src/librustc_codegen_utils/symbol_names/v0.rs - third_party/rust - Git at Google

 use rustc::hir;
 use rustc::hir::def_id::{CrateNum, DefId};
 use rustc::hir::map::{DefPathData, DisambiguatedDefPathData};
 use rustc::ty::{self, Ty, TyCtxt, TypeFoldable, Instance};
 use rustc::ty::print::{Printer, Print};
 use rustc::ty::subst::{Kind, Subst, UnpackedKind};
 use rustc_data_structures::base_n;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_target::spec::abi::Abi;
 use syntax::ast::{IntTy, UintTy, FloatTy};

 use std::fmt::Write;
 use std::ops::Range;

 pub(super) fn mangle(
     tcx: TyCtxt<'tcx>,
     instance: Instance<'tcx>,
     instantiating_crate: Option<CrateNum>,
 ) -> String {
     let def_id = instance.def_id();
     // FIXME(eddyb) this should ideally not be needed.
     let substs =
         tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), instance.substs);

     let prefix = "_R";
     let mut cx = SymbolMangler {
         tcx,
         compress: Some(Box::new(CompressionCaches {
             start_offset: prefix.len(),

             paths: FxHashMap::default(),
             types: FxHashMap::default(),
             consts: FxHashMap::default(),
         })),
         binders: vec![],
         out: String::from(prefix),
     };
     cx = if instance.is_vtable_shim() {
         cx.path_append_ns(
             |cx| cx.print_def_path(def_id, substs),
             'S',
             0,
             "",
         ).unwrap()
     } else {
         cx.print_def_path(def_id, substs).unwrap()
     };
     if let Some(instantiating_crate) = instantiating_crate {
         cx = cx.print_def_path(instantiating_crate.as_def_id(), &[]).unwrap();
     }
     cx.out
 }

 struct CompressionCaches<'tcx> {
     // The length of the prefix in `out` (e.g. 2 for `_R`).
     start_offset: usize,

     // The values are start positions in `out`, in bytes.
     paths: FxHashMap<(DefId, &'tcx [Kind<'tcx>]), usize>,
     types: FxHashMap<Ty<'tcx>, usize>,
     consts: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
 }

 struct BinderLevel {
     /// The range of distances from the root of what's
     /// being printed, to the lifetimes in a binder.
     /// Specifically, a `BrAnon(i)` lifetime has depth
     /// `lifetime_depths.start + i`, going away from the
     /// the root and towards its use site, as `i` increases.
     /// This is used to flatten rustc's pairing of `BrAnon`
     /// (intra-binder disambiguation) with a `DebruijnIndex`
     /// (binder addressing), to "true" de Bruijn indices,
     /// by subtracting the depth of a certain lifetime, from
     /// the innermost depth at its use site.
     lifetime_depths: Range<u32>,
 }

 struct SymbolMangler<'tcx> {
     tcx: TyCtxt<'tcx>,
     compress: Option<Box<CompressionCaches<'tcx>>>,
     binders: Vec<BinderLevel>,
     out: String,
 }

 impl SymbolMangler<'tcx> {
     fn push(&mut self, s: &str) {
         self.out.push_str(s);
     }

     /// Push a `_`-terminated base 62 integer, using the format
     /// specified in the RFC as `<base-62-number>`, that is:
     /// * `x = 0` is encoded as just the `"_"` terminator
     /// * `x > 0` is encoded as `x - 1` in base 62, followed by `"_"`,
     ///   e.g. `1` becomes `"0_"`, `62` becomes `"Z_"`, etc.
     fn push_integer_62(&mut self, x: u64) {
         if let Some(x) = x.checked_sub(1) {
             base_n::push_str(x as u128, 62, &mut self.out);
         }
         self.push("_");
     }

     /// Push a `tag`-prefixed base 62 integer, when larger than `0`, that is:
     /// * `x = 0` is encoded as `""` (nothing)
     /// * `x > 0` is encoded as the `tag` followed by `push_integer_62(x - 1)`
     ///   e.g. `1` becomes `tag + "_"`, `2` becomes `tag + "0_"`, etc.
     fn push_opt_integer_62(&mut self, tag: &str, x: u64) {
         if let Some(x) = x.checked_sub(1) {
             self.push(tag);
             self.push_integer_62(x);
         }
     }

     fn push_disambiguator(&mut self, dis: u64) {
         self.push_opt_integer_62("s", dis);
     }

     fn push_ident(&mut self, ident: &str) {
         let mut use_punycode = false;
         for b in ident.bytes() {
             match b {
                 b'_' | b'a'..=b'z' | b'A'..=b'Z' | b'0'..=b'9' => {}
                 0x80..=0xff => use_punycode = true,
                 _ => bug!("symbol_names: bad byte {} in ident {:?}", b, ident),
             }
         }

         let punycode_string;
         let ident = if use_punycode {
             self.push("u");

             // FIXME(eddyb) we should probably roll our own punycode implementation.
             let mut punycode_bytes = match ::punycode::encode(ident) {
                 Ok(s) => s.into_bytes(),
                 Err(()) => bug!("symbol_names: punycode encoding failed for ident {:?}", ident),
             };

             // Replace `-` with `_`.
             if let Some(c) = punycode_bytes.iter_mut().rfind(|&&mut c| c == b'-') {
                 *c = b'_';
             }

             // FIXME(eddyb) avoid rechecking UTF-8 validity.
             punycode_string = String::from_utf8(punycode_bytes).unwrap();
             &punycode_string
         } else {
             ident
         };

         let _ = write!(self.out, "{}", ident.len());

         // Write a separating `_` if necessary (leading digit or `_`).
         match ident.chars().next() {
             Some('_') | Some('0'..='9') => {
                 self.push("_");
             }
             _ => {}
         }

         self.push(ident);
     }

     fn path_append_ns(
         mut self,
         print_prefix: impl FnOnce(Self) -> Result<Self, !>,
         ns: char,
         disambiguator: u64,
         name: &str,
     ) -> Result<Self, !> {
         self.push("N");
         self.out.push(ns);
         self = print_prefix(self)?;
         self.push_disambiguator(disambiguator as u64);
         self.push_ident(name);
         Ok(self)
     }

     fn print_backref(mut self, i: usize) -> Result<Self, !> {
         self.push("B");
         self.push_integer_62((i - self.compress.as_ref().unwrap().start_offset) as u64);
         Ok(self)
     }

     fn in_binder<T>(
         mut self,
         value: &ty::Binder<T>,
         print_value: impl FnOnce(Self, &T) -> Result<Self, !>
     ) -> Result<Self, !>
         where T: TypeFoldable<'tcx>
     {
         let regions = if value.has_late_bound_regions() {
             self.tcx.collect_referenced_late_bound_regions(value)
         } else {
             FxHashSet::default()
         };

         let mut lifetime_depths =
             self.binders.last().map(|b| b.lifetime_depths.end).map_or(0..0, |i| i..i);

         let lifetimes = regions.into_iter().map(|br| {
             match br {
                 ty::BrAnon(i) => {
                     // FIXME(eddyb) for some reason, `anonymize_late_bound_regions` starts at `1`.
                     assert_ne!(i, 0);
                     i - 1
                 },
                 _ => bug!("symbol_names: non-anonymized region `{:?}` in `{:?}`", br, value),
             }
         }).max().map_or(0, |max| max + 1);

         self.push_opt_integer_62("G", lifetimes as u64);
         lifetime_depths.end += lifetimes;

         self.binders.push(BinderLevel { lifetime_depths });
         self = print_value(self, value.skip_binder())?;
         self.binders.pop();

         Ok(self)
     }
 }

 impl Printer<'tcx> for SymbolMangler<'tcx> {
     type Error = !;

     type Path = Self;
     type Region = Self;
     type Type = Self;
     type DynExistential = Self;
     type Const = Self;

     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }

     fn print_def_path(
         mut self,
         def_id: DefId,
         substs: &'tcx [Kind<'tcx>],
     ) -> Result<Self::Path, Self::Error> {
         if let Some(&i) = self.compress.as_ref().and_then(|c| c.paths.get(&(def_id, substs))) {
             return self.print_backref(i);
         }
         let start = self.out.len();

         self = self.default_print_def_path(def_id, substs)?;

         // Only cache paths that do not refer to an enclosing
         // binder (which would change depending on context).
         if !substs.iter().any(|k| k.has_escaping_bound_vars()) {
             if let Some(c) = &mut self.compress {
                 c.paths.insert((def_id, substs), start);
             }
         }
         Ok(self)
     }

     fn print_impl_path(
         self,
         impl_def_id: DefId,
         substs: &'tcx [Kind<'tcx>],
         mut self_ty: Ty<'tcx>,
         mut impl_trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<Self::Path, Self::Error> {
         let key = self.tcx.def_key(impl_def_id);
         let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };

         let mut param_env = self.tcx.param_env(impl_def_id)
             .with_reveal_all();
         if !substs.is_empty() {
             param_env = param_env.subst(self.tcx, substs);
         }

         match &mut impl_trait_ref {
             Some(impl_trait_ref) => {
                 assert_eq!(impl_trait_ref.self_ty(), self_ty);
                 *impl_trait_ref =
                     self.tcx.normalize_erasing_regions(param_env, *impl_trait_ref);
                 self_ty = impl_trait_ref.self_ty();
             }
             None => {
                 self_ty = self.tcx.normalize_erasing_regions(param_env, self_ty);
             }
         }

         self.path_append_impl(
             |cx| cx.print_def_path(parent_def_id, &[]),
             &key.disambiguated_data,
             self_ty,
             impl_trait_ref,
         )
     }

     fn print_region(
         mut self,
         region: ty::Region<'_>,
     ) -> Result<Self::Region, Self::Error> {
         let i = match *region {
             // Erased lifetimes use the index 0, for a
             // shorter mangling of `L_`.
             ty::ReErased => 0,

             // Late-bound lifetimes use indices starting at 1,
             // see `BinderLevel` for more details.
             ty::ReLateBound(debruijn, ty::BrAnon(i)) => {
                 // FIXME(eddyb) for some reason, `anonymize_late_bound_regions` starts at `1`.
                 assert_ne!(i, 0);
                 let i = i - 1;

                 let binder = &self.binders[self.binders.len() - 1 - debruijn.index()];
                 let depth = binder.lifetime_depths.start + i;

                 1 + (self.binders.last().unwrap().lifetime_depths.end - 1 - depth)
             }

             _ => bug!("symbol_names: non-erased region `{:?}`", region),
         };
         self.push("L");
         self.push_integer_62(i as u64);
         Ok(self)
     }

     fn print_type(
         mut self,
         ty: Ty<'tcx>,
     ) -> Result<Self::Type, Self::Error> {
         // Basic types, never cached (single-character).
         let basic_type = match ty.sty {
             ty::Bool => "b",
             ty::Char => "c",
             ty::Str => "e",
             ty::Tuple(_) if ty.is_unit() => "u",
             ty::Int(IntTy::I8) => "a",
             ty::Int(IntTy::I16) => "s",
             ty::Int(IntTy::I32) => "l",
             ty::Int(IntTy::I64) => "x",
             ty::Int(IntTy::I128) => "n",
             ty::Int(IntTy::Isize) => "i",
             ty::Uint(UintTy::U8) => "h",
             ty::Uint(UintTy::U16) => "t",
             ty::Uint(UintTy::U32) => "m",
             ty::Uint(UintTy::U64) => "y",
             ty::Uint(UintTy::U128) => "o",
             ty::Uint(UintTy::Usize) => "j",
             ty::Float(FloatTy::F32) => "f",
             ty::Float(FloatTy::F64) => "d",
             ty::Never => "z",

             // Placeholders (should be demangled as `_`).
             ty::Param(_) | ty::Bound(..) | ty::Placeholder(_) |
             ty::Infer(_) | ty::Error => "p",

             _ => "",
         };
         if !basic_type.is_empty() {
             self.push(basic_type);
             return Ok(self);
         }

         if let Some(&i) = self.compress.as_ref().and_then(|c| c.types.get(&ty)) {
             return self.print_backref(i);
         }
         let start = self.out.len();

         match ty.sty {
             // Basic types, handled above.
             ty::Bool | ty::Char | ty::Str |
             ty::Int(_) | ty::Uint(_) | ty::Float(_) |
             ty::Never => unreachable!(),
             ty::Tuple(_) if ty.is_unit() => unreachable!(),

             // Placeholders, also handled as part of basic types.
             ty::Param(_) | ty::Bound(..) | ty::Placeholder(_) |
             ty::Infer(_) | ty::Error => unreachable!(),

             ty::Ref(r, ty, mutbl) => {
                 self.push(match mutbl {
                     hir::MutImmutable => "R",
                     hir::MutMutable => "Q",
                 });
                 if *r != ty::ReErased {
                     self = r.print(self)?;
                 }
                 self = ty.print(self)?;
             }

             ty::RawPtr(mt) => {
                 self.push(match mt.mutbl {
                     hir::MutImmutable => "P",
                     hir::MutMutable => "O",
                 });
                 self = mt.ty.print(self)?;
             }

             ty::Array(ty, len) => {
                 self.push("A");
                 self = ty.print(self)?;
                 self = self.print_const(len)?;
             }
             ty::Slice(ty) => {
                 self.push("S");
                 self = ty.print(self)?;
             }

             ty::Tuple(tys) => {
                 self.push("T");
                 for ty in tys.iter().map(|k| k.expect_ty()) {
                     self = ty.print(self)?;
                 }
                 self.push("E");
             }

             // Mangle all nominal types as paths.
             ty::Adt(&ty::AdtDef { did: def_id, .. }, substs) |
             ty::FnDef(def_id, substs) |
             ty::Opaque(def_id, substs) |
             ty::Projection(ty::ProjectionTy { item_def_id: def_id, substs }) |
             ty::UnnormalizedProjection(ty::ProjectionTy { item_def_id: def_id, substs }) |
             ty::Closure(def_id, ty::ClosureSubsts { substs }) |
             ty::Generator(def_id, ty::GeneratorSubsts { substs }, _) => {
                 self = self.print_def_path(def_id, substs)?;
             }
             ty::Foreign(def_id) => {
                 self = self.print_def_path(def_id, &[])?;
             }

             ty::FnPtr(sig) => {
                 self.push("F");
                 self = self.in_binder(&sig, |mut cx, sig| {
                     if sig.unsafety == hir::Unsafety::Unsafe {
                         cx.push("U");
                     }
                     match sig.abi {
                         Abi::Rust => {}
                         Abi::C => cx.push("KC"),
                         abi => {
                             cx.push("K");
                             let name = abi.name();
                             if name.contains('-') {
                                 cx.push_ident(&name.replace('-', "_"));
                             } else {
                                 cx.push_ident(name);
                             }
                         }
                     }
                     for &ty in sig.inputs() {
                         cx = ty.print(cx)?;
                     }
                     if sig.c_variadic {
                         cx.push("v");
                     }
                     cx.push("E");
                     sig.output().print(cx)
                 })?;
             }

             ty::Dynamic(predicates, r) => {
                 self.push("D");
                 self = self.in_binder(&predicates, |cx, predicates| {
                     cx.print_dyn_existential(predicates)
                 })?;
                 self = r.print(self)?;
             }

             ty::GeneratorWitness(_) => {
                 bug!("symbol_names: unexpected `GeneratorWitness`")
             }
         }

         // Only cache types that do not refer to an enclosing
         // binder (which would change depending on context).
         if !ty.has_escaping_bound_vars() {
             if let Some(c) = &mut self.compress {
                 c.types.insert(ty, start);
             }
         }
         Ok(self)
     }

     fn print_dyn_existential(
         mut self,
         predicates: &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
     ) -> Result<Self::DynExistential, Self::Error> {
         for predicate in predicates {
             match *predicate {
                 ty::ExistentialPredicate::Trait(trait_ref) => {
                     // Use a type that can't appear in defaults of type parameters.
                     let dummy_self = self.tcx.mk_ty_infer(ty::FreshTy(0));
                     let trait_ref = trait_ref.with_self_ty(self.tcx, dummy_self);
                     self = self.print_def_path(trait_ref.def_id, trait_ref.substs)?;
                 }
                 ty::ExistentialPredicate::Projection(projection) => {
                     let name = self.tcx.associated_item(projection.item_def_id).ident;
                     self.push("p");
                     self.push_ident(&name.as_str());
                     self = projection.ty.print(self)?;
                 }
                 ty::ExistentialPredicate::AutoTrait(def_id) => {
                     self = self.print_def_path(def_id, &[])?;
                 }
             }
         }
         self.push("E");
         Ok(self)
     }

     fn print_const(
         mut self,
         ct: &'tcx ty::Const<'tcx>,
     ) -> Result<Self::Const, Self::Error> {
         if let Some(&i) = self.compress.as_ref().and_then(|c| c.consts.get(&ct)) {
             return self.print_backref(i);
         }
         let start = self.out.len();

         match ct.ty.sty {
             ty::Uint(_) => {}
             _ => {
                 bug!("symbol_names: unsupported constant of type `{}` ({:?})",
                     ct.ty, ct);
             }
         }
         self = ct.ty.print(self)?;

         if let Some(bits) = ct.try_eval_bits(self.tcx, ty::ParamEnv::reveal_all(), ct.ty) {
             let _ = write!(self.out, "{:x}_", bits);
         } else {
             // NOTE(eddyb) despite having the path, we need to
             // encode a placeholder, as the path could refer
             // back to e.g. an `impl` using the constant.
             self.push("p");
         }

         // Only cache consts that do not refer to an enclosing
         // binder (which would change depending on context).
         if !ct.has_escaping_bound_vars() {
             if let Some(c) = &mut self.compress {
                 c.consts.insert(ct, start);
             }
         }
         Ok(self)
     }

     fn path_crate(
         mut self,
         cnum: CrateNum,
     ) -> Result<Self::Path, Self::Error> {
         self.push("C");
         let fingerprint = self.tcx.crate_disambiguator(cnum).to_fingerprint();
         self.push_disambiguator(fingerprint.to_smaller_hash());
         let name = self.tcx.original_crate_name(cnum).as_str();
         self.push_ident(&name);
         Ok(self)
     }
     fn path_qualified(
         mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<Self::Path, Self::Error> {
         assert!(trait_ref.is_some());
         let trait_ref = trait_ref.unwrap();

         self.push("Y");
         self = self_ty.print(self)?;
         self.print_def_path(trait_ref.def_id, trait_ref.substs)
     }

     fn path_append_impl(
         mut self,
         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
         disambiguated_data: &DisambiguatedDefPathData,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<Self::Path, Self::Error> {
         self.push(match trait_ref {
             Some(_) => "X",
             None => "M",
         });
         self.push_disambiguator(disambiguated_data.disambiguator as u64);
         self = print_prefix(self)?;
         self = self_ty.print(self)?;
         if let Some(trait_ref) = trait_ref {
             self = self.print_def_path(trait_ref.def_id, trait_ref.substs)?;
         }
         Ok(self)
     }
     fn path_append(
         self,
         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
         disambiguated_data: &DisambiguatedDefPathData,
     ) -> Result<Self::Path, Self::Error> {
         let ns = match disambiguated_data.data {
             // Uppercase categories are more stable than lowercase ones.
             DefPathData::TypeNs(_) => 't',
             DefPathData::ValueNs(_) => 'v',
             DefPathData::ClosureExpr => 'C',
             DefPathData::Ctor => 'c',
             DefPathData::AnonConst => 'k',
             DefPathData::ImplTrait => 'i',

             // These should never show up as `path_append` arguments.
             DefPathData::CrateRoot
             | DefPathData::Misc
             | DefPathData::Impl
             | DefPathData::MacroNs(_)
             | DefPathData::LifetimeNs(_)
             | DefPathData::GlobalMetaData(_) => {
                 bug!("symbol_names: unexpected DefPathData: {:?}", disambiguated_data.data)
             }
         };

         let name = disambiguated_data.data.get_opt_name().map(|s| s.as_str());

         self.path_append_ns(
             print_prefix,
             ns,
             disambiguated_data.disambiguator as u64,
             name.as_ref().map_or("", |s| &s[..])
         )
     }
     fn path_generic_args(
         mut self,
         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
         args: &[Kind<'tcx>],
     ) -> Result<Self::Path, Self::Error> {
         // Don't print any regions if they're all erased.
         let print_regions = args.iter().any(|arg| {
             match arg.unpack() {
                 UnpackedKind::Lifetime(r) => *r != ty::ReErased,
                 _ => false,
             }
         });
         let args = args.iter().cloned().filter(|arg| {
             match arg.unpack() {
                 UnpackedKind::Lifetime(_) => print_regions,
                 _ => true,
             }
         });

         if args.clone().next().is_none() {
             return print_prefix(self);
         }

         self.push("I");
         self = print_prefix(self)?;
         for arg in args {
             match arg.unpack() {
                 UnpackedKind::Lifetime(lt) => {
                     self = lt.print(self)?;
                 }
                 UnpackedKind::Type(ty) => {
                     self = ty.print(self)?;
                 }
                 UnpackedKind::Const(c) => {
                     self.push("K");
                     // FIXME(const_generics) implement `ty::print::Print` on `ty::Const`.
                     // self = c.print(self)?;
                     self = self.print_const(c)?;
                 }
             }
         }
         self.push("E");

         Ok(self)
     }
 }
	use rustc::hir;
	use rustc::hir::def_id::{CrateNum, DefId};
	use rustc::hir::map::{DefPathData, DisambiguatedDefPathData};
	use rustc::ty::{self, Ty, TyCtxt, TypeFoldable, Instance};
	use rustc::ty::print::{Printer, Print};
	use rustc::ty::subst::{Kind, Subst, UnpackedKind};
	use rustc_data_structures::base_n;
	use rustc_data_structures::fx::{FxHashMap, FxHashSet};
	use rustc_target::spec::abi::Abi;
	use syntax::ast::{IntTy, UintTy, FloatTy};

	use std::fmt::Write;
	use std::ops::Range;

	pub(super) fn mangle(
	tcx: TyCtxt<'tcx>,
	instance: Instance<'tcx>,
	instantiating_crate: Option<CrateNum>,
	) -> String {
	let def_id = instance.def_id();
	// FIXME(eddyb) this should ideally not be needed.
	let substs =
	tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), instance.substs);

	let prefix = "_R";
	let mut cx = SymbolMangler {
	tcx,
	compress: Some(Box::new(CompressionCaches {
	start_offset: prefix.len(),

	paths: FxHashMap::default(),
	types: FxHashMap::default(),
	consts: FxHashMap::default(),
	})),
	binders: vec![],
	out: String::from(prefix),
	};
	cx = if instance.is_vtable_shim() {
	cx.path_append_ns(
	\|cx\| cx.print_def_path(def_id, substs),
	'S',
	0,
	"",
	).unwrap()
	} else {
	cx.print_def_path(def_id, substs).unwrap()
	};
	if let Some(instantiating_crate) = instantiating_crate {
	cx = cx.print_def_path(instantiating_crate.as_def_id(), &[]).unwrap();
	}
	cx.out
	}

	struct CompressionCaches<'tcx> {
	// The length of the prefix in `out` (e.g. 2 for `_R`).
	start_offset: usize,

	// The values are start positions in `out`, in bytes.
	paths: FxHashMap<(DefId, &'tcx [Kind<'tcx>]), usize>,
	types: FxHashMap<Ty<'tcx>, usize>,
	consts: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
	}

	struct BinderLevel {
	/// The range of distances from the root of what's
	/// being printed, to the lifetimes in a binder.
	/// Specifically, a `BrAnon(i)` lifetime has depth
	/// `lifetime_depths.start + i`, going away from the
	/// the root and towards its use site, as `i` increases.
	/// This is used to flatten rustc's pairing of `BrAnon`
	/// (intra-binder disambiguation) with a `DebruijnIndex`
	/// (binder addressing), to "true" de Bruijn indices,
	/// by subtracting the depth of a certain lifetime, from
	/// the innermost depth at its use site.
	lifetime_depths: Range<u32>,
	}

	struct SymbolMangler<'tcx> {
	tcx: TyCtxt<'tcx>,
	compress: Option<Box<CompressionCaches<'tcx>>>,
	binders: Vec<BinderLevel>,
	out: String,
	}

	impl SymbolMangler<'tcx> {
	fn push(&mut self, s: &str) {
	self.out.push_str(s);
	}

	/// Push a `_`-terminated base 62 integer, using the format
	/// specified in the RFC as `<base-62-number>`, that is:
	/// * `x = 0` is encoded as just the `"_"` terminator
	/// * `x > 0` is encoded as `x - 1` in base 62, followed by `"_"`,
	/// e.g. `1` becomes `"0_"`, `62` becomes `"Z_"`, etc.
	fn push_integer_62(&mut self, x: u64) {
	if let Some(x) = x.checked_sub(1) {
	base_n::push_str(x as u128, 62, &mut self.out);
	}
	self.push("_");
	}

	/// Push a `tag`-prefixed base 62 integer, when larger than `0`, that is:
	/// * `x = 0` is encoded as `""` (nothing)
	/// * `x > 0` is encoded as the `tag` followed by `push_integer_62(x - 1)`
	/// e.g. `1` becomes `tag + "_"`, `2` becomes `tag + "0_"`, etc.
	fn push_opt_integer_62(&mut self, tag: &str, x: u64) {
	if let Some(x) = x.checked_sub(1) {
	self.push(tag);
	self.push_integer_62(x);
	}
	}

	fn push_disambiguator(&mut self, dis: u64) {
	self.push_opt_integer_62("s", dis);
	}

	fn push_ident(&mut self, ident: &str) {
	let mut use_punycode = false;
	for b in ident.bytes() {
	match b {
	b'_' \| b'a'..=b'z' \| b'A'..=b'Z' \| b'0'..=b'9' => {}
	0x80..=0xff => use_punycode = true,
	_ => bug!("symbol_names: bad byte {} in ident {:?}", b, ident),
	}
	}

	let punycode_string;
	let ident = if use_punycode {
	self.push("u");

	// FIXME(eddyb) we should probably roll our own punycode implementation.
	let mut punycode_bytes = match ::punycode::encode(ident) {
	Ok(s) => s.into_bytes(),
	Err(()) => bug!("symbol_names: punycode encoding failed for ident {:?}", ident),
	};

	// Replace `-` with `_`.
	if let Some(c) = punycode_bytes.iter_mut().rfind(\|&&mut c\| c == b'-') {
	*c = b'_';
	}

	// FIXME(eddyb) avoid rechecking UTF-8 validity.
	punycode_string = String::from_utf8(punycode_bytes).unwrap();
	&punycode_string
	} else {
	ident
	};

	let _ = write!(self.out, "{}", ident.len());

	// Write a separating `_` if necessary (leading digit or `_`).
	match ident.chars().next() {
	Some('_') \| Some('0'..='9') => {
	self.push("_");
	}
	_ => {}
	}

	self.push(ident);
	}

	fn path_append_ns(
	mut self,
	print_prefix: impl FnOnce(Self) -> Result<Self, !>,
	ns: char,
	disambiguator: u64,
	name: &str,
	) -> Result<Self, !> {
	self.push("N");
	self.out.push(ns);
	self = print_prefix(self)?;
	self.push_disambiguator(disambiguator as u64);
	self.push_ident(name);
	Ok(self)
	}

	fn print_backref(mut self, i: usize) -> Result<Self, !> {
	self.push("B");
	self.push_integer_62((i - self.compress.as_ref().unwrap().start_offset) as u64);
	Ok(self)
	}

	fn in_binder<T>(
	mut self,
	value: &ty::Binder<T>,
	print_value: impl FnOnce(Self, &T) -> Result<Self, !>
	) -> Result<Self, !>
	where T: TypeFoldable<'tcx>
	{
	let regions = if value.has_late_bound_regions() {
	self.tcx.collect_referenced_late_bound_regions(value)
	} else {
	FxHashSet::default()
	};

	let mut lifetime_depths =
	self.binders.last().map(\|b\| b.lifetime_depths.end).map_or(0..0, \|i\| i..i);

	let lifetimes = regions.into_iter().map(\|br\| {
	match br {
	ty::BrAnon(i) => {
	// FIXME(eddyb) for some reason, `anonymize_late_bound_regions` starts at `1`.
	assert_ne!(i, 0);
	i - 1
	},
	_ => bug!("symbol_names: non-anonymized region `{:?}` in `{:?}`", br, value),
	}
	}).max().map_or(0, \|max\| max + 1);

	self.push_opt_integer_62("G", lifetimes as u64);
	lifetime_depths.end += lifetimes;

	self.binders.push(BinderLevel { lifetime_depths });
	self = print_value(self, value.skip_binder())?;
	self.binders.pop();

	Ok(self)
	}
	}

	impl Printer<'tcx> for SymbolMangler<'tcx> {
	type Error = !;

	type Path = Self;
	type Region = Self;
	type Type = Self;
	type DynExistential = Self;
	type Const = Self;

	fn tcx(&self) -> TyCtxt<'tcx> {
	self.tcx
	}

	fn print_def_path(
	mut self,
	def_id: DefId,
	substs: &'tcx [Kind<'tcx>],
	) -> Result<Self::Path, Self::Error> {
	if let Some(&i) = self.compress.as_ref().and_then(\|c\| c.paths.get(&(def_id, substs))) {
	return self.print_backref(i);
	}
	let start = self.out.len();

	self = self.default_print_def_path(def_id, substs)?;

	// Only cache paths that do not refer to an enclosing
	// binder (which would change depending on context).
	if !substs.iter().any(\|k\| k.has_escaping_bound_vars()) {
	if let Some(c) = &mut self.compress {
	c.paths.insert((def_id, substs), start);
	}
	}
	Ok(self)
	}

	fn print_impl_path(
	self,
	impl_def_id: DefId,
	substs: &'tcx [Kind<'tcx>],
	mut self_ty: Ty<'tcx>,
	mut impl_trait_ref: Option<ty::TraitRef<'tcx>>,
	) -> Result<Self::Path, Self::Error> {
	let key = self.tcx.def_key(impl_def_id);
	let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };

	let mut param_env = self.tcx.param_env(impl_def_id)
	.with_reveal_all();
	if !substs.is_empty() {
	param_env = param_env.subst(self.tcx, substs);
	}

	match &mut impl_trait_ref {
	Some(impl_trait_ref) => {
	assert_eq!(impl_trait_ref.self_ty(), self_ty);
	*impl_trait_ref =
	self.tcx.normalize_erasing_regions(param_env, *impl_trait_ref);
	self_ty = impl_trait_ref.self_ty();
	}
	None => {
	self_ty = self.tcx.normalize_erasing_regions(param_env, self_ty);
	}
	}

	self.path_append_impl(
	\|cx\| cx.print_def_path(parent_def_id, &[]),
	&key.disambiguated_data,
	self_ty,
	impl_trait_ref,
	)
	}

	fn print_region(
	mut self,
	region: ty::Region<'_>,
	) -> Result<Self::Region, Self::Error> {
	let i = match *region {
	// Erased lifetimes use the index 0, for a
	// shorter mangling of `L_`.
	ty::ReErased => 0,

	// Late-bound lifetimes use indices starting at 1,
	// see `BinderLevel` for more details.
	ty::ReLateBound(debruijn, ty::BrAnon(i)) => {
	// FIXME(eddyb) for some reason, `anonymize_late_bound_regions` starts at `1`.
	assert_ne!(i, 0);
	let i = i - 1;

	let binder = &self.binders[self.binders.len() - 1 - debruijn.index()];
	let depth = binder.lifetime_depths.start + i;

	1 + (self.binders.last().unwrap().lifetime_depths.end - 1 - depth)
	}

	_ => bug!("symbol_names: non-erased region `{:?}`", region),
	};
	self.push("L");
	self.push_integer_62(i as u64);
	Ok(self)
	}

	fn print_type(
	mut self,
	ty: Ty<'tcx>,
	) -> Result<Self::Type, Self::Error> {
	// Basic types, never cached (single-character).
	let basic_type = match ty.sty {
	ty::Bool => "b",
	ty::Char => "c",
	ty::Str => "e",
	ty::Tuple(_) if ty.is_unit() => "u",
	ty::Int(IntTy::I8) => "a",
	ty::Int(IntTy::I16) => "s",
	ty::Int(IntTy::I32) => "l",
	ty::Int(IntTy::I64) => "x",
	ty::Int(IntTy::I128) => "n",
	ty::Int(IntTy::Isize) => "i",
	ty::Uint(UintTy::U8) => "h",
	ty::Uint(UintTy::U16) => "t",
	ty::Uint(UintTy::U32) => "m",
	ty::Uint(UintTy::U64) => "y",
	ty::Uint(UintTy::U128) => "o",
	ty::Uint(UintTy::Usize) => "j",
	ty::Float(FloatTy::F32) => "f",
	ty::Float(FloatTy::F64) => "d",
	ty::Never => "z",

	// Placeholders (should be demangled as `_`).
	ty::Param(_) \| ty::Bound(..) \| ty::Placeholder(_) \|
	ty::Infer(_) \| ty::Error => "p",

	_ => "",
	};
	if !basic_type.is_empty() {
	self.push(basic_type);
	return Ok(self);
	}

	if let Some(&i) = self.compress.as_ref().and_then(\|c\| c.types.get(&ty)) {
	return self.print_backref(i);
	}
	let start = self.out.len();

	match ty.sty {
	// Basic types, handled above.
	ty::Bool \| ty::Char \| ty::Str \|
	ty::Int(_) \| ty::Uint(_) \| ty::Float(_) \|
	ty::Never => unreachable!(),
	ty::Tuple(_) if ty.is_unit() => unreachable!(),

	// Placeholders, also handled as part of basic types.
	ty::Param(_) \| ty::Bound(..) \| ty::Placeholder(_) \|
	ty::Infer(_) \| ty::Error => unreachable!(),

	ty::Ref(r, ty, mutbl) => {
	self.push(match mutbl {
	hir::MutImmutable => "R",
	hir::MutMutable => "Q",
	});
	if *r != ty::ReErased {
	self = r.print(self)?;
	}
	self = ty.print(self)?;
	}

	ty::RawPtr(mt) => {
	self.push(match mt.mutbl {
	hir::MutImmutable => "P",
	hir::MutMutable => "O",
	});
	self = mt.ty.print(self)?;
	}

	ty::Array(ty, len) => {
	self.push("A");
	self = ty.print(self)?;
	self = self.print_const(len)?;
	}
	ty::Slice(ty) => {
	self.push("S");
	self = ty.print(self)?;
	}

	ty::Tuple(tys) => {
	self.push("T");
	for ty in tys.iter().map(\|k\| k.expect_ty()) {
	self = ty.print(self)?;
	}
	self.push("E");
	}

	// Mangle all nominal types as paths.
	ty::Adt(&ty::AdtDef { did: def_id, .. }, substs) \|
	ty::FnDef(def_id, substs) \|
	ty::Opaque(def_id, substs) \|
	ty::Projection(ty::ProjectionTy { item_def_id: def_id, substs }) \|
	ty::UnnormalizedProjection(ty::ProjectionTy { item_def_id: def_id, substs }) \|
	ty::Closure(def_id, ty::ClosureSubsts { substs }) \|
	ty::Generator(def_id, ty::GeneratorSubsts { substs }, _) => {
	self = self.print_def_path(def_id, substs)?;
	}
	ty::Foreign(def_id) => {
	self = self.print_def_path(def_id, &[])?;
	}

	ty::FnPtr(sig) => {
	self.push("F");
	self = self.in_binder(&sig, \|mut cx, sig\| {
	if sig.unsafety == hir::Unsafety::Unsafe {
	cx.push("U");
	}
	match sig.abi {
	Abi::Rust => {}
	Abi::C => cx.push("KC"),
	abi => {
	cx.push("K");
	let name = abi.name();
	if name.contains('-') {
	cx.push_ident(&name.replace('-', "_"));
	} else {
	cx.push_ident(name);
	}
	}
	}
	for &ty in sig.inputs() {
	cx = ty.print(cx)?;
	}
	if sig.c_variadic {
	cx.push("v");
	}
	cx.push("E");
	sig.output().print(cx)
	})?;
	}

	ty::Dynamic(predicates, r) => {
	self.push("D");
	self = self.in_binder(&predicates, \|cx, predicates\| {
	cx.print_dyn_existential(predicates)
	})?;
	self = r.print(self)?;
	}

	ty::GeneratorWitness(_) => {
	bug!("symbol_names: unexpected `GeneratorWitness`")
	}
	}

	// Only cache types that do not refer to an enclosing
	// binder (which would change depending on context).
	if !ty.has_escaping_bound_vars() {
	if let Some(c) = &mut self.compress {
	c.types.insert(ty, start);
	}
	}
	Ok(self)
	}

	fn print_dyn_existential(
	mut self,
	predicates: &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
	) -> Result<Self::DynExistential, Self::Error> {
	for predicate in predicates {
	match *predicate {
	ty::ExistentialPredicate::Trait(trait_ref) => {
	// Use a type that can't appear in defaults of type parameters.
	let dummy_self = self.tcx.mk_ty_infer(ty::FreshTy(0));
	let trait_ref = trait_ref.with_self_ty(self.tcx, dummy_self);
	self = self.print_def_path(trait_ref.def_id, trait_ref.substs)?;
	}
	ty::ExistentialPredicate::Projection(projection) => {
	let name = self.tcx.associated_item(projection.item_def_id).ident;
	self.push("p");
	self.push_ident(&name.as_str());
	self = projection.ty.print(self)?;
	}
	ty::ExistentialPredicate::AutoTrait(def_id) => {
	self = self.print_def_path(def_id, &[])?;
	}
	}
	}
	self.push("E");
	Ok(self)
	}

	fn print_const(
	mut self,
	ct: &'tcx ty::Const<'tcx>,
	) -> Result<Self::Const, Self::Error> {
	if let Some(&i) = self.compress.as_ref().and_then(\|c\| c.consts.get(&ct)) {
	return self.print_backref(i);
	}
	let start = self.out.len();

	match ct.ty.sty {
	ty::Uint(_) => {}
	_ => {
	bug!("symbol_names: unsupported constant of type `{}` ({:?})",
	ct.ty, ct);
	}
	}
	self = ct.ty.print(self)?;

	if let Some(bits) = ct.try_eval_bits(self.tcx, ty::ParamEnv::reveal_all(), ct.ty) {
	let _ = write!(self.out, "{:x}_", bits);
	} else {
	// NOTE(eddyb) despite having the path, we need to
	// encode a placeholder, as the path could refer
	// back to e.g. an `impl` using the constant.
	self.push("p");
	}

	// Only cache consts that do not refer to an enclosing
	// binder (which would change depending on context).
	if !ct.has_escaping_bound_vars() {
	if let Some(c) = &mut self.compress {
	c.consts.insert(ct, start);
	}
	}
	Ok(self)
	}

	fn path_crate(
	mut self,
	cnum: CrateNum,
	) -> Result<Self::Path, Self::Error> {
	self.push("C");
	let fingerprint = self.tcx.crate_disambiguator(cnum).to_fingerprint();
	self.push_disambiguator(fingerprint.to_smaller_hash());
	let name = self.tcx.original_crate_name(cnum).as_str();
	self.push_ident(&name);
	Ok(self)
	}
	fn path_qualified(
	mut self,
	self_ty: Ty<'tcx>,
	trait_ref: Option<ty::TraitRef<'tcx>>,
	) -> Result<Self::Path, Self::Error> {
	assert!(trait_ref.is_some());
	let trait_ref = trait_ref.unwrap();

	self.push("Y");
	self = self_ty.print(self)?;
	self.print_def_path(trait_ref.def_id, trait_ref.substs)
	}

	fn path_append_impl(
	mut self,
	print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
	disambiguated_data: &DisambiguatedDefPathData,
	self_ty: Ty<'tcx>,
	trait_ref: Option<ty::TraitRef<'tcx>>,
	) -> Result<Self::Path, Self::Error> {
	self.push(match trait_ref {
	Some(_) => "X",
	None => "M",
	});
	self.push_disambiguator(disambiguated_data.disambiguator as u64);
	self = print_prefix(self)?;
	self = self_ty.print(self)?;
	if let Some(trait_ref) = trait_ref {
	self = self.print_def_path(trait_ref.def_id, trait_ref.substs)?;
	}
	Ok(self)
	}
	fn path_append(
	self,
	print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
	disambiguated_data: &DisambiguatedDefPathData,
	) -> Result<Self::Path, Self::Error> {
	let ns = match disambiguated_data.data {
	// Uppercase categories are more stable than lowercase ones.
	DefPathData::TypeNs(_) => 't',
	DefPathData::ValueNs(_) => 'v',
	DefPathData::ClosureExpr => 'C',
	DefPathData::Ctor => 'c',
	DefPathData::AnonConst => 'k',
	DefPathData::ImplTrait => 'i',

	// These should never show up as `path_append` arguments.
	DefPathData::CrateRoot
	\| DefPathData::Misc
	\| DefPathData::Impl
	\| DefPathData::MacroNs(_)
	\| DefPathData::LifetimeNs(_)
	\| DefPathData::GlobalMetaData(_) => {
	bug!("symbol_names: unexpected DefPathData: {:?}", disambiguated_data.data)
	}
	};

	let name = disambiguated_data.data.get_opt_name().map(\|s\| s.as_str());

	self.path_append_ns(
	print_prefix,
	ns,
	disambiguated_data.disambiguator as u64,
	name.as_ref().map_or("", \|s\| &s[..])
	)
	}
	fn path_generic_args(
	mut self,
	print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
	args: &[Kind<'tcx>],
	) -> Result<Self::Path, Self::Error> {
	// Don't print any regions if they're all erased.
	let print_regions = args.iter().any(\|arg\| {
	match arg.unpack() {
	UnpackedKind::Lifetime(r) => *r != ty::ReErased,
	_ => false,
	}
	});
	let args = args.iter().cloned().filter(\|arg\| {
	match arg.unpack() {
	UnpackedKind::Lifetime(_) => print_regions,
	_ => true,
	}
	});

	if args.clone().next().is_none() {
	return print_prefix(self);
	}

	self.push("I");
	self = print_prefix(self)?;
	for arg in args {
	match arg.unpack() {
	UnpackedKind::Lifetime(lt) => {
	self = lt.print(self)?;
	}
	UnpackedKind::Type(ty) => {
	self = ty.print(self)?;
	}
	UnpackedKind::Const(c) => {
	self.push("K");
	// FIXME(const_generics) implement `ty::print::Print` on `ty::Const`.
	// self = c.print(self)?;
	self = self.print_const(c)?;
	}
	}
	}
	self.push("E");

	Ok(self)
	}
	}