Adjust type Debruijn depth calculations

Author: Alex Muscar

src/librustc/middle/resolve_lifetime.rs

@@ -137,14 +137,14 @@ impl Region {
         match self {
             Region::LateBound(debruijn, id, origin) => Region::LateBound(
                 ty::DebruijnIndex {
-                    depth: debruijn.depth - (depth - 1),
+                    depth: debruijn.depth - depth,
                 },
                 id,
                 origin,
             ),
             Region::LateBoundAnon(debruijn, index) => Region::LateBoundAnon(
                 ty::DebruijnIndex {
-                    depth: debruijn.depth - (depth - 1),
+                    depth: debruijn.depth - depth,
                 },
                 index,
             ),
@@ -1781,7 +1781,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
             .map(|(i, input)| {
                 let mut gather = GatherLifetimes {
                     map: self.map,
-                    binder_depth: 1,
+                    binder_depth: 0,
                     have_bound_regions: false,
                     lifetimes: FxHashSet(),
                 };

src/librustc/ty/fold.rs

@@ -292,7 +292,7 @@ impl<'a, 'gcx, 'tcx> RegionFolder<'a, 'gcx, 'tcx> {
         RegionFolder {
             tcx,
             skipped_regions,
-            current_depth: 1,
+            current_depth: 0,
             fld_r,
         }
     }
@@ -460,7 +460,7 @@ impl<'a, 'gcx, 'tcx> RegionReplacer<'a, 'gcx, 'tcx> {
     {
         RegionReplacer {
             tcx,
-            current_depth: 1,
+            current_depth: 0,
             fld_r,
             map: BTreeMap::default()
         }
@@ -478,7 +478,7 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
     }
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        if !t.has_regions_escaping_depth(self.current_depth-1) {
+        if !t.has_regions_escaping_depth(self.current_depth) {
             return t;
         }
 
@@ -635,7 +635,7 @@ struct LateBoundRegionsCollector {
 impl LateBoundRegionsCollector {
     fn new(just_constrained: bool) -> Self {
         LateBoundRegionsCollector {
-            current_depth: 1,
+            current_depth: 0,
             regions: FxHashSet(),
             just_constrained,
         }

src/librustc/ty/sty.rs

@@ -1187,11 +1187,11 @@ impl RegionKind {
         }
     }
 
-    /// Returns the depth of `self` from the (1-based) binding level `depth`
+    /// Returns the depth of `self` from the (0-based) binding level `depth`
     pub fn from_depth(&self, depth: u32) -> RegionKind {
         match *self {
             ty::ReLateBound(debruijn, r) => ty::ReLateBound(DebruijnIndex {
-                depth: debruijn.depth - (depth - 1)
+                depth: debruijn.depth - depth
             }, r),
             r => r
         }