crates/hir_ty/src/display.rs

   1 //! FIXME: write short doc here
   2
   3 use std::{borrow::Cow, fmt};
   4
   5 use arrayvec::ArrayVec;
   6 use chalk_ir::Mutability;
   7 use hir_def::{
   8     db::DefDatabase, find_path, generics::TypeParamProvenance, item_scope::ItemInNs,
   9     AssocContainerId, HasModule, Lookup, ModuleId, TraitId,
  10 };
  11 use hir_expand::name::Name;
  12
  13 use crate::{
  14     db::HirDatabase, primitive, utils::generics, AdtId, AliasTy, CallableDefId, CallableSig,
  15     GenericPredicate, Lifetime, Obligation, OpaqueTy, OpaqueTyId, ProjectionTy, Scalar, Substs,
  16     TraitRef, Ty,
  17 };
  18
  19 pub struct HirFormatter<'a> {
  20     pub db: &'a dyn HirDatabase,
  21     fmt: &'a mut dyn fmt::Write,
  22     buf: String,
  23     curr_size: usize,
  24     pub(crate) max_size: Option<usize>,
  25     omit_verbose_types: bool,
  26     display_target: DisplayTarget,
  27 }
  28
  29 pub trait HirDisplay {
  30     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError>;
  31
  32     /// Returns a `Display`able type that is human-readable.
  33     fn into_displayable<'a>(
  34         &'a self,
  35         db: &'a dyn HirDatabase,
  36         max_size: Option<usize>,
  37         omit_verbose_types: bool,
  38         display_target: DisplayTarget,
  39     ) -> HirDisplayWrapper<'a, Self>
  40     where
  41         Self: Sized,
  42     {
  43         HirDisplayWrapper { db, t: self, max_size, omit_verbose_types, display_target }
  44     }
  45
  46     /// Returns a `Display`able type that is human-readable.
  47     /// Use this for showing types to the user (e.g. diagnostics)
  48     fn display<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
  49     where
  50         Self: Sized,
  51     {
  52         HirDisplayWrapper {
  53             db,
  54             t: self,
  55             max_size: None,
  56             omit_verbose_types: false,
  57             display_target: DisplayTarget::Diagnostics,
  58         }
  59     }
  60
  61     /// Returns a `Display`able type that is human-readable and tries to be succinct.
  62     /// Use this for showing types to the user where space is constrained (e.g. doc popups)
  63     fn display_truncated<'a>(
  64         &'a self,
  65         db: &'a dyn HirDatabase,
  66         max_size: Option<usize>,
  67     ) -> HirDisplayWrapper<'a, Self>
  68     where
  69         Self: Sized,
  70     {
  71         HirDisplayWrapper {
  72             db,
  73             t: self,
  74             max_size,
  75             omit_verbose_types: true,
  76             display_target: DisplayTarget::Diagnostics,
  77         }
  78     }
  79
  80     /// Returns a String representation of `self` that can be inserted into the given module.
  81     /// Use this when generating code (e.g. assists)
  82     fn display_source_code<'a>(
  83         &'a self,
  84         db: &'a dyn HirDatabase,
  85         module_id: ModuleId,
  86     ) -> Result<String, DisplaySourceCodeError> {
  87         let mut result = String::new();
  88         match self.hir_fmt(&mut HirFormatter {
  89             db,
  90             fmt: &mut result,
  91             buf: String::with_capacity(20),
  92             curr_size: 0,
  93             max_size: None,
  94             omit_verbose_types: false,
  95             display_target: DisplayTarget::SourceCode { module_id },
  96         }) {
  97             Ok(()) => {}
  98             Err(HirDisplayError::FmtError) => panic!("Writing to String can't fail!"),
  99             Err(HirDisplayError::DisplaySourceCodeError(e)) => return Err(e),
 100         };
 101         Ok(result)
 102     }
 103
 104     /// Returns a String representation of `self` for test purposes
 105     fn display_test<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
 106     where
 107         Self: Sized,
 108     {
 109         HirDisplayWrapper {
 110             db,
 111             t: self,
 112             max_size: None,
 113             omit_verbose_types: false,
 114             display_target: DisplayTarget::Test,
 115         }
 116     }
 117 }
 118
 119 impl<'a> HirFormatter<'a> {
 120     pub fn write_joined<T: HirDisplay>(
 121         &mut self,
 122         iter: impl IntoIterator<Item = T>,
 123         sep: &str,
 124     ) -> Result<(), HirDisplayError> {
 125         let mut first = true;
 126         for e in iter {
 127             if !first {
 128                 write!(self, "{}", sep)?;
 129             }
 130             first = false;
 131             e.hir_fmt(self)?;
 132         }
 133         Ok(())
 134     }
 135
 136     /// This allows using the `write!` macro directly with a `HirFormatter`.
 137     pub fn write_fmt(&mut self, args: fmt::Arguments) -> Result<(), HirDisplayError> {
 138         // We write to a buffer first to track output size
 139         self.buf.clear();
 140         fmt::write(&mut self.buf, args)?;
 141         self.curr_size += self.buf.len();
 142
 143         // Then we write to the internal formatter from the buffer
 144         self.fmt.write_str(&self.buf).map_err(HirDisplayError::from)
 145     }
 146
 147     pub fn should_truncate(&self) -> bool {
 148         if let Some(max_size) = self.max_size {
 149             self.curr_size >= max_size
 150         } else {
 151             false
 152         }
 153     }
 154
 155     pub fn omit_verbose_types(&self) -> bool {
 156         self.omit_verbose_types
 157     }
 158 }
 159
 160 #[derive(Clone, Copy)]
 161 pub enum DisplayTarget {
 162     /// Display types for inlays, doc popups, autocompletion, etc...
 163     /// Showing `{unknown}` or not qualifying paths is fine here.
 164     /// There's no reason for this to fail.
 165     Diagnostics,
 166     /// Display types for inserting them in source files.
 167     /// The generated code should compile, so paths need to be qualified.
 168     SourceCode { module_id: ModuleId },
 169     /// Only for test purpose to keep real types
 170     Test,
 171 }
 172
 173 impl DisplayTarget {
 174     fn is_source_code(&self) -> bool {
 175         matches!(self, Self::SourceCode { .. })
 176     }
 177     fn is_test(&self) -> bool {
 178         matches!(self, Self::Test)
 179     }
 180 }
 181
 182 #[derive(Debug)]
 183 pub enum DisplaySourceCodeError {
 184     PathNotFound,
 185     UnknownType,
 186 }
 187
 188 pub enum HirDisplayError {
 189     /// Errors that can occur when generating source code
 190     DisplaySourceCodeError(DisplaySourceCodeError),
 191     /// `FmtError` is required to be compatible with std::fmt::Display
 192     FmtError,
 193 }
 194 impl From<fmt::Error> for HirDisplayError {
 195     fn from(_: fmt::Error) -> Self {
 196         Self::FmtError
 197     }
 198 }
 199
 200 pub struct HirDisplayWrapper<'a, T> {
 201     db: &'a dyn HirDatabase,
 202     t: &'a T,
 203     max_size: Option<usize>,
 204     omit_verbose_types: bool,
 205     display_target: DisplayTarget,
 206 }
 207
 208 impl<'a, T> fmt::Display for HirDisplayWrapper<'a, T>
 209 where
 210     T: HirDisplay,
 211 {
 212     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 213         match self.t.hir_fmt(&mut HirFormatter {
 214             db: self.db,
 215             fmt: f,
 216             buf: String::with_capacity(20),
 217             curr_size: 0,
 218             max_size: self.max_size,
 219             omit_verbose_types: self.omit_verbose_types,
 220             display_target: self.display_target,
 221         }) {
 222             Ok(()) => Ok(()),
 223             Err(HirDisplayError::FmtError) => Err(fmt::Error),
 224             Err(HirDisplayError::DisplaySourceCodeError(_)) => {
 225                 // This should never happen
 226                 panic!("HirDisplay failed when calling Display::fmt!")
 227             }
 228         }
 229     }
 230 }
 231
 232 const TYPE_HINT_TRUNCATION: &str = "…";
 233
 234 impl HirDisplay for &Ty {
 235     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 236         HirDisplay::hir_fmt(*self, f)
 237     }
 238 }
 239
 240 impl HirDisplay for ProjectionTy {
 241     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 242         if f.should_truncate() {
 243             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 244         }
 245
 246         let trait_ = f.db.trait_data(self.trait_(f.db));
 247         let first_parameter = self.parameters[0].into_displayable(
 248             f.db,
 249             f.max_size,
 250             f.omit_verbose_types,
 251             f.display_target,
 252         );
 253         write!(f, "<{} as {}", first_parameter, trait_.name)?;
 254         if self.parameters.len() > 1 {
 255             write!(f, "<")?;
 256             f.write_joined(&self.parameters[1..], ", ")?;
 257             write!(f, ">")?;
 258         }
 259         write!(f, ">::{}", f.db.type_alias_data(self.associated_ty).name)?;
 260         Ok(())
 261     }
 262 }
 263
 264 impl HirDisplay for Ty {
 265     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 266         if f.should_truncate() {
 267             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 268         }
 269
 270         match self {
 271             Ty::Never => write!(f, "!")?,
 272             Ty::Str => write!(f, "str")?,
 273             Ty::Scalar(Scalar::Bool) => write!(f, "bool")?,
 274             Ty::Scalar(Scalar::Char) => write!(f, "char")?,
 275             &Ty::Scalar(Scalar::Float(t)) => write!(f, "{}", primitive::float_ty_to_string(t))?,
 276             &Ty::Scalar(Scalar::Int(t)) => write!(f, "{}", primitive::int_ty_to_string(t))?,
 277             &Ty::Scalar(Scalar::Uint(t)) => write!(f, "{}", primitive::uint_ty_to_string(t))?,
 278             Ty::Slice(parameters) => {
 279                 let t = parameters.as_single();
 280                 write!(f, "[")?;
 281                 t.hir_fmt(f)?;
 282                 write!(f, "]")?;
 283             }
 284             Ty::Array(parameters) => {
 285                 let t = parameters.as_single();
 286                 write!(f, "[")?;
 287                 t.hir_fmt(f)?;
 288                 write!(f, "; _]")?;
 289             }
 290             Ty::Raw(m, parameters) | Ty::Ref(m, parameters) => {
 291                 let t = parameters.as_single();
 292                 let ty_display =
 293                     t.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
 294
 295                 if matches!(self, Ty::Raw(..)) {
 296                     write!(
 297                         f,
 298                         "*{}",
 299                         match m {
 300                             Mutability::Not => "const ",
 301                             Mutability::Mut => "mut ",
 302                         }
 303                     )?;
 304                 } else {
 305                     write!(
 306                         f,
 307                         "&{}",
 308                         match m {
 309                             Mutability::Not => "",
 310                             Mutability::Mut => "mut ",
 311                         }
 312                     )?;
 313                 }
 314
 315                 let datas;
 316                 let predicates = match t {
 317                     Ty::Dyn(predicates) if predicates.len() > 1 => {
 318                         Cow::Borrowed(predicates.as_ref())
 319                     }
 320                     &Ty::Alias(AliasTy::Opaque(OpaqueTy {
 321                         opaque_ty_id: OpaqueTyId::ReturnTypeImplTrait(func, idx),
 322                         ref parameters,
 323                     })) => {
 324                         datas =
 325                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 326                         let data = (*datas)
 327                             .as_ref()
 328                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 329                         let bounds = data.subst(parameters);
 330                         Cow::Owned(bounds.value)
 331                     }
 332                     _ => Cow::Borrowed(&[][..]),
 333                 };
 334
 335                 if let [GenericPredicate::Implemented(trait_ref), _] = predicates.as_ref() {
 336                     let trait_ = trait_ref.trait_;
 337                     if fn_traits(f.db.upcast(), trait_).any(|it| it == trait_) {
 338                         return write!(f, "{}", ty_display);
 339                     }
 340                 }
 341
 342                 if predicates.len() > 1 {
 343                     write!(f, "(")?;
 344                     write!(f, "{}", ty_display)?;
 345                     write!(f, ")")?;
 346                 } else {
 347                     write!(f, "{}", ty_display)?;
 348                 }
 349             }
 350             Ty::Tuple(_, substs) => {
 351                 if substs.len() == 1 {
 352                     write!(f, "(")?;
 353                     substs[0].hir_fmt(f)?;
 354                     write!(f, ",)")?;
 355                 } else {
 356                     write!(f, "(")?;
 357                     f.write_joined(&*substs.0, ", ")?;
 358                     write!(f, ")")?;
 359                 }
 360             }
 361             Ty::Function(fn_ptr) => {
 362                 let sig = CallableSig::from_fn_ptr(fn_ptr);
 363                 sig.hir_fmt(f)?;
 364             }
 365             Ty::FnDef(def, parameters) => {
 366                 let def = *def;
 367                 let sig = f.db.callable_item_signature(def).subst(parameters);
 368                 match def {
 369                     CallableDefId::FunctionId(ff) => {
 370                         write!(f, "fn {}", f.db.function_data(ff).name)?
 371                     }
 372                     CallableDefId::StructId(s) => write!(f, "{}", f.db.struct_data(s).name)?,
 373                     CallableDefId::EnumVariantId(e) => {
 374                         write!(f, "{}", f.db.enum_data(e.parent).variants[e.local_id].name)?
 375                     }
 376                 };
 377                 if parameters.len() > 0 {
 378                     let generics = generics(f.db.upcast(), def.into());
 379                     let (parent_params, self_param, type_params, _impl_trait_params) =
 380                         generics.provenance_split();
 381                     let total_len = parent_params + self_param + type_params;
 382                     // We print all params except implicit impl Trait params. Still a bit weird; should we leave out parent and self?
 383                     if total_len > 0 {
 384                         write!(f, "<")?;
 385                         f.write_joined(&parameters.0[..total_len], ", ")?;
 386                         write!(f, ">")?;
 387                     }
 388                 }
 389                 write!(f, "(")?;
 390                 f.write_joined(sig.params(), ", ")?;
 391                 write!(f, ")")?;
 392                 let ret = sig.ret();
 393                 if *ret != Ty::unit() {
 394                     let ret_display = ret.into_displayable(
 395                         f.db,
 396                         f.max_size,
 397                         f.omit_verbose_types,
 398                         f.display_target,
 399                     );
 400
 401                     write!(f, " -> {}", ret_display)?;
 402                 }
 403             }
 404             Ty::Adt(AdtId(def_id), parameters) => {
 405                 match f.display_target {
 406                     DisplayTarget::Diagnostics | DisplayTarget::Test => {
 407                         let name = match *def_id {
 408                             hir_def::AdtId::StructId(it) => f.db.struct_data(it).name.clone(),
 409                             hir_def::AdtId::UnionId(it) => f.db.union_data(it).name.clone(),
 410                             hir_def::AdtId::EnumId(it) => f.db.enum_data(it).name.clone(),
 411                         };
 412                         write!(f, "{}", name)?;
 413                     }
 414                     DisplayTarget::SourceCode { module_id } => {
 415                         if let Some(path) = find_path::find_path(
 416                             f.db.upcast(),
 417                             ItemInNs::Types((*def_id).into()),
 418                             module_id,
 419                         ) {
 420                             write!(f, "{}", path)?;
 421                         } else {
 422                             return Err(HirDisplayError::DisplaySourceCodeError(
 423                                 DisplaySourceCodeError::PathNotFound,
 424                             ));
 425                         }
 426                     }
 427                 }
 428
 429                 if parameters.len() > 0 {
 430                     let parameters_to_write =
 431                         if f.display_target.is_source_code() || f.omit_verbose_types() {
 432                             match self
 433                                 .as_generic_def()
 434                                 .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
 435                                 .filter(|defaults| !defaults.is_empty())
 436                             {
 437                                 None => parameters.0.as_ref(),
 438                                 Some(default_parameters) => {
 439                                     let mut default_from = 0;
 440                                     for (i, parameter) in parameters.iter().enumerate() {
 441                                         match (parameter, default_parameters.get(i)) {
 442                                             (&Ty::Unknown, _) | (_, None) => {
 443                                                 default_from = i + 1;
 444                                             }
 445                                             (_, Some(default_parameter)) => {
 446                                                 let actual_default = default_parameter
 447                                                     .clone()
 448                                                     .subst(&parameters.prefix(i));
 449                                                 if parameter != &actual_default {
 450                                                     default_from = i + 1;
 451                                                 }
 452                                             }
 453                                         }
 454                                     }
 455                                     &parameters.0[0..default_from]
 456                                 }
 457                             }
 458                         } else {
 459                             parameters.0.as_ref()
 460                         };
 461                     if !parameters_to_write.is_empty() {
 462                         write!(f, "<")?;
 463                         f.write_joined(parameters_to_write, ", ")?;
 464                         write!(f, ">")?;
 465                     }
 466                 }
 467             }
 468             Ty::AssociatedType(type_alias, parameters) => {
 469                 let trait_ = match type_alias.lookup(f.db.upcast()).container {
 470                     AssocContainerId::TraitId(it) => it,
 471                     _ => panic!("not an associated type"),
 472                 };
 473                 let trait_ = f.db.trait_data(trait_);
 474                 let type_alias_data = f.db.type_alias_data(*type_alias);
 475
 476                 // Use placeholder associated types when the target is test (https://rust-lang.github.io/chalk/book/clauses/type_equality.html#placeholder-associated-types)
 477                 if f.display_target.is_test() {
 478                     write!(f, "{}::{}", trait_.name, type_alias_data.name)?;
 479                     if parameters.len() > 0 {
 480                         write!(f, "<")?;
 481                         f.write_joined(&*parameters.0, ", ")?;
 482                         write!(f, ">")?;
 483                     }
 484                 } else {
 485                     let projection_ty =
 486                         ProjectionTy { associated_ty: *type_alias, parameters: parameters.clone() };
 487
 488                     projection_ty.hir_fmt(f)?;
 489                 }
 490             }
 491             Ty::ForeignType(type_alias) => {
 492                 let type_alias = f.db.type_alias_data(*type_alias);
 493                 write!(f, "{}", type_alias.name)?;
 494             }
 495             Ty::OpaqueType(opaque_ty_id, parameters) => {
 496                 match opaque_ty_id {
 497                     &OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
 498                         let datas =
 499                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 500                         let data = (*datas)
 501                             .as_ref()
 502                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 503                         let bounds = data.subst(&parameters);
 504                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
 505                         // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
 506                     }
 507                     OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
 508                         write!(f, "impl Future<Output = ")?;
 509                         parameters[0].hir_fmt(f)?;
 510                         write!(f, ">")?;
 511                     }
 512                 }
 513             }
 514             Ty::Closure(.., substs) => {
 515                 let sig = substs[0].callable_sig(f.db);
 516                 if let Some(sig) = sig {
 517                     if sig.params().is_empty() {
 518                         write!(f, "||")?;
 519                     } else if f.omit_verbose_types() {
 520                         write!(f, "|{}|", TYPE_HINT_TRUNCATION)?;
 521                     } else {
 522                         write!(f, "|")?;
 523                         f.write_joined(sig.params(), ", ")?;
 524                         write!(f, "|")?;
 525                     };
 526
 527                     let ret_display = sig.ret().into_displayable(
 528                         f.db,
 529                         f.max_size,
 530                         f.omit_verbose_types,
 531                         f.display_target,
 532                     );
 533                     write!(f, " -> {}", ret_display)?;
 534                 } else {
 535                     write!(f, "{{closure}}")?;
 536                 }
 537             }
 538             Ty::Placeholder(id) => {
 539                 let generics = generics(f.db.upcast(), id.parent);
 540                 let param_data = &generics.params.types[id.local_id];
 541                 match param_data.provenance {
 542                     TypeParamProvenance::TypeParamList | TypeParamProvenance::TraitSelf => {
 543                         write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
 544                     }
 545                     TypeParamProvenance::ArgumentImplTrait => {
 546                         let bounds = f.db.generic_predicates_for_param(*id);
 547                         let substs = Substs::type_params_for_generics(&generics);
 548                         write_bounds_like_dyn_trait_with_prefix(
 549                             "impl",
 550                             &bounds.iter().map(|b| b.clone().subst(&substs)).collect::<Vec<_>>(),
 551                             f,
 552                         )?;
 553                     }
 554                 }
 555             }
 556             Ty::BoundVar(idx) => write!(f, "?{}.{}", idx.debruijn.depth(), idx.index)?,
 557             Ty::Dyn(predicates) => {
 558                 write_bounds_like_dyn_trait_with_prefix("dyn", predicates, f)?;
 559             }
 560             Ty::Alias(AliasTy::Projection(p_ty)) => p_ty.hir_fmt(f)?,
 561             Ty::Alias(AliasTy::Opaque(opaque_ty)) => {
 562                 match opaque_ty.opaque_ty_id {
 563                     OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
 564                         let datas =
 565                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
 566                         let data = (*datas)
 567                             .as_ref()
 568                             .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
 569                         let bounds = data.subst(&opaque_ty.parameters);
 570                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
 571                     }
 572                     OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
 573                         write!(f, "{{async block}}")?;
 574                     }
 575                 };
 576             }
 577             Ty::Unknown => {
 578                 if f.display_target.is_source_code() {
 579                     return Err(HirDisplayError::DisplaySourceCodeError(
 580                         DisplaySourceCodeError::UnknownType,
 581                     ));
 582                 }
 583                 write!(f, "{{unknown}}")?;
 584             }
 585             Ty::InferenceVar(..) => write!(f, "_")?,
 586         }
 587         Ok(())
 588     }
 589 }
 590
 591 impl HirDisplay for CallableSig {
 592     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 593         write!(f, "fn(")?;
 594         f.write_joined(self.params(), ", ")?;
 595         if self.is_varargs {
 596             if self.params().is_empty() {
 597                 write!(f, "...")?;
 598             } else {
 599                 write!(f, ", ...")?;
 600             }
 601         }
 602         write!(f, ")")?;
 603         let ret = self.ret();
 604         if *ret != Ty::unit() {
 605             let ret_display =
 606                 ret.into_displayable(f.db, f.max_size, f.omit_verbose_types, f.display_target);
 607             write!(f, " -> {}", ret_display)?;
 608         }
 609         Ok(())
 610     }
 611 }
 612
 613 fn fn_traits(db: &dyn DefDatabase, trait_: TraitId) -> impl Iterator<Item = TraitId> {
 614     let krate = trait_.lookup(db).container.module(db).krate();
 615     let fn_traits = [
 616         db.lang_item(krate, "fn".into()),
 617         db.lang_item(krate, "fn_mut".into()),
 618         db.lang_item(krate, "fn_once".into()),
 619     ];
 620     // FIXME: Replace ArrayVec when into_iter is a thing on arrays
 621     ArrayVec::from(fn_traits).into_iter().flatten().flat_map(|it| it.as_trait())
 622 }
 623
 624 pub fn write_bounds_like_dyn_trait_with_prefix(
 625     prefix: &str,
 626     predicates: &[GenericPredicate],
 627     f: &mut HirFormatter,
 628 ) -> Result<(), HirDisplayError> {
 629     write!(f, "{}", prefix)?;
 630     if !predicates.is_empty() {
 631         write!(f, " ")?;
 632         write_bounds_like_dyn_trait(predicates, f)
 633     } else {
 634         Ok(())
 635     }
 636 }
 637
 638 fn write_bounds_like_dyn_trait(
 639     predicates: &[GenericPredicate],
 640     f: &mut HirFormatter,
 641 ) -> Result<(), HirDisplayError> {
 642     // Note: This code is written to produce nice results (i.e.
 643     // corresponding to surface Rust) for types that can occur in
 644     // actual Rust. It will have weird results if the predicates
 645     // aren't as expected (i.e. self types = $0, projection
 646     // predicates for a certain trait come after the Implemented
 647     // predicate for that trait).
 648     let mut first = true;
 649     let mut angle_open = false;
 650     let mut is_fn_trait = false;
 651     for p in predicates.iter() {
 652         match p {
 653             GenericPredicate::Implemented(trait_ref) => {
 654                 let trait_ = trait_ref.trait_;
 655                 if !is_fn_trait {
 656                     is_fn_trait = fn_traits(f.db.upcast(), trait_).any(|it| it == trait_);
 657                 }
 658                 if !is_fn_trait && angle_open {
 659                     write!(f, ">")?;
 660                     angle_open = false;
 661                 }
 662                 if !first {
 663                     write!(f, " + ")?;
 664                 }
 665                 // We assume that the self type is $0 (i.e. the
 666                 // existential) here, which is the only thing that's
 667                 // possible in actual Rust, and hence don't print it
 668                 write!(f, "{}", f.db.trait_data(trait_).name)?;
 669                 if let [_, params @ ..] = &*trait_ref.substs.0 {
 670                     if is_fn_trait {
 671                         if let Some(args) = params.first().and_then(|it| it.as_tuple()) {
 672                             write!(f, "(")?;
 673                             f.write_joined(&*args.0, ", ")?;
 674                             write!(f, ")")?;
 675                         }
 676                     } else if !params.is_empty() {
 677                         write!(f, "<")?;
 678                         f.write_joined(params, ", ")?;
 679                         // there might be assoc type bindings, so we leave the angle brackets open
 680                         angle_open = true;
 681                     }
 682                 }
 683             }
 684             GenericPredicate::Projection(projection_pred) if is_fn_trait => {
 685                 is_fn_trait = false;
 686                 write!(f, " -> ")?;
 687                 projection_pred.ty.hir_fmt(f)?;
 688             }
 689             GenericPredicate::Projection(projection_pred) => {
 690                 // in types in actual Rust, these will always come
 691                 // after the corresponding Implemented predicate
 692                 if angle_open {
 693                     write!(f, ", ")?;
 694                 } else {
 695                     write!(f, "<")?;
 696                     angle_open = true;
 697                 }
 698                 let type_alias = f.db.type_alias_data(projection_pred.projection_ty.associated_ty);
 699                 write!(f, "{} = ", type_alias.name)?;
 700                 projection_pred.ty.hir_fmt(f)?;
 701             }
 702             GenericPredicate::Error => {
 703                 if angle_open {
 704                     // impl Trait<X, {error}>
 705                     write!(f, ", ")?;
 706                 } else if !first {
 707                     // impl Trait + {error}
 708                     write!(f, " + ")?;
 709                 }
 710                 p.hir_fmt(f)?;
 711             }
 712         }
 713         first = false;
 714     }
 715     if angle_open {
 716         write!(f, ">")?;
 717     }
 718     Ok(())
 719 }
 720
 721 impl TraitRef {
 722     fn hir_fmt_ext(&self, f: &mut HirFormatter, use_as: bool) -> Result<(), HirDisplayError> {
 723         if f.should_truncate() {
 724             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 725         }
 726
 727         self.substs[0].hir_fmt(f)?;
 728         if use_as {
 729             write!(f, " as ")?;
 730         } else {
 731             write!(f, ": ")?;
 732         }
 733         write!(f, "{}", f.db.trait_data(self.trait_).name)?;
 734         if self.substs.len() > 1 {
 735             write!(f, "<")?;
 736             f.write_joined(&self.substs[1..], ", ")?;
 737             write!(f, ">")?;
 738         }
 739         Ok(())
 740     }
 741 }
 742
 743 impl HirDisplay for TraitRef {
 744     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 745         self.hir_fmt_ext(f, false)
 746     }
 747 }
 748
 749 impl HirDisplay for &GenericPredicate {
 750     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 751         HirDisplay::hir_fmt(*self, f)
 752     }
 753 }
 754
 755 impl HirDisplay for GenericPredicate {
 756     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 757         if f.should_truncate() {
 758             return write!(f, "{}", TYPE_HINT_TRUNCATION);
 759         }
 760
 761         match self {
 762             GenericPredicate::Implemented(trait_ref) => trait_ref.hir_fmt(f)?,
 763             GenericPredicate::Projection(projection_pred) => {
 764                 write!(f, "<")?;
 765                 projection_pred.projection_ty.trait_ref(f.db).hir_fmt_ext(f, true)?;
 766                 write!(
 767                     f,
 768                     ">::{} = ",
 769                     f.db.type_alias_data(projection_pred.projection_ty.associated_ty).name,
 770                 )?;
 771                 projection_pred.ty.hir_fmt(f)?;
 772             }
 773             GenericPredicate::Error => write!(f, "{{error}}")?,
 774         }
 775         Ok(())
 776     }
 777 }
 778
 779 impl HirDisplay for Lifetime {
 780     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 781         match self {
 782             Lifetime::Parameter(id) => {
 783                 let generics = generics(f.db.upcast(), id.parent);
 784                 let param_data = &generics.params.lifetimes[id.local_id];
 785                 write!(f, "{}", &param_data.name)
 786             }
 787             Lifetime::Static => write!(f, "'static"),
 788         }
 789     }
 790 }
 791
 792 impl HirDisplay for Obligation {
 793     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
 794         match self {
 795             Obligation::Trait(tr) => {
 796                 write!(f, "Implements(")?;
 797                 tr.hir_fmt(f)?;
 798                 write!(f, ")")
 799             }
 800             Obligation::Projection(proj) => {
 801                 write!(f, "Normalize(")?;
 802                 proj.projection_ty.hir_fmt(f)?;
 803                 write!(f, " => ")?;
 804                 proj.ty.hir_fmt(f)?;
 805                 write!(f, ")")
 806             }
 807         }
 808     }
 809 }