only remove keys that mention skolemized regions

src/librustc/infer/higher_ranked/mod.rs

@@ -839,6 +839,9 @@ pub fn pop_skolemized(&self,
         debug!("pop_skolemized({:?})", skol_map);
         let skol_regions: FnvHashSet<_> = skol_map.values().cloned().collect();
         self.region_vars.pop_skolemized(&skol_regions, &snapshot.region_vars_snapshot);
-        self.projection_cache.borrow_mut().partial_rollback(&snapshot.projection_cache_snapshot);
+        if !skol_map.is_empty() {
+            self.projection_cache.borrow_mut().rollback_skolemized(
+                &snapshot.projection_cache_snapshot);
+        }
     }
 }

src/librustc/traits/project.rs

@@ -1398,8 +1398,8 @@ pub fn rollback_to(&mut self, snapshot: ProjectionCacheSnapshot) {
         self.map.rollback_to(snapshot.snapshot);
     }
 
-    pub fn partial_rollback(&mut self, snapshot: &ProjectionCacheSnapshot) {
-        self.map.partial_rollback(&snapshot.snapshot);
+    pub fn rollback_skolemized(&mut self, snapshot: &ProjectionCacheSnapshot) {
+        self.map.partial_rollback(&snapshot.snapshot, &|k| k.has_re_skol());
     }
 
     pub fn commit(&mut self, snapshot: ProjectionCacheSnapshot) {

src/librustc/ty/flags.rs

@@ -11,6 +11,7 @@
 use ty::subst::Substs;
 use ty::{self, Ty, TypeFlags, TypeFoldable};
 
+#[derive(Debug)]
 pub struct FlagComputation {
     pub flags: TypeFlags,
 
@@ -182,24 +183,9 @@ fn add_fn_sig(&mut self, fn_sig: &ty::PolyFnSig) {
     }
 
     fn add_region(&mut self, r: &ty::Region) {
-        match *r {
-            ty::ReVar(..) => {
-                self.add_flags(TypeFlags::HAS_RE_INFER);
-                self.add_flags(TypeFlags::KEEP_IN_LOCAL_TCX);
-            }
-            ty::ReSkolemized(..) => {
-                self.add_flags(TypeFlags::HAS_RE_INFER);
-                self.add_flags(TypeFlags::HAS_RE_SKOL);
-                self.add_flags(TypeFlags::KEEP_IN_LOCAL_TCX);
-            }
-            ty::ReLateBound(debruijn, _) => { self.add_depth(debruijn.depth); }
-            ty::ReEarlyBound(..) => { self.add_flags(TypeFlags::HAS_RE_EARLY_BOUND); }
-            ty::ReStatic | ty::ReErased => {}
-            _ => { self.add_flags(TypeFlags::HAS_FREE_REGIONS); }
-        }
-
-        if !r.is_global() {
-            self.add_flags(TypeFlags::HAS_LOCAL_NAMES);
+        self.add_flags(r.type_flags());
+        if let ty::ReLateBound(debruijn, _) = *r {
+            self.add_depth(debruijn.depth);
         }
     }
 

src/librustc/ty/fold.rs

@@ -91,6 +91,9 @@ fn needs_infer(&self) -> bool {
     fn needs_subst(&self) -> bool {
         self.has_type_flags(TypeFlags::NEEDS_SUBST)
     }
+    fn has_re_skol(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_RE_SKOL)
+    }
     fn has_closure_types(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_TY_CLOSURE)
     }
@@ -632,26 +635,15 @@ struct HasTypeFlagsVisitor {
 
 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
     fn visit_ty(&mut self, t: Ty) -> bool {
-        t.flags.get().intersects(self.flags)
+        let flags = t.flags.get();
+        debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, flags, self.flags);
+        flags.intersects(self.flags)
     }
 
     fn visit_region(&mut self, r: &'tcx ty::Region) -> bool {
-        if self.flags.intersects(ty::TypeFlags::HAS_LOCAL_NAMES) {
-            // does this represent a region that cannot be named
-            // in a global way? used in fulfillment caching.
-            match *r {
-                ty::ReStatic | ty::ReEmpty | ty::ReErased => {}
-                _ => return true,
-            }
-        }
-        if self.flags.intersects(ty::TypeFlags::HAS_RE_INFER |
-                                 ty::TypeFlags::KEEP_IN_LOCAL_TCX) {
-            match *r {
-                ty::ReVar(_) | ty::ReSkolemized(..) => { return true }
-                _ => {}
-            }
-        }
-        false
+        let flags = r.type_flags();
+        debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
+        flags.intersects(self.flags)
     }
 }
 

src/librustc/ty/mod.rs

@@ -477,6 +477,7 @@ pub enum FragmentInfo {
                                   TypeFlags::HAS_SELF.bits |
                                   TypeFlags::HAS_TY_INFER.bits |
                                   TypeFlags::HAS_RE_INFER.bits |
+                                  TypeFlags::HAS_RE_SKOL.bits |
                                   TypeFlags::HAS_RE_EARLY_BOUND.bits |
                                   TypeFlags::HAS_FREE_REGIONS.bits |
                                   TypeFlags::HAS_TY_ERR.bits |

src/librustc/ty/sty.rs

@@ -406,7 +406,7 @@ pub fn map_bound<F,U>(self, f: F) -> Binder<U>
 
 impl fmt::Debug for TypeFlags {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", self.bits)
+        write!(f, "{:x}", self.bits)
     }
 }
 
@@ -866,6 +866,35 @@ pub fn from_depth(&self, depth: u32) -> Region {
             r => r
         }
     }
+
+    pub fn type_flags(&self) -> TypeFlags {
+        let mut flags = TypeFlags::empty();
+
+        match *self {
+            ty::ReVar(..) => {
+                flags = flags | TypeFlags::HAS_RE_INFER;
+                flags = flags | TypeFlags::KEEP_IN_LOCAL_TCX;
+            }
+            ty::ReSkolemized(..) => {
+                flags = flags | TypeFlags::HAS_RE_INFER;
+                flags = flags | TypeFlags::HAS_RE_SKOL;
+                flags = flags | TypeFlags::KEEP_IN_LOCAL_TCX;
+            }
+            ty::ReLateBound(..) => { }
+            ty::ReEarlyBound(..) => { flags = flags | TypeFlags::HAS_RE_EARLY_BOUND; }
+            ty::ReStatic | ty::ReErased => { }
+            _ => { flags = flags | TypeFlags::HAS_FREE_REGIONS; }
+        }
+
+        match *self {
+            ty::ReStatic | ty::ReEmpty | ty::ReErased => (),
+            _ => flags = flags | TypeFlags::HAS_LOCAL_NAMES,
+        }
+
+        debug!("type_flags({:?}) = {:?}", self, flags);
+
+        flags
+    }
 }
 
 // Type utilities

src/librustc_data_structures/snapshot_map/mod.rs

@@ -102,15 +102,19 @@ pub fn commit(&mut self, snapshot: Snapshot) {
         }
     }
 
-    pub fn partial_rollback(&mut self, snapshot: &Snapshot) {
+    pub fn partial_rollback<F>(&mut self,
+                               snapshot: &Snapshot,
+                               should_revert_key: &F)
+        where F: Fn(&K) -> bool
+    {
         self.assert_open_snapshot(snapshot);
         for i in (snapshot.len + 1..self.undo_log.len()).rev() {
             let reverse = match self.undo_log[i] {
                 UndoLog::OpenSnapshot => false,
                 UndoLog::CommittedSnapshot => false,
                 UndoLog::Noop => false,
-                UndoLog::Inserted(..) => true,
-                UndoLog::Overwrite(..) => true,
+                UndoLog::Inserted(ref k) => should_revert_key(k),
+                UndoLog::Overwrite(ref k, _) => should_revert_key(k),
             };
 
             if reverse {