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