src/librustc/ty/print/pretty.rs

   1 use crate::hir;
   2 use crate::hir::def::Namespace;
   3 use crate::hir::map::DefPathData;
   4 use crate::hir::def_id::{CrateNum, DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
   5 use crate::middle::cstore::{ExternCrate, ExternCrateSource};
   6 use crate::middle::region;
   7 use crate::ty::{self, DefIdTree, ParamConst, Ty, TyCtxt, TypeFoldable};
   8 use crate::ty::subst::{Kind, Subst, SubstsRef, UnpackedKind};
   9 use crate::mir::interpret::ConstValue;
  10 use syntax::symbol::{keywords, Symbol};
  11
  12 use syntax::symbol::InternedString;
  13
  14 use std::cell::Cell;
  15 use std::fmt::{self, Write as _};
  16 use std::iter;
  17
  18 // `pretty` is a separate module only for organization.
  19 use super::*;
  20
  21 macro_rules! nest {
  22     ($closure:expr) => {
  23         scoped_cx!() = scoped_cx!().nest($closure)?
  24     }
  25 }
  26 macro_rules! print_inner {
  27     (write ($($data:expr),+)) => {
  28         write!(scoped_cx!().printer, $($data),+)?
  29     };
  30     ($kind:ident ($data:expr)) => {
  31         nest!(|cx| $data.$kind(cx))
  32     };
  33 }
  34 macro_rules! p {
  35     ($($kind:ident $data:tt),+) => {
  36         {
  37             $(print_inner!($kind $data));+
  38         }
  39     };
  40 }
  41 macro_rules! define_scoped_cx {
  42     ($cx:ident) => {
  43         #[allow(unused_macros)]
  44         macro_rules! scoped_cx {
  45             () => ($cx)
  46         }
  47     };
  48 }
  49
  50 thread_local! {
  51     static FORCE_IMPL_FILENAME_LINE: Cell<bool> = Cell::new(false);
  52     static SHOULD_PREFIX_WITH_CRATE: Cell<bool> = Cell::new(false);
  53 }
  54
  55 /// Force us to name impls with just the filename/line number. We
  56 /// normally try to use types. But at some points, notably while printing
  57 /// cycle errors, this can result in extra or suboptimal error output,
  58 /// so this variable disables that check.
  59 pub fn with_forced_impl_filename_line<F: FnOnce() -> R, R>(f: F) -> R {
  60     FORCE_IMPL_FILENAME_LINE.with(|force| {
  61         let old = force.get();
  62         force.set(true);
  63         let result = f();
  64         force.set(old);
  65         result
  66     })
  67 }
  68
  69 /// Adds the `crate::` prefix to paths where appropriate.
  70 pub fn with_crate_prefix<F: FnOnce() -> R, R>(f: F) -> R {
  71     SHOULD_PREFIX_WITH_CRATE.with(|flag| {
  72         let old = flag.get();
  73         flag.set(true);
  74         let result = f();
  75         flag.set(old);
  76         result
  77     })
  78 }
  79
  80 /// The "region highlights" are used to control region printing during
  81 /// specific error messages. When a "region highlight" is enabled, it
  82 /// gives an alternate way to print specific regions. For now, we
  83 /// always print those regions using a number, so something like "`'0`".
  84 ///
  85 /// Regions not selected by the region highlight mode are presently
  86 /// unaffected.
  87 #[derive(Copy, Clone, Default)]
  88 pub struct RegionHighlightMode {
  89     /// If enabled, when we see the selected region, use "`'N`"
  90     /// instead of the ordinary behavior.
  91     highlight_regions: [Option<(ty::RegionKind, usize)>; 3],
  92
  93     /// If enabled, when printing a "free region" that originated from
  94     /// the given `ty::BoundRegion`, print it as "`'1`". Free regions that would ordinarily
  95     /// have names print as normal.
  96     ///
  97     /// This is used when you have a signature like `fn foo(x: &u32,
  98     /// y: &'a u32)` and we want to give a name to the region of the
  99     /// reference `x`.
 100     highlight_bound_region: Option<(ty::BoundRegion, usize)>,
 101 }
 102
 103 impl RegionHighlightMode {
 104     /// If `region` and `number` are both `Some`, invokes
 105     /// `highlighting_region`.
 106     pub fn maybe_highlighting_region(
 107         &mut self,
 108         region: Option<ty::Region<'_>>,
 109         number: Option<usize>,
 110     ) {
 111         if let Some(k) = region {
 112             if let Some(n) = number {
 113                 self.highlighting_region(k, n);
 114             }
 115         }
 116     }
 117
 118     /// Highlights the region inference variable `vid` as `'N`.
 119     pub fn highlighting_region(
 120         &mut self,
 121         region: ty::Region<'_>,
 122         number: usize,
 123     ) {
 124         let num_slots = self.highlight_regions.len();
 125         let first_avail_slot = self.highlight_regions.iter_mut()
 126             .filter(|s| s.is_none())
 127             .next()
 128             .unwrap_or_else(|| {
 129                 bug!(
 130                     "can only highlight {} placeholders at a time",
 131                     num_slots,
 132                 )
 133             });
 134         *first_avail_slot = Some((*region, number));
 135     }
 136
 137     /// Convenience wrapper for `highlighting_region`.
 138     pub fn highlighting_region_vid(
 139         &mut self,
 140         vid: ty::RegionVid,
 141         number: usize,
 142     ) {
 143         self.highlighting_region(&ty::ReVar(vid), number)
 144     }
 145
 146     /// Returns `Some(n)` with the number to use for the given region, if any.
 147     fn region_highlighted(&self, region: ty::Region<'_>) -> Option<usize> {
 148         self
 149             .highlight_regions
 150             .iter()
 151             .filter_map(|h| match h {
 152                 Some((r, n)) if r == region => Some(*n),
 153                 _ => None,
 154             })
 155             .next()
 156     }
 157
 158     /// Highlight the given bound region.
 159     /// We can only highlight one bound region at a time. See
 160     /// the field `highlight_bound_region` for more detailed notes.
 161     pub fn highlighting_bound_region(
 162         &mut self,
 163         br: ty::BoundRegion,
 164         number: usize,
 165     ) {
 166         assert!(self.highlight_bound_region.is_none());
 167         self.highlight_bound_region = Some((br, number));
 168     }
 169 }
 170
 171 /// Trait for printers that pretty-print using `fmt::Write` to the printer.
 172 pub trait PrettyPrinter:
 173     Printer<
 174         Error = fmt::Error,
 175         Path = Self,
 176         Region = Self,
 177         Type = Self,
 178     > +
 179     fmt::Write
 180 {
 181     /// Enter a nested print context, for pretty-printing
 182     /// nested components in some larger context.
 183     fn nest<'a, 'gcx, 'tcx, E>(
 184         self: PrintCx<'a, 'gcx, 'tcx, Self>,
 185         f: impl FnOnce(PrintCx<'_, 'gcx, 'tcx, Self>) -> Result<Self, E>,
 186     ) -> Result<PrintCx<'a, 'gcx, 'tcx, Self>, E> {
 187         let printer = f(PrintCx {
 188             tcx: self.tcx,
 189             printer: self.printer,
 190             config: self.config,
 191         })?;
 192         Ok(PrintCx {
 193             tcx: self.tcx,
 194             printer,
 195             config: self.config,
 196         })
 197     }
 198
 199     /// Like `print_def_path` but for value paths.
 200     fn print_value_path(
 201         self: PrintCx<'_, '_, 'tcx, Self>,
 202         def_id: DefId,
 203         substs: Option<SubstsRef<'tcx>>,
 204     ) -> Result<Self::Path, Self::Error> {
 205         self.print_def_path(def_id, substs, iter::empty())
 206     }
 207
 208     /// Print `<...>` around what `f` prints.
 209     fn generic_delimiters<'gcx, 'tcx>(
 210         self: PrintCx<'_, 'gcx, 'tcx, Self>,
 211         f: impl FnOnce(PrintCx<'_, 'gcx, 'tcx, Self>) -> Result<Self, Self::Error>,
 212     ) -> Result<Self, Self::Error>;
 213
 214     /// Return `true` if the region should be printed in path generic args
 215     /// even when it's `'_`, such as in e.g. `Foo<'_, '_, '_>`.
 216     fn always_print_region_in_paths(
 217         self: &PrintCx<'_, '_, '_, Self>,
 218         _region: ty::Region<'_>,
 219     ) -> bool {
 220         false
 221     }
 222
 223     // HACK(eddyb) Trying to print a lifetime might not print anything, which
 224     // may need special handling in the caller (of `ty::RegionKind::print`).
 225     // To avoid printing to a temporary string (which isn't even supported),
 226     // the `print_region_outputs_anything` method can instead be used to
 227     // determine this, ahead of time.
 228     //
 229     // NB: this must be kept in sync with the implementation of `print_region`.
 230     fn print_region_outputs_anything(
 231         self: &PrintCx<'_, '_, '_, Self>,
 232         region: ty::Region<'_>,
 233     ) -> bool;
 234 }
 235
 236 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 237     // HACK(eddyb) get rid of `def_path_str` and/or pass `Namespace` explicitly always
 238     // (but also some things just print a `DefId` generally so maybe we need this?)
 239     fn guess_def_namespace(self, def_id: DefId) -> Namespace {
 240         match self.def_key(def_id).disambiguated_data.data {
 241             DefPathData::ValueNs(..) |
 242             DefPathData::EnumVariant(..) |
 243             DefPathData::Field(..) |
 244             DefPathData::AnonConst |
 245             DefPathData::ConstParam(..) |
 246             DefPathData::ClosureExpr |
 247             DefPathData::StructCtor => Namespace::ValueNS,
 248
 249             DefPathData::MacroDef(..) => Namespace::MacroNS,
 250
 251             _ => Namespace::TypeNS,
 252         }
 253     }
 254
 255     /// Returns a string identifying this `DefId. This string is
 256     /// suitable for user output.
 257     pub fn def_path_str(self, def_id: DefId) -> String {
 258         let ns = self.guess_def_namespace(def_id);
 259         debug!("def_path_str: def_id={:?}, ns={:?}", def_id, ns);
 260         let mut s = String::new();
 261         let _ = PrintCx::with(self, FmtPrinter::new(&mut s, ns), |cx| {
 262             cx.print_def_path(def_id, None, iter::empty())
 263         });
 264         s
 265     }
 266 }
 267
 268 pub struct FmtPrinter<F: fmt::Write> {
 269     fmt: F,
 270     empty: bool,
 271     in_value: bool,
 272     pub region_highlight_mode: RegionHighlightMode,
 273 }
 274
 275 impl<F: fmt::Write> FmtPrinter<F> {
 276     pub fn new(fmt: F, ns: Namespace) -> Self {
 277         FmtPrinter {
 278             fmt,
 279             empty: true,
 280             in_value: ns == Namespace::ValueNS,
 281             region_highlight_mode: RegionHighlightMode::default(),
 282         }
 283     }
 284 }
 285
 286 impl<'gcx, 'tcx, P: PrettyPrinter> PrintCx<'_, 'gcx, 'tcx, P> {
 287     /// If possible, this returns a global path resolving to `def_id` that is visible
 288     /// from at least one local module and returns true. If the crate defining `def_id` is
 289     /// declared with an `extern crate`, the path is guaranteed to use the `extern crate`.
 290     fn try_print_visible_def_path(
 291         mut self,
 292         def_id: DefId,
 293     ) -> Result<(P, bool), P::Error> {
 294         define_scoped_cx!(self);
 295
 296         debug!("try_print_visible_def_path: def_id={:?}", def_id);
 297
 298         // If `def_id` is a direct or injected extern crate, return the
 299         // path to the crate followed by the path to the item within the crate.
 300         if def_id.index == CRATE_DEF_INDEX {
 301             let cnum = def_id.krate;
 302
 303             if cnum == LOCAL_CRATE {
 304                 return Ok((self.path_crate(cnum)?, true));
 305             }
 306
 307             // In local mode, when we encounter a crate other than
 308             // LOCAL_CRATE, execution proceeds in one of two ways:
 309             //
 310             // 1. for a direct dependency, where user added an
 311             //    `extern crate` manually, we put the `extern
 312             //    crate` as the parent. So you wind up with
 313             //    something relative to the current crate.
 314             // 2. for an extern inferred from a path or an indirect crate,
 315             //    where there is no explicit `extern crate`, we just prepend
 316             //    the crate name.
 317             match *self.tcx.extern_crate(def_id) {
 318                 Some(ExternCrate {
 319                     src: ExternCrateSource::Extern(def_id),
 320                     direct: true,
 321                     span,
 322                     ..
 323                 }) => {
 324                     debug!("try_print_visible_def_path: def_id={:?}", def_id);
 325                     return Ok((if !span.is_dummy() {
 326                         self.print_def_path(def_id, None, iter::empty())?
 327                     } else {
 328                         self.path_crate(cnum)?
 329                     }, true));
 330                 }
 331                 None => {
 332                     return Ok((self.path_crate(cnum)?, true));
 333                 }
 334                 _ => {},
 335             }
 336         }
 337
 338         if def_id.is_local() {
 339             return Ok((self.printer, false));
 340         }
 341
 342         let visible_parent_map = self.tcx.visible_parent_map(LOCAL_CRATE);
 343
 344         let mut cur_def_key = self.tcx.def_key(def_id);
 345         debug!("try_print_visible_def_path: cur_def_key={:?}", cur_def_key);
 346
 347         // For a UnitStruct or TupleStruct we want the name of its parent rather than <unnamed>.
 348         if let DefPathData::StructCtor = cur_def_key.disambiguated_data.data {
 349             let parent = DefId {
 350                 krate: def_id.krate,
 351                 index: cur_def_key.parent.expect("DefPathData::StructCtor missing a parent"),
 352             };
 353
 354             cur_def_key = self.tcx.def_key(parent);
 355         }
 356
 357         let visible_parent = match visible_parent_map.get(&def_id).cloned() {
 358             Some(parent) => parent,
 359             None => return Ok((self.printer, false)),
 360         };
 361         // HACK(eddyb) this uses `nest` to avoid knowing ahead of time whether
 362         // the entire path will succeed or not. To support printers that do not
 363         // implement `PrettyPrinter`, a `Vec` or linked list on the stack would
 364         // need to be built, before starting to print anything.
 365         let mut prefix_success = false;
 366         nest!(|cx| {
 367             let (printer, success) = cx.try_print_visible_def_path(visible_parent)?;
 368             prefix_success = success;
 369             Ok(printer)
 370         });
 371         if !prefix_success {
 372             return Ok((self.printer, false));
 373         };
 374         let actual_parent = self.tcx.parent(def_id);
 375         debug!(
 376             "try_print_visible_def_path: visible_parent={:?} actual_parent={:?}",
 377             visible_parent, actual_parent,
 378         );
 379
 380         let data = cur_def_key.disambiguated_data.data;
 381         debug!(
 382             "try_print_visible_def_path: data={:?} visible_parent={:?} actual_parent={:?}",
 383             data, visible_parent, actual_parent,
 384         );
 385
 386         let symbol = match data {
 387             // In order to output a path that could actually be imported (valid and visible),
 388             // we need to handle re-exports correctly.
 389             //
 390             // For example, take `std::os::unix::process::CommandExt`, this trait is actually
 391             // defined at `std::sys::unix::ext::process::CommandExt` (at time of writing).
 392             //
 393             // `std::os::unix` rexports the contents of `std::sys::unix::ext`. `std::sys` is
 394             // private so the "true" path to `CommandExt` isn't accessible.
 395             //
 396             // In this case, the `visible_parent_map` will look something like this:
 397             //
 398             // (child) -> (parent)
 399             // `std::sys::unix::ext::process::CommandExt` -> `std::sys::unix::ext::process`
 400             // `std::sys::unix::ext::process` -> `std::sys::unix::ext`
 401             // `std::sys::unix::ext` -> `std::os`
 402             //
 403             // This is correct, as the visible parent of `std::sys::unix::ext` is in fact
 404             // `std::os`.
 405             //
 406             // When printing the path to `CommandExt` and looking at the `cur_def_key` that
 407             // corresponds to `std::sys::unix::ext`, we would normally print `ext` and then go
 408             // to the parent - resulting in a mangled path like
 409             // `std::os::ext::process::CommandExt`.
 410             //
 411             // Instead, we must detect that there was a re-export and instead print `unix`
 412             // (which is the name `std::sys::unix::ext` was re-exported as in `std::os`). To
 413             // do this, we compare the parent of `std::sys::unix::ext` (`std::sys::unix`) with
 414             // the visible parent (`std::os`). If these do not match, then we iterate over
 415             // the children of the visible parent (as was done when computing
 416             // `visible_parent_map`), looking for the specific child we currently have and then
 417             // have access to the re-exported name.
 418             DefPathData::Module(actual_name) |
 419             DefPathData::TypeNs(actual_name) if Some(visible_parent) != actual_parent => {
 420                 self.tcx.item_children(visible_parent)
 421                     .iter()
 422                     .find(|child| child.def.def_id() == def_id)
 423                     .map(|child| child.ident.as_str())
 424                     .unwrap_or_else(|| actual_name.as_str())
 425             }
 426             _ => {
 427                 data.get_opt_name().map(|n| n.as_str()).unwrap_or_else(|| {
 428                     // Re-exported `extern crate` (#43189).
 429                     if let DefPathData::CrateRoot = data {
 430                         self.tcx.original_crate_name(def_id.krate).as_str()
 431                     } else {
 432                         Symbol::intern("<unnamed>").as_str()
 433                     }
 434                 })
 435             },
 436         };
 437         debug!("try_print_visible_def_path: symbol={:?}", symbol);
 438         Ok((self.path_append(|cx| Ok(cx.printer), &symbol)?, true))
 439     }
 440
 441     pub fn pretty_path_qualified(
 442         self,
 443         self_ty: Ty<'tcx>,
 444         trait_ref: Option<ty::TraitRef<'tcx>>,
 445     ) -> Result<P::Path, P::Error> {
 446         if trait_ref.is_none() {
 447             // Inherent impls. Try to print `Foo::bar` for an inherent
 448             // impl on `Foo`, but fallback to `<Foo>::bar` if self-type is
 449             // anything other than a simple path.
 450             match self_ty.sty {
 451                 ty::Adt(..) | ty::Foreign(_) |
 452                 ty::Bool | ty::Char | ty::Str |
 453                 ty::Int(_) | ty::Uint(_) | ty::Float(_) => {
 454                     return self_ty.print_display(self);
 455                 }
 456
 457                 _ => {}
 458             }
 459         }
 460
 461         self.generic_delimiters(|mut cx| {
 462             define_scoped_cx!(cx);
 463
 464             p!(print_display(self_ty));
 465             if let Some(trait_ref) = trait_ref {
 466                 p!(write(" as "), print_display(trait_ref));
 467             }
 468             Ok(cx.printer)
 469         })
 470     }
 471
 472     pub fn pretty_path_append_impl(
 473         mut self,
 474         print_prefix: impl FnOnce(
 475             PrintCx<'_, 'gcx, 'tcx, P>,
 476         ) -> Result<P::Path, P::Error>,
 477         self_ty: Ty<'tcx>,
 478         trait_ref: Option<ty::TraitRef<'tcx>>,
 479     ) -> Result<P::Path, P::Error> {
 480         self = self.nest(print_prefix)?;
 481
 482         self.generic_delimiters(|mut cx| {
 483             define_scoped_cx!(cx);
 484
 485             p!(write("impl "));
 486             if let Some(trait_ref) = trait_ref {
 487                 p!(print_display(trait_ref), write(" for "));
 488             }
 489             p!(print_display(self_ty));
 490
 491             Ok(cx.printer)
 492         })
 493     }
 494
 495     pub fn pretty_path_generic_args(
 496         mut self,
 497         print_prefix: impl FnOnce(
 498             PrintCx<'_, 'gcx, 'tcx, P>,
 499         ) -> Result<P::Path, P::Error>,
 500         params: &[ty::GenericParamDef],
 501         substs: SubstsRef<'tcx>,
 502         projections: impl Iterator<Item = ty::ExistentialProjection<'tcx>>,
 503     ) -> Result<P::Path, P::Error> {
 504         self = self.nest(print_prefix)?;
 505
 506         // Don't print `'_` if there's no printed region.
 507         let print_regions = params.iter().any(|param| {
 508             match substs[param.index as usize].unpack() {
 509                 UnpackedKind::Lifetime(r) => {
 510                     self.always_print_region_in_paths(r) ||
 511                     self.print_region_outputs_anything(r)
 512                 }
 513                 _ => false,
 514             }
 515         });
 516
 517         // Don't print args that are the defaults of their respective parameters.
 518         let num_supplied_defaults = if self.tcx.sess.verbose() {
 519             0
 520         } else {
 521             params.iter().rev().take_while(|param| {
 522                 match param.kind {
 523                     ty::GenericParamDefKind::Lifetime => false,
 524                     ty::GenericParamDefKind::Type { has_default, .. } => {
 525                         has_default && substs[param.index as usize] == Kind::from(
 526                             self.tcx.type_of(param.def_id).subst(self.tcx, substs)
 527                         )
 528                     }
 529                     ty::GenericParamDefKind::Const => false, // FIXME(const_generics:defaults)
 530                 }
 531             }).count()
 532         };
 533
 534         let params = &params[..params.len() - num_supplied_defaults];
 535         let mut args = params.iter().map(|param| {
 536             substs[param.index as usize]
 537         }).filter(|arg| {
 538             match arg.unpack() {
 539                 UnpackedKind::Lifetime(_) => print_regions,
 540                 _ => true,
 541             }
 542         });
 543         let arg0 = args.next();
 544
 545         let mut projections = projections;
 546         let projection0 = projections.next();
 547
 548         if arg0.is_none() && projection0.is_none() {
 549             return Ok(self.printer);
 550         }
 551
 552         self.generic_delimiters(|mut cx| {
 553             define_scoped_cx!(cx);
 554
 555             let mut empty = true;
 556             let mut maybe_comma = |cx: &mut Self| {
 557                 if empty {
 558                     empty = false;
 559                     Ok(())
 560                 } else {
 561                     write!(cx.printer, ", ")
 562                 }
 563             };
 564
 565             for arg in arg0.into_iter().chain(args) {
 566                 maybe_comma(&mut cx)?;
 567
 568                 if let UnpackedKind::Lifetime(region) = arg.unpack() {
 569                     if !cx.print_region_outputs_anything(region) {
 570                         // This happens when the value of the region
 571                         // parameter is not easily serialized. This may be
 572                         // because the user omitted it in the first place,
 573                         // or because it refers to some block in the code,
 574                         // etc. I'm not sure how best to serialize this.
 575                         p!(write("'_"));
 576
 577                         continue;
 578                     }
 579                 }
 580
 581                 p!(print_display(arg));
 582             }
 583
 584             for projection in projection0.into_iter().chain(projections) {
 585                 maybe_comma(&mut cx)?;
 586
 587                 p!(write("{}=", cx.tcx.associated_item(projection.item_def_id).ident),
 588                    print_display(projection.ty));
 589             }
 590
 591             Ok(cx.printer)
 592         })
 593     }
 594 }
 595
 596 impl<F: fmt::Write> fmt::Write for FmtPrinter<F> {
 597     fn write_str(&mut self, s: &str) -> fmt::Result {
 598         self.empty &= s.is_empty();
 599         self.fmt.write_str(s)
 600     }
 601 }
 602
 603 impl<F: fmt::Write> Printer for FmtPrinter<F> {
 604     type Error = fmt::Error;
 605
 606     type Path = Self;
 607     type Region = Self;
 608     type Type = Self;
 609
 610     fn print_def_path(
 611         mut self: PrintCx<'_, '_, 'tcx, Self>,
 612         def_id: DefId,
 613         substs: Option<SubstsRef<'tcx>>,
 614         projections: impl Iterator<Item = ty::ExistentialProjection<'tcx>>,
 615     ) -> Result<Self::Path, Self::Error> {
 616         // FIXME(eddyb) avoid querying `tcx.generics_of` and `tcx.def_key`
 617         // both here and in `default_print_def_path`.
 618         let generics = substs.map(|_| self.tcx.generics_of(def_id));
 619         if generics.as_ref().and_then(|g| g.parent).is_none() {
 620             let mut visible_path_success = false;
 621             self = self.nest(|cx| {
 622                 let (printer, success) = cx.try_print_visible_def_path(def_id)?;
 623                 visible_path_success = success;
 624                 Ok(printer)
 625             })?;
 626             if visible_path_success {
 627                 return if let (Some(generics), Some(substs)) = (generics, substs) {
 628                     let has_own_self = generics.has_self && generics.parent_count == 0;
 629                     let params = &generics.params[has_own_self as usize..];
 630                     self.path_generic_args(|cx| Ok(cx.printer), params, substs, projections)
 631                 } else {
 632                     Ok(self.printer)
 633                 };
 634             }
 635         }
 636
 637         let key = self.tcx.def_key(def_id);
 638         if let DefPathData::Impl = key.disambiguated_data.data {
 639             // Always use types for non-local impls, where types are always
 640             // available, and filename/line-number is mostly uninteresting.
 641             let use_types =
 642                 !def_id.is_local() || {
 643                     // Otherwise, use filename/line-number if forced.
 644                     let force_no_types = FORCE_IMPL_FILENAME_LINE.with(|f| f.get());
 645                     !force_no_types
 646                 };
 647
 648             if !use_types {
 649                 // If no type info is available, fall back to
 650                 // pretty printing some span information. This should
 651                 // only occur very early in the compiler pipeline.
 652                 let parent_def_id = DefId { index: key.parent.unwrap(), ..def_id };
 653                 let span = self.tcx.def_span(def_id);
 654                 return self.path_append(
 655                     |cx| cx.print_def_path(parent_def_id, None, iter::empty()),
 656                     &format!("<impl at {:?}>", span),
 657                 );
 658             }
 659         }
 660
 661         self.default_print_def_path(def_id, substs, projections)
 662     }
 663
 664     fn print_region(
 665         self: PrintCx<'_, '_, '_, Self>,
 666         region: ty::Region<'_>,
 667     ) -> Result<Self::Region, Self::Error> {
 668         self.pretty_print_region(region)
 669     }
 670
 671     fn print_type(
 672         self: PrintCx<'_, '_, 'tcx, Self>,
 673         ty: Ty<'tcx>,
 674     ) -> Result<Self::Type, Self::Error> {
 675         self.pretty_print_type(ty)
 676     }
 677
 678     fn path_crate(
 679         mut self: PrintCx<'_, '_, '_, Self>,
 680         cnum: CrateNum,
 681     ) -> Result<Self::Path, Self::Error> {
 682         if cnum == LOCAL_CRATE {
 683             if self.tcx.sess.rust_2018() {
 684                 // We add the `crate::` keyword on Rust 2018, only when desired.
 685                 if SHOULD_PREFIX_WITH_CRATE.with(|flag| flag.get()) {
 686                     write!(self.printer, "{}", keywords::Crate.name())?;
 687                 }
 688             }
 689             Ok(self.printer)
 690         } else {
 691             write!(self.printer, "{}", self.tcx.crate_name(cnum))?;
 692             Ok(self.printer)
 693         }
 694     }
 695     fn path_qualified(
 696         self: PrintCx<'_, '_, 'tcx, Self>,
 697         self_ty: Ty<'tcx>,
 698         trait_ref: Option<ty::TraitRef<'tcx>>,
 699     ) -> Result<Self::Path, Self::Error> {
 700         self.pretty_path_qualified(self_ty, trait_ref)
 701     }
 702
 703     fn path_append_impl<'gcx, 'tcx>(
 704         self: PrintCx<'_, 'gcx, 'tcx, Self>,
 705         print_prefix: impl FnOnce(
 706             PrintCx<'_, 'gcx, 'tcx, Self>,
 707         ) -> Result<Self::Path, Self::Error>,
 708         self_ty: Ty<'tcx>,
 709         trait_ref: Option<ty::TraitRef<'tcx>>,
 710     ) -> Result<Self::Path, Self::Error> {
 711         self.pretty_path_append_impl(|cx| {
 712             let mut printer = print_prefix(cx)?;
 713
 714             // HACK(eddyb) this accounts for `generic_delimiters`
 715             // printing `::<` instead of `<` if `in_value` is set.
 716             if !printer.empty && !printer.in_value {
 717                 write!(printer, "::")?;
 718             }
 719
 720             Ok(printer)
 721         }, self_ty, trait_ref)
 722     }
 723     fn path_append<'gcx, 'tcx>(
 724         self: PrintCx<'_, 'gcx, 'tcx, Self>,
 725         print_prefix: impl FnOnce(
 726             PrintCx<'_, 'gcx, 'tcx, Self>,
 727         ) -> Result<Self::Path, Self::Error>,
 728         text: &str,
 729     ) -> Result<Self::Path, Self::Error> {
 730         let mut printer = print_prefix(self)?;
 731
 732         // FIXME(eddyb) `text` should never be empty, but it
 733         // currently is for `extern { ... }` "foreign modules".
 734         if !text.is_empty() {
 735             if !printer.empty {
 736                 write!(printer, "::")?;
 737             }
 738             write!(printer, "{}", text)?;
 739         }
 740
 741         Ok(printer)
 742     }
 743     fn path_generic_args<'gcx, 'tcx>(
 744         self: PrintCx<'_, 'gcx, 'tcx, Self>,
 745         print_prefix: impl FnOnce(
 746             PrintCx<'_, 'gcx, 'tcx, Self>,
 747         ) -> Result<Self::Path, Self::Error>,
 748         params: &[ty::GenericParamDef],
 749         substs: SubstsRef<'tcx>,
 750         projections: impl Iterator<Item = ty::ExistentialProjection<'tcx>>,
 751     ) -> Result<Self::Path, Self::Error> {
 752         self.pretty_path_generic_args(print_prefix, params, substs, projections)
 753     }
 754 }
 755
 756 impl<F: fmt::Write> PrettyPrinter for FmtPrinter<F> {
 757     fn nest<'a, 'gcx, 'tcx, E>(
 758         mut self: PrintCx<'a, 'gcx, 'tcx, Self>,
 759         f: impl FnOnce(PrintCx<'_, 'gcx, 'tcx, Self>) -> Result<Self, E>,
 760     ) -> Result<PrintCx<'a, 'gcx, 'tcx, Self>, E> {
 761         let was_empty = std::mem::replace(&mut self.printer.empty, true);
 762         let mut printer = f(PrintCx {
 763             tcx: self.tcx,
 764             printer: self.printer,
 765             config: self.config,
 766         })?;
 767         printer.empty &= was_empty;
 768         Ok(PrintCx {
 769             tcx: self.tcx,
 770             printer,
 771             config: self.config,
 772         })
 773     }
 774
 775     fn print_value_path(
 776         mut self: PrintCx<'_, '_, 'tcx, Self>,
 777         def_id: DefId,
 778         substs: Option<SubstsRef<'tcx>>,
 779     ) -> Result<Self::Path, Self::Error> {
 780         let was_in_value = std::mem::replace(&mut self.printer.in_value, true);
 781         let mut printer = self.print_def_path(def_id, substs, iter::empty())?;
 782         printer.in_value = was_in_value;
 783
 784         Ok(printer)
 785     }
 786
 787     fn generic_delimiters<'gcx, 'tcx>(
 788         mut self: PrintCx<'_, 'gcx, 'tcx, Self>,
 789         f: impl FnOnce(PrintCx<'_, 'gcx, 'tcx, Self>) -> Result<Self, Self::Error>,
 790     ) -> Result<Self, Self::Error> {
 791         if !self.printer.empty && self.printer.in_value {
 792             write!(self.printer, "::<")?;
 793         } else {
 794             write!(self.printer, "<")?;
 795         }
 796
 797         let was_in_value = std::mem::replace(&mut self.printer.in_value, false);
 798         let mut printer = f(self)?;
 799         printer.in_value = was_in_value;
 800
 801         write!(printer, ">")?;
 802         Ok(printer)
 803     }
 804
 805     fn always_print_region_in_paths(
 806         self: &PrintCx<'_, '_, '_, Self>,
 807         region: ty::Region<'_>,
 808     ) -> bool {
 809         *region != ty::ReErased
 810     }
 811
 812     fn print_region_outputs_anything(
 813         self: &PrintCx<'_, '_, '_, Self>,
 814         region: ty::Region<'_>,
 815     ) -> bool {
 816         let highlight = self.printer.region_highlight_mode;
 817         if highlight.region_highlighted(region).is_some() {
 818             return true;
 819         }
 820
 821         if self.tcx.sess.verbose() {
 822             return true;
 823         }
 824
 825         let identify_regions = self.tcx.sess.opts.debugging_opts.identify_regions;
 826
 827         match *region {
 828             ty::ReEarlyBound(ref data) => {
 829                 data.name != "" && data.name != "'_"
 830             }
 831
 832             ty::ReLateBound(_, br) |
 833             ty::ReFree(ty::FreeRegion { bound_region: br, .. }) |
 834             ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
 835                 if let ty::BrNamed(_, name) = br {
 836                     if name != "" && name != "'_" {
 837                         return true;
 838                     }
 839                 }
 840
 841                 if let Some((region, _)) = highlight.highlight_bound_region {
 842                     if br == region {
 843                         return true;
 844                     }
 845                 }
 846
 847                 false
 848             }
 849
 850             ty::ReScope(_) |
 851             ty::ReVar(_) if identify_regions => true,
 852
 853             ty::ReVar(_) |
 854             ty::ReScope(_) |
 855             ty::ReErased => false,
 856
 857             ty::ReStatic |
 858             ty::ReEmpty |
 859             ty::ReClosureBound(_) => true,
 860         }
 861     }
 862 }
 863
 864 // HACK(eddyb) limited to `FmtPrinter` because of `region_highlight_mode`.
 865 impl<F: fmt::Write> FmtPrinter<F> {
 866     pub fn pretty_print_region(
 867         mut self: PrintCx<'_, '_, '_, Self>,
 868         region: ty::Region<'_>,
 869     ) -> Result<Self, fmt::Error> {
 870         define_scoped_cx!(self);
 871
 872         // Watch out for region highlights.
 873         let highlight = self.printer.region_highlight_mode;
 874         if let Some(n) = highlight.region_highlighted(region) {
 875             p!(write("'{}", n));
 876             return Ok(self.printer);
 877         }
 878
 879         if self.tcx.sess.verbose() {
 880             return region.print_debug(self);
 881         }
 882
 883         let identify_regions = self.tcx.sess.opts.debugging_opts.identify_regions;
 884
 885         // These printouts are concise.  They do not contain all the information
 886         // the user might want to diagnose an error, but there is basically no way
 887         // to fit that into a short string.  Hence the recommendation to use
 888         // `explain_region()` or `note_and_explain_region()`.
 889         match *region {
 890             ty::ReEarlyBound(ref data) => {
 891                 if data.name != "'_" {
 892                     p!(write("{}", data.name));
 893                 }
 894             }
 895             ty::ReLateBound(_, br) |
 896             ty::ReFree(ty::FreeRegion { bound_region: br, .. }) |
 897             ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
 898                 if let ty::BrNamed(_, name) = br {
 899                     if name != "" && name != "'_" {
 900                         p!(write("{}", name));
 901                         return Ok(self.printer);
 902                     }
 903                 }
 904
 905                 if let Some((region, counter)) = highlight.highlight_bound_region {
 906                     if br == region {
 907                         p!(write("'{}", counter));
 908                     }
 909                 }
 910             }
 911             ty::ReScope(scope) if identify_regions => {
 912                 match scope.data {
 913                     region::ScopeData::Node =>
 914                         p!(write("'{}s", scope.item_local_id().as_usize())),
 915                     region::ScopeData::CallSite =>
 916                         p!(write("'{}cs", scope.item_local_id().as_usize())),
 917                     region::ScopeData::Arguments =>
 918                         p!(write("'{}as", scope.item_local_id().as_usize())),
 919                     region::ScopeData::Destruction =>
 920                         p!(write("'{}ds", scope.item_local_id().as_usize())),
 921                     region::ScopeData::Remainder(first_statement_index) => p!(write(
 922                         "'{}_{}rs",
 923                         scope.item_local_id().as_usize(),
 924                         first_statement_index.index()
 925                     )),
 926                 }
 927             }
 928             ty::ReVar(region_vid) if identify_regions => {
 929                 p!(write("{:?}", region_vid));
 930             }
 931             ty::ReVar(_) => {}
 932             ty::ReScope(_) |
 933             ty::ReErased => {}
 934             ty::ReStatic => p!(write("'static")),
 935             ty::ReEmpty => p!(write("'<empty>")),
 936
 937             // The user should never encounter these in unsubstituted form.
 938             ty::ReClosureBound(vid) => p!(write("{:?}", vid)),
 939         }
 940
 941         Ok(self.printer)
 942     }
 943 }
 944
 945 impl<'gcx, 'tcx, P: PrettyPrinter> PrintCx<'_, 'gcx, 'tcx, P> {
 946     pub fn pretty_print_type(
 947         mut self,
 948         ty: Ty<'tcx>,
 949     ) -> Result<P::Type, P::Error> {
 950         define_scoped_cx!(self);
 951
 952         match ty.sty {
 953             ty::Bool => p!(write("bool")),
 954             ty::Char => p!(write("char")),
 955             ty::Int(t) => p!(write("{}", t.ty_to_string())),
 956             ty::Uint(t) => p!(write("{}", t.ty_to_string())),
 957             ty::Float(t) => p!(write("{}", t.ty_to_string())),
 958             ty::RawPtr(ref tm) => {
 959                 p!(write("*{} ", match tm.mutbl {
 960                     hir::MutMutable => "mut",
 961                     hir::MutImmutable => "const",
 962                 }));
 963                 p!(print(tm.ty))
 964             }
 965             ty::Ref(r, ty, mutbl) => {
 966                 p!(write("&"));
 967                 if self.print_region_outputs_anything(r) {
 968                     p!(print_display(r), write(" "));
 969                 }
 970                 p!(print(ty::TypeAndMut { ty, mutbl }))
 971             }
 972             ty::Never => p!(write("!")),
 973             ty::Tuple(ref tys) => {
 974                 p!(write("("));
 975                 let mut tys = tys.iter();
 976                 if let Some(&ty) = tys.next() {
 977                     p!(print(ty), write(","));
 978                     if let Some(&ty) = tys.next() {
 979                         p!(write(" "), print(ty));
 980                         for &ty in tys {
 981                             p!(write(", "), print(ty));
 982                         }
 983                     }
 984                 }
 985                 p!(write(")"))
 986             }
 987             ty::FnDef(def_id, substs) => {
 988                 let sig = self.tcx.fn_sig(def_id).subst(self.tcx, substs);
 989                 p!(print(sig), write(" {{"));
 990                 nest!(|cx| cx.print_value_path(def_id, Some(substs)));
 991                 p!(write("}}"))
 992             }
 993             ty::FnPtr(ref bare_fn) => {
 994                 p!(print(bare_fn))
 995             }
 996             ty::Infer(infer_ty) => p!(write("{}", infer_ty)),
 997             ty::Error => p!(write("[type error]")),
 998             ty::Param(ref param_ty) => p!(write("{}", param_ty)),
 999             ty::Bound(debruijn, bound_ty) => {
1000                 match bound_ty.kind {
1001                     ty::BoundTyKind::Anon => {
1002                         if debruijn == ty::INNERMOST {
1003                             p!(write("^{}", bound_ty.var.index()))
1004                         } else {
1005                             p!(write("^{}_{}", debruijn.index(), bound_ty.var.index()))
1006                         }
1007                     }
1008
1009                     ty::BoundTyKind::Param(p) => p!(write("{}", p)),
1010                 }
1011             }
1012             ty::Adt(def, substs) => {
1013                 nest!(|cx| cx.print_def_path(def.did, Some(substs), iter::empty()));
1014             }
1015             ty::Dynamic(data, r) => {
1016                 let print_r = self.print_region_outputs_anything(r);
1017                 if print_r {
1018                     p!(write("("));
1019                 }
1020                 p!(write("dyn "), print(data));
1021                 if print_r {
1022                     p!(write(" + "), print_display(r), write(")"));
1023                 }
1024             }
1025             ty::Foreign(def_id) => {
1026                 nest!(|cx| cx.print_def_path(def_id, None, iter::empty()));
1027             }
1028             ty::Projection(ref data) => p!(print(data)),
1029             ty::UnnormalizedProjection(ref data) => {
1030                 p!(write("Unnormalized("), print(data), write(")"))
1031             }
1032             ty::Placeholder(placeholder) => {
1033                 p!(write("Placeholder({:?})", placeholder))
1034             }
1035             ty::Opaque(def_id, substs) => {
1036                 if self.tcx.sess.verbose() {
1037                     p!(write("Opaque({:?}, {:?})", def_id, substs));
1038                     return Ok(self.printer);
1039                 }
1040
1041                 let def_key = self.tcx.def_key(def_id);
1042                 if let Some(name) = def_key.disambiguated_data.data.get_opt_name() {
1043                     p!(write("{}", name));
1044                     let mut substs = substs.iter();
1045                     // FIXME(eddyb) print this with `print_def_path`.
1046                     if let Some(first) = substs.next() {
1047                         p!(write("::<"));
1048                         p!(print_display(first));
1049                         for subst in substs {
1050                             p!(write(", "), print_display(subst));
1051                         }
1052                         p!(write(">"));
1053                     }
1054                     return Ok(self.printer);
1055                 }
1056                 // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
1057                 // by looking up the projections associated with the def_id.
1058                 let bounds = self.tcx.predicates_of(def_id).instantiate(self.tcx, substs);
1059
1060                 let mut first = true;
1061                 let mut is_sized = false;
1062                 p!(write("impl"));
1063                 for predicate in bounds.predicates {
1064                     if let Some(trait_ref) = predicate.to_opt_poly_trait_ref() {
1065                         // Don't print +Sized, but rather +?Sized if absent.
1066                         if Some(trait_ref.def_id()) == self.tcx.lang_items().sized_trait() {
1067                             is_sized = true;
1068                             continue;
1069                         }
1070
1071                         p!(
1072                                 write("{}", if first { " " } else { "+" }),
1073                                 print(trait_ref));
1074                         first = false;
1075                     }
1076                 }
1077                 if !is_sized {
1078                     p!(write("{}?Sized", if first { " " } else { "+" }));
1079                 } else if first {
1080                     p!(write(" Sized"));
1081                 }
1082             }
1083             ty::Str => p!(write("str")),
1084             ty::Generator(did, substs, movability) => {
1085                 let upvar_tys = substs.upvar_tys(did, self.tcx);
1086                 let witness = substs.witness(did, self.tcx);
1087                 if movability == hir::GeneratorMovability::Movable {
1088                     p!(write("[generator"));
1089                 } else {
1090                     p!(write("[static generator"));
1091                 }
1092
1093                 // FIXME(eddyb) should use `def_span`.
1094                 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(did) {
1095                     p!(write("@{:?}", self.tcx.hir().span_by_hir_id(hir_id)));
1096                     let mut sep = " ";
1097                     for (freevar, upvar_ty) in self.tcx.freevars(did)
1098                         .as_ref()
1099                         .map_or(&[][..], |fv| &fv[..])
1100                         .iter()
1101                         .zip(upvar_tys)
1102                     {
1103                         p!(
1104                             write("{}{}:",
1105                                     sep,
1106                                     self.tcx.hir().name(freevar.var_id())),
1107                             print(upvar_ty));
1108                         sep = ", ";
1109                     }
1110                 } else {
1111                     // cross-crate closure types should only be
1112                     // visible in codegen bug reports, I imagine.
1113                     p!(write("@{:?}", did));
1114                     let mut sep = " ";
1115                     for (index, upvar_ty) in upvar_tys.enumerate() {
1116                         p!(
1117                                 write("{}{}:", sep, index),
1118                                 print(upvar_ty));
1119                         sep = ", ";
1120                     }
1121                 }
1122
1123                 p!(write(" "), print(witness), write("]"))
1124             },
1125             ty::GeneratorWitness(types) => {
1126                 nest!(|cx| cx.pretty_in_binder(&types))
1127             }
1128             ty::Closure(did, substs) => {
1129                 let upvar_tys = substs.upvar_tys(did, self.tcx);
1130                 p!(write("[closure"));
1131
1132                 // FIXME(eddyb) should use `def_span`.
1133                 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(did) {
1134                     if self.tcx.sess.opts.debugging_opts.span_free_formats {
1135                         p!(write("@{:?}", hir_id));
1136                     } else {
1137                         p!(write("@{:?}", self.tcx.hir().span_by_hir_id(hir_id)));
1138                     }
1139                     let mut sep = " ";
1140                     for (freevar, upvar_ty) in self.tcx.freevars(did)
1141                         .as_ref()
1142                         .map_or(&[][..], |fv| &fv[..])
1143                         .iter()
1144                         .zip(upvar_tys)
1145                     {
1146                         p!(
1147                             write("{}{}:",
1148                                     sep,
1149                                     self.tcx.hir().name(freevar.var_id())),
1150                             print(upvar_ty));
1151                         sep = ", ";
1152                     }
1153                 } else {
1154                     // cross-crate closure types should only be
1155                     // visible in codegen bug reports, I imagine.
1156                     p!(write("@{:?}", did));
1157                     let mut sep = " ";
1158                     for (index, upvar_ty) in upvar_tys.enumerate() {
1159                         p!(
1160                                 write("{}{}:", sep, index),
1161                                 print(upvar_ty));
1162                         sep = ", ";
1163                     }
1164                 }
1165
1166                 if self.config.is_verbose {
1167                     p!(write(
1168                         " closure_kind_ty={:?} closure_sig_ty={:?}",
1169                         substs.closure_kind_ty(did, self.tcx),
1170                         substs.closure_sig_ty(did, self.tcx)
1171                     ));
1172                 }
1173
1174                 p!(write("]"))
1175             },
1176             ty::Array(ty, sz) => {
1177                 p!(write("["), print(ty), write("; "));
1178                 match sz {
1179                     ty::LazyConst::Unevaluated(_def_id, _substs) => {
1180                         p!(write("_"));
1181                     }
1182                     ty::LazyConst::Evaluated(c) => {
1183                         match c.val {
1184                             ConstValue::Infer(..) => p!(write("_")),
1185                             ConstValue::Param(ParamConst { name, .. }) =>
1186                                 p!(write("{}", name)),
1187                             _ => p!(write("{}", c.unwrap_usize(self.tcx))),
1188                         }
1189                     }
1190                 }
1191                 p!(write("]"))
1192             }
1193             ty::Slice(ty) => {
1194                 p!(write("["), print(ty), write("]"))
1195             }
1196         }
1197
1198         Ok(self.printer)
1199     }
1200
1201     pub fn pretty_fn_sig(
1202         mut self,
1203         inputs: &[Ty<'tcx>],
1204         c_variadic: bool,
1205         output: Ty<'tcx>,
1206     ) -> Result<P, fmt::Error> {
1207         define_scoped_cx!(self);
1208
1209         p!(write("("));
1210         let mut inputs = inputs.iter();
1211         if let Some(&ty) = inputs.next() {
1212             p!(print_display(ty));
1213             for &ty in inputs {
1214                 p!(write(", "), print_display(ty));
1215             }
1216             if c_variadic {
1217                 p!(write(", ..."));
1218             }
1219         }
1220         p!(write(")"));
1221         if !output.is_unit() {
1222             p!(write(" -> "), print_display(output));
1223         }
1224
1225         Ok(self.printer)
1226     }
1227
1228     pub fn pretty_in_binder<T>(mut self, value: &ty::Binder<T>) -> Result<P, fmt::Error>
1229         where T: Print<'tcx, P, Output = P, Error = fmt::Error> + TypeFoldable<'tcx>
1230     {
1231         fn name_by_region_index(index: usize) -> InternedString {
1232             match index {
1233                 0 => Symbol::intern("'r"),
1234                 1 => Symbol::intern("'s"),
1235                 i => Symbol::intern(&format!("'t{}", i-2)),
1236             }.as_interned_str()
1237         }
1238
1239         // Replace any anonymous late-bound regions with named
1240         // variants, using gensym'd identifiers, so that we can
1241         // clearly differentiate between named and unnamed regions in
1242         // the output. We'll probably want to tweak this over time to
1243         // decide just how much information to give.
1244         if self.config.binder_depth == 0 {
1245             self.prepare_late_bound_region_info(value);
1246         }
1247
1248         let mut empty = true;
1249         let mut start_or_continue = |cx: &mut Self, start: &str, cont: &str| {
1250             write!(cx.printer, "{}", if empty {
1251                 empty = false;
1252                 start
1253             } else {
1254                 cont
1255             })
1256         };
1257
1258         // NOTE(eddyb) this must be below `start_or_continue`'s definition
1259         // as that also has a `define_scoped_cx` and that kind of shadowing
1260         // is disallowed (name resolution thinks `scoped_cx!` is ambiguous).
1261         define_scoped_cx!(self);
1262
1263         let old_region_index = self.config.region_index;
1264         let mut region_index = old_region_index;
1265         let new_value = self.tcx.replace_late_bound_regions(value, |br| {
1266             let _ = start_or_continue(&mut self, "for<", ", ");
1267             let br = match br {
1268                 ty::BrNamed(_, name) => {
1269                     let _ = write!(self.printer, "{}", name);
1270                     br
1271                 }
1272                 ty::BrAnon(_) |
1273                 ty::BrFresh(_) |
1274                 ty::BrEnv => {
1275                     let name = loop {
1276                         let name = name_by_region_index(region_index);
1277                         region_index += 1;
1278                         if !self.is_name_used(&name) {
1279                             break name;
1280                         }
1281                     };
1282                     let _ = write!(self.printer, "{}", name);
1283                     ty::BrNamed(DefId::local(CRATE_DEF_INDEX), name)
1284                 }
1285             };
1286             self.tcx.mk_region(ty::ReLateBound(ty::INNERMOST, br))
1287         }).0;
1288         start_or_continue(&mut self, "", "> ")?;
1289
1290         // Push current state to gcx, and restore after writing new_value.
1291         self.config.binder_depth += 1;
1292         self.config.region_index = region_index;
1293         let result = new_value.print_display(PrintCx {
1294             tcx: self.tcx,
1295             printer: self.printer,
1296             config: self.config,
1297         });
1298         self.config.region_index = old_region_index;
1299         self.config.binder_depth -= 1;
1300         result
1301     }
1302
1303     fn is_name_used(&self, name: &InternedString) -> bool {
1304         match self.config.used_region_names {
1305             Some(ref names) => names.contains(name),
1306             None => false,
1307         }
1308     }
1309 }