src/librustc_symbol_mangling/v0.rs

   1 use rustc_ast::{FloatTy, IntTy, UintTy};
   2 use rustc_data_structures::base_n;
   3 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   4 use rustc_hir as hir;
   5 use rustc_hir::def_id::{CrateNum, DefId};
   6 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
   7 use rustc_middle::ty::print::{Print, Printer};
   8 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
   9 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeFoldable};
  10 use rustc_target::spec::abi::Abi;
  11
  12 use std::fmt::Write;
  13 use std::ops::Range;
  14
  15 pub(super) fn mangle(
  16     tcx: TyCtxt<'tcx>,
  17     instance: Instance<'tcx>,
  18     instantiating_crate: Option<CrateNum>,
  19 ) -> String {
  20     let def_id = instance.def_id();
  21     // FIXME(eddyb) this should ideally not be needed.
  22     let substs = tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), instance.substs);
  23
  24     let prefix = "_R";
  25     let mut cx = SymbolMangler {
  26         tcx,
  27         compress: Some(Box::new(CompressionCaches {
  28             start_offset: prefix.len(),
  29
  30             paths: FxHashMap::default(),
  31             types: FxHashMap::default(),
  32             consts: FxHashMap::default(),
  33         })),
  34         binders: vec![],
  35         out: String::from(prefix),
  36     };
  37
  38     // Append `::{shim:...#0}` to shims that can coexist with a non-shim instance.
  39     let shim_kind = match instance.def {
  40         ty::InstanceDef::VtableShim(_) => Some("vtable"),
  41         ty::InstanceDef::ReifyShim(_) => Some("reify"),
  42
  43         _ => None,
  44     };
  45
  46     cx = if let Some(shim_kind) = shim_kind {
  47         cx.path_append_ns(|cx| cx.print_def_path(def_id, substs), 'S', 0, shim_kind).unwrap()
  48     } else {
  49         cx.print_def_path(def_id, substs).unwrap()
  50     };
  51     if let Some(instantiating_crate) = instantiating_crate {
  52         cx = cx.print_def_path(instantiating_crate.as_def_id(), &[]).unwrap();
  53     }
  54     cx.out
  55 }
  56
  57 struct CompressionCaches<'tcx> {
  58     // The length of the prefix in `out` (e.g. 2 for `_R`).
  59     start_offset: usize,
  60
  61     // The values are start positions in `out`, in bytes.
  62     paths: FxHashMap<(DefId, &'tcx [GenericArg<'tcx>]), usize>,
  63     types: FxHashMap<Ty<'tcx>, usize>,
  64     consts: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
  65 }
  66
  67 struct BinderLevel {
  68     /// The range of distances from the root of what's
  69     /// being printed, to the lifetimes in a binder.
  70     /// Specifically, a `BrAnon(i)` lifetime has depth
  71     /// `lifetime_depths.start + i`, going away from the
  72     /// the root and towards its use site, as `i` increases.
  73     /// This is used to flatten rustc's pairing of `BrAnon`
  74     /// (intra-binder disambiguation) with a `DebruijnIndex`
  75     /// (binder addressing), to "true" de Bruijn indices,
  76     /// by subtracting the depth of a certain lifetime, from
  77     /// the innermost depth at its use site.
  78     lifetime_depths: Range<u32>,
  79 }
  80
  81 struct SymbolMangler<'tcx> {
  82     tcx: TyCtxt<'tcx>,
  83     compress: Option<Box<CompressionCaches<'tcx>>>,
  84     binders: Vec<BinderLevel>,
  85     out: String,
  86 }
  87
  88 impl SymbolMangler<'tcx> {
  89     fn push(&mut self, s: &str) {
  90         self.out.push_str(s);
  91     }
  92
  93     /// Push a `_`-terminated base 62 integer, using the format
  94     /// specified in the RFC as `<base-62-number>`, that is:
  95     /// * `x = 0` is encoded as just the `"_"` terminator
  96     /// * `x > 0` is encoded as `x - 1` in base 62, followed by `"_"`,
  97     ///   e.g. `1` becomes `"0_"`, `62` becomes `"Z_"`, etc.
  98     fn push_integer_62(&mut self, x: u64) {
  99         if let Some(x) = x.checked_sub(1) {
 100             base_n::push_str(x as u128, 62, &mut self.out);
 101         }
 102         self.push("_");
 103     }
 104
 105     /// Push a `tag`-prefixed base 62 integer, when larger than `0`, that is:
 106     /// * `x = 0` is encoded as `""` (nothing)
 107     /// * `x > 0` is encoded as the `tag` followed by `push_integer_62(x - 1)`
 108     ///   e.g. `1` becomes `tag + "_"`, `2` becomes `tag + "0_"`, etc.
 109     fn push_opt_integer_62(&mut self, tag: &str, x: u64) {
 110         if let Some(x) = x.checked_sub(1) {
 111             self.push(tag);
 112             self.push_integer_62(x);
 113         }
 114     }
 115
 116     fn push_disambiguator(&mut self, dis: u64) {
 117         self.push_opt_integer_62("s", dis);
 118     }
 119
 120     fn push_ident(&mut self, ident: &str) {
 121         let mut use_punycode = false;
 122         for b in ident.bytes() {
 123             match b {
 124                 b'_' | b'a'..=b'z' | b'A'..=b'Z' | b'0'..=b'9' => {}
 125                 0x80..=0xff => use_punycode = true,
 126                 _ => bug!("symbol_names: bad byte {} in ident {:?}", b, ident),
 127             }
 128         }
 129
 130         let punycode_string;
 131         let ident = if use_punycode {
 132             self.push("u");
 133
 134             // FIXME(eddyb) we should probably roll our own punycode implementation.
 135             let mut punycode_bytes = match ::punycode::encode(ident) {
 136                 Ok(s) => s.into_bytes(),
 137                 Err(()) => bug!("symbol_names: punycode encoding failed for ident {:?}", ident),
 138             };
 139
 140             // Replace `-` with `_`.
 141             if let Some(c) = punycode_bytes.iter_mut().rfind(|&&mut c| c == b'-') {
 142                 *c = b'_';
 143             }
 144
 145             // FIXME(eddyb) avoid rechecking UTF-8 validity.
 146             punycode_string = String::from_utf8(punycode_bytes).unwrap();
 147             &punycode_string
 148         } else {
 149             ident
 150         };
 151
 152         let _ = write!(self.out, "{}", ident.len());
 153
 154         // Write a separating `_` if necessary (leading digit or `_`).
 155         match ident.chars().next() {
 156             Some('_' | '0'..='9') => {
 157                 self.push("_");
 158             }
 159             _ => {}
 160         }
 161
 162         self.push(ident);
 163     }
 164
 165     fn path_append_ns(
 166         mut self,
 167         print_prefix: impl FnOnce(Self) -> Result<Self, !>,
 168         ns: char,
 169         disambiguator: u64,
 170         name: &str,
 171     ) -> Result<Self, !> {
 172         self.push("N");
 173         self.out.push(ns);
 174         self = print_prefix(self)?;
 175         self.push_disambiguator(disambiguator as u64);
 176         self.push_ident(name);
 177         Ok(self)
 178     }
 179
 180     fn print_backref(mut self, i: usize) -> Result<Self, !> {
 181         self.push("B");
 182         self.push_integer_62((i - self.compress.as_ref().unwrap().start_offset) as u64);
 183         Ok(self)
 184     }
 185
 186     fn in_binder<T>(
 187         mut self,
 188         value: &ty::Binder<T>,
 189         print_value: impl FnOnce(Self, &T) -> Result<Self, !>,
 190     ) -> Result<Self, !>
 191     where
 192         T: TypeFoldable<'tcx>,
 193     {
 194         let regions = if value.has_late_bound_regions() {
 195             self.tcx.collect_referenced_late_bound_regions(value)
 196         } else {
 197             FxHashSet::default()
 198         };
 199
 200         let mut lifetime_depths =
 201             self.binders.last().map(|b| b.lifetime_depths.end).map_or(0..0, |i| i..i);
 202
 203         let lifetimes = regions
 204             .into_iter()
 205             .map(|br| {
 206                 match br {
 207                     ty::BrAnon(i) => {
 208                         // FIXME(eddyb) for some reason, `anonymize_late_bound_regions` starts at `1`.
 209                         assert_ne!(i, 0);
 210                         i - 1
 211                     }
 212                     _ => bug!("symbol_names: non-anonymized region `{:?}` in `{:?}`", br, value),
 213                 }
 214             })
 215             .max()
 216             .map_or(0, |max| max + 1);
 217
 218         self.push_opt_integer_62("G", lifetimes as u64);
 219         lifetime_depths.end += lifetimes;
 220
 221         self.binders.push(BinderLevel { lifetime_depths });
 222         self = print_value(self, value.as_ref().skip_binder())?;
 223         self.binders.pop();
 224
 225         Ok(self)
 226     }
 227 }
 228
 229 impl Printer<'tcx> for SymbolMangler<'tcx> {
 230     type Error = !;
 231
 232     type Path = Self;
 233     type Region = Self;
 234     type Type = Self;
 235     type DynExistential = Self;
 236     type Const = Self;
 237
 238     fn tcx(&self) -> TyCtxt<'tcx> {
 239         self.tcx
 240     }
 241
 242     fn print_def_path(
 243         mut self,
 244         def_id: DefId,
 245         substs: &'tcx [GenericArg<'tcx>],
 246     ) -> Result<Self::Path, Self::Error> {
 247         if let Some(&i) = self.compress.as_ref().and_then(|c| c.paths.get(&(def_id, substs))) {
 248             return self.print_backref(i);
 249         }
 250         let start = self.out.len();
 251
 252         self = self.default_print_def_path(def_id, substs)?;
 253
 254         // Only cache paths that do not refer to an enclosing
 255         // binder (which would change depending on context).
 256         if !substs.iter().any(|k| k.has_escaping_bound_vars()) {
 257             if let Some(c) = &mut self.compress {
 258                 c.paths.insert((def_id, substs), start);
 259             }
 260         }
 261         Ok(self)
 262     }
 263
 264     fn print_impl_path(
 265         self,
 266         impl_def_id: DefId,
 267         substs: &'tcx [GenericArg<'tcx>],
 268         mut self_ty: Ty<'tcx>,
 269         mut impl_trait_ref: Option<ty::TraitRef<'tcx>>,
 270     ) -> Result<Self::Path, Self::Error> {
 271         let key = self.tcx.def_key(impl_def_id);
 272         let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };
 273
 274         let mut param_env = self.tcx.param_env_reveal_all_normalized(impl_def_id);
 275         if !substs.is_empty() {
 276             param_env = param_env.subst(self.tcx, substs);
 277         }
 278
 279         match &mut impl_trait_ref {
 280             Some(impl_trait_ref) => {
 281                 assert_eq!(impl_trait_ref.self_ty(), self_ty);
 282                 *impl_trait_ref = self.tcx.normalize_erasing_regions(param_env, *impl_trait_ref);
 283                 self_ty = impl_trait_ref.self_ty();
 284             }
 285             None => {
 286                 self_ty = self.tcx.normalize_erasing_regions(param_env, self_ty);
 287             }
 288         }
 289
 290         self.path_append_impl(
 291             |cx| cx.print_def_path(parent_def_id, &[]),
 292             &key.disambiguated_data,
 293             self_ty,
 294             impl_trait_ref,
 295         )
 296     }
 297
 298     fn print_region(mut self, region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
 299         let i = match *region {
 300             // Erased lifetimes use the index 0, for a
 301             // shorter mangling of `L_`.
 302             ty::ReErased => 0,
 303
 304             // Late-bound lifetimes use indices starting at 1,
 305             // see `BinderLevel` for more details.
 306             ty::ReLateBound(debruijn, ty::BrAnon(i)) => {
 307                 // FIXME(eddyb) for some reason, `anonymize_late_bound_regions` starts at `1`.
 308                 assert_ne!(i, 0);
 309                 let i = i - 1;
 310
 311                 let binder = &self.binders[self.binders.len() - 1 - debruijn.index()];
 312                 let depth = binder.lifetime_depths.start + i;
 313
 314                 1 + (self.binders.last().unwrap().lifetime_depths.end - 1 - depth)
 315             }
 316
 317             _ => bug!("symbol_names: non-erased region `{:?}`", region),
 318         };
 319         self.push("L");
 320         self.push_integer_62(i as u64);
 321         Ok(self)
 322     }
 323
 324     fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
 325         // Basic types, never cached (single-character).
 326         let basic_type = match ty.kind {
 327             ty::Bool => "b",
 328             ty::Char => "c",
 329             ty::Str => "e",
 330             ty::Tuple(_) if ty.is_unit() => "u",
 331             ty::Int(IntTy::I8) => "a",
 332             ty::Int(IntTy::I16) => "s",
 333             ty::Int(IntTy::I32) => "l",
 334             ty::Int(IntTy::I64) => "x",
 335             ty::Int(IntTy::I128) => "n",
 336             ty::Int(IntTy::Isize) => "i",
 337             ty::Uint(UintTy::U8) => "h",
 338             ty::Uint(UintTy::U16) => "t",
 339             ty::Uint(UintTy::U32) => "m",
 340             ty::Uint(UintTy::U64) => "y",
 341             ty::Uint(UintTy::U128) => "o",
 342             ty::Uint(UintTy::Usize) => "j",
 343             ty::Float(FloatTy::F32) => "f",
 344             ty::Float(FloatTy::F64) => "d",
 345             ty::Never => "z",
 346
 347             // Placeholders (should be demangled as `_`).
 348             ty::Param(_) | ty::Bound(..) | ty::Placeholder(_) | ty::Infer(_) | ty::Error(_) => "p",
 349
 350             _ => "",
 351         };
 352         if !basic_type.is_empty() {
 353             self.push(basic_type);
 354             return Ok(self);
 355         }
 356
 357         if let Some(&i) = self.compress.as_ref().and_then(|c| c.types.get(&ty)) {
 358             return self.print_backref(i);
 359         }
 360         let start = self.out.len();
 361
 362         match ty.kind {
 363             // Basic types, handled above.
 364             ty::Bool | ty::Char | ty::Str | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Never => {
 365                 unreachable!()
 366             }
 367             ty::Tuple(_) if ty.is_unit() => unreachable!(),
 368
 369             // Placeholders, also handled as part of basic types.
 370             ty::Param(_) | ty::Bound(..) | ty::Placeholder(_) | ty::Infer(_) | ty::Error(_) => {
 371                 unreachable!()
 372             }
 373
 374             ty::Ref(r, ty, mutbl) => {
 375                 self.push(match mutbl {
 376                     hir::Mutability::Not => "R",
 377                     hir::Mutability::Mut => "Q",
 378                 });
 379                 if *r != ty::ReErased {
 380                     self = r.print(self)?;
 381                 }
 382                 self = ty.print(self)?;
 383             }
 384
 385             ty::RawPtr(mt) => {
 386                 self.push(match mt.mutbl {
 387                     hir::Mutability::Not => "P",
 388                     hir::Mutability::Mut => "O",
 389                 });
 390                 self = mt.ty.print(self)?;
 391             }
 392
 393             ty::Array(ty, len) => {
 394                 self.push("A");
 395                 self = ty.print(self)?;
 396                 self = self.print_const(len)?;
 397             }
 398             ty::Slice(ty) => {
 399                 self.push("S");
 400                 self = ty.print(self)?;
 401             }
 402
 403             ty::Tuple(tys) => {
 404                 self.push("T");
 405                 for ty in tys.iter().map(|k| k.expect_ty()) {
 406                     self = ty.print(self)?;
 407                 }
 408                 self.push("E");
 409             }
 410
 411             // Mangle all nominal types as paths.
 412             ty::Adt(&ty::AdtDef { did: def_id, .. }, substs)
 413             | ty::FnDef(def_id, substs)
 414             | ty::Opaque(def_id, substs)
 415             | ty::Projection(ty::ProjectionTy { item_def_id: def_id, substs })
 416             | ty::Closure(def_id, substs)
 417             | ty::Generator(def_id, substs, _) => {
 418                 self = self.print_def_path(def_id, substs)?;
 419             }
 420             ty::Foreign(def_id) => {
 421                 self = self.print_def_path(def_id, &[])?;
 422             }
 423
 424             ty::FnPtr(sig) => {
 425                 self.push("F");
 426                 self = self.in_binder(&sig, |mut cx, sig| {
 427                     if sig.unsafety == hir::Unsafety::Unsafe {
 428                         cx.push("U");
 429                     }
 430                     match sig.abi {
 431                         Abi::Rust => {}
 432                         Abi::C => cx.push("KC"),
 433                         abi => {
 434                             cx.push("K");
 435                             let name = abi.name();
 436                             if name.contains('-') {
 437                                 cx.push_ident(&name.replace('-', "_"));
 438                             } else {
 439                                 cx.push_ident(name);
 440                             }
 441                         }
 442                     }
 443                     for &ty in sig.inputs() {
 444                         cx = ty.print(cx)?;
 445                     }
 446                     if sig.c_variadic {
 447                         cx.push("v");
 448                     }
 449                     cx.push("E");
 450                     sig.output().print(cx)
 451                 })?;
 452             }
 453
 454             ty::Dynamic(predicates, r) => {
 455                 self.push("D");
 456                 self = self.in_binder(&predicates, |cx, predicates| {
 457                     cx.print_dyn_existential(predicates)
 458                 })?;
 459                 self = r.print(self)?;
 460             }
 461
 462             ty::GeneratorWitness(_) => bug!("symbol_names: unexpected `GeneratorWitness`"),
 463         }
 464
 465         // Only cache types that do not refer to an enclosing
 466         // binder (which would change depending on context).
 467         if !ty.has_escaping_bound_vars() {
 468             if let Some(c) = &mut self.compress {
 469                 c.types.insert(ty, start);
 470             }
 471         }
 472         Ok(self)
 473     }
 474
 475     fn print_dyn_existential(
 476         mut self,
 477         predicates: &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
 478     ) -> Result<Self::DynExistential, Self::Error> {
 479         for predicate in predicates {
 480             match predicate {
 481                 ty::ExistentialPredicate::Trait(trait_ref) => {
 482                     // Use a type that can't appear in defaults of type parameters.
 483                     let dummy_self = self.tcx.mk_ty_infer(ty::FreshTy(0));
 484                     let trait_ref = trait_ref.with_self_ty(self.tcx, dummy_self);
 485                     self = self.print_def_path(trait_ref.def_id, trait_ref.substs)?;
 486                 }
 487                 ty::ExistentialPredicate::Projection(projection) => {
 488                     let name = self.tcx.associated_item(projection.item_def_id).ident;
 489                     self.push("p");
 490                     self.push_ident(&name.as_str());
 491                     self = projection.ty.print(self)?;
 492                 }
 493                 ty::ExistentialPredicate::AutoTrait(def_id) => {
 494                     self = self.print_def_path(def_id, &[])?;
 495                 }
 496             }
 497         }
 498         self.push("E");
 499         Ok(self)
 500     }
 501
 502     fn print_const(mut self, ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
 503         if let Some(&i) = self.compress.as_ref().and_then(|c| c.consts.get(&ct)) {
 504             return self.print_backref(i);
 505         }
 506         let start = self.out.len();
 507
 508         match ct.ty.kind {
 509             ty::Uint(_) => {}
 510             _ => {
 511                 bug!("symbol_names: unsupported constant of type `{}` ({:?})", ct.ty, ct);
 512             }
 513         }
 514         self = ct.ty.print(self)?;
 515
 516         if let Some(bits) = ct.try_eval_bits(self.tcx, ty::ParamEnv::reveal_all(), ct.ty) {
 517             let _ = write!(self.out, "{:x}_", bits);
 518         } else {
 519             // NOTE(eddyb) despite having the path, we need to
 520             // encode a placeholder, as the path could refer
 521             // back to e.g. an `impl` using the constant.
 522             self.push("p");
 523         }
 524
 525         // Only cache consts that do not refer to an enclosing
 526         // binder (which would change depending on context).
 527         if !ct.has_escaping_bound_vars() {
 528             if let Some(c) = &mut self.compress {
 529                 c.consts.insert(ct, start);
 530             }
 531         }
 532         Ok(self)
 533     }
 534
 535     fn path_crate(mut self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
 536         self.push("C");
 537         let fingerprint = self.tcx.crate_disambiguator(cnum).to_fingerprint();
 538         self.push_disambiguator(fingerprint.to_smaller_hash());
 539         let name = self.tcx.original_crate_name(cnum).as_str();
 540         self.push_ident(&name);
 541         Ok(self)
 542     }
 543     fn path_qualified(
 544         mut self,
 545         self_ty: Ty<'tcx>,
 546         trait_ref: Option<ty::TraitRef<'tcx>>,
 547     ) -> Result<Self::Path, Self::Error> {
 548         assert!(trait_ref.is_some());
 549         let trait_ref = trait_ref.unwrap();
 550
 551         self.push("Y");
 552         self = self_ty.print(self)?;
 553         self.print_def_path(trait_ref.def_id, trait_ref.substs)
 554     }
 555
 556     fn path_append_impl(
 557         mut self,
 558         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
 559         disambiguated_data: &DisambiguatedDefPathData,
 560         self_ty: Ty<'tcx>,
 561         trait_ref: Option<ty::TraitRef<'tcx>>,
 562     ) -> Result<Self::Path, Self::Error> {
 563         self.push(match trait_ref {
 564             Some(_) => "X",
 565             None => "M",
 566         });
 567         self.push_disambiguator(disambiguated_data.disambiguator as u64);
 568         self = print_prefix(self)?;
 569         self = self_ty.print(self)?;
 570         if let Some(trait_ref) = trait_ref {
 571             self = self.print_def_path(trait_ref.def_id, trait_ref.substs)?;
 572         }
 573         Ok(self)
 574     }
 575     fn path_append(
 576         self,
 577         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
 578         disambiguated_data: &DisambiguatedDefPathData,
 579     ) -> Result<Self::Path, Self::Error> {
 580         let ns = match disambiguated_data.data {
 581             // Uppercase categories are more stable than lowercase ones.
 582             DefPathData::TypeNs(_) => 't',
 583             DefPathData::ValueNs(_) => 'v',
 584             DefPathData::ClosureExpr => 'C',
 585             DefPathData::Ctor => 'c',
 586             DefPathData::AnonConst => 'k',
 587             DefPathData::ImplTrait => 'i',
 588
 589             // These should never show up as `path_append` arguments.
 590             DefPathData::CrateRoot
 591             | DefPathData::Misc
 592             | DefPathData::Impl
 593             | DefPathData::MacroNs(_)
 594             | DefPathData::LifetimeNs(_) => {
 595                 bug!("symbol_names: unexpected DefPathData: {:?}", disambiguated_data.data)
 596             }
 597         };
 598
 599         let name = disambiguated_data.data.get_opt_name().map(|s| s.as_str());
 600
 601         self.path_append_ns(
 602             print_prefix,
 603             ns,
 604             disambiguated_data.disambiguator as u64,
 605             name.as_ref().map_or("", |s| &s[..]),
 606         )
 607     }
 608     fn path_generic_args(
 609         mut self,
 610         print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
 611         args: &[GenericArg<'tcx>],
 612     ) -> Result<Self::Path, Self::Error> {
 613         // Don't print any regions if they're all erased.
 614         let print_regions = args.iter().any(|arg| match arg.unpack() {
 615             GenericArgKind::Lifetime(r) => *r != ty::ReErased,
 616             _ => false,
 617         });
 618         let args = args.iter().cloned().filter(|arg| match arg.unpack() {
 619             GenericArgKind::Lifetime(_) => print_regions,
 620             _ => true,
 621         });
 622
 623         if args.clone().next().is_none() {
 624             return print_prefix(self);
 625         }
 626
 627         self.push("I");
 628         self = print_prefix(self)?;
 629         for arg in args {
 630             match arg.unpack() {
 631                 GenericArgKind::Lifetime(lt) => {
 632                     self = lt.print(self)?;
 633                 }
 634                 GenericArgKind::Type(ty) => {
 635                     self = ty.print(self)?;
 636                 }
 637                 GenericArgKind::Const(c) => {
 638                     self.push("K");
 639                     self = c.print(self)?;
 640                 }
 641             }
 642         }
 643         self.push("E");
 644
 645         Ok(self)
 646     }
 647 }