
 114             _ => None,
 115         }
 116     }
 117
 118     fn on_unimplemented_note(
 119         &self,
 120         trait_ref: ty::PolyTraitRef<'tcx>,
 121         obligation: &PredicateObligation<'tcx>,
 122     ) -> OnUnimplementedNote {
 123         let def_id =
 124             self.impl_similar_to(trait_ref, obligation).unwrap_or_else(|| trait_ref.def_id());
 125         let trait_ref = trait_ref.skip_binder();
 126
 127         let mut flags = vec![];
 128         flags.push((
 129             sym::ItemContext,
 130             self.describe_enclosure(obligation.cause.body_id).map(|s| s.to_owned()),
 131         ));
 132
 133         match obligation.cause.code {
 134             ObligationCauseCode::BuiltinDerivedObligation(..)
 135             | ObligationCauseCode::ImplDerivedObligation(..)
 136             | ObligationCauseCode::DerivedObligation(..) => {}
 137             _ => {
 138                 // this is a "direct", user-specified, rather than derived,
 139                 // obligation.
 140                 flags.push((sym::direct, None));
 141             }
 142         }
 143
 144         if let ObligationCauseCode::ItemObligation(item)
 145         | ObligationCauseCode::BindingObligation(item, _) = obligation.cause.code
 146         {
 147             // FIXME: maybe also have some way of handling methods
 148             // from other traits? That would require name resolution,
 149             // which we might want to be some sort of hygienic.
 150             //
 151             // Currently I'm leaving it for what I need for `try`.
 152             if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
 153                 let method = self.tcx.item_name(item);
 154                 flags.push((sym::from_method, None));
 155                 flags.push((sym::from_method, Some(method.to_string())));
 156             }
 157         }
 158         if let Some((t, _)) = self.get_parent_trait_ref(&obligation.cause.code) {
 159             flags.push((sym::parent_trait, Some(t)));
 160         }
 161
 162         if let Some(k) = obligation.cause.span.desugaring_kind() {
 163             flags.push((sym::from_desugaring, None));
 164             flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
 165         }
 166         let generics = self.tcx.generics_of(def_id);
 167         let self_ty = trait_ref.self_ty();
 168         // This is also included through the generics list as `Self`,
 169         // but the parser won't allow you to use it
 170         flags.push((sym::_Self, Some(self_ty.to_string())));
 171         if let Some(def) = self_ty.ty_adt_def() {
 172             // We also want to be able to select self's original
 173             // signature with no type arguments resolved
 174             flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
 175         }
 176
 177         for param in generics.params.iter() {
 178             let value = match param.kind {
 179                 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
 180                     trait_ref.substs[param.index as usize].to_string()
 181                 }
 182                 GenericParamDefKind::Lifetime => continue,
 183             };
 184             let name = param.name;
 185             flags.push((name, Some(value)));
 186         }
 187
 188         if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
 189             flags.push((sym::crate_local, None));
 190         }
 191
 192         // Allow targeting all integers using `{integral}`, even if the exact type was resolved
 193         if self_ty.is_integral() {
 194             flags.push((sym::_Self, Some("{integral}".to_owned())));
 195         }
 196
 197         if let ty::Array(aty, len) = self_ty.kind() {
 198             flags.push((sym::_Self, Some("[]".to_owned())));
 199             flags.push((sym::_Self, Some(format!("[{}]", aty))));
 200             if let Some(def) = aty.ty_adt_def() {
 201                 // We also want to be able to select the array's type's original
 202                 // signature with no type arguments resolved
 203                 flags.push((
 204                     sym::_Self,
 205                     Some(format!("[{}]", self.tcx.type_of(def.did).to_string())),
 206                 ));
 207                 let tcx = self.tcx;
 208                 if let Some(len) = len.try_eval_usize(tcx, ty::ParamEnv::empty()) {
 209                     flags.push((
 210                         sym::_Self,
 211                         Some(format!("[{}; {}]", self.tcx.type_of(def.did).to_string(), len)),
 212                     ));
 213                 } else {
 214                     flags.push((
 215                         sym::_Self,
 216                         Some(format!("[{}; _]", self.tcx.type_of(def.did).to_string())),
 217                     ));
 218                 }
 219             }
 220         }
 221         if let ty::Dynamic(traits, _) = self_ty.kind() {
 222             for t in traits.skip_binder() {
 223                 if let ty::ExistentialPredicate::Trait(trait_ref) = t {
 224                     flags.push((sym::_Self, Some(self.tcx.def_path_str(trait_ref.def_id))))
 225                 }
 226             }
 227         }
 228
 229         if let Ok(Some(command)) =
 230             OnUnimplementedDirective::of_item(self.tcx, trait_ref.def_id, def_id)
 231         {
 232             command.evaluate(self.tcx, trait_ref, &flags[..])
 233         } else {
 234             OnUnimplementedNote::default()
 235         }
 236     }
 237 }