Make unboxed_closure_kind return Option to allow for the possibility that its value is not yet known.

src/librustc/middle/mem_categorization.rs

@@ -594,8 +594,16 @@ impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> {
               let ty = try!(self.node_ty(fn_node_id));
               match ty.sty {
                   ty::ty_closure(closure_id, _, _) => {
-                      let kind = self.typer.closure_kind(closure_id);
-                      self.cat_upvar(id, span, var_id, fn_node_id, kind)
+                      match self.typer.closure_kind(closure_id) {
+                          Some(kind) => {
+                              self.cat_upvar(id, span, var_id, fn_node_id, kind)
+                          }
+                          None => {
+                              self.tcx().sess.span_bug(
+                                  span,
+                                  &*format!("No closure kind for {:?}", closure_id));
+                          }
+                      }
                   }
                   _ => {
                       self.tcx().sess.span_bug(

src/librustc/middle/traits/select.rs

@@ -1024,12 +1024,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                kind,
                obligation.repr(self.tcx()));
 
-        let closure_kind = self.closure_typer.closure_kind(closure_def_id);
-
-        debug!("closure_kind = {:?}", closure_kind);
-
-        if closure_kind == kind {
-            candidates.vec.push(ClosureCandidate(closure_def_id, substs.clone()));
+        match self.closure_typer.closure_kind(closure_def_id) {
+            Some(closure_kind) => {
+                debug!("assemble_unboxed_candidates: closure_kind = {:?}", closure_kind);
+                if closure_kind == kind {
+                    candidates.vec.push(ClosureCandidate(closure_def_id, substs.clone()));
+                }
+            }
+            None => {
+                debug!("assemble_unboxed_candidates: closure_kind not yet known");
+                candidates.ambiguous = true;
+            }
         }
 
         Ok(())

src/librustc/middle/ty.rs

@@ -2288,14 +2288,22 @@ impl ClosureKind {
 pub trait ClosureTyper<'tcx> {
     fn param_env<'a>(&'a self) -> &'a ty::ParameterEnvironment<'a, 'tcx>;
 
-    fn closure_kind(&self, def_id: ast::DefId) -> ty::ClosureKind;
+    /// Is this a `Fn`, `FnMut` or `FnOnce` closure? During typeck,
+    /// returns `None` if the kind of this closure has not yet been
+    /// inferred.
+    fn closure_kind(&self,
+                    def_id: ast::DefId)
+                    -> Option<ty::ClosureKind>;
 
+    /// Returns the argument/return types of this closure.
     fn closure_type(&self,
                     def_id: ast::DefId,
                     substs: &subst::Substs<'tcx>)
                     -> ty::ClosureTy<'tcx>;
 
-    // Returns `None` if the upvar types cannot yet be definitively determined.
+    /// Returns the set of all upvars and their transformed
+    /// types. During typeck, maybe return `None` if the upvar types
+    /// have not yet been inferred.
     fn closure_upvars(&self,
                       def_id: ast::DefId,
                       substs: &Substs<'tcx>)
@@ -6473,8 +6481,11 @@ impl<'a,'tcx> ClosureTyper<'tcx> for ty::ParameterEnvironment<'a,'tcx> {
         self
     }
 
-    fn closure_kind(&self, def_id: ast::DefId) -> ty::ClosureKind {
-        self.tcx.closure_kind(def_id)
+    fn closure_kind(&self,
+                    def_id: ast::DefId)
+                    -> Option<ty::ClosureKind>
+    {
+        Some(self.tcx.closure_kind(def_id))
     }
 
     fn closure_type(&self,

src/librustc_trans/trans/common.rs

@@ -693,7 +693,10 @@ impl<'blk, 'tcx> ty::ClosureTyper<'tcx> for BlockS<'blk, 'tcx> {
         &self.fcx.param_env
     }
 
-    fn closure_kind(&self, def_id: ast::DefId) -> ty::ClosureKind {
+    fn closure_kind(&self,
+                    def_id: ast::DefId)
+                    -> Option<ty::ClosureKind>
+    {
         let typer = NormalizingClosureTyper::new(self.tcx());
         typer.closure_kind(def_id)
     }
@@ -1065,8 +1068,11 @@ impl<'a,'tcx> ty::ClosureTyper<'tcx> for NormalizingClosureTyper<'a,'tcx> {
         &self.param_env
     }
 
-    fn closure_kind(&self, def_id: ast::DefId) -> ty::ClosureKind {
-        self.param_env.tcx.closure_kind(def_id)
+    fn closure_kind(&self,
+                    def_id: ast::DefId)
+                    -> Option<ty::ClosureKind>
+    {
+        self.param_env.closure_kind(def_id)
     }
 
     fn closure_type(&self,

src/librustc_typeck/check/mod.rs

@@ -348,8 +348,11 @@ impl<'a, 'tcx> ty::ClosureTyper<'tcx> for FnCtxt<'a, 'tcx> {
         &self.inh.param_env
     }
 
-    fn closure_kind(&self, def_id: ast::DefId) -> ty::ClosureKind {
-        self.inh.closures.borrow()[def_id].kind
+    fn closure_kind(&self,
+                    def_id: ast::DefId)
+                    -> Option<ty::ClosureKind>
+    {
+        Some(self.inh.closures.borrow()[def_id].kind)
     }
 
     fn closure_type(&self,