Auto merge of #34012 - eddyb:tick-erased, r=nikomatsakis

rustc: add ReErased to be used by trait selection, MIR and trans.

`ReErased` replaces `ReStatic` (i.e. `'static`) for erasing regions.
Using a distinct lifetime helps prevent accidental mix-ups between the two.
It also allows cleaner type printing (see test changes), including in symbol names:
```rust
str..pattern..CharSearcher$LT$$u27$static$GT$::drop.30560::h840c2f2afc03bbea // before
str..pattern..CharSearcher::drop.30561::h6bd31d2af614377a // after
```
Not that we should be producing symbols this way, but it's still better.

Author: bors

src/librustc/infer/combine.rs

@@ -337,8 +337,10 @@ impl<'cx, 'gcx, 'tcx> ty::fold::TypeFolder<'gcx, 'tcx> for Generalizer<'cx, 'gcx
 
     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
         match r {
-            // Never make variables for regions bound within the type itself.
-            ty::ReLateBound(..) => { return r; }
+            // Never make variables for regions bound within the type itself,
+            // nor for erased regions.
+            ty::ReLateBound(..) |
+            ty::ReErased => { return r; }
 
             // Early-bound regions should really have been substituted away before
             // we get to this point.

src/librustc/infer/error_reporting.rs

@@ -216,7 +216,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             //
             // We shouldn't really be having unification failures with ReVar
             // and ReLateBound though.
-            ty::ReSkolemized(..) | ty::ReVar(_) | ty::ReLateBound(..) => {
+            ty::ReSkolemized(..) |
+            ty::ReVar(_) |
+            ty::ReLateBound(..) |
+            ty::ReErased => {
                 (format!("lifetime {:?}", region), None)
             }
         };

src/librustc/infer/freshen.rs

@@ -23,7 +23,7 @@
 //! error messages or in any other form. Freshening is only really useful as an internal detail.
 //!
 //! __An important detail concerning regions.__ The freshener also replaces *all* regions with
-//! 'static. The reason behind this is that, in general, we do not take region relationships into
+//! 'erased. The reason behind this is that, in general, we do not take region relationships into
 //! account when making type-overloaded decisions. This is important because of the design of the
 //! region inferencer, which is not based on unification but rather on accumulating and then
 //! solving a set of constraints. In contrast, the type inferencer assigns a value to each type
@@ -96,9 +96,10 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
             ty::ReScope(_) |
             ty::ReVar(_) |
             ty::ReSkolemized(..) |
-            ty::ReEmpty => {
-                // replace all free regions with 'static
-                ty::ReStatic
+            ty::ReEmpty |
+            ty::ReErased => {
+                // replace all free regions with 'erased
+                ty::ReErased
             }
         }
     }

src/librustc/infer/region_inference/mod.rs

@@ -25,7 +25,7 @@ use rustc_data_structures::unify::{self, UnificationTable};
 use middle::free_region::FreeRegionMap;
 use ty::{self, Ty, TyCtxt};
 use ty::{BoundRegion, Region, RegionVid};
-use ty::{ReEmpty, ReStatic, ReFree, ReEarlyBound};
+use ty::{ReEmpty, ReStatic, ReFree, ReEarlyBound, ReErased};
 use ty::{ReLateBound, ReScope, ReVar, ReSkolemized, BrFresh};
 
 use std::cell::{Cell, RefCell};
@@ -918,8 +918,10 @@ impl<'a, 'gcx, 'tcx> RegionVarBindings<'a, 'gcx, 'tcx> {
             (ReLateBound(..), _) |
             (_, ReLateBound(..)) |
             (ReEarlyBound(..), _) |
-            (_, ReEarlyBound(..)) => {
-                bug!("cannot relate bound region: LUB({:?}, {:?})", a, b);
+            (_, ReEarlyBound(..)) |
+            (ReErased, _) |
+            (_, ReErased) => {
+                bug!("cannot relate region: LUB({:?}, {:?})", a, b);
             }
 
             (ReStatic, _) | (_, ReStatic) => {

src/librustc/ty/flags.rs

@@ -187,7 +187,7 @@ impl FlagComputation {
             }
             ty::ReLateBound(debruijn, _) => { self.add_depth(debruijn.depth); }
             ty::ReEarlyBound(..) => { self.add_flags(TypeFlags::HAS_RE_EARLY_BOUND); }
-            ty::ReStatic => {}
+            ty::ReStatic | ty::ReErased => {}
             _ => { self.add_flags(TypeFlags::HAS_FREE_REGIONS); }
         }
 

src/librustc/ty/fold.rs

@@ -421,12 +421,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         collector.regions
     }
 
-    /// Replace any late-bound regions bound in `value` with `'static`. Useful in trans but also
+    /// Replace any late-bound regions bound in `value` with `'erased`. Useful in trans but also
     /// method lookup and a few other places where precise region relationships are not required.
     pub fn erase_late_bound_regions<T>(self, value: &Binder<T>) -> T
         where T : TypeFoldable<'tcx>
     {
-        self.replace_late_bound_regions(value, |_| ty::ReStatic).0
+        self.replace_late_bound_regions(value, |_| ty::ReErased).0
     }
 
     /// Rewrite any late-bound regions so that they are anonymous.  Region numbers are
@@ -547,15 +547,15 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             fn fold_region(&mut self, r: ty::Region) -> ty::Region {
                 // because late-bound regions affect subtyping, we can't
                 // erase the bound/free distinction, but we can replace
-                // all free regions with 'static.
+                // all free regions with 'erased.
                 //
                 // Note that we *CAN* replace early-bound regions -- the
                 // type system never "sees" those, they get substituted
-                // away. In trans, they will always be erased to 'static
+                // away. In trans, they will always be erased to 'erased
                 // whenever a substitution occurs.
                 match r {
                     ty::ReLateBound(..) => r,
-                    _ => ty::ReStatic
+                    _ => ty::ReErased
                 }
             }
         }
@@ -651,7 +651,7 @@ impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
             // does this represent a region that cannot be named
             // in a global way? used in fulfillment caching.
             match r {
-                ty::ReStatic | ty::ReEmpty => {}
+                ty::ReStatic | ty::ReEmpty | ty::ReErased => {}
                 _ => return true,
             }
         }

src/librustc/ty/sty.rs

@@ -705,6 +705,9 @@ pub enum Region {
     /// The only way to get an instance of ReEmpty is to have a region
     /// variable with no constraints.
     ReEmpty,
+
+    /// Erased region, used by trait selection, in MIR and during trans.
+    ReErased,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]

src/librustc/ty/subst.rs

@@ -89,7 +89,7 @@ impl<'a, 'gcx, 'tcx> Substs<'tcx> {
 
     pub fn erase_regions(self) -> Substs<'tcx> {
         let Substs { types, regions } = self;
-        let regions = regions.map(|_| ty::ReStatic);
+        let regions = regions.map(|_| ty::ReErased);
         Substs { types: types, regions: regions }
     }
 

src/librustc/ty/util.rs

@@ -348,7 +348,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
             let region = |state: &mut SipHasher, r: ty::Region| {
                 match r {
-                    ty::ReStatic => {}
+                    ty::ReStatic | ty::ReErased => {}
                     ty::ReLateBound(db, ty::BrAnon(i)) => {
                         db.hash(state);
                         i.hash(state);

src/librustc/util/ppaux.rs

@@ -148,28 +148,36 @@ pub fn parameterized<GG>(f: &mut fmt::Formatter,
             write!(f, "{}", cont)
         }
     };
-    let print_region = |f: &mut fmt::Formatter, region: &ty::Region| -> _ {
-        if verbose {
-            write!(f, "{:?}", region)
-        } else {
-            let s = region.to_string();
-            if s.is_empty() {
-                // This happens when the value of the region
-                // parameter is not easily serialized. This may be
-                // because the user omitted it in the first place,
-                // or because it refers to some block in the code,
-                // etc. I'm not sure how best to serialize this.
-                write!(f, "'_")
+
+    let print_regions = |f: &mut fmt::Formatter, start: &str, regions: &[ty::Region]| {
+        // Don't print any regions if they're all erased.
+        if regions.iter().all(|r| *r == ty::ReErased) {
+            return Ok(());
+        }
+
+        for region in regions {
+            start_or_continue(f, start, ", ")?;
+            if verbose {
+                write!(f, "{:?}", region)?;
             } else {
-                write!(f, "{}", s)
+                let s = region.to_string();
+                if s.is_empty() {
+                    // This happens when the value of the region
+                    // parameter is not easily serialized. This may be
+                    // because the user omitted it in the first place,
+                    // or because it refers to some block in the code,
+                    // etc. I'm not sure how best to serialize this.
+                    write!(f, "'_")?;
+                } else {
+                    write!(f, "{}", s)?;
+                }
             }
         }
+
+        Ok(())
     };
 
-    for region in substs.regions.get_slice(subst::TypeSpace) {
-        start_or_continue(f, "<", ", ")?;
-        print_region(f, region)?;
-    }
+    print_regions(f, "<", substs.regions.get_slice(subst::TypeSpace))?;
 
     let num_supplied_defaults = if verbose {
         0
@@ -211,10 +219,7 @@ pub fn parameterized<GG>(f: &mut fmt::Formatter,
             write!(f, "::{}", item_name)?;
         }
 
-        for region in substs.regions.get_slice(subst::FnSpace) {
-            start_or_continue(f, "::<", ", ")?;
-            print_region(f, region)?;
-        }
+        print_regions(f, "::<", substs.regions.get_slice(subst::FnSpace))?;
 
         // FIXME: consider being smart with defaults here too
         for ty in substs.types.get_slice(subst::FnSpace) {
@@ -536,7 +541,9 @@ impl fmt::Debug for ty::Region {
                 write!(f, "ReSkolemized({}, {:?})", id.index, bound_region)
             }
 
-            ty::ReEmpty => write!(f, "ReEmpty")
+            ty::ReEmpty => write!(f, "ReEmpty"),
+
+            ty::ReErased => write!(f, "ReErased")
         }
     }
 }
@@ -600,7 +607,8 @@ impl fmt::Display for ty::Region {
                 write!(f, "{}", br)
             }
             ty::ReScope(_) |
-            ty::ReVar(_) => Ok(()),
+            ty::ReVar(_) |
+            ty::ReErased => Ok(()),
             ty::ReStatic => write!(f, "'static"),
             ty::ReEmpty => write!(f, "'<empty>"),
         }

src/librustc_borrowck/borrowck/gather_loans/mod.rs

@@ -369,7 +369,8 @@ impl<'a, 'tcx> GatherLoanCtxt<'a, 'tcx> {
                     ty::ReLateBound(..) |
                     ty::ReEarlyBound(..) |
                     ty::ReVar(..) |
-                    ty::ReSkolemized(..) => {
+                    ty::ReSkolemized(..) |
+                    ty::ReErased => {
                         span_bug!(
                             cmt.span,
                             "invalid borrow lifetime: {:?}",

src/librustc_metadata/tydecode.rs

@@ -221,12 +221,9 @@ impl<'a,'tcx> TyDecoder<'a,'tcx> {
                 assert_eq!(self.next(), '|');
                 ty::ReScope(scope)
             }
-            't' => {
-                ty::ReStatic
-            }
-            'e' => {
-                ty::ReStatic
-            }
+            't' => ty::ReStatic,
+            'e' => ty::ReEmpty,
+            'E' => ty::ReErased,
             _ => bug!("parse_region: bad input")
         }
     }

src/librustc_metadata/tyencode.rs

@@ -283,6 +283,9 @@ pub fn enc_region(w: &mut Cursor<Vec<u8>>, cx: &ctxt, r: ty::Region) {
         ty::ReEmpty => {
             write!(w, "e");
         }
+        ty::ReErased => {
+            write!(w, "E");
+        }
         ty::ReVar(_) | ty::ReSkolemized(..) => {
             // these should not crop up after typeck
             bug!("cannot encode region variables");

src/librustc_trans/_match.rs

@@ -731,7 +731,7 @@ fn bind_subslice_pat(bcx: Block,
     let slice_begin = InBoundsGEP(bcx, base, &[C_uint(bcx.ccx(), offset_left)]);
     let slice_len_offset = C_uint(bcx.ccx(), offset_left + offset_right);
     let slice_len = Sub(bcx, len, slice_len_offset, DebugLoc::None);
-    let slice_ty = bcx.tcx().mk_imm_ref(bcx.tcx().mk_region(ty::ReStatic),
+    let slice_ty = bcx.tcx().mk_imm_ref(bcx.tcx().mk_region(ty::ReErased),
                                          bcx.tcx().mk_slice(unit_ty));
     let scratch = rvalue_scratch_datum(bcx, slice_ty, "");
     Store(bcx, slice_begin, expr::get_dataptr(bcx, scratch.val));

src/librustc_trans/callee.rs

@@ -328,7 +328,7 @@ pub fn trans_fn_pointer_shim<'a, 'tcx>(
     };
 
     let bare_fn_ty_maybe_ref = if is_by_ref {
-        tcx.mk_imm_ref(tcx.mk_region(ty::ReStatic), bare_fn_ty)
+        tcx.mk_imm_ref(tcx.mk_region(ty::ReErased), bare_fn_ty)
     } else {
         bare_fn_ty
     };

src/librustc_trans/closure.rs

@@ -123,10 +123,10 @@ fn get_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                            -> Ty<'tcx> {
     match tcx.closure_kind(closure_id) {
         ty::ClosureKind::Fn => {
-            tcx.mk_imm_ref(tcx.mk_region(ty::ReStatic), fn_ty)
+            tcx.mk_imm_ref(tcx.mk_region(ty::ReErased), fn_ty)
         }
         ty::ClosureKind::FnMut => {
-            tcx.mk_mut_ref(tcx.mk_region(ty::ReStatic), fn_ty)
+            tcx.mk_mut_ref(tcx.mk_region(ty::ReErased), fn_ty)
         }
         ty::ClosureKind::FnOnce => fn_ty,
     }
@@ -344,7 +344,7 @@ fn trans_fn_once_adapter_shim<'a, 'tcx>(
     // Find a version of the closure type. Substitute static for the
     // region since it doesn't really matter.
     let closure_ty = tcx.mk_closure_from_closure_substs(closure_def_id, substs);
-    let ref_closure_ty = tcx.mk_imm_ref(tcx.mk_region(ty::ReStatic), closure_ty);
+    let ref_closure_ty = tcx.mk_imm_ref(tcx.mk_region(ty::ReErased), closure_ty);
 
     // Make a version with the type of by-ref closure.
     let ty::ClosureTy { unsafety, abi, mut sig } =

src/librustc_trans/consts.rs

@@ -382,7 +382,7 @@ pub fn const_expr<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                     // Don't copy data to do a deref+ref
                     // (i.e., skip the last auto-deref).
                     llconst = addr_of(cx, llconst, type_of::align_of(cx, ty), "autoref");
-                    ty = cx.tcx().mk_imm_ref(cx.tcx().mk_region(ty::ReStatic), ty);
+                    ty = cx.tcx().mk_imm_ref(cx.tcx().mk_region(ty::ReErased), ty);
                 }
             } else if adj.autoderefs > 0 {
                 let (dv, dt) = const_deref(cx, llconst, ty);

src/librustc_trans/context.rs

@@ -495,7 +495,7 @@ impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
         assert!(scheme.generics.types.is_empty());
         self.tcx().mk_substs(
             Substs::new(VecPerParamSpace::empty(),
-                        scheme.generics.regions.map(|_| ty::ReStatic)))
+                        scheme.generics.regions.map(|_| ty::ReErased)))
     }
 
     pub fn symbol_hasher(&self) -> &RefCell<Sha256> {

src/librustc_trans/expr.rs

@@ -1978,7 +1978,7 @@ fn auto_ref<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     // Compute final type. Note that we are loose with the region and
     // mutability, since those things don't matter in trans.
     let referent_ty = lv_datum.ty;
-    let ptr_ty = bcx.tcx().mk_imm_ref(bcx.tcx().mk_region(ty::ReStatic), referent_ty);
+    let ptr_ty = bcx.tcx().mk_imm_ref(bcx.tcx().mk_region(ty::ReErased), referent_ty);
 
     // Construct the resulting datum. The right datum to return here would be an Lvalue datum,
     // because there is cleanup scheduled and the datum doesn't own the data, but for thin pointers

src/librustc_trans/meth.rs

@@ -271,7 +271,7 @@ pub fn get_vtable_methods<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             // the method may have some early-bound lifetimes, add
             // regions for those
             let num_dummy_regions = trait_method_type.generics.regions.len(FnSpace);
-            let dummy_regions = vec![ty::ReStatic; num_dummy_regions];
+            let dummy_regions = vec![ty::ReErased; num_dummy_regions];
             let method_substs = substs.clone()
                                       .with_method(vec![], dummy_regions);
             let method_substs = tcx.mk_substs(method_substs);

src/librustc_trans/mir/constant.rs

@@ -715,7 +715,7 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {
                 let tr_lvalue = self.const_lvalue(lvalue, span)?;
 
                 let ty = tr_lvalue.ty;
-                let ref_ty = tcx.mk_ref(tcx.mk_region(ty::ReStatic),
+                let ref_ty = tcx.mk_ref(tcx.mk_region(ty::ReErased),
                     ty::TypeAndMut { ty: ty, mutbl: bk.to_mutbl_lossy() });
 
                 let base = match tr_lvalue.base {

src/librustc_trans/mir/rvalue.rs

@@ -373,7 +373,7 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
 
                 let ty = tr_lvalue.ty.to_ty(bcx.tcx());
                 let ref_ty = bcx.tcx().mk_ref(
-                    bcx.tcx().mk_region(ty::ReStatic),
+                    bcx.tcx().mk_region(ty::ReErased),
                     ty::TypeAndMut { ty: ty, mutbl: bk.to_mutbl_lossy() }
                 );
 

src/librustc_trans/monomorphize.rs

@@ -180,7 +180,7 @@ impl<'tcx> fmt::Display for Instance<'tcx> {
 impl<'tcx> Instance<'tcx> {
     pub fn new(def_id: DefId, substs: &'tcx Substs<'tcx>)
                -> Instance<'tcx> {
-        assert!(substs.regions.iter().all(|&r| r == ty::ReStatic));
+        assert!(substs.regions.iter().all(|&r| r == ty::ReErased));
         Instance { def: def_id, substs: substs }
     }
     pub fn mono<'a>(scx: &SharedCrateContext<'a, 'tcx>, def_id: DefId) -> Instance<'tcx> {