Rollup merge of #36002 - eddyb:abstract-kindness, r=nikomatsakis

Combine types and regions in Substs into one interleaved list.

Previously, `Substs` would contain types and regions, in two separate vectors, for example:
```rust
<X as Trait<'a, 'b, A, B>>::method::<'p, 'q, T, U>
/* corresponds to */
Substs { regions: ['a, 'b, 'p, 'q], types: [X, A, B, T, U] }
```

This PR continues the work started in #35605 by further removing the distinction.
A new abstraction over types and regions is introduced in the compiler, `Kind`.
Each `Kind` is a pointer (`&TyS` or `&Region`), with the lowest two bits used as a tag.
Two bits were used instead of just one (type = `0`, region = `1`) to allow adding more kinds.

`Substs` contain only a `Vec<Kind>`, with `Self` first, followed by regions and types (in the definition order):
```rust
Substs { params: [X, 'a, 'b, A, B, 'p, 'q, T, U] }
```
The resulting interleaved list has the property of being the concatenation of parameters for the (potentially) nested generic items it describes, and can be sliced back into those components:
```rust
params[0..5] = [X, 'a, 'b, A, B] // <X as Trait<'a, 'b, A, B>>
params[5..9] = ['p, 'q, T, U] // <_>::method::<'p, 'q, T, U>
```

r? @nikomatsakis

Author: Manishearth

src/librustc/infer/bivariate.rs

@@ -106,7 +106,8 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
         }
     }
 
-    fn regions(&mut self, a: ty::Region, _: ty::Region) -> RelateResult<'tcx, ty::Region> {
+    fn regions(&mut self, a: &'tcx ty::Region, _: &'tcx ty::Region)
+               -> RelateResult<'tcx, &'tcx ty::Region> {
         Ok(a)
     }
 

src/librustc/infer/combine.rs

@@ -329,8 +329,8 @@ 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 {
+    fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
+        match *r {
             // Never make variables for regions bound within the type itself,
             // nor for erased regions.
             ty::ReLateBound(..) |

src/librustc/infer/equate.rs

@@ -79,7 +79,8 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
         }
     }
 
-    fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
+    fn regions(&mut self, a: &'tcx ty::Region, b: &'tcx ty::Region)
+               -> RelateResult<'tcx, &'tcx ty::Region> {
         debug!("{}.regions({:?}, {:?})",
                self.tag(),
                a,

src/librustc/infer/error_reporting.rs

@@ -99,7 +99,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn note_and_explain_region(self,
                                    err: &mut DiagnosticBuilder,
                                    prefix: &str,
-                                   region: ty::Region,
+                                   region: &'tcx ty::Region,
                                    suffix: &str) {
         fn item_scope_tag(item: &hir::Item) -> &'static str {
             match item.node {
@@ -120,7 +120,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
              Some(span))
         }
 
-        let (description, span) = match region {
+        let (description, span) = match *region {
             ty::ReScope(scope) => {
                 let new_string;
                 let unknown_scope = || {
@@ -405,12 +405,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         }
 
         fn free_regions_from_same_fn<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
-                                                     sub: Region,
-                                                     sup: Region)
+                                                     sub: &'tcx Region,
+                                                     sup: &'tcx Region)
                                                      -> Option<FreeRegionsFromSameFn> {
             debug!("free_regions_from_same_fn(sub={:?}, sup={:?})", sub, sup);
             let (scope_id, fr1, fr2) = match (sub, sup) {
-                (ReFree(fr1), ReFree(fr2)) => {
+                (&ReFree(fr1), &ReFree(fr2)) => {
                     if fr1.scope != fr2.scope {
                         return None
                     }
@@ -602,7 +602,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     fn report_generic_bound_failure(&self,
                                     origin: SubregionOrigin<'tcx>,
                                     bound_kind: GenericKind<'tcx>,
-                                    sub: Region)
+                                    sub: &'tcx Region)
     {
         // FIXME: it would be better to report the first error message
         // with the span of the parameter itself, rather than the span
@@ -616,7 +616,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 format!("the associated type `{}`", p),
         };
 
-        let mut err = match sub {
+        let mut err = match *sub {
             ty::ReFree(ty::FreeRegion {bound_region: ty::BrNamed(..), ..}) => {
                 // Does the required lifetime have a nice name we can print?
                 let mut err = struct_span_err!(self.tcx.sess,
@@ -667,8 +667,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
     fn report_concrete_failure(&self,
                                origin: SubregionOrigin<'tcx>,
-                               sub: Region,
-                               sup: Region)
+                               sub: &'tcx Region,
+                               sup: &'tcx Region)
                                 -> DiagnosticBuilder<'tcx> {
         match origin {
             infer::Subtype(trace) => {
@@ -939,9 +939,9 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     fn report_sub_sup_conflict(&self,
                                var_origin: RegionVariableOrigin,
                                sub_origin: SubregionOrigin<'tcx>,
-                               sub_region: Region,
+                               sub_region: &'tcx Region,
                                sup_origin: SubregionOrigin<'tcx>,
-                               sup_region: Region) {
+                               sup_region: &'tcx Region) {
         let mut err = self.report_inference_failure(var_origin);
 
         self.tcx.note_and_explain_region(&mut err,

src/librustc/infer/freshen.rs

@@ -83,8 +83,8 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
         self.infcx.tcx
     }
 
-    fn fold_region(&mut self, r: ty::Region) -> ty::Region {
-        match r {
+    fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
+        match *r {
             ty::ReEarlyBound(..) |
             ty::ReLateBound(..) => {
                 // leave bound regions alone
@@ -99,7 +99,7 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
             ty::ReEmpty |
             ty::ReErased => {
                 // replace all free regions with 'erased
-                ty::ReErased
+                self.tcx().mk_region(ty::ReErased)
             }
         }
     }

src/librustc/infer/glb.rs

@@ -57,7 +57,8 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
         lattice::super_lattice_tys(self, a, b)
     }
 
-    fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
+    fn regions(&mut self, a: &'tcx ty::Region, b: &'tcx ty::Region)
+               -> RelateResult<'tcx, &'tcx ty::Region> {
         debug!("{}.regions({:?}, {:?})",
                self.tag(),
                a,

src/librustc/infer/higher_ranked/mod.rs

@@ -164,7 +164,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                 .map(|(&skol, &(br, ref regions))| {
                     let representative =
                         regions.iter()
-                               .filter(|r| !skol_resolution_map.contains_key(r))
+                               .filter(|&&r| !skol_resolution_map.contains_key(r))
                                .cloned()
                                .next()
                                .unwrap_or_else(|| { // [1]
@@ -268,9 +268,9 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                                              snapshot: &CombinedSnapshot,
                                              debruijn: ty::DebruijnIndex,
                                              new_vars: &[ty::RegionVid],
-                                             a_map: &FnvHashMap<ty::BoundRegion, ty::Region>,
-                                             r0: ty::Region)
-                                             -> ty::Region {
+                                             a_map: &FnvHashMap<ty::BoundRegion, &'tcx ty::Region>,
+                                             r0: &'tcx ty::Region)
+                                             -> &'tcx ty::Region {
             // Regions that pre-dated the LUB computation stay as they are.
             if !is_var_in_set(new_vars, r0) {
                 assert!(!r0.is_bound());
@@ -301,7 +301,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                     debug!("generalize_region(r0={:?}): \
                             replacing with {:?}, tainted={:?}",
                            r0, *a_br, tainted);
-                    return ty::ReLateBound(debruijn, *a_br);
+                    return infcx.tcx.mk_region(ty::ReLateBound(debruijn, *a_br));
                 }
             }
 
@@ -364,10 +364,12 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                                              snapshot: &CombinedSnapshot,
                                              debruijn: ty::DebruijnIndex,
                                              new_vars: &[ty::RegionVid],
-                                             a_map: &FnvHashMap<ty::BoundRegion, ty::Region>,
+                                             a_map: &FnvHashMap<ty::BoundRegion,
+                                                                &'tcx ty::Region>,
                                              a_vars: &[ty::RegionVid],
                                              b_vars: &[ty::RegionVid],
-                                             r0: ty::Region) -> ty::Region {
+                                             r0: &'tcx ty::Region)
+                                             -> &'tcx ty::Region {
             if !is_var_in_set(new_vars, r0) {
                 assert!(!r0.is_bound());
                 return r0;
@@ -419,7 +421,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
 
             if a_r.is_some() && b_r.is_some() && only_new_vars {
                 // Related to exactly one bound variable from each fn:
-                return rev_lookup(span, a_map, a_r.unwrap());
+                return rev_lookup(infcx, span, a_map, a_r.unwrap());
             } else if a_r.is_none() && b_r.is_none() {
                 // Not related to bound variables from either fn:
                 assert!(!r0.is_bound());
@@ -430,13 +432,14 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
             }
         }
 
-        fn rev_lookup(span: Span,
-                      a_map: &FnvHashMap<ty::BoundRegion, ty::Region>,
-                      r: ty::Region) -> ty::Region
+        fn rev_lookup<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
+                                      span: Span,
+                                      a_map: &FnvHashMap<ty::BoundRegion, &'tcx ty::Region>,
+                                      r: &'tcx ty::Region) -> &'tcx ty::Region
         {
             for (a_br, a_r) in a_map {
                 if *a_r == r {
-                    return ty::ReLateBound(ty::DebruijnIndex::new(1), *a_br);
+                    return infcx.tcx.mk_region(ty::ReLateBound(ty::DebruijnIndex::new(1), *a_br));
                 }
             }
             span_bug!(
@@ -445,19 +448,21 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                 r);
         }
 
-        fn fresh_bound_variable(infcx: &InferCtxt, debruijn: ty::DebruijnIndex) -> ty::Region {
+        fn fresh_bound_variable<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
+                                                debruijn: ty::DebruijnIndex)
+                                                -> &'tcx ty::Region {
             infcx.region_vars.new_bound(debruijn)
         }
     }
 }
 
 fn var_ids<'a, 'gcx, 'tcx>(fields: &CombineFields<'a, 'gcx, 'tcx>,
-                           map: &FnvHashMap<ty::BoundRegion, ty::Region>)
+                           map: &FnvHashMap<ty::BoundRegion, &'tcx ty::Region>)
                            -> Vec<ty::RegionVid> {
     map.iter()
-       .map(|(_, r)| match *r {
+       .map(|(_, &r)| match *r {
            ty::ReVar(r) => { r }
-           r => {
+           _ => {
                span_bug!(
                    fields.trace.origin.span(),
                    "found non-region-vid: {:?}",
@@ -467,8 +472,8 @@ fn var_ids<'a, 'gcx, 'tcx>(fields: &CombineFields<'a, 'gcx, 'tcx>,
        .collect()
 }
 
-fn is_var_in_set(new_vars: &[ty::RegionVid], r: ty::Region) -> bool {
-    match r {
+fn is_var_in_set(new_vars: &[ty::RegionVid], r: &ty::Region) -> bool {
+    match *r {
         ty::ReVar(ref v) => new_vars.iter().any(|x| x == v),
         _ => false
     }
@@ -479,13 +484,13 @@ fn fold_regions_in<'a, 'gcx, 'tcx, T, F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
                                          mut fldr: F)
                                          -> T
     where T: TypeFoldable<'tcx>,
-          F: FnMut(ty::Region, ty::DebruijnIndex) -> ty::Region,
+          F: FnMut(&'tcx ty::Region, ty::DebruijnIndex) -> &'tcx ty::Region,
 {
     tcx.fold_regions(unbound_value, &mut false, |region, current_depth| {
         // we should only be encountering "escaping" late-bound regions here,
         // because the ones at the current level should have been replaced
         // with fresh variables
-        assert!(match region {
+        assert!(match *region {
             ty::ReLateBound(..) => false,
             _ => true
         });
@@ -497,9 +502,9 @@ fn fold_regions_in<'a, 'gcx, 'tcx, T, F>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     fn tainted_regions(&self,
                        snapshot: &CombinedSnapshot,
-                       r: ty::Region,
+                       r: &'tcx ty::Region,
                        directions: TaintDirections)
-                       -> FnvHashSet<ty::Region> {
+                       -> FnvHashSet<&'tcx ty::Region> {
         self.region_vars.tainted(&snapshot.region_vars_snapshot, r, directions)
     }
 
@@ -596,7 +601,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     pub fn skolemize_late_bound_regions<T>(&self,
                                            binder: &ty::Binder<T>,
                                            snapshot: &CombinedSnapshot)
-                                           -> (T, SkolemizationMap)
+                                           -> (T, SkolemizationMap<'tcx>)
         where T : TypeFoldable<'tcx>
     {
         let (result, map) = self.tcx.replace_late_bound_regions(binder, |br| {
@@ -619,7 +624,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     pub fn leak_check(&self,
                       overly_polymorphic: bool,
                       span: Span,
-                      skol_map: &SkolemizationMap,
+                      skol_map: &SkolemizationMap<'tcx>,
                       snapshot: &CombinedSnapshot)
                       -> RelateResult<'tcx, ()>
     {
@@ -673,7 +678,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             for &tainted_region in &incoming_taints {
                 // Each skolemized should only be relatable to itself
                 // or new variables:
-                match tainted_region {
+                match *tainted_region {
                     ty::ReVar(vid) => {
                         if new_vars.contains(&vid) {
                             warnings.extend(
@@ -742,7 +747,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     /// to the depth of the predicate, in this case 1, so that the final
     /// predicate is `for<'a> &'a int : Clone`.
     pub fn plug_leaks<T>(&self,
-                         skol_map: SkolemizationMap,
+                         skol_map: SkolemizationMap<'tcx>,
                          snapshot: &CombinedSnapshot,
                          value: &T) -> T
         where T : TypeFoldable<'tcx>
@@ -755,7 +760,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         // region back to the `ty::BoundRegion` that it originally
         // represented. Because `leak_check` passed, we know that
         // these taint sets are mutually disjoint.
-        let inv_skol_map: FnvHashMap<ty::Region, ty::BoundRegion> =
+        let inv_skol_map: FnvHashMap<&'tcx ty::Region, ty::BoundRegion> =
             skol_map
             .iter()
             .flat_map(|(&skol_br, &skol)| {
@@ -794,15 +799,16 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     // (which ought not to escape the snapshot, but we
                     // don't check that) or itself
                     assert!(
-                        match r {
+                        match *r {
                             ty::ReVar(_) => true,
                             ty::ReSkolemized(_, ref br1) => br == br1,
                             _ => false,
                         },
                         "leak-check would have us replace {:?} with {:?}",
                         r, br);
 
-                    ty::ReLateBound(ty::DebruijnIndex::new(current_depth - 1), br.clone())
+                    self.tcx.mk_region(ty::ReLateBound(
+                        ty::DebruijnIndex::new(current_depth - 1), br.clone()))
                 }
             }
         });
@@ -826,7 +832,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     ///
     /// Note: popping also occurs implicitly as part of `leak_check`.
     pub fn pop_skolemized(&self,
-                          skol_map: SkolemizationMap,
+                          skol_map: SkolemizationMap<'tcx>,
                           snapshot: &CombinedSnapshot)
     {
         debug!("pop_skolemized({:?})", skol_map);

src/librustc/infer/lub.rs

@@ -57,7 +57,8 @@ impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
         lattice::super_lattice_tys(self, a, b)
     }
 
-    fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
+    fn regions(&mut self, a: &'tcx ty::Region, b: &'tcx ty::Region)
+               -> RelateResult<'tcx, &'tcx ty::Region> {
         debug!("{}.regions({:?}, {:?})",
                self.tag(),
                a,