crates/hir_ty/src/display.rs

   1 //! FIXME: write short doc here
   2
   3 use std::{borrow::Cow, fmt};
   4
   5 use arrayvec::ArrayVec;
   6 use chalk_ir::Mutability;
   7 use hir_def::{
   8     db::DefDatabase,
   9     find_path,
  10     generics::TypeParamProvenance,
  11     item_scope::ItemInNs,
  12     path::{GenericArg, Path, PathKind},
  13     type_ref::{TypeBound, TypeRef},
  14     visibility::Visibility,
  15     AssocContainerId, Lookup, ModuleId, TraitId,
  16 };
  17 use hir_expand::name::Name;
  18
  19 use crate::{
  20     db::HirDatabase, from_assoc_type_id, from_foreign_def_id, from_placeholder_idx, primitive,
  21     to_assoc_type_id, traits::chalk::from_chalk, utils::generics, AdtId, AliasTy, CallableDefId,
  22     CallableSig, GenericPredicate, ImplTraitId, Interner, Lifetime, Obligation, OpaqueTy,
  23     ProjectionTy, Scalar, Substitution, TraitRef, Ty, TyKind,
  24 };
  25
  26 pub struct HirFormatter<'a> {
  27     pub db: &'a dyn HirDatabase,
  28     fmt: &'a mut dyn fmt::Write,
  29     buf: String,
  30     curr_size: usize,
  31     pub(crate) max_size: Option<usize>,
  32     omit_verbose_types: bool,
  33     display_target: DisplayTarget,
  34 }
  35
  36 pub trait HirDisplay {
  37     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError>;
  38
  39     /// Returns a `Display`able type that is human-readable.
  40     fn into_displayable<'a>(
  41         &'a self,
  42         db: &'a dyn HirDatabase,
  43         max_size: Option<usize>,
  44         omit_verbose_types: bool,
  45         display_target: DisplayTarget,
  46     ) -> HirDisplayWrapper<'a, Self>
  47     where
  48         Self: Sized,
  49     {
  50         HirDisplayWrapper { db, t: self, max_size, omit_verbose_types, display_target }
  51     }
  52
  53     /// Returns a `Display`able type that is human-readable.
  54     /// Use this for showing types to the user (e.g. diagnostics)
  55     fn display<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
  56     where
  57         Self: Sized,
  58     {
  59         HirDisplayWrapper {
  60             db,
  61             t: self,
  62             max_size: None,
  63             omit_verbose_types: false,
  64             display_target: DisplayTarget::Diagnostics,
  65         }
  66     }
  67
  68     /// Returns a `Display`able type that is human-readable and tries to be succinct.
  69     /// Use this for showing types to the user where space is constrained (e.g. doc popups)
  70     fn display_truncated<'a>(
  71         &'a self,
  72         db: &'a dyn HirDatabase,
  73         max_size: Option<usize>,
  74     ) -> HirDisplayWrapper<'a, Self>
  75     where
  76         Self: Sized,
  77     {
  78         HirDisplayWrapper {
  79             db,
  80             t: self,
  81             max_size,
  82             omit_verbose_types: true,
  83             display_target: DisplayTarget::Diagnostics,
  84         }
  85     }
  86
  87     /// Returns a String representation of `self` that can be inserted into the given module.
  88     /// Use this when generating code (e.g. assists)
  89     fn display_source_code<'a>(
  90         &'a self,
  91         db: &'a dyn HirDatabase,
  92         module_id: ModuleId,
  93     ) -> Result<String, DisplaySourceCodeError> {
  94         let mut result = String::new();
  95         match self.hir_fmt(&mut HirFormatter {
  96             db,
  97             fmt: &mut result,
  98             buf: String::with_capacity(20),
  99             curr_size: 0,
 100             max_size: None,
 101             omit_verbose_types: false,
 102             display_target: DisplayTarget::SourceCode { module_id },
 103         }) {
 104             Ok(()) => {}
 105             Err(HirDisplayError::FmtError) => panic!("Writing to String can't fail!"),
 106             Err(HirDisplayError::DisplaySourceCodeError(e)) => return Err(e),
 107         };
 108         Ok(result)
 109     }
 110
 111     /// Returns a String representation of `self` for test purposes
 112     fn display_test<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
 113     where
 114         Self: Sized,
 115     {
 116         HirDisplayWrapper {
 117             db,
 118             t: self,
 119             max_size: None,
 120             omit_verbose_types: false,
 121             display_target: DisplayTarget::Test,
 122         }
 123     }
 124 }
 125
 126 impl<'a> HirFormatter<'a> {
 127     pub fn write_joined<T: HirDisplay>(
 128         &mut self,
 129         iter: impl IntoIterator<Item = T>,
 130         sep: &str,
 131     ) -> Result<(), HirDisplayError> {
 132         let mut first = true;
 133         for e in iter {
 134             if !first {
 135                 write!(self, "{}", sep)?;
 136             }
 137             first = false;
 138             e.hir_fmt(self)?;
 139         }
 140         Ok(())
 141     }
 142
 143     /// This allows using the `write!` macro directly with a `HirFormatter`.
 144     pub fn write_fmt(&mut self, args: fmt::Arguments) -> Result<(), HirDisplayError> {
 145         // We write to a buffer first to track output size
 146         self.buf.clear();
 147         fmt::write(&mut self.buf, args)?;
 148         self.curr_size += self.buf.len();
 149
 150         // Then we write to the internal formatter from the buffer
 151         self.fmt.write_str(&self.buf).map_err(HirDisplayError::from)
 152     }
 153
 154     pub fn should_truncate(&self) -> bool {
 155         if let Some(max_size) = self.max_size {
 156             self.curr_size >= max_size
 157         } else {
 158             false
 159         }
 160     }
 161
 162     pub fn omit_verbose_types(&self) -> bool {
 163         self.omit_verbose_types
 164     }
 165 }
 166
 167 #[derive(Clone, Copy)]
 168 pub enum DisplayTarget {
 169     /// Display types for inlays, doc popups, autocompletion, etc...
 170     /// Showing `{unknown}` or not qualifying paths is fine here.
 171     /// There's no reason for this to fail.
 172     Diagnostics,
 173     /// Display types for inserting them in source files.
 174     /// The generated code should compile, so paths need to be qualified.
 175     SourceCode { module_id: ModuleId },
 176     /// Only for test purpose to keep real types
 177     Test,
 178 }
 179
 180 impl DisplayTarget {
 181     fn is_source_code(&self) -> bool {
 182         matches!(self, Self::SourceCode { .. })
 183     }
 184     fn is_test(&self) -> bool {
 185         matches!(self, Self::Test)
 186     }
 187 }
 188
 189 #[derive(Debug)]
 190 pub enum DisplaySourceCodeError {
 191     PathNotFound,
 192     UnknownType,
 193 }
 194
 195 pub enum HirDisplayError {
 196     /// Errors that can occur when generating source code
 197     DisplaySourceCodeError(DisplaySourceCodeError),
 198     /// `FmtError` is required to be compatible with std::fmt::Display
 199     FmtError,
 200 }
 201 impl From<fmt::Error> for HirDisplayError {
 202     fn from(_: fmt::Error) -> Self {
 203         Self::FmtError
 204     }
 205 }
 206
 207 pub struct HirDisplayWrapper<'a, T> {
 208     db: &'a dyn HirDatabase,
 209     t: &'a T,
 210     max_size: Option<usize>,
 211     omit_verbose_types: bool,
 212     display_target: DisplayTarget,
 213 }
 214
 215 impl<'a, T> fmt::Display for HirDisplayWrapper<'a, T>
 216 where
 217     T: HirDisplay,
 218 {
 219     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 220         match self.t.hir_fmt(&mut HirFormatter {
 221             db: self.db,
 222             fmt: f,
 223             buf: String::with_capacity(20),
 224             curr_size: 0,
 225             max_size: self.max_size,
 226             omit_verbose_types: self.omit_verbose_types,
 227             display_target: self.display_target,
 228         }) {
 229             Ok(()) => Ok(()),
 230             Err(HirDisplayError::FmtError) => Err(fmt::Error),
 231             Err(HirDisplayError::DisplaySourceCodeError(_)) => {
 232                 // This should never happen
 233                 panic!("HirDisplay failed when calling Display::fmt!")
 234             }
 235         }
 236     }
 237 }
 238
 239 const TYPE_HINT_TRUNCATION: &str = "…";
 240
 241 impl<T: HirDisplay> HirDisplay for &'_ T {
 242     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 243         HirDisplay::hir_fmt(*self, f)
 244     }
 245 }
 246
 247 impl HirDisplay for ProjectionTy {
 248     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 249         if f.should_truncate() {
 250             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 251         }
 252
 253         let trait_ = f.db.trait_data(self.trait_(f.db));
 254         let first_parameter = self.substitution[0].into_displayable(
 255             f.db,
 256             f.max_size,
 257             f.omit_verbose_types,
 258             f.display_target,
 259         );
 260         write!(f, "<{} as {}", first_parameter, trait_.name)?;
 261         if self.substitution.len() > 1 {
 262             write!(f, "<")?;
 263             f.write_joined(&self.substitution[1..], ", ")?;
 264             write!(f, ">")?;
 265         }
 266         write!(f, ">::{}", f.db.type_alias_data(from_assoc_type_id(self.associated_ty_id)).name)?;
 267         Ok(())
 268     }
 269 }
 270
 271 impl HirDisplay for Ty {
 272     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 273         if f.should_truncate() {
 274             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 275         }
 276
 277         match self.interned(&Interner) {
 278             TyKind::Never => write!(f, "!")?,
 279             TyKind::Str => write!(f, "str")?,
 280             TyKind::Scalar(Scalar::Bool) => write!(f, "bool")?,
 281             TyKind::Scalar(Scalar::Char) => write!(f, "char")?,
 282             &TyKind::Scalar(Scalar::Float(t)) => write!(f, "{}", primitive::float_ty_to_string(t))?,
 283             &TyKind::Scalar(Scalar::Int(t)) => write!(f, "{}", primitive::int_ty_to_string(t))?,
 284             &TyKind::Scalar(Scalar::Uint(t)) => write!(f, "{}", primitive::uint_ty_to_string(t))?,
 285             TyKind::Slice(t) => {
 286                 write!(f, "[")?;
 287                 t.hir_fmt(f)?;
 288                 write!(f, "]")?;
 289             }
 290             TyKind::Array(t) => {
 291                 write!(f, "[")?;
 292                 t.hir_fmt(f)?;
 293                 write!(f, "; _]")?;
 294             }
 295             TyKind::Raw(m, t) | TyKind::Ref(m, t) => {
 296                 let ty_display =
 297                     t.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
 298
 299                 if matches!(self.interned(&Interner), TyKind::Raw(..)) {
 300                     write!(
 301                         f,
 302                         "*{}",
 303                         match m {
 304                             Mutability::Not => "const ",
 305                             Mutability::Mut => "mut ",
 306                         }
 307                     )?;
 308                 } else {
 309                     write!(
 310                         f,
 311                         "&{}",
 312                         match m {
 313                             Mutability::Not => "",
 314                             Mutability::Mut => "mut ",
 315                         }
 316                     )?;
 317                 }
 318
 319                 // FIXME: all this just to decide whether to use parentheses...
 320                 let datas;
 321                 let predicates = match t.interned(&Interner) {
 322                     TyKind::Dyn(predicates) if predicates.len() > 1 => {
 323                         Cow::Borrowed(predicates.as_ref())
 324                     }
 325                     &TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 326                         opaque_ty_id,
 327                         substitution: ref parameters,
 328                     })) => {
 329                         let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty_id.into());
 330                         if let ImplTraitId::ReturnTypeImplTrait(func, idx) = impl_trait_id {
 331                             datas =
 332                                 f.db.return_type_impl_traits(func)
 333                                     .expect("impl trait id without data");
 334                             let data = (*datas)
 335                                 .as_ref()
 336                                 .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 337                             let bounds = data.subst(parameters);
 338                             Cow::Owned(bounds.value)
 339                         } else {
 340                             Cow::Borrowed(&[][..])
 341                         }
 342                     }
 343                     _ => Cow::Borrowed(&[][..]),
 344                 };
 345
 346                 if let [GenericPredicate::Implemented(trait_ref), _] = predicates.as_ref() {
 347                     let trait_ = trait_ref.trait_;
 348                     if fn_traits(f.db.upcast(), trait_).any(|it| it == trait_) {
 349                         return write!(f, "{}", ty_display);
 350                     }
 351                 }
 352
 353                 if predicates.len() > 1 {
 354                     write!(f, "(")?;
 355                     write!(f, "{}", ty_display)?;
 356                     write!(f, ")")?;
 357                 } else {
 358                     write!(f, "{}", ty_display)?;
 359                 }
 360             }
 361             TyKind::Tuple(_, substs) => {
 362                 if substs.len() == 1 {
 363                     write!(f, "(")?;
 364                     substs[0].hir_fmt(f)?;
 365                     write!(f, ",)")?;
 366                 } else {
 367                     write!(f, "(")?;
 368                     f.write_joined(&*substs.0, ", ")?;
 369                     write!(f, ")")?;
 370                 }
 371             }
 372             TyKind::Function(fn_ptr) => {
 373                 let sig = CallableSig::from_fn_ptr(fn_ptr);
 374                 sig.hir_fmt(f)?;
 375             }
 376             TyKind::FnDef(def, parameters) => {
 377                 let def = from_chalk(f.db, *def);
 378                 let sig = f.db.callable_item_signature(def).subst(parameters);
 379                 match def {
 380                     CallableDefId::FunctionId(ff) => {
 381                         write!(f, "fn {}", f.db.function_data(ff).name)?
 382                     }
 383                     CallableDefId::StructId(s) => write!(f, "{}", f.db.struct_data(s).name)?,
 384                     CallableDefId::EnumVariantId(e) => {
 385                         write!(f, "{}", f.db.enum_data(e.parent).variants[e.local_id].name)?
 386                     }
 387                 };
 388                 if parameters.len() > 0 {
 389                     let generics = generics(f.db.upcast(), def.into());
 390                     let (parent_params, self_param, type_params, _impl_trait_params) =
 391                         generics.provenance_split();
 392                     let total_len = parent_params + self_param + type_params;
 393                     // We print all params except implicit impl Trait params. Still a bit weird; should we leave out parent and self?
 394                     if total_len > 0 {
 395                         write!(f, "<")?;
 396                         f.write_joined(&parameters.0[..total_len], ", ")?;
 397                         write!(f, ">")?;
 398                     }
 399                 }
 400                 write!(f, "(")?;
 401                 f.write_joined(sig.params(), ", ")?;
 402                 write!(f, ")")?;
 403                 let ret = sig.ret();
 404                 if *ret != Ty::unit() {
 405                     let ret_display = ret.into_displayable(
 406                         f.db,
 407                         f.max_size,
 408                         f.omit_verbose_types,
 409                         f.display_target,
 410                     );
 411
 412                     write!(f, " -> {}", ret_display)?;
 413                 }
 414             }
 415             TyKind::Adt(AdtId(def_id), parameters) => {
 416                 match f.display_target {
 417                     DisplayTarget::Diagnostics | DisplayTarget::Test => {
 418                         let name = match *def_id {
 419                             hir_def::AdtId::StructId(it) => f.db.struct_data(it).name.clone(),
 420                             hir_def::AdtId::UnionId(it) => f.db.union_data(it).name.clone(),
 421                             hir_def::AdtId::EnumId(it) => f.db.enum_data(it).name.clone(),
 422                         };
 423                         write!(f, "{}", name)?;
 424                     }
 425                     DisplayTarget::SourceCode { module_id } => {
 426                         if let Some(path) = find_path::find_path(
 427                             f.db.upcast(),
 428                             ItemInNs::Types((*def_id).into()),
 429                             module_id,
 430                         ) {
 431                             write!(f, "{}", path)?;
 432                         } else {
 433                             return Err(HirDisplayError::DisplaySourceCodeError(
 434                                 DisplaySourceCodeError::PathNotFound,
 435                             ));
 436                         }
 437                     }
 438                 }
 439
 440                 if parameters.len() > 0 {
 441                     let parameters_to_write = if f.display_target.is_source_code()
 442                         || f.omit_verbose_types()
 443                     {
 444                         match self
 445                             .as_generic_def(f.db)
 446                             .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
 447                             .filter(|defaults| !defaults.is_empty())
 448                         {
 449                             None => parameters.0.as_ref(),
 450                             Some(default_parameters) => {
 451                                 let mut default_from = 0;
 452                                 for (i, parameter) in parameters.iter().enumerate() {
 453                                     match (parameter.interned(&Interner), default_parameters.get(i))
 454                                     {
 455                                         (&TyKind::Unknown, _) | (_, None) => {
 456                                             default_from = i + 1;
 457                                         }
 458                                         (_, Some(default_parameter)) => {
 459                                             let actual_default = default_parameter
 460                                                 .clone()
 461                                                 .subst(&parameters.prefix(i));
 462                                             if parameter != &actual_default {
 463                                                 default_from = i + 1;
 464                                             }
 465                                         }
 466                                     }
 467                                 }
 468                                 &parameters.0[0..default_from]
 469                             }
 470                         }
 471                     } else {
 472                         parameters.0.as_ref()
 473                     };
 474                     if !parameters_to_write.is_empty() {
 475                         write!(f, "<")?;
 476                         f.write_joined(parameters_to_write, ", ")?;
 477                         write!(f, ">")?;
 478                     }
 479                 }
 480             }
 481             TyKind::AssociatedType(assoc_type_id, parameters) => {
 482                 let type_alias = from_assoc_type_id(*assoc_type_id);
 483                 let trait_ = match type_alias.lookup(f.db.upcast()).container {
 484                     AssocContainerId::TraitId(it) => it,
 485                     _ => panic!("not an associated type"),
 486                 };
 487                 let trait_ = f.db.trait_data(trait_);
 488                 let type_alias_data = f.db.type_alias_data(type_alias);
 489
 490                 // Use placeholder associated types when the target is test (https://rust-lang.github.io/chalk/book/clauses/type_equality.html#placeholder-associated-types)
 491                 if f.display_target.is_test() {
 492                     write!(f, "{}::{}", trait_.name, type_alias_data.name)?;
 493                     if parameters.len() > 0 {
 494                         write!(f, "<")?;
 495                         f.write_joined(&*parameters.0, ", ")?;
 496                         write!(f, ">")?;
 497                     }
 498                 } else {
 499                     let projection_ty = ProjectionTy {
 500                         associated_ty_id: to_assoc_type_id(type_alias),
 501                         substitution: parameters.clone(),
 502                     };
 503
 504                     projection_ty.hir_fmt(f)?;
 505                 }
 506             }
 507             TyKind::ForeignType(type_alias) => {
 508                 let type_alias = f.db.type_alias_data(from_foreign_def_id(*type_alias));
 509                 write!(f, "{}", type_alias.name)?;
 510             }
 511             TyKind::OpaqueType(opaque_ty_id, parameters) => {
 512                 let impl_trait_id = f.db.lookup_intern_impl_trait_id((*opaque_ty_id).into());
 513                 match impl_trait_id {
 514                     ImplTraitId::ReturnTypeImplTrait(func, idx) => {
 515                         let datas =
 516                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 517                         let data = (*datas)
 518                             .as_ref()
 519                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 520                         let bounds = data.subst(&parameters);
 521                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
 522                         // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
 523                     }
 524                     ImplTraitId::AsyncBlockTypeImplTrait(..) => {
 525                         write!(f, "impl Future<Output = ")?;
 526                         parameters[0].hir_fmt(f)?;
 527                         write!(f, ">")?;
 528                     }
 529                 }
 530             }
 531             TyKind::Closure(.., substs) => {
 532                 let sig = substs[0].callable_sig(f.db);
 533                 if let Some(sig) = sig {
 534                     if sig.params().is_empty() {
 535                         write!(f, "||")?;
 536                     } else if f.omit_verbose_types() {
 537                         write!(f, "|{}|", TYPE_HINT_TRUNCATION)?;
 538                     } else {
 539                         write!(f, "|")?;
 540                         f.write_joined(sig.params(), ", ")?;
 541                         write!(f, "|")?;
 542                     };
 543
 544                     let ret_display = sig.ret().into_displayable(
 545                         f.db,
 546                         f.max_size,
 547                         f.omit_verbose_types,
 548                         f.display_target,
 549                     );
 550                     write!(f, " -> {}", ret_display)?;
 551                 } else {
 552                     write!(f, "{{closure}}")?;
 553                 }
 554             }
 555             TyKind::Placeholder(idx) => {
 556                 let id = from_placeholder_idx(f.db, *idx);
 557                 let generics = generics(f.db.upcast(), id.parent);
 558                 let param_data = &generics.params.types[id.local_id];
 559                 match param_data.provenance {
 560                     TypeParamProvenance::TypeParamList | TypeParamProvenance::TraitSelf => {
 561                         write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
 562                     }
 563                     TypeParamProvenance::ArgumentImplTrait => {
 564                         let bounds = f.db.generic_predicates_for_param(id);
 565                         let substs = Substitution::type_params_for_generics(f.db, &generics);
 566                         write_bounds_like_dyn_trait_with_prefix(
 567                             "impl",
 568                             &bounds.iter().map(|b| b.clone().subst(&substs)).collect::<Vec<_>>(),
 569                             f,
 570                         )?;
 571                     }
 572                 }
 573             }
 574             TyKind::BoundVar(idx) => write!(f, "?{}.{}", idx.debruijn.depth(), idx.index)?,
 575             TyKind::Dyn(predicates) => {
 576                 write_bounds_like_dyn_trait_with_prefix("dyn", predicates, f)?;
 577             }
 578             TyKind::Alias(AliasTy::Projection(p_ty)) => p_ty.hir_fmt(f)?,
 579             TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
 580                 let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into());
 581                 match impl_trait_id {
 582                     ImplTraitId::ReturnTypeImplTrait(func, idx) => {
 583                         let datas =
 584                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 585                         let data = (*datas)
 586                             .as_ref()
 587                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 588                         let bounds = data.subst(&opaque_ty.substitution);
 589                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
 590                     }
 591                     ImplTraitId::AsyncBlockTypeImplTrait(..) => {
 592                         write!(f, "{{async block}}")?;
 593                     }
 594                 };
 595             }
 596             TyKind::Unknown => {
 597                 if f.display_target.is_source_code() {
 598                     return Err(HirDisplayError::DisplaySourceCodeError(
 599                         DisplaySourceCodeError::UnknownType,
 600                     ));
 601                 }
 602                 write!(f, "{{unknown}}")?;
 603             }
 604             TyKind::InferenceVar(..) => write!(f, "_")?,
 605         }
 606         Ok(())
 607     }
 608 }
 609
 610 impl HirDisplay for CallableSig {
 611     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 612         write!(f, "fn(")?;
 613         f.write_joined(self.params(), ", ")?;
 614         if self.is_varargs {
 615             if self.params().is_empty() {
 616                 write!(f, "...")?;
 617             } else {
 618                 write!(f, ", ...")?;
 619             }
 620         }
 621         write!(f, ")")?;
 622         let ret = self.ret();
 623         if *ret != Ty::unit() {
 624             let ret_display =
 625                 ret.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
 626             write!(f, " -> {}", ret_display)?;
 627         }
 628         Ok(())
 629     }
 630 }
 631
 632 fn fn_traits(db: &dyn DefDatabase, trait_: TraitId) -> impl Iterator<Item = TraitId> {
 633     let krate = trait_.lookup(db).container.krate();
 634     let fn_traits = [
 635         db.lang_item(krate, "fn".into()),
 636         db.lang_item(krate, "fn_mut".into()),
 637         db.lang_item(krate, "fn_once".into()),
 638     ];
 639     // FIXME: Replace ArrayVec when into_iter is a thing on arrays
 640     ArrayVec::from(fn_traits).into_iter().flatten().flat_map(|it| it.as_trait())
 641 }
 642
 643 pub fn write_bounds_like_dyn_trait_with_prefix(
 644     prefix: &str,
 645     predicates: &[GenericPredicate],
 646     f: &mut HirFormatter,
 647 ) -> Result<(), HirDisplayError> {
 648     write!(f, "{}", prefix)?;
 649     if !predicates.is_empty() {
 650         write!(f, " ")?;
 651         write_bounds_like_dyn_trait(predicates, f)
 652     } else {
 653         Ok(())
 654     }
 655 }
 656
 657 fn write_bounds_like_dyn_trait(
 658     predicates: &[GenericPredicate],
 659     f: &mut HirFormatter,
 660 ) -> Result<(), HirDisplayError> {
 661     // Note: This code is written to produce nice results (i.e.
 662     // corresponding to surface Rust) for types that can occur in
 663     // actual Rust. It will have weird results if the predicates
 664     // aren't as expected (i.e. self types = $0, projection
 665     // predicates for a certain trait come after the Implemented
 666     // predicate for that trait).
 667     let mut first = true;
 668     let mut angle_open = false;
 669     let mut is_fn_trait = false;
 670     for p in predicates.iter() {
 671         match p {
 672             GenericPredicate::Implemented(trait_ref) => {
 673                 let trait_ = trait_ref.trait_;
 674                 if !is_fn_trait {
 675                     is_fn_trait = fn_traits(f.db.upcast(), trait_).any(|it| it == trait_);
 676                 }
 677                 if !is_fn_trait && angle_open {
 678                     write!(f, ">")?;
 679                     angle_open = false;
 680                 }
 681                 if !first {
 682                     write!(f, " + ")?;
 683                 }
 684                 // We assume that the self type is $0 (i.e. the
 685                 // existential) here, which is the only thing that's
 686                 // possible in actual Rust, and hence don't print it
 687                 write!(f, "{}", f.db.trait_data(trait_).name)?;
 688                 if let [_, params @ ..] = &*trait_ref.substs.0 {
 689                     if is_fn_trait {
 690                         if let Some(args) = params.first().and_then(|it| it.as_tuple()) {
 691                             write!(f, "(")?;
 692                             f.write_joined(&*args.0, ", ")?;
 693                             write!(f, ")")?;
 694                         }
 695                     } else if !params.is_empty() {
 696                         write!(f, "<")?;
 697                         f.write_joined(params, ", ")?;
 698                         // there might be assoc type bindings, so we leave the angle brackets open
 699                         angle_open = true;
 700                     }
 701                 }
 702             }
 703             GenericPredicate::Projection(projection_pred) if is_fn_trait => {
 704                 is_fn_trait = false;
 705                 write!(f, " -> ")?;
 706                 projection_pred.ty.hir_fmt(f)?;
 707             }
 708             GenericPredicate::Projection(projection_pred) => {
 709                 // in types in actual Rust, these will always come
 710                 // after the corresponding Implemented predicate
 711                 if angle_open {
 712                     write!(f, ", ")?;
 713                 } else {
 714                     write!(f, "<")?;
 715                     angle_open = true;
 716                 }
 717                 let type_alias = f.db.type_alias_data(from_assoc_type_id(
 718                     projection_pred.projection_ty.associated_ty_id,
 719                 ));
 720                 write!(f, "{} = ", type_alias.name)?;
 721                 projection_pred.ty.hir_fmt(f)?;
 722             }
 723             GenericPredicate::Error => {
 724                 if angle_open {
 725                     // impl Trait<X, {error}>
 726                     write!(f, ", ")?;
 727                 } else if !first {
 728                     // impl Trait + {error}
 729                     write!(f, " + ")?;
 730                 }
 731                 p.hir_fmt(f)?;
 732             }
 733         }
 734         first = false;
 735     }
 736     if angle_open {
 737         write!(f, ">")?;
 738     }
 739     Ok(())
 740 }
 741
 742 impl TraitRef {
 743     fn hir_fmt_ext(&self, f: &mut HirFormatter, use_as: bool) -> Result<(), HirDisplayError> {
 744         if f.should_truncate() {
 745             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 746         }
 747
 748         self.substs[0].hir_fmt(f)?;
 749         if use_as {
 750             write!(f, " as ")?;
 751         } else {
 752             write!(f, ": ")?;
 753         }
 754         write!(f, "{}", f.db.trait_data(self.trait_).name)?;
 755         if self.substs.len() > 1 {
 756             write!(f, "<")?;
 757             f.write_joined(&self.substs[1..], ", ")?;
 758             write!(f, ">")?;
 759         }
 760         Ok(())
 761     }
 762 }
 763
 764 impl HirDisplay for TraitRef {
 765     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 766         self.hir_fmt_ext(f, false)
 767     }
 768 }
 769
 770 impl HirDisplay for GenericPredicate {
 771     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 772         if f.should_truncate() {
 773             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 774         }
 775
 776         match self {
 777             GenericPredicate::Implemented(trait_ref) => trait_ref.hir_fmt(f)?,
 778             GenericPredicate::Projection(projection_pred) => {
 779                 write!(f, "<")?;
 780                 projection_pred.projection_ty.trait_ref(f.db).hir_fmt_ext(f, true)?;
 781                 write!(
 782                     f,
 783                     ">::{} = ",
 784                     f.db.type_alias_data(from_assoc_type_id(
 785                         projection_pred.projection_ty.associated_ty_id
 786                     ))
 787                     .name,
 788                 )?;
 789                 projection_pred.ty.hir_fmt(f)?;
 790             }
 791             GenericPredicate::Error => write!(f, "{{error}}")?,
 792         }
 793         Ok(())
 794     }
 795 }
 796
 797 impl HirDisplay for Lifetime {
 798     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 799         match self {
 800             Lifetime::Parameter(id) => {
 801                 let generics = generics(f.db.upcast(), id.parent);
 802                 let param_data = &generics.params.lifetimes[id.local_id];
 803                 write!(f, "{}", &param_data.name)
 804             }
 805             Lifetime::Static => write!(f, "'static"),
 806         }
 807     }
 808 }
 809
 810 impl HirDisplay for Obligation {
 811     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 812         match self {
 813             Obligation::Trait(tr) => {
 814                 write!(f, "Implements(")?;
 815                 tr.hir_fmt(f)?;
 816                 write!(f, ")")
 817             }
 818             Obligation::Projection(proj) => {
 819                 write!(f, "Normalize(")?;
 820                 proj.projection_ty.hir_fmt(f)?;
 821                 write!(f, " => ")?;
 822                 proj.ty.hir_fmt(f)?;
 823                 write!(f, ")")
 824             }
 825         }
 826     }
 827 }
 828
 829 pub fn write_visibility(
 830     module_id: ModuleId,
 831     vis: Visibility,
 832     f: &mut HirFormatter,
 833 ) -> Result<(), HirDisplayError> {
 834     match vis {
 835         Visibility::Public => write!(f, "pub "),
 836         Visibility::Module(vis_id) => {
 837             let def_map = module_id.def_map(f.db.upcast());
 838             let root_module_id = def_map.module_id(def_map.root());
 839             if vis_id == module_id {
 840                 // pub(self) or omitted
 841                 Ok(())
 842             } else if root_module_id == vis_id {
 843                 write!(f, "pub(crate) ")
 844             } else if module_id.containing_module(f.db.upcast()) == Some(vis_id) {
 845                 write!(f, "pub(super) ")
 846             } else {
 847                 write!(f, "pub(in ...) ")
 848             }
 849         }
 850     }
 851 }
 852
 853 impl HirDisplay for TypeRef {
 854     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 855         match self {
 856             TypeRef::Never => write!(f, "!")?,
 857             TypeRef::Placeholder => write!(f, "_")?,
 858             TypeRef::Tuple(elems) => {
 859                 write!(f, "(")?;
 860                 f.write_joined(elems, ", ")?;
 861                 if elems.len() == 1 {
 862                     write!(f, ",")?;
 863                 }
 864                 write!(f, ")")?;
 865             }
 866             TypeRef::Path(path) => path.hir_fmt(f)?,
 867             TypeRef::RawPtr(inner, mutability) => {
 868                 let mutability = match mutability {
 869                     hir_def::type_ref::Mutability::Shared => "*const ",
 870                     hir_def::type_ref::Mutability::Mut => "*mut ",
 871                 };
 872                 write!(f, "{}", mutability)?;
 873                 inner.hir_fmt(f)?;
 874             }
 875             TypeRef::Reference(inner, lifetime, mutability) => {
 876                 let mutability = match mutability {
 877                     hir_def::type_ref::Mutability::Shared => "",
 878                     hir_def::type_ref::Mutability::Mut => "mut ",
 879                 };
 880                 write!(f, "&")?;
 881                 if let Some(lifetime) = lifetime {
 882                     write!(f, "{} ", lifetime.name)?;
 883                 }
 884                 write!(f, "{}", mutability)?;
 885                 inner.hir_fmt(f)?;
 886             }
 887             TypeRef::Array(inner) => {
 888                 write!(f, "[")?;
 889                 inner.hir_fmt(f)?;
 890                 // FIXME: Array length?
 891                 write!(f, "; _]")?;
 892             }
 893             TypeRef::Slice(inner) => {
 894                 write!(f, "[")?;
 895                 inner.hir_fmt(f)?;
 896                 write!(f, "]")?;
 897             }
 898             TypeRef::Fn(tys, is_varargs) => {
 899                 // FIXME: Function pointer qualifiers.
 900                 write!(f, "fn(")?;
 901                 f.write_joined(&tys[..tys.len() - 1], ", ")?;
 902                 if *is_varargs {
 903                     write!(f, "{}...", if tys.len() == 1 { "" } else { ", " })?;
 904                 }
 905                 write!(f, ")")?;
 906                 let ret_ty = tys.last().unwrap();
 907                 match ret_ty {
 908                     TypeRef::Tuple(tup) if tup.is_empty() => {}
 909                     _ => {
 910                         write!(f, " -> ")?;
 911                         ret_ty.hir_fmt(f)?;
 912                     }
 913                 }
 914             }
 915             TypeRef::ImplTrait(bounds) => {
 916                 write!(f, "impl ")?;
 917                 f.write_joined(bounds, " + ")?;
 918             }
 919             TypeRef::DynTrait(bounds) => {
 920                 write!(f, "dyn ")?;
 921                 f.write_joined(bounds, " + ")?;
 922             }
 923             TypeRef::Error => write!(f, "{{error}}")?,
 924         }
 925         Ok(())
 926     }
 927 }
 928
 929 impl HirDisplay for TypeBound {
 930     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 931         match self {
 932             TypeBound::Path(path) => path.hir_fmt(f),
 933             TypeBound::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
 934             TypeBound::Error => write!(f, "{{error}}"),
 935         }
 936     }
 937 }
 938
 939 impl HirDisplay for Path {
 940     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 941         match (self.type_anchor(), self.kind()) {
 942             (Some(anchor), _) => {
 943                 write!(f, "<")?;
 944                 anchor.hir_fmt(f)?;
 945                 write!(f, ">")?;
 946             }
 947             (_, PathKind::Plain) => {}
 948             (_, PathKind::Abs) => write!(f, "::")?,
 949             (_, PathKind::Crate) => write!(f, "crate")?,
 950             (_, PathKind::Super(0)) => write!(f, "self")?,
 951             (_, PathKind::Super(n)) => {
 952                 write!(f, "super")?;
 953                 for _ in 0..*n {
 954                     write!(f, "::super")?;
 955                 }
 956             }
 957             (_, PathKind::DollarCrate(_)) => write!(f, "{{extern_crate}}")?,
 958         }
 959
 960         for (seg_idx, segment) in self.segments().iter().enumerate() {
 961             if seg_idx != 0 {
 962                 write!(f, "::")?;
 963             }
 964             write!(f, "{}", segment.name)?;
 965             if let Some(generic_args) = segment.args_and_bindings {
 966                 // We should be in type context, so format as `Foo<Bar>` instead of `Foo::<Bar>`.
 967                 // Do we actually format expressions?
 968                 write!(f, "<")?;
 969                 let mut first = true;
 970                 for arg in &generic_args.args {
 971                     if first {
 972                         first = false;
 973                         if generic_args.has_self_type {
 974                             // FIXME: Convert to `<Ty as Trait>` form.
 975                             write!(f, "Self = ")?;
 976                         }
 977                     } else {
 978                         write!(f, ", ")?;
 979                     }
 980                     arg.hir_fmt(f)?;
 981                 }
 982                 for binding in &generic_args.bindings {
 983                     if first {
 984                         first = false;
 985                     } else {
 986                         write!(f, ", ")?;
 987                     }
 988                     write!(f, "{}", binding.name)?;
 989                     match &binding.type_ref {
 990                         Some(ty) => {
 991                             write!(f, " = ")?;
 992                             ty.hir_fmt(f)?
 993                         }
 994                         None => {
 995                             write!(f, ": ")?;
 996                             f.write_joined(&binding.bounds, " + ")?;
 997                         }
 998                     }
 999                 }
1000                 write!(f, ">")?;
1001             }
1002         }
1003         Ok(())
1004     }
1005 }
1006
1007 impl HirDisplay for GenericArg {
1008     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
1009         match self {
1010             GenericArg::Type(ty) => ty.hir_fmt(f),
1011             GenericArg::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
1012         }
1013     }
1014 }