compiler/rustc_middle/src/ty/print/mod.rs

   1 use crate::ty::subst::{GenericArg, Subst};
   2 use crate::ty::{self, DefIdTree, Ty, TyCtxt};
   3
   4 use rustc_data_structures::fx::FxHashSet;
   5 use rustc_data_structures::sso::SsoHashSet;
   6 use rustc_hir::def_id::{CrateNum, DefId};
   7 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
   8
   9 // `pretty` is a separate module only for organization.
  10 mod pretty;
  11 pub use self::pretty::*;
  12
  13 // FIXME(eddyb) false positive, the lifetime parameters are used with `P:  Printer<...>`.
  14 #[allow(unused_lifetimes)]
  15 pub trait Print<'tcx, P> {
  16     type Output;
  17     type Error;
  18
  19     fn print(&self, cx: P) -> Result<Self::Output, Self::Error>;
  20 }
  21
  22 /// Interface for outputting user-facing "type-system entities"
  23 /// (paths, types, lifetimes, constants, etc.) as a side-effect
  24 /// (e.g. formatting, like `PrettyPrinter` implementors do) or by
  25 /// constructing some alternative representation (e.g. an AST),
  26 /// which the associated types allow passing through the methods.
  27 ///
  28 /// For pretty-printing/formatting in particular, see `PrettyPrinter`.
  29 //
  30 // FIXME(eddyb) find a better name; this is more general than "printing".
  31 pub trait Printer<'tcx>: Sized {
  32     type Error;
  33
  34     type Path;
  35     type Region;
  36     type Type;
  37     type DynExistential;
  38     type Const;
  39
  40     fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
  41
  42     fn print_def_path(
  43         self,
  44         def_id: DefId,
  45         substs: &'tcx [GenericArg<'tcx>],
  46     ) -> Result<Self::Path, Self::Error> {
  47         self.default_print_def_path(def_id, substs)
  48     }
  49
  50     fn print_impl_path(
  51         self,
  52         impl_def_id: DefId,
  53         substs: &'tcx [GenericArg<'tcx>],
  54         self_ty: Ty<'tcx>,
  55         trait_ref: Option<ty::TraitRef<'tcx>>,
  56     ) -> Result<Self::Path, Self::Error> {
  57         self.default_print_impl_path(impl_def_id, substs, self_ty, trait_ref)
  58     }
  59
  60     fn print_region(self, region: ty::Region<'tcx>) -> Result<Self::Region, Self::Error>;
  61
  62     fn print_type(self, ty: Ty<'tcx>) -> Result<Self::Type, Self::Error>;
  63
  64     fn print_dyn_existential(
  65         self,
  66         predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
  67     ) -> Result<Self::DynExistential, Self::Error>;
  68
  69     fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self::Const, Self::Error>;
  70
  71     fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error>;
  72
  73     fn path_qualified(
  74         self,
  75         self_ty: Ty<'tcx>,
  76         trait_ref: Option<ty::TraitRef<'tcx>>,
  77     ) -> Result<Self::Path, Self::Error>;
  78
  79     fn path_append_impl(
  80         self,
  81         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
  82         disambiguated_data: &DisambiguatedDefPathData,
  83         self_ty: Ty<'tcx>,
  84         trait_ref: Option<ty::TraitRef<'tcx>>,
  85     ) -> Result<Self::Path, Self::Error>;
  86
  87     fn path_append(
  88         self,
  89         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
  90         disambiguated_data: &DisambiguatedDefPathData,
  91     ) -> Result<Self::Path, Self::Error>;
  92
  93     fn path_generic_args(
  94         self,
  95         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
  96         args: &[GenericArg<'tcx>],
  97     ) -> Result<Self::Path, Self::Error>;
  98
  99     // Defaults (should not be overridden):
 100
 101     #[instrument(skip(self), level = "debug")]
 102     fn default_print_def_path(
 103         self,
 104         def_id: DefId,
 105         substs: &'tcx [GenericArg<'tcx>],
 106     ) -> Result<Self::Path, Self::Error> {
 107         let key = self.tcx().def_key(def_id);
 108         debug!(?key);
 109
 110         match key.disambiguated_data.data {
 111             DefPathData::CrateRoot => {
 112                 assert!(key.parent.is_none());
 113                 self.path_crate(def_id.krate)
 114             }
 115
 116             DefPathData::Impl => {
 117                 let generics = self.tcx().generics_of(def_id);
 118                 let self_ty = self.tcx().bound_type_of(def_id);
 119                 let impl_trait_ref = self.tcx().bound_impl_trait_ref(def_id);
 120                 let (self_ty, impl_trait_ref) = if substs.len() >= generics.count() {
 121                     (
 122                         self_ty.subst(self.tcx(), substs),
 123                         impl_trait_ref.map(|i| i.subst(self.tcx(), substs)),
 124                     )
 125                 } else {
 126                     (self_ty.0, impl_trait_ref.map(|i| i.0))
 127                 };
 128                 self.print_impl_path(def_id, substs, self_ty, impl_trait_ref)
 129             }
 130
 131             _ => {
 132                 let parent_def_id = DefId { index: key.parent.unwrap(), ..def_id };
 133
 134                 let mut parent_substs = substs;
 135                 let mut trait_qualify_parent = false;
 136                 if !substs.is_empty() {
 137                     let generics = self.tcx().generics_of(def_id);
 138                     parent_substs = &substs[..generics.parent_count.min(substs.len())];
 139
 140                     match key.disambiguated_data.data {
 141                         // Closures' own generics are only captures, don't print them.
 142                         DefPathData::ClosureExpr => {}
 143                         // This covers both `DefKind::AnonConst` and `DefKind::InlineConst`.
 144                         // Anon consts doesn't have their own generics, and inline consts' own
 145                         // generics are their inferred types, so don't print them.
 146                         DefPathData::AnonConst => {}
 147
 148                         // If we have any generic arguments to print, we do that
 149                         // on top of the same path, but without its own generics.
 150                         _ => {
 151                             if !generics.params.is_empty() && substs.len() >= generics.count() {
 152                                 let args = generics.own_substs_no_defaults(self.tcx(), substs);
 153                                 return self.path_generic_args(
 154                                     |cx| cx.print_def_path(def_id, parent_substs),
 155                                     args,
 156                                 );
 157                             }
 158                         }
 159                     }
 160
 161                     // FIXME(eddyb) try to move this into the parent's printing
 162                     // logic, instead of doing it when printing the child.
 163                     trait_qualify_parent = generics.has_self
 164                         && generics.parent == Some(parent_def_id)
 165                         && parent_substs.len() == generics.parent_count
 166                         && self.tcx().generics_of(parent_def_id).parent_count == 0;
 167                 }
 168
 169                 self.path_append(
 170                     |cx: Self| {
 171                         if trait_qualify_parent {
 172                             let trait_ref = ty::TraitRef::new(
 173                                 parent_def_id,
 174                                 cx.tcx().intern_substs(parent_substs),
 175                             );
 176                             cx.path_qualified(trait_ref.self_ty(), Some(trait_ref))
 177                         } else {
 178                             cx.print_def_path(parent_def_id, parent_substs)
 179                         }
 180                     },
 181                     &key.disambiguated_data,
 182                 )
 183             }
 184         }
 185     }
 186
 187     fn default_print_impl_path(
 188         self,
 189         impl_def_id: DefId,
 190         _substs: &'tcx [GenericArg<'tcx>],
 191         self_ty: Ty<'tcx>,
 192         impl_trait_ref: Option<ty::TraitRef<'tcx>>,
 193     ) -> Result<Self::Path, Self::Error> {
 194         debug!(
 195             "default_print_impl_path: impl_def_id={:?}, self_ty={}, impl_trait_ref={:?}",
 196             impl_def_id, self_ty, impl_trait_ref
 197         );
 198
 199         let key = self.tcx().def_key(impl_def_id);
 200         let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };
 201
 202         // Decide whether to print the parent path for the impl.
 203         // Logically, since impls are global, it's never needed, but
 204         // users may find it useful. Currently, we omit the parent if
 205         // the impl is either in the same module as the self-type or
 206         // as the trait.
 207         let in_self_mod = match characteristic_def_id_of_type(self_ty) {
 208             None => false,
 209             Some(ty_def_id) => self.tcx().parent(ty_def_id) == parent_def_id,
 210         };
 211         let in_trait_mod = match impl_trait_ref {
 212             None => false,
 213             Some(trait_ref) => self.tcx().parent(trait_ref.def_id) == parent_def_id,
 214         };
 215
 216         if !in_self_mod && !in_trait_mod {
 217             // If the impl is not co-located with either self-type or
 218             // trait-type, then fallback to a format that identifies
 219             // the module more clearly.
 220             self.path_append_impl(
 221                 |cx| cx.print_def_path(parent_def_id, &[]),
 222                 &key.disambiguated_data,
 223                 self_ty,
 224                 impl_trait_ref,
 225             )
 226         } else {
 227             // Otherwise, try to give a good form that would be valid language
 228             // syntax. Preferably using associated item notation.
 229             self.path_qualified(self_ty, impl_trait_ref)
 230         }
 231     }
 232 }
 233
 234 /// As a heuristic, when we see an impl, if we see that the
 235 /// 'self type' is a type defined in the same module as the impl,
 236 /// we can omit including the path to the impl itself. This
 237 /// function tries to find a "characteristic `DefId`" for a
 238 /// type. It's just a heuristic so it makes some questionable
 239 /// decisions and we may want to adjust it later.
 240 ///
 241 /// Visited set is needed to avoid full iteration over
 242 /// deeply nested tuples that have no DefId.
 243 fn characteristic_def_id_of_type_cached<'a>(
 244     ty: Ty<'a>,
 245     visited: &mut SsoHashSet<Ty<'a>>,
 246 ) -> Option<DefId> {
 247     match *ty.kind() {
 248         ty::Adt(adt_def, _) => Some(adt_def.did()),
 249
 250         ty::Dynamic(data, ..) => data.principal_def_id(),
 251
 252         ty::Array(subty, _) | ty::Slice(subty) => {
 253             characteristic_def_id_of_type_cached(subty, visited)
 254         }
 255
 256         ty::RawPtr(mt) => characteristic_def_id_of_type_cached(mt.ty, visited),
 257
 258         ty::Ref(_, ty, _) => characteristic_def_id_of_type_cached(ty, visited),
 259
 260         ty::Tuple(ref tys) => tys.iter().find_map(|ty| {
 261             if visited.insert(ty) {
 262                 return characteristic_def_id_of_type_cached(ty, visited);
 263             }
 264             return None;
 265         }),
 266
 267         ty::FnDef(def_id, _)
 268         | ty::Closure(def_id, _)
 269         | ty::Generator(def_id, _, _)
 270         | ty::Foreign(def_id) => Some(def_id),
 271
 272         ty::Bool
 273         | ty::Char
 274         | ty::Int(_)
 275         | ty::Uint(_)
 276         | ty::Str
 277         | ty::FnPtr(_)
 278         | ty::Projection(_)
 279         | ty::Placeholder(..)
 280         | ty::Param(_)
 281         | ty::Opaque(..)
 282         | ty::Infer(_)
 283         | ty::Bound(..)
 284         | ty::Error(_)
 285         | ty::GeneratorWitness(..)
 286         | ty::Never
 287         | ty::Float(_) => None,
 288     }
 289 }
 290 pub fn characteristic_def_id_of_type(ty: Ty<'_>) -> Option<DefId> {
 291     characteristic_def_id_of_type_cached(ty, &mut SsoHashSet::new())
 292 }
 293
 294 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for ty::Region<'tcx> {
 295     type Output = P::Region;
 296     type Error = P::Error;
 297     fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
 298         cx.print_region(*self)
 299     }
 300 }
 301
 302 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for Ty<'tcx> {
 303     type Output = P::Type;
 304     type Error = P::Error;
 305
 306     fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
 307         cx.print_type(*self)
 308     }
 309 }
 310
 311 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P>
 312     for &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
 313 {
 314     type Output = P::DynExistential;
 315     type Error = P::Error;
 316     fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
 317         cx.print_dyn_existential(self)
 318     }
 319 }
 320
 321 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for ty::Const<'tcx> {
 322     type Output = P::Const;
 323     type Error = P::Error;
 324     fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
 325         cx.print_const(*self)
 326     }
 327 }