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 use std::iter;
  11
  12 use super::InferCtxtPrivExt;
  13
  14 crate trait InferCtxtExt<'tcx> {
  15     /*private*/
  16     fn impl_similar_to(
  17         &self,
  18         trait_ref: ty::PolyTraitRef<'tcx>,
  19         obligation: &PredicateObligation<'tcx>,
  20     ) -> Option<DefId>;
  21
  22     /*private*/
  23     fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str>;
  24
  25     fn on_unimplemented_note(
  26         &self,
  27         trait_ref: ty::PolyTraitRef<'tcx>,
  28         obligation: &PredicateObligation<'tcx>,
  29     ) -> OnUnimplementedNote;
  30 }
  31
  32 impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
  33     fn impl_similar_to(
  34         &self,
  35         trait_ref: ty::PolyTraitRef<'tcx>,
  36         obligation: &PredicateObligation<'tcx>,
  37     ) -> Option<DefId> {
  38         let tcx = self.tcx;
  39         let param_env = obligation.param_env;
  40         let trait_ref = tcx.erase_late_bound_regions(trait_ref);
  41         let trait_self_ty = trait_ref.self_ty();
  42
  43         let mut self_match_impls = vec![];
  44         let mut fuzzy_match_impls = vec![];
  45
  46         self.tcx.for_each_relevant_impl(trait_ref.def_id, trait_self_ty, |def_id| {
  47             let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
  48             let impl_trait_ref = tcx.impl_trait_ref(def_id).unwrap().subst(tcx, impl_substs);
  49
  50             let impl_self_ty = impl_trait_ref.self_ty();
  51
  52             if let Ok(..) = self.can_eq(param_env, trait_self_ty, impl_self_ty) {
  53                 self_match_impls.push(def_id);
  54
  55                 if iter::zip(
  56                     trait_ref.substs.types().skip(1),
  57                     impl_trait_ref.substs.types().skip(1),
  58                 )
  59                 .all(|(u, v)| self.fuzzy_match_tys(u, v, false).is_some())
  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             sym::ItemContext,
 129             self.describe_enclosure(obligation.cause.body_id).map(|s| s.to_owned()),
 130         )];
 131
 132         match obligation.cause.code() {
 133             ObligationCauseCode::BuiltinDerivedObligation(..)
 134             | ObligationCauseCode::ImplDerivedObligation(..)
 135             | ObligationCauseCode::DerivedObligation(..) => {}
 136             _ => {
 137                 // this is a "direct", user-specified, rather than derived,
 138                 // obligation.
 139                 flags.push((sym::direct, None));
 140             }
 141         }
 142
 143         if let ObligationCauseCode::ItemObligation(item)
 144         | ObligationCauseCode::BindingObligation(item, _) = *obligation.cause.code()
 145         {
 146             // FIXME: maybe also have some way of handling methods
 147             // from other traits? That would require name resolution,
 148             // which we might want to be some sort of hygienic.
 149             //
 150             // Currently I'm leaving it for what I need for `try`.
 151             if self.tcx.trait_of_item(item) == Some(trait_ref.def_id) {
 152                 let method = self.tcx.item_name(item);
 153                 flags.push((sym::from_method, None));
 154                 flags.push((sym::from_method, Some(method.to_string())));
 155             }
 156         }
 157
 158         if let Some(k) = obligation.cause.span.desugaring_kind() {
 159             flags.push((sym::from_desugaring, None));
 160             flags.push((sym::from_desugaring, Some(format!("{:?}", k))));
 161         }
 162
 163         // Add all types without trimmed paths.
 164         ty::print::with_no_trimmed_paths(|| {
 165             let generics = self.tcx.generics_of(def_id);
 166             let self_ty = trait_ref.self_ty();
 167             // This is also included through the generics list as `Self`,
 168             // but the parser won't allow you to use it
 169             flags.push((sym::_Self, Some(self_ty.to_string())));
 170             if let Some(def) = self_ty.ty_adt_def() {
 171                 // We also want to be able to select self's original
 172                 // signature with no type arguments resolved
 173                 flags.push((sym::_Self, Some(self.tcx.type_of(def.did).to_string())));
 174             }
 175
 176             for param in generics.params.iter() {
 177                 let value = match param.kind {
 178                     GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
 179                         trait_ref.substs[param.index as usize].to_string()
 180                     }
 181                     GenericParamDefKind::Lifetime => continue,
 182                 };
 183                 let name = param.name;
 184                 flags.push((name, Some(value)));
 185
 186                 if let GenericParamDefKind::Type { .. } = param.kind {
 187                     let param_ty = trait_ref.substs[param.index as usize].expect_ty();
 188                     if let Some(def) = param_ty.ty_adt_def() {
 189                         // We also want to be able to select the parameter's
 190                         // original signature with no type arguments resolved
 191                         flags.push((name, Some(self.tcx.type_of(def.did).to_string())));
 192                     }
 193                 }
 194             }
 195
 196             if let Some(true) = self_ty.ty_adt_def().map(|def| def.did.is_local()) {
 197                 flags.push((sym::crate_local, None));
 198             }
 199
 200             // Allow targeting all integers using `{integral}`, even if the exact type was resolved
 201             if self_ty.is_integral() {
 202                 flags.push((sym::_Self, Some("{integral}".to_owned())));
 203             }
 204
 205             if let ty::Array(aty, len) = self_ty.kind() {
 206                 flags.push((sym::_Self, Some("[]".to_owned())));
 207                 flags.push((sym::_Self, Some(format!("[{}]", aty))));
 208                 if let Some(def) = aty.ty_adt_def() {
 209                     // We also want to be able to select the array's type's original
 210                     // signature with no type arguments resolved
 211                     let type_string = self.tcx.type_of(def.did).to_string();
 212                     flags.push((sym::_Self, Some(format!("[{}]", type_string))));
 213
 214                     let len =
 215                         len.val().try_to_value().and_then(|v| v.try_to_machine_usize(self.tcx));
 216                     let string = match len {
 217                         Some(n) => format!("[{}; {}]", type_string, n),
 218                         None => format!("[{}; _]", type_string),
 219                     };
 220                     flags.push((sym::_Self, Some(string)));
 221                 }
 222             }
 223             if let ty::Dynamic(traits, _) = self_ty.kind() {
 224                 for t in traits.iter() {
 225                     if let ty::ExistentialPredicate::Trait(trait_ref) = t.skip_binder() {
 226                         flags.push((sym::_Self, Some(self.tcx.def_path_str(trait_ref.def_id))))
 227                     }
 228                 }
 229             }
 230         });
 231
 232         if let Ok(Some(command)) =
 233             OnUnimplementedDirective::of_item(self.tcx, trait_ref.def_id, def_id)
 234         {
 235             command.evaluate(self.tcx, trait_ref, &flags)
 236         } else {
 237             OnUnimplementedNote::default()
 238         }
 239     }
 240 }