Remove the Option<> since when computing LUB since I believe that the

case where `None` was returned should never happen in practice; it
amounts to comparing regions from two unrelated hierarchies. (I was also
not able to make it happen.)

src/librustc/middle/infer/region_inference/mod.rs

@@ -760,15 +760,17 @@ fn lub_concrete_regions(&self, a: Region, b: Region) -> Region {
             // at least as big as the block fr.scope_id".  So, we can
             // reasonably compare free regions and scopes:
             let fr_scope = fr.scope.to_code_extent();
-            match self.tcx.region_maps.nearest_common_ancestor(fr_scope, s_id) {
+            let r_id = self.tcx.region_maps.nearest_common_ancestor(fr_scope, s_id);
+
+            if r_id == fr_scope {
               // if the free region's scope `fr.scope_id` is bigger than
               // the scope region `s_id`, then the LUB is the free
               // region itself:
-              Some(r_id) if r_id == fr_scope => f,
-
+              f
+            } else {
               // otherwise, we don't know what the free region is,
               // so we must conservatively say the LUB is static:
-              _ => ReStatic
+              ReStatic
             }
           }
 
@@ -776,10 +778,7 @@ fn lub_concrete_regions(&self, a: Region, b: Region) -> Region {
             // The region corresponding to an outer block is a
             // subtype of the region corresponding to an inner
             // block.
-            match self.tcx.region_maps.nearest_common_ancestor(a_id, b_id) {
-              Some(r_id) => ReScope(r_id),
-              _ => ReStatic
-            }
+            ReScope(self.tcx.region_maps.nearest_common_ancestor(a_id, b_id))
           }
 
           (ReFree(ref a_fr), ReFree(ref b_fr)) => {
@@ -866,9 +865,10 @@ fn glb_concrete_regions(&self,
                 // is the scope `s_id`.  Otherwise, as we do not know
                 // big the free region is precisely, the GLB is undefined.
                 let fr_scope = fr.scope.to_code_extent();
-                match self.tcx.region_maps.nearest_common_ancestor(fr_scope, s_id) {
-                    Some(r_id) if r_id == fr_scope => Ok(s),
-                    _ => Err(ty::terr_regions_no_overlap(b, a))
+                if self.tcx.region_maps.nearest_common_ancestor(fr_scope, s_id) == fr_scope {
+                    Ok(s)
+                } else {
+                    Err(ty::terr_regions_no_overlap(b, a))
                 }
             }
 
@@ -934,10 +934,13 @@ fn intersect_scopes(&self,
         // it. Otherwise fail.
         debug!("intersect_scopes(scope_a={:?}, scope_b={:?}, region_a={:?}, region_b={:?})",
                scope_a, scope_b, region_a, region_b);
-        match self.tcx.region_maps.nearest_common_ancestor(scope_a, scope_b) {
-            Some(r_id) if scope_a == r_id => Ok(ReScope(scope_b)),
-            Some(r_id) if scope_b == r_id => Ok(ReScope(scope_a)),
-            _ => Err(ty::terr_regions_no_overlap(region_a, region_b))
+        let r_id = self.tcx.region_maps.nearest_common_ancestor(scope_a, scope_b);
+        if r_id == scope_a {
+            Ok(ReScope(scope_b))
+        } else if r_id == scope_b {
+            Ok(ReScope(scope_a))
+        } else {
+            Err(ty::terr_regions_no_overlap(region_a, region_b))
         }
     }
 }

src/librustc/middle/region.rs

@@ -607,8 +607,8 @@ pub fn is_subregion_of(&self,
     pub fn nearest_common_ancestor(&self,
                                    scope_a: CodeExtent,
                                    scope_b: CodeExtent)
-                                   -> Option<CodeExtent> {
-        if scope_a == scope_b { return Some(scope_a); }
+                                   -> CodeExtent {
+        if scope_a == scope_b { return scope_a; }
 
         let a_ancestors = ancestors_of(self, scope_a);
         let b_ancestors = ancestors_of(self, scope_b);
@@ -636,13 +636,13 @@ pub fn nearest_common_ancestor(&self,
                  CodeExtent::DestructionScope(b_root_id)) => {
                     if self.fn_is_enclosed_by(a_root_id, b_root_id) {
                         // `a` is enclosed by `b`, hence `b` is the ancestor of everything in `a`
-                        Some(scope_b)
+                        scope_b
                     } else if self.fn_is_enclosed_by(b_root_id, a_root_id) {
                         // `b` is enclosed by `a`, hence `a` is the ancestor of everything in `b`
-                        Some(scope_a)
+                        scope_a
                     } else {
                         // neither fn encloses the other
-                        None
+                        unreachable!()
                     }
                 }
                 _ => {
@@ -655,17 +655,16 @@ pub fn nearest_common_ancestor(&self,
         loop {
             // Loop invariant: a_ancestors[a_index] == b_ancestors[b_index]
             // for all indices between a_index and the end of the array
-            if a_index == 0 { return Some(scope_a); }
-            if b_index == 0 { return Some(scope_b); }
+            if a_index == 0 { return scope_a; }
+            if b_index == 0 { return scope_b; }
             a_index -= 1;
             b_index -= 1;
             if a_ancestors[a_index] != b_ancestors[b_index] {
-                return Some(a_ancestors[a_index + 1]);
+                return a_ancestors[a_index + 1];
             }
         }
 
-        fn ancestors_of(this: &RegionMaps, scope: CodeExtent)
-            -> Vec<CodeExtent> {
+        fn ancestors_of(this: &RegionMaps, scope: CodeExtent) -> Vec<CodeExtent> {
             // debug!("ancestors_of(scope={:?})", scope);
             let mut result = vec!(scope);
             let mut scope = scope;