src/tools/rust-analyzer/crates/hir-ty/src/display.rs

   1 //! The `HirDisplay` trait, which serves two purposes: Turning various bits from
   2 //! HIR back into source code, and just displaying them for debugging/testing
   3 //! purposes.
   4
   5 use std::fmt::{self, Debug};
   6
   7 use base_db::CrateId;
   8 use chalk_ir::BoundVar;
   9 use hir_def::{
  10     body,
  11     db::DefDatabase,
  12     find_path,
  13     generics::{TypeOrConstParamData, TypeParamProvenance},
  14     intern::{Internable, Interned},
  15     item_scope::ItemInNs,
  16     path::{Path, PathKind},
  17     type_ref::{ConstScalar, TraitBoundModifier, TypeBound, TypeRef},
  18     visibility::Visibility,
  19     HasModule, ItemContainerId, Lookup, ModuleId, TraitId,
  20 };
  21 use hir_expand::{hygiene::Hygiene, name::Name};
  22 use itertools::Itertools;
  23 use smallvec::SmallVec;
  24 use syntax::SmolStr;
  25
  26 use crate::{
  27     db::HirDatabase,
  28     from_assoc_type_id, from_foreign_def_id, from_placeholder_idx, lt_from_placeholder_idx,
  29     mapping::from_chalk,
  30     primitive, to_assoc_type_id,
  31     utils::{self, generics},
  32     AdtId, AliasEq, AliasTy, Binders, CallableDefId, CallableSig, Const, ConstValue, DomainGoal,
  33     GenericArg, ImplTraitId, Interner, Lifetime, LifetimeData, LifetimeOutlives, Mutability,
  34     OpaqueTy, ProjectionTy, ProjectionTyExt, QuantifiedWhereClause, Scalar, Substitution, TraitRef,
  35     TraitRefExt, Ty, TyExt, TyKind, WhereClause,
  36 };
  37
  38 pub struct HirFormatter<'a> {
  39     pub db: &'a dyn HirDatabase,
  40     fmt: &'a mut dyn fmt::Write,
  41     buf: String,
  42     curr_size: usize,
  43     pub(crate) max_size: Option<usize>,
  44     omit_verbose_types: bool,
  45     display_target: DisplayTarget,
  46 }
  47
  48 pub trait HirDisplay {
  49     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError>;
  50
  51     /// Returns a `Display`able type that is human-readable.
  52     fn into_displayable<'a>(
  53         &'a self,
  54         db: &'a dyn HirDatabase,
  55         max_size: Option<usize>,
  56         omit_verbose_types: bool,
  57         display_target: DisplayTarget,
  58     ) -> HirDisplayWrapper<'a, Self>
  59     where
  60         Self: Sized,
  61     {
  62         assert!(
  63             !matches!(display_target, DisplayTarget::SourceCode { .. }),
  64             "HirDisplayWrapper cannot fail with DisplaySourceCodeError, use HirDisplay::hir_fmt directly instead"
  65         );
  66         HirDisplayWrapper { db, t: self, max_size, omit_verbose_types, display_target }
  67     }
  68
  69     /// Returns a `Display`able type that is human-readable.
  70     /// Use this for showing types to the user (e.g. diagnostics)
  71     fn display<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
  72     where
  73         Self: Sized,
  74     {
  75         HirDisplayWrapper {
  76             db,
  77             t: self,
  78             max_size: None,
  79             omit_verbose_types: false,
  80             display_target: DisplayTarget::Diagnostics,
  81         }
  82     }
  83
  84     /// Returns a `Display`able type that is human-readable and tries to be succinct.
  85     /// Use this for showing types to the user where space is constrained (e.g. doc popups)
  86     fn display_truncated<'a>(
  87         &'a self,
  88         db: &'a dyn HirDatabase,
  89         max_size: Option<usize>,
  90     ) -> HirDisplayWrapper<'a, Self>
  91     where
  92         Self: Sized,
  93     {
  94         HirDisplayWrapper {
  95             db,
  96             t: self,
  97             max_size,
  98             omit_verbose_types: true,
  99             display_target: DisplayTarget::Diagnostics,
 100         }
 101     }
 102
 103     /// Returns a String representation of `self` that can be inserted into the given module.
 104     /// Use this when generating code (e.g. assists)
 105     fn display_source_code<'a>(
 106         &'a self,
 107         db: &'a dyn HirDatabase,
 108         module_id: ModuleId,
 109     ) -> Result<String, DisplaySourceCodeError> {
 110         let mut result = String::new();
 111         match self.hir_fmt(&mut HirFormatter {
 112             db,
 113             fmt: &mut result,
 114             buf: String::with_capacity(20),
 115             curr_size: 0,
 116             max_size: None,
 117             omit_verbose_types: false,
 118             display_target: DisplayTarget::SourceCode { module_id },
 119         }) {
 120             Ok(()) => {}
 121             Err(HirDisplayError::FmtError) => panic!("Writing to String can't fail!"),
 122             Err(HirDisplayError::DisplaySourceCodeError(e)) => return Err(e),
 123         };
 124         Ok(result)
 125     }
 126
 127     /// Returns a String representation of `self` for test purposes
 128     fn display_test<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
 129     where
 130         Self: Sized,
 131     {
 132         HirDisplayWrapper {
 133             db,
 134             t: self,
 135             max_size: None,
 136             omit_verbose_types: false,
 137             display_target: DisplayTarget::Test,
 138         }
 139     }
 140 }
 141
 142 impl<'a> HirFormatter<'a> {
 143     pub fn write_joined<T: HirDisplay>(
 144         &mut self,
 145         iter: impl IntoIterator<Item = T>,
 146         sep: &str,
 147     ) -> Result<(), HirDisplayError> {
 148         let mut first = true;
 149         for e in iter {
 150             if !first {
 151                 write!(self, "{}", sep)?;
 152             }
 153             first = false;
 154
 155             // Abbreviate multiple omitted types with a single ellipsis.
 156             if self.should_truncate() {
 157                 return write!(self, "{}", TYPE_HINT_TRUNCATION);
 158             }
 159
 160             e.hir_fmt(self)?;
 161         }
 162         Ok(())
 163     }
 164
 165     /// This allows using the `write!` macro directly with a `HirFormatter`.
 166     pub fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> Result<(), HirDisplayError> {
 167         // We write to a buffer first to track output size
 168         self.buf.clear();
 169         fmt::write(&mut self.buf, args)?;
 170         self.curr_size += self.buf.len();
 171
 172         // Then we write to the internal formatter from the buffer
 173         self.fmt.write_str(&self.buf).map_err(HirDisplayError::from)
 174     }
 175
 176     pub fn write_str(&mut self, s: &str) -> Result<(), HirDisplayError> {
 177         self.fmt.write_str(s)?;
 178         Ok(())
 179     }
 180
 181     pub fn write_char(&mut self, c: char) -> Result<(), HirDisplayError> {
 182         self.fmt.write_char(c)?;
 183         Ok(())
 184     }
 185
 186     pub fn should_truncate(&self) -> bool {
 187         match self.max_size {
 188             Some(max_size) => self.curr_size >= max_size,
 189             None => false,
 190         }
 191     }
 192
 193     pub fn omit_verbose_types(&self) -> bool {
 194         self.omit_verbose_types
 195     }
 196 }
 197
 198 #[derive(Clone, Copy)]
 199 pub enum DisplayTarget {
 200     /// Display types for inlays, doc popups, autocompletion, etc...
 201     /// Showing `{unknown}` or not qualifying paths is fine here.
 202     /// There's no reason for this to fail.
 203     Diagnostics,
 204     /// Display types for inserting them in source files.
 205     /// The generated code should compile, so paths need to be qualified.
 206     SourceCode { module_id: ModuleId },
 207     /// Only for test purpose to keep real types
 208     Test,
 209 }
 210
 211 impl DisplayTarget {
 212     fn is_source_code(&self) -> bool {
 213         matches!(self, Self::SourceCode { .. })
 214     }
 215     fn is_test(&self) -> bool {
 216         matches!(self, Self::Test)
 217     }
 218 }
 219
 220 #[derive(Debug)]
 221 pub enum DisplaySourceCodeError {
 222     PathNotFound,
 223     UnknownType,
 224     Closure,
 225     Generator,
 226 }
 227
 228 pub enum HirDisplayError {
 229     /// Errors that can occur when generating source code
 230     DisplaySourceCodeError(DisplaySourceCodeError),
 231     /// `FmtError` is required to be compatible with std::fmt::Display
 232     FmtError,
 233 }
 234 impl From<fmt::Error> for HirDisplayError {
 235     fn from(_: fmt::Error) -> Self {
 236         Self::FmtError
 237     }
 238 }
 239
 240 pub struct HirDisplayWrapper<'a, T> {
 241     db: &'a dyn HirDatabase,
 242     t: &'a T,
 243     max_size: Option<usize>,
 244     omit_verbose_types: bool,
 245     display_target: DisplayTarget,
 246 }
 247
 248 impl<'a, T> fmt::Display for HirDisplayWrapper<'a, T>
 249 where
 250     T: HirDisplay,
 251 {
 252     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 253         match self.t.hir_fmt(&mut HirFormatter {
 254             db: self.db,
 255             fmt: f,
 256             buf: String::with_capacity(20),
 257             curr_size: 0,
 258             max_size: self.max_size,
 259             omit_verbose_types: self.omit_verbose_types,
 260             display_target: self.display_target,
 261         }) {
 262             Ok(()) => Ok(()),
 263             Err(HirDisplayError::FmtError) => Err(fmt::Error),
 264             Err(HirDisplayError::DisplaySourceCodeError(_)) => {
 265                 // This should never happen
 266                 panic!("HirDisplay::hir_fmt failed with DisplaySourceCodeError when calling Display::fmt!")
 267             }
 268         }
 269     }
 270 }
 271
 272 const TYPE_HINT_TRUNCATION: &str = "…";
 273
 274 impl<T: HirDisplay> HirDisplay for &'_ T {
 275     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 276         HirDisplay::hir_fmt(*self, f)
 277     }
 278 }
 279
 280 impl<T: HirDisplay + Internable> HirDisplay for Interned<T> {
 281     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 282         HirDisplay::hir_fmt(self.as_ref(), f)
 283     }
 284 }
 285
 286 impl HirDisplay for ProjectionTy {
 287     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 288         if f.should_truncate() {
 289             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 290         }
 291
 292         let trait_ref = self.trait_ref(f.db);
 293         write!(f, "<")?;
 294         fmt_trait_ref(&trait_ref, f, true)?;
 295         write!(f, ">::{}", f.db.type_alias_data(from_assoc_type_id(self.associated_ty_id)).name)?;
 296         let proj_params_count =
 297             self.substitution.len(Interner) - trait_ref.substitution.len(Interner);
 298         let proj_params = &self.substitution.as_slice(Interner)[..proj_params_count];
 299         if !proj_params.is_empty() {
 300             write!(f, "<")?;
 301             f.write_joined(proj_params, ", ")?;
 302             write!(f, ">")?;
 303         }
 304         Ok(())
 305     }
 306 }
 307
 308 impl HirDisplay for OpaqueTy {
 309     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 310         if f.should_truncate() {
 311             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 312         }
 313
 314         self.substitution.at(Interner, 0).hir_fmt(f)
 315     }
 316 }
 317
 318 impl HirDisplay for GenericArg {
 319     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 320         match self.interned() {
 321             crate::GenericArgData::Ty(ty) => ty.hir_fmt(f),
 322             crate::GenericArgData::Lifetime(lt) => lt.hir_fmt(f),
 323             crate::GenericArgData::Const(c) => c.hir_fmt(f),
 324         }
 325     }
 326 }
 327
 328 impl HirDisplay for Const {
 329     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 330         let data = self.interned();
 331         match data.value {
 332             ConstValue::BoundVar(idx) => idx.hir_fmt(f),
 333             ConstValue::InferenceVar(..) => write!(f, "#c#"),
 334             ConstValue::Placeholder(idx) => {
 335                 let id = from_placeholder_idx(f.db, idx);
 336                 let generics = generics(f.db.upcast(), id.parent);
 337                 let param_data = &generics.params.type_or_consts[id.local_id];
 338                 write!(f, "{}", param_data.name().unwrap())
 339             }
 340             ConstValue::Concrete(c) => write!(f, "{}", c.interned),
 341         }
 342     }
 343 }
 344
 345 impl HirDisplay for BoundVar {
 346     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 347         write!(f, "?{}.{}", self.debruijn.depth(), self.index)
 348     }
 349 }
 350
 351 impl HirDisplay for Ty {
 352     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 353         if f.should_truncate() {
 354             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 355         }
 356
 357         match self.kind(Interner) {
 358             TyKind::Never => write!(f, "!")?,
 359             TyKind::Str => write!(f, "str")?,
 360             TyKind::Scalar(Scalar::Bool) => write!(f, "bool")?,
 361             TyKind::Scalar(Scalar::Char) => write!(f, "char")?,
 362             &TyKind::Scalar(Scalar::Float(t)) => write!(f, "{}", primitive::float_ty_to_string(t))?,
 363             &TyKind::Scalar(Scalar::Int(t)) => write!(f, "{}", primitive::int_ty_to_string(t))?,
 364             &TyKind::Scalar(Scalar::Uint(t)) => write!(f, "{}", primitive::uint_ty_to_string(t))?,
 365             TyKind::Slice(t) => {
 366                 write!(f, "[")?;
 367                 t.hir_fmt(f)?;
 368                 write!(f, "]")?;
 369             }
 370             TyKind::Array(t, c) => {
 371                 write!(f, "[")?;
 372                 t.hir_fmt(f)?;
 373                 write!(f, "; ")?;
 374                 c.hir_fmt(f)?;
 375                 write!(f, "]")?;
 376             }
 377             TyKind::Raw(m, t) | TyKind::Ref(m, _, t) => {
 378                 if matches!(self.kind(Interner), TyKind::Raw(..)) {
 379                     write!(
 380                         f,
 381                         "*{}",
 382                         match m {
 383                             Mutability::Not => "const ",
 384                             Mutability::Mut => "mut ",
 385                         }
 386                     )?;
 387                 } else {
 388                     write!(
 389                         f,
 390                         "&{}",
 391                         match m {
 392                             Mutability::Not => "",
 393                             Mutability::Mut => "mut ",
 394                         }
 395                     )?;
 396                 }
 397
 398                 // FIXME: all this just to decide whether to use parentheses...
 399                 let contains_impl_fn = |bounds: &[QuantifiedWhereClause]| {
 400                     bounds.iter().any(|bound| {
 401                         if let WhereClause::Implemented(trait_ref) = bound.skip_binders() {
 402                             let trait_ = trait_ref.hir_trait_id();
 403                             fn_traits(f.db.upcast(), trait_).any(|it| it == trait_)
 404                         } else {
 405                             false
 406                         }
 407                     })
 408                 };
 409                 let (preds_to_print, has_impl_fn_pred) = match t.kind(Interner) {
 410                     TyKind::Dyn(dyn_ty) if dyn_ty.bounds.skip_binders().interned().len() > 1 => {
 411                         let bounds = dyn_ty.bounds.skip_binders().interned();
 412                         (bounds.len(), contains_impl_fn(bounds))
 413                     }
 414                     TyKind::Alias(AliasTy::Opaque(OpaqueTy {
 415                         opaque_ty_id,
 416                         substitution: parameters,
 417                     }))
 418                     | TyKind::OpaqueType(opaque_ty_id, parameters) => {
 419                         let impl_trait_id =
 420                             f.db.lookup_intern_impl_trait_id((*opaque_ty_id).into());
 421                         if let ImplTraitId::ReturnTypeImplTrait(func, idx) = impl_trait_id {
 422                             let datas =
 423                                 f.db.return_type_impl_traits(func)
 424                                     .expect("impl trait id without data");
 425                             let data = (*datas)
 426                                 .as_ref()
 427                                 .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 428                             let bounds = data.substitute(Interner, parameters);
 429                             let mut len = bounds.skip_binders().len();
 430
 431                             // Don't count Sized but count when it absent
 432                             // (i.e. when explicit ?Sized bound is set).
 433                             let default_sized = SizedByDefault::Sized {
 434                                 anchor: func.lookup(f.db.upcast()).module(f.db.upcast()).krate(),
 435                             };
 436                             let sized_bounds = bounds
 437                                 .skip_binders()
 438                                 .iter()
 439                                 .filter(|b| {
 440                                     matches!(
 441                                         b.skip_binders(),
 442                                         WhereClause::Implemented(trait_ref)
 443                                             if default_sized.is_sized_trait(
 444                                                 trait_ref.hir_trait_id(),
 445                                                 f.db.upcast(),
 446                                             ),
 447                                     )
 448                                 })
 449                                 .count();
 450                             match sized_bounds {
 451                                 0 => len += 1,
 452                                 _ => {
 453                                     len = len.saturating_sub(sized_bounds);
 454                                 }
 455                             }
 456
 457                             (len, contains_impl_fn(bounds.skip_binders()))
 458                         } else {
 459                             (0, false)
 460                         }
 461                     }
 462                     _ => (0, false),
 463                 };
 464
 465                 if has_impl_fn_pred && preds_to_print <= 2 {
 466                     return t.hir_fmt(f);
 467                 }
 468
 469                 if preds_to_print > 1 {
 470                     write!(f, "(")?;
 471                     t.hir_fmt(f)?;
 472                     write!(f, ")")?;
 473                 } else {
 474                     t.hir_fmt(f)?;
 475                 }
 476             }
 477             TyKind::Tuple(_, substs) => {
 478                 if substs.len(Interner) == 1 {
 479                     write!(f, "(")?;
 480                     substs.at(Interner, 0).hir_fmt(f)?;
 481                     write!(f, ",)")?;
 482                 } else {
 483                     write!(f, "(")?;
 484                     f.write_joined(&*substs.as_slice(Interner), ", ")?;
 485                     write!(f, ")")?;
 486                 }
 487             }
 488             TyKind::Function(fn_ptr) => {
 489                 let sig = CallableSig::from_fn_ptr(fn_ptr);
 490                 sig.hir_fmt(f)?;
 491             }
 492             TyKind::FnDef(def, parameters) => {
 493                 let def = from_chalk(f.db, *def);
 494                 let sig = f.db.callable_item_signature(def).substitute(Interner, parameters);
 495                 match def {
 496                     CallableDefId::FunctionId(ff) => {
 497                         write!(f, "fn {}", f.db.function_data(ff).name)?
 498                     }
 499                     CallableDefId::StructId(s) => write!(f, "{}", f.db.struct_data(s).name)?,
 500                     CallableDefId::EnumVariantId(e) => {
 501                         write!(f, "{}", f.db.enum_data(e.parent).variants[e.local_id].name)?
 502                     }
 503                 };
 504                 if parameters.len(Interner) > 0 {
 505                     let generics = generics(f.db.upcast(), def.into());
 506                     let (parent_params, self_param, type_params, const_params, _impl_trait_params) =
 507                         generics.provenance_split();
 508                     let total_len = parent_params + self_param + type_params + const_params;
 509                     // We print all params except implicit impl Trait params. Still a bit weird; should we leave out parent and self?
 510                     if total_len > 0 {
 511                         // `parameters` are in the order of fn's params (including impl traits),
 512                         // parent's params (those from enclosing impl or trait, if any).
 513                         let parameters = parameters.as_slice(Interner);
 514                         let fn_params_len = self_param + type_params + const_params;
 515                         let fn_params = parameters.get(..fn_params_len);
 516                         let parent_params = parameters.get(parameters.len() - parent_params..);
 517                         let params = parent_params.into_iter().chain(fn_params).flatten();
 518                         write!(f, "<")?;
 519                         f.write_joined(params, ", ")?;
 520                         write!(f, ">")?;
 521                     }
 522                 }
 523                 write!(f, "(")?;
 524                 f.write_joined(sig.params(), ", ")?;
 525                 write!(f, ")")?;
 526                 let ret = sig.ret();
 527                 if !ret.is_unit() {
 528                     write!(f, " -> ")?;
 529                     ret.hir_fmt(f)?;
 530                 }
 531             }
 532             TyKind::Adt(AdtId(def_id), parameters) => {
 533                 match f.display_target {
 534                     DisplayTarget::Diagnostics | DisplayTarget::Test => {
 535                         let name = match *def_id {
 536                             hir_def::AdtId::StructId(it) => f.db.struct_data(it).name.clone(),
 537                             hir_def::AdtId::UnionId(it) => f.db.union_data(it).name.clone(),
 538                             hir_def::AdtId::EnumId(it) => f.db.enum_data(it).name.clone(),
 539                         };
 540                         write!(f, "{}", name)?;
 541                     }
 542                     DisplayTarget::SourceCode { module_id } => {
 543                         if let Some(path) = find_path::find_path(
 544                             f.db.upcast(),
 545                             ItemInNs::Types((*def_id).into()),
 546                             module_id,
 547                             false,
 548                         ) {
 549                             write!(f, "{}", path)?;
 550                         } else {
 551                             return Err(HirDisplayError::DisplaySourceCodeError(
 552                                 DisplaySourceCodeError::PathNotFound,
 553                             ));
 554                         }
 555                     }
 556                 }
 557
 558                 if parameters.len(Interner) > 0 {
 559                     let parameters_to_write = if f.display_target.is_source_code()
 560                         || f.omit_verbose_types()
 561                     {
 562                         match self
 563                             .as_generic_def(f.db)
 564                             .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
 565                             .filter(|defaults| !defaults.is_empty())
 566                         {
 567                             None => parameters.as_slice(Interner),
 568                             Some(default_parameters) => {
 569                                 fn should_show(
 570                                     parameter: &GenericArg,
 571                                     default_parameters: &[Binders<GenericArg>],
 572                                     i: usize,
 573                                     parameters: &Substitution,
 574                                 ) -> bool {
 575                                     if parameter.ty(Interner).map(|x| x.kind(Interner))
 576                                         == Some(&TyKind::Error)
 577                                     {
 578                                         return true;
 579                                     }
 580                                     if let Some(ConstValue::Concrete(c)) =
 581                                         parameter.constant(Interner).map(|x| x.data(Interner).value)
 582                                     {
 583                                         if c.interned == ConstScalar::Unknown {
 584                                             return true;
 585                                         }
 586                                     }
 587                                     let default_parameter = match default_parameters.get(i) {
 588                                         Some(x) => x,
 589                                         None => return true,
 590                                     };
 591                                     let actual_default =
 592                                         default_parameter.clone().substitute(Interner, &parameters);
 593                                     parameter != &actual_default
 594                                 }
 595                                 let mut default_from = 0;
 596                                 for (i, parameter) in parameters.iter(Interner).enumerate() {
 597                                     if should_show(parameter, &default_parameters, i, parameters) {
 598                                         default_from = i + 1;
 599                                     }
 600                                 }
 601                                 &parameters.as_slice(Interner)[0..default_from]
 602                             }
 603                         }
 604                     } else {
 605                         parameters.as_slice(Interner)
 606                     };
 607                     if !parameters_to_write.is_empty() {
 608                         write!(f, "<")?;
 609
 610                         if f.display_target.is_source_code() {
 611                             let mut first = true;
 612                             for generic_arg in parameters_to_write {
 613                                 if !first {
 614                                     write!(f, ", ")?;
 615                                 }
 616                                 first = false;
 617
 618                                 if generic_arg.ty(Interner).map(|ty| ty.kind(Interner))
 619                                     == Some(&TyKind::Error)
 620                                 {
 621                                     write!(f, "_")?;
 622                                 } else {
 623                                     generic_arg.hir_fmt(f)?;
 624                                 }
 625                             }
 626                         } else {
 627                             f.write_joined(parameters_to_write, ", ")?;
 628                         }
 629
 630                         write!(f, ">")?;
 631                     }
 632                 }
 633             }
 634             TyKind::AssociatedType(assoc_type_id, parameters) => {
 635                 let type_alias = from_assoc_type_id(*assoc_type_id);
 636                 let trait_ = match type_alias.lookup(f.db.upcast()).container {
 637                     ItemContainerId::TraitId(it) => it,
 638                     _ => panic!("not an associated type"),
 639                 };
 640                 let trait_ = f.db.trait_data(trait_);
 641                 let type_alias_data = f.db.type_alias_data(type_alias);
 642
 643                 // Use placeholder associated types when the target is test (https://rust-lang.github.io/chalk/book/clauses/type_equality.html#placeholder-associated-types)
 644                 if f.display_target.is_test() {
 645                     write!(f, "{}::{}", trait_.name, type_alias_data.name)?;
 646                     // Note that the generic args for the associated type come before those for the
 647                     // trait (including the self type).
 648                     // FIXME: reconsider the generic args order upon formatting?
 649                     if parameters.len(Interner) > 0 {
 650                         write!(f, "<")?;
 651                         f.write_joined(parameters.as_slice(Interner), ", ")?;
 652                         write!(f, ">")?;
 653                     }
 654                 } else {
 655                     let projection_ty = ProjectionTy {
 656                         associated_ty_id: to_assoc_type_id(type_alias),
 657                         substitution: parameters.clone(),
 658                     };
 659
 660                     projection_ty.hir_fmt(f)?;
 661                 }
 662             }
 663             TyKind::Foreign(type_alias) => {
 664                 let type_alias = f.db.type_alias_data(from_foreign_def_id(*type_alias));
 665                 write!(f, "{}", type_alias.name)?;
 666             }
 667             TyKind::OpaqueType(opaque_ty_id, parameters) => {
 668                 let impl_trait_id = f.db.lookup_intern_impl_trait_id((*opaque_ty_id).into());
 669                 match impl_trait_id {
 670                     ImplTraitId::ReturnTypeImplTrait(func, idx) => {
 671                         let datas =
 672                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 673                         let data = (*datas)
 674                             .as_ref()
 675                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 676                         let bounds = data.substitute(Interner, &parameters);
 677                         let krate = func.lookup(f.db.upcast()).module(f.db.upcast()).krate();
 678                         write_bounds_like_dyn_trait_with_prefix(
 679                             "impl",
 680                             bounds.skip_binders(),
 681                             SizedByDefault::Sized { anchor: krate },
 682                             f,
 683                         )?;
 684                         // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
 685                     }
 686                     ImplTraitId::AsyncBlockTypeImplTrait(..) => {
 687                         write!(f, "impl Future<Output = ")?;
 688                         parameters.at(Interner, 0).hir_fmt(f)?;
 689                         write!(f, ">")?;
 690                     }
 691                 }
 692             }
 693             TyKind::Closure(.., substs) => {
 694                 if f.display_target.is_source_code() {
 695                     return Err(HirDisplayError::DisplaySourceCodeError(
 696                         DisplaySourceCodeError::Closure,
 697                     ));
 698                 }
 699                 let sig = substs.at(Interner, 0).assert_ty_ref(Interner).callable_sig(f.db);
 700                 if let Some(sig) = sig {
 701                     if sig.params().is_empty() {
 702                         write!(f, "||")?;
 703                     } else if f.should_truncate() {
 704                         write!(f, "|{}|", TYPE_HINT_TRUNCATION)?;
 705                     } else {
 706                         write!(f, "|")?;
 707                         f.write_joined(sig.params(), ", ")?;
 708                         write!(f, "|")?;
 709                     };
 710
 711                     write!(f, " -> ")?;
 712                     sig.ret().hir_fmt(f)?;
 713                 } else {
 714                     write!(f, "{{closure}}")?;
 715                 }
 716             }
 717             TyKind::Placeholder(idx) => {
 718                 let id = from_placeholder_idx(f.db, *idx);
 719                 let generics = generics(f.db.upcast(), id.parent);
 720                 let param_data = &generics.params.type_or_consts[id.local_id];
 721                 match param_data {
 722                     TypeOrConstParamData::TypeParamData(p) => match p.provenance {
 723                         TypeParamProvenance::TypeParamList | TypeParamProvenance::TraitSelf => {
 724                             write!(f, "{}", p.name.clone().unwrap_or_else(Name::missing))?
 725                         }
 726                         TypeParamProvenance::ArgumentImplTrait => {
 727                             let substs = generics.placeholder_subst(f.db);
 728                             let bounds =
 729                                 f.db.generic_predicates(id.parent)
 730                                     .iter()
 731                                     .map(|pred| pred.clone().substitute(Interner, &substs))
 732                                     .filter(|wc| match &wc.skip_binders() {
 733                                         WhereClause::Implemented(tr) => {
 734                                             &tr.self_type_parameter(Interner) == self
 735                                         }
 736                                         WhereClause::AliasEq(AliasEq {
 737                                             alias: AliasTy::Projection(proj),
 738                                             ty: _,
 739                                         }) => &proj.self_type_parameter(f.db) == self,
 740                                         _ => false,
 741                                     })
 742                                     .collect::<Vec<_>>();
 743                             let krate = id.parent.module(f.db.upcast()).krate();
 744                             write_bounds_like_dyn_trait_with_prefix(
 745                                 "impl",
 746                                 &bounds,
 747                                 SizedByDefault::Sized { anchor: krate },
 748                                 f,
 749                             )?;
 750                         }
 751                     },
 752                     TypeOrConstParamData::ConstParamData(p) => {
 753                         write!(f, "{}", p.name)?;
 754                     }
 755                 }
 756             }
 757             TyKind::BoundVar(idx) => idx.hir_fmt(f)?,
 758             TyKind::Dyn(dyn_ty) => {
 759                 // Reorder bounds to satisfy `write_bounds_like_dyn_trait()`'s expectation.
 760                 // FIXME: `Iterator::partition_in_place()` or `Vec::drain_filter()` may make it
 761                 // more efficient when either of them hits stable.
 762                 let mut bounds: SmallVec<[_; 4]> =
 763                     dyn_ty.bounds.skip_binders().iter(Interner).cloned().collect();
 764                 let (auto_traits, others): (SmallVec<[_; 4]>, _) =
 765                     bounds.drain(1..).partition(|b| b.skip_binders().trait_id().is_some());
 766                 bounds.extend(others);
 767                 bounds.extend(auto_traits);
 768
 769                 write_bounds_like_dyn_trait_with_prefix(
 770                     "dyn",
 771                     &bounds,
 772                     SizedByDefault::NotSized,
 773                     f,
 774                 )?;
 775             }
 776             TyKind::Alias(AliasTy::Projection(p_ty)) => p_ty.hir_fmt(f)?,
 777             TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
 778                 let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into());
 779                 match impl_trait_id {
 780                     ImplTraitId::ReturnTypeImplTrait(func, idx) => {
 781                         let datas =
 782                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 783                         let data = (*datas)
 784                             .as_ref()
 785                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 786                         let bounds = data.substitute(Interner, &opaque_ty.substitution);
 787                         let krate = func.lookup(f.db.upcast()).module(f.db.upcast()).krate();
 788                         write_bounds_like_dyn_trait_with_prefix(
 789                             "impl",
 790                             bounds.skip_binders(),
 791                             SizedByDefault::Sized { anchor: krate },
 792                             f,
 793                         )?;
 794                     }
 795                     ImplTraitId::AsyncBlockTypeImplTrait(..) => {
 796                         write!(f, "{{async block}}")?;
 797                     }
 798                 };
 799             }
 800             TyKind::Error => {
 801                 if f.display_target.is_source_code() {
 802                     return Err(HirDisplayError::DisplaySourceCodeError(
 803                         DisplaySourceCodeError::UnknownType,
 804                     ));
 805                 }
 806                 write!(f, "{{unknown}}")?;
 807             }
 808             TyKind::InferenceVar(..) => write!(f, "_")?,
 809             TyKind::Generator(_, subst) => {
 810                 if f.display_target.is_source_code() {
 811                     return Err(HirDisplayError::DisplaySourceCodeError(
 812                         DisplaySourceCodeError::Generator,
 813                     ));
 814                 }
 815
 816                 let subst = subst.as_slice(Interner);
 817                 let a: Option<SmallVec<[&Ty; 3]>> = subst
 818                     .get(subst.len() - 3..)
 819                     .map(|args| args.iter().map(|arg| arg.ty(Interner)).collect())
 820                     .flatten();
 821
 822                 if let Some([resume_ty, yield_ty, ret_ty]) = a.as_deref() {
 823                     write!(f, "|")?;
 824                     resume_ty.hir_fmt(f)?;
 825                     write!(f, "|")?;
 826
 827                     write!(f, " yields ")?;
 828                     yield_ty.hir_fmt(f)?;
 829
 830                     write!(f, " -> ")?;
 831                     ret_ty.hir_fmt(f)?;
 832                 } else {
 833                     // This *should* be unreachable, but fallback just in case.
 834                     write!(f, "{{generator}}")?;
 835                 }
 836             }
 837             TyKind::GeneratorWitness(..) => write!(f, "{{generator witness}}")?,
 838         }
 839         Ok(())
 840     }
 841 }
 842
 843 impl HirDisplay for CallableSig {
 844     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
 845         write!(f, "fn(")?;
 846         f.write_joined(self.params(), ", ")?;
 847         if self.is_varargs {
 848             if self.params().is_empty() {
 849                 write!(f, "...")?;
 850             } else {
 851                 write!(f, ", ...")?;
 852             }
 853         }
 854         write!(f, ")")?;
 855         let ret = self.ret();
 856         if !ret.is_unit() {
 857             write!(f, " -> ")?;
 858             ret.hir_fmt(f)?;
 859         }
 860         Ok(())
 861     }
 862 }
 863
 864 fn fn_traits(db: &dyn DefDatabase, trait_: TraitId) -> impl Iterator<Item = TraitId> {
 865     let krate = trait_.lookup(db).container.krate();
 866     utils::fn_traits(db, krate)
 867 }
 868
 869 #[derive(Clone, Copy, PartialEq, Eq)]
 870 pub enum SizedByDefault {
 871     NotSized,
 872     Sized { anchor: CrateId },
 873 }
 874
 875 impl SizedByDefault {
 876     fn is_sized_trait(self, trait_: TraitId, db: &dyn DefDatabase) -> bool {
 877         match self {
 878             Self::NotSized => false,
 879             Self::Sized { anchor } => {
 880                 let sized_trait = db
 881                     .lang_item(anchor, SmolStr::new_inline("sized"))
 882                     .and_then(|lang_item| lang_item.as_trait());
 883                 Some(trait_) == sized_trait
 884             }
 885         }
 886     }
 887 }
 888
 889 pub fn write_bounds_like_dyn_trait_with_prefix(
 890     prefix: &str,
 891     predicates: &[QuantifiedWhereClause],
 892     default_sized: SizedByDefault,
 893     f: &mut HirFormatter<'_>,
 894 ) -> Result<(), HirDisplayError> {
 895     write!(f, "{}", prefix)?;
 896     if !predicates.is_empty()
 897         || predicates.is_empty() && matches!(default_sized, SizedByDefault::Sized { .. })
 898     {
 899         write!(f, " ")?;
 900         write_bounds_like_dyn_trait(predicates, default_sized, f)
 901     } else {
 902         Ok(())
 903     }
 904 }
 905
 906 fn write_bounds_like_dyn_trait(
 907     predicates: &[QuantifiedWhereClause],
 908     default_sized: SizedByDefault,
 909     f: &mut HirFormatter<'_>,
 910 ) -> Result<(), HirDisplayError> {
 911     // Note: This code is written to produce nice results (i.e.
 912     // corresponding to surface Rust) for types that can occur in
 913     // actual Rust. It will have weird results if the predicates
 914     // aren't as expected (i.e. self types = $0, projection
 915     // predicates for a certain trait come after the Implemented
 916     // predicate for that trait).
 917     let mut first = true;
 918     let mut angle_open = false;
 919     let mut is_fn_trait = false;
 920     let mut is_sized = false;
 921     for p in predicates.iter() {
 922         match p.skip_binders() {
 923             WhereClause::Implemented(trait_ref) => {
 924                 let trait_ = trait_ref.hir_trait_id();
 925                 if default_sized.is_sized_trait(trait_, f.db.upcast()) {
 926                     is_sized = true;
 927                     if matches!(default_sized, SizedByDefault::Sized { .. }) {
 928                         // Don't print +Sized, but rather +?Sized if absent.
 929                         continue;
 930                     }
 931                 }
 932                 if !is_fn_trait {
 933                     is_fn_trait = fn_traits(f.db.upcast(), trait_).any(|it| it == trait_);
 934                 }
 935                 if !is_fn_trait && angle_open {
 936                     write!(f, ">")?;
 937                     angle_open = false;
 938                 }
 939                 if !first {
 940                     write!(f, " + ")?;
 941                 }
 942                 // We assume that the self type is ^0.0 (i.e. the
 943                 // existential) here, which is the only thing that's
 944                 // possible in actual Rust, and hence don't print it
 945                 write!(f, "{}", f.db.trait_data(trait_).name)?;
 946                 if let [_, params @ ..] = &*trait_ref.substitution.as_slice(Interner) {
 947                     if is_fn_trait {
 948                         if let Some(args) =
 949                             params.first().and_then(|it| it.assert_ty_ref(Interner).as_tuple())
 950                         {
 951                             write!(f, "(")?;
 952                             f.write_joined(args.as_slice(Interner), ", ")?;
 953                             write!(f, ")")?;
 954                         }
 955                     } else if !params.is_empty() {
 956                         write!(f, "<")?;
 957                         f.write_joined(params, ", ")?;
 958                         // there might be assoc type bindings, so we leave the angle brackets open
 959                         angle_open = true;
 960                     }
 961                 }
 962             }
 963             WhereClause::AliasEq(alias_eq) if is_fn_trait => {
 964                 is_fn_trait = false;
 965                 if !alias_eq.ty.is_unit() {
 966                     write!(f, " -> ")?;
 967                     alias_eq.ty.hir_fmt(f)?;
 968                 }
 969             }
 970             WhereClause::AliasEq(AliasEq { ty, alias }) => {
 971                 // in types in actual Rust, these will always come
 972                 // after the corresponding Implemented predicate
 973                 if angle_open {
 974                     write!(f, ", ")?;
 975                 } else {
 976                     write!(f, "<")?;
 977                     angle_open = true;
 978                 }
 979                 if let AliasTy::Projection(proj) = alias {
 980                     let assoc_ty_id = from_assoc_type_id(proj.associated_ty_id);
 981                     let type_alias = f.db.type_alias_data(assoc_ty_id);
 982                     write!(f, "{}", type_alias.name)?;
 983
 984                     let proj_arg_count = generics(f.db.upcast(), assoc_ty_id.into()).len_self();
 985                     if proj_arg_count > 0 {
 986                         write!(f, "<")?;
 987                         f.write_joined(
 988                             &proj.substitution.as_slice(Interner)[..proj_arg_count],
 989                             ", ",
 990                         )?;
 991                         write!(f, ">")?;
 992                     }
 993                     write!(f, " = ")?;
 994                 }
 995                 ty.hir_fmt(f)?;
 996             }
 997
 998             // FIXME implement these
 999             WhereClause::LifetimeOutlives(_) => {}
1000             WhereClause::TypeOutlives(_) => {}
1001         }
1002         first = false;
1003     }
1004     if angle_open {
1005         write!(f, ">")?;
1006     }
1007     if matches!(default_sized, SizedByDefault::Sized { .. }) {
1008         if !is_sized {
1009             write!(f, "{}?Sized", if first { "" } else { " + " })?;
1010         } else if first {
1011             write!(f, "Sized")?;
1012         }
1013     }
1014     Ok(())
1015 }
1016
1017 fn fmt_trait_ref(
1018     tr: &TraitRef,
1019     f: &mut HirFormatter<'_>,
1020     use_as: bool,
1021 ) -> Result<(), HirDisplayError> {
1022     if f.should_truncate() {
1023         return write!(f, "{}", TYPE_HINT_TRUNCATION);
1024     }
1025
1026     tr.self_type_parameter(Interner).hir_fmt(f)?;
1027     if use_as {
1028         write!(f, " as ")?;
1029     } else {
1030         write!(f, ": ")?;
1031     }
1032     write!(f, "{}", f.db.trait_data(tr.hir_trait_id()).name)?;
1033     if tr.substitution.len(Interner) > 1 {
1034         write!(f, "<")?;
1035         f.write_joined(&tr.substitution.as_slice(Interner)[1..], ", ")?;
1036         write!(f, ">")?;
1037     }
1038     Ok(())
1039 }
1040
1041 impl HirDisplay for TraitRef {
1042     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1043         fmt_trait_ref(self, f, false)
1044     }
1045 }
1046
1047 impl HirDisplay for WhereClause {
1048     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1049         if f.should_truncate() {
1050             return write!(f, "{}", TYPE_HINT_TRUNCATION);
1051         }
1052
1053         match self {
1054             WhereClause::Implemented(trait_ref) => trait_ref.hir_fmt(f)?,
1055             WhereClause::AliasEq(AliasEq { alias: AliasTy::Projection(projection_ty), ty }) => {
1056                 write!(f, "<")?;
1057                 fmt_trait_ref(&projection_ty.trait_ref(f.db), f, true)?;
1058                 write!(
1059                     f,
1060                     ">::{} = ",
1061                     f.db.type_alias_data(from_assoc_type_id(projection_ty.associated_ty_id)).name,
1062                 )?;
1063                 ty.hir_fmt(f)?;
1064             }
1065             WhereClause::AliasEq(_) => write!(f, "{{error}}")?,
1066
1067             // FIXME implement these
1068             WhereClause::TypeOutlives(..) => {}
1069             WhereClause::LifetimeOutlives(..) => {}
1070         }
1071         Ok(())
1072     }
1073 }
1074
1075 impl HirDisplay for LifetimeOutlives {
1076     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1077         self.a.hir_fmt(f)?;
1078         write!(f, ": ")?;
1079         self.b.hir_fmt(f)
1080     }
1081 }
1082
1083 impl HirDisplay for Lifetime {
1084     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1085         self.interned().hir_fmt(f)
1086     }
1087 }
1088
1089 impl HirDisplay for LifetimeData {
1090     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1091         match self {
1092             LifetimeData::BoundVar(idx) => idx.hir_fmt(f),
1093             LifetimeData::InferenceVar(_) => write!(f, "_"),
1094             LifetimeData::Placeholder(idx) => {
1095                 let id = lt_from_placeholder_idx(f.db, *idx);
1096                 let generics = generics(f.db.upcast(), id.parent);
1097                 let param_data = &generics.params.lifetimes[id.local_id];
1098                 write!(f, "{}", param_data.name)
1099             }
1100             LifetimeData::Static => write!(f, "'static"),
1101             LifetimeData::Empty(_) => Ok(()),
1102             LifetimeData::Erased => Ok(()),
1103             LifetimeData::Phantom(_, _) => Ok(()),
1104         }
1105     }
1106 }
1107
1108 impl HirDisplay for DomainGoal {
1109     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1110         match self {
1111             DomainGoal::Holds(wc) => {
1112                 write!(f, "Holds(")?;
1113                 wc.hir_fmt(f)?;
1114                 write!(f, ")")?;
1115             }
1116             _ => write!(f, "?")?,
1117         }
1118         Ok(())
1119     }
1120 }
1121
1122 pub fn write_visibility(
1123     module_id: ModuleId,
1124     vis: Visibility,
1125     f: &mut HirFormatter<'_>,
1126 ) -> Result<(), HirDisplayError> {
1127     match vis {
1128         Visibility::Public => write!(f, "pub "),
1129         Visibility::Module(vis_id) => {
1130             let def_map = module_id.def_map(f.db.upcast());
1131             let root_module_id = def_map.module_id(def_map.root());
1132             if vis_id == module_id {
1133                 // pub(self) or omitted
1134                 Ok(())
1135             } else if root_module_id == vis_id {
1136                 write!(f, "pub(crate) ")
1137             } else if module_id.containing_module(f.db.upcast()) == Some(vis_id) {
1138                 write!(f, "pub(super) ")
1139             } else {
1140                 write!(f, "pub(in ...) ")
1141             }
1142         }
1143     }
1144 }
1145
1146 impl HirDisplay for TypeRef {
1147     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1148         match self {
1149             TypeRef::Never => write!(f, "!")?,
1150             TypeRef::Placeholder => write!(f, "_")?,
1151             TypeRef::Tuple(elems) => {
1152                 write!(f, "(")?;
1153                 f.write_joined(elems, ", ")?;
1154                 if elems.len() == 1 {
1155                     write!(f, ",")?;
1156                 }
1157                 write!(f, ")")?;
1158             }
1159             TypeRef::Path(path) => path.hir_fmt(f)?,
1160             TypeRef::RawPtr(inner, mutability) => {
1161                 let mutability = match mutability {
1162                     hir_def::type_ref::Mutability::Shared => "*const ",
1163                     hir_def::type_ref::Mutability::Mut => "*mut ",
1164                 };
1165                 write!(f, "{}", mutability)?;
1166                 inner.hir_fmt(f)?;
1167             }
1168             TypeRef::Reference(inner, lifetime, mutability) => {
1169                 let mutability = match mutability {
1170                     hir_def::type_ref::Mutability::Shared => "",
1171                     hir_def::type_ref::Mutability::Mut => "mut ",
1172                 };
1173                 write!(f, "&")?;
1174                 if let Some(lifetime) = lifetime {
1175                     write!(f, "{} ", lifetime.name)?;
1176                 }
1177                 write!(f, "{}", mutability)?;
1178                 inner.hir_fmt(f)?;
1179             }
1180             TypeRef::Array(inner, len) => {
1181                 write!(f, "[")?;
1182                 inner.hir_fmt(f)?;
1183                 write!(f, "; {}]", len)?;
1184             }
1185             TypeRef::Slice(inner) => {
1186                 write!(f, "[")?;
1187                 inner.hir_fmt(f)?;
1188                 write!(f, "]")?;
1189             }
1190             &TypeRef::Fn(ref parameters, is_varargs, is_unsafe) => {
1191                 // FIXME: Function pointer qualifiers.
1192                 if is_unsafe {
1193                     write!(f, "unsafe ")?;
1194                 }
1195                 write!(f, "fn(")?;
1196                 if let Some(((_, return_type), function_parameters)) = parameters.split_last() {
1197                     for index in 0..function_parameters.len() {
1198                         let (param_name, param_type) = &function_parameters[index];
1199                         if let Some(name) = param_name {
1200                             write!(f, "{}: ", name)?;
1201                         }
1202
1203                         param_type.hir_fmt(f)?;
1204
1205                         if index != function_parameters.len() - 1 {
1206                             write!(f, ", ")?;
1207                         }
1208                     }
1209                     if is_varargs {
1210                         write!(f, "{}...", if parameters.len() == 1 { "" } else { ", " })?;
1211                     }
1212                     write!(f, ")")?;
1213                     match &return_type {
1214                         TypeRef::Tuple(tup) if tup.is_empty() => {}
1215                         _ => {
1216                             write!(f, " -> ")?;
1217                             return_type.hir_fmt(f)?;
1218                         }
1219                     }
1220                 }
1221             }
1222             TypeRef::ImplTrait(bounds) => {
1223                 write!(f, "impl ")?;
1224                 f.write_joined(bounds, " + ")?;
1225             }
1226             TypeRef::DynTrait(bounds) => {
1227                 write!(f, "dyn ")?;
1228                 f.write_joined(bounds, " + ")?;
1229             }
1230             TypeRef::Macro(macro_call) => {
1231                 let macro_call = macro_call.to_node(f.db.upcast());
1232                 let ctx = body::LowerCtx::with_hygiene(f.db.upcast(), &Hygiene::new_unhygienic());
1233                 match macro_call.path() {
1234                     Some(path) => match Path::from_src(path, &ctx) {
1235                         Some(path) => path.hir_fmt(f)?,
1236                         None => write!(f, "{{macro}}")?,
1237                     },
1238                     None => write!(f, "{{macro}}")?,
1239                 }
1240                 write!(f, "!(..)")?;
1241             }
1242             TypeRef::Error => write!(f, "{{error}}")?,
1243         }
1244         Ok(())
1245     }
1246 }
1247
1248 impl HirDisplay for TypeBound {
1249     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1250         match self {
1251             TypeBound::Path(path, modifier) => {
1252                 match modifier {
1253                     TraitBoundModifier::None => (),
1254                     TraitBoundModifier::Maybe => write!(f, "?")?,
1255                 }
1256                 path.hir_fmt(f)
1257             }
1258             TypeBound::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
1259             TypeBound::ForLifetime(lifetimes, path) => {
1260                 write!(f, "for<{}> ", lifetimes.iter().format(", "))?;
1261                 path.hir_fmt(f)
1262             }
1263             TypeBound::Error => write!(f, "{{error}}"),
1264         }
1265     }
1266 }
1267
1268 impl HirDisplay for Path {
1269     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1270         match (self.type_anchor(), self.kind()) {
1271             (Some(anchor), _) => {
1272                 write!(f, "<")?;
1273                 anchor.hir_fmt(f)?;
1274                 write!(f, ">")?;
1275             }
1276             (_, PathKind::Plain) => {}
1277             (_, PathKind::Abs) => {}
1278             (_, PathKind::Crate) => write!(f, "crate")?,
1279             (_, PathKind::Super(0)) => write!(f, "self")?,
1280             (_, PathKind::Super(n)) => {
1281                 for i in 0..*n {
1282                     if i > 0 {
1283                         write!(f, "::")?;
1284                     }
1285                     write!(f, "super")?;
1286                 }
1287             }
1288             (_, PathKind::DollarCrate(id)) => {
1289                 // Resolve `$crate` to the crate's display name.
1290                 // FIXME: should use the dependency name instead if available, but that depends on
1291                 // the crate invoking `HirDisplay`
1292                 let crate_graph = f.db.crate_graph();
1293                 let name = crate_graph[*id]
1294                     .display_name
1295                     .as_ref()
1296                     .map(|name| name.canonical_name())
1297                     .unwrap_or("$crate");
1298                 write!(f, "{name}")?
1299             }
1300         }
1301
1302         for (seg_idx, segment) in self.segments().iter().enumerate() {
1303             if !matches!(self.kind(), PathKind::Plain) || seg_idx > 0 {
1304                 write!(f, "::")?;
1305             }
1306             write!(f, "{}", segment.name)?;
1307             if let Some(generic_args) = segment.args_and_bindings {
1308                 // We should be in type context, so format as `Foo<Bar>` instead of `Foo::<Bar>`.
1309                 // Do we actually format expressions?
1310                 if generic_args.desugared_from_fn {
1311                     // First argument will be a tuple, which already includes the parentheses.
1312                     // If the tuple only contains 1 item, write it manually to avoid the trailing `,`.
1313                     if let hir_def::path::GenericArg::Type(TypeRef::Tuple(v)) =
1314                         &generic_args.args[0]
1315                     {
1316                         if v.len() == 1 {
1317                             write!(f, "(")?;
1318                             v[0].hir_fmt(f)?;
1319                             write!(f, ")")?;
1320                         } else {
1321                             generic_args.args[0].hir_fmt(f)?;
1322                         }
1323                     }
1324                     if let Some(ret) = &generic_args.bindings[0].type_ref {
1325                         if !matches!(ret, TypeRef::Tuple(v) if v.is_empty()) {
1326                             write!(f, " -> ")?;
1327                             ret.hir_fmt(f)?;
1328                         }
1329                     }
1330                     return Ok(());
1331                 }
1332
1333                 write!(f, "<")?;
1334                 let mut first = true;
1335                 for arg in &generic_args.args {
1336                     if first {
1337                         first = false;
1338                         if generic_args.has_self_type {
1339                             // FIXME: Convert to `<Ty as Trait>` form.
1340                             write!(f, "Self = ")?;
1341                         }
1342                     } else {
1343                         write!(f, ", ")?;
1344                     }
1345                     arg.hir_fmt(f)?;
1346                 }
1347                 for binding in &generic_args.bindings {
1348                     if first {
1349                         first = false;
1350                     } else {
1351                         write!(f, ", ")?;
1352                     }
1353                     write!(f, "{}", binding.name)?;
1354                     match &binding.type_ref {
1355                         Some(ty) => {
1356                             write!(f, " = ")?;
1357                             ty.hir_fmt(f)?
1358                         }
1359                         None => {
1360                             write!(f, ": ")?;
1361                             f.write_joined(&binding.bounds, " + ")?;
1362                         }
1363                     }
1364                 }
1365                 write!(f, ">")?;
1366             }
1367         }
1368         Ok(())
1369     }
1370 }
1371
1372 impl HirDisplay for hir_def::path::GenericArg {
1373     fn hir_fmt(&self, f: &mut HirFormatter<'_>) -> Result<(), HirDisplayError> {
1374         match self {
1375             hir_def::path::GenericArg::Type(ty) => ty.hir_fmt(f),
1376             hir_def::path::GenericArg::Const(c) => write!(f, "{}", c),
1377             hir_def::path::GenericArg::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
1378         }
1379     }
1380 }