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