crates/hir_ty/src/display.rs

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