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