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