Rollup merge of rust-lang#56906 - blitzerr:master, r=nikomatsakis

Issue rust-lang#56905

Adding a map to TypeckTables to get the list of all the Upvars
given a closureID. This is help us get rid of the recurring
pattern in the codebase of iterating over the free vars
using with_freevars.

Author: pietroalbini

src/librustc/ty/context.rs

@@ -434,6 +434,12 @@ pub struct TypeckTables<'tcx> {
     /// All the existential types that are restricted to concrete types
     /// by this function
     pub concrete_existential_types: FxHashMap<DefId, Ty<'tcx>>,
+
+    /// Given the closure ID this map provides the list of UpvarIDs used by it.
+    /// The upvarID contains the HIR node ID and it also contains the full path
+    /// leading to the member of the struct or tuple that is used instead of the
+    /// entire variable.
+    pub upvar_list: ty::UpvarListMap<'tcx>,
 }
 
 impl<'tcx> TypeckTables<'tcx> {
@@ -459,6 +465,7 @@ impl<'tcx> TypeckTables<'tcx> {
             tainted_by_errors: false,
             free_region_map: Default::default(),
             concrete_existential_types: Default::default(),
+            upvar_list: Default::default(),
         }
     }
 
@@ -768,6 +775,8 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
             tainted_by_errors,
             ref free_region_map,
             ref concrete_existential_types,
+            ref upvar_list,
+
         } = *self;
 
         hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
@@ -811,6 +820,7 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
             tainted_by_errors.hash_stable(hcx, hasher);
             free_region_map.hash_stable(hcx, hasher);
             concrete_existential_types.hash_stable(hcx, hasher);
+            upvar_list.hash_stable(hcx, hasher);
         })
     }
 }

src/librustc/ty/mod.rs

@@ -598,6 +598,8 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for ty::TyS<'gcx> {
 
 pub type Ty<'tcx> = &'tcx TyS<'tcx>;
 
+pub type UpvarListMap<'tcx> = FxHashMap<DefId, Vec<UpvarId>>;
+
 impl<'tcx> serialize::UseSpecializedEncodable for Ty<'tcx> {}
 impl<'tcx> serialize::UseSpecializedDecodable for Ty<'tcx> {}
 

src/librustc_typeck/check/upvar.rs

@@ -132,14 +132,18 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         };
 
         self.tcx.with_freevars(closure_node_id, |freevars| {
+            let mut freevar_list: Vec<ty::UpvarId> = Vec::with_capacity(freevars.len());
             for freevar in freevars {
                 let upvar_id = ty::UpvarId {
                     var_path: ty::UpvarPath {
-                        hir_id : self.tcx.hir().node_to_hir_id(freevar.var_id()),
+                        hir_id: self.tcx.hir().node_to_hir_id(freevar.var_id()),
                     },
                     closure_expr_id: LocalDefId::from_def_id(closure_def_id),
                 };
                 debug!("seed upvar_id {:?}", upvar_id);
+                // Adding the upvar Id to the list of Upvars, which will be added
+                // to the map for the closure at the end of the for loop.
+                freevar_list.push(upvar_id);
 
                 let capture_kind = match capture_clause {
                     hir::CaptureByValue => ty::UpvarCapture::ByValue,
@@ -159,6 +163,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     .upvar_capture_map
                     .insert(upvar_id, capture_kind);
             }
+            // Add the vector of freevars to the map keyed with the closure id.
+            // This gives us an easier access to them without having to call
+            // with_freevars again..
+            self.tables
+                .borrow_mut()
+                .upvar_list
+                .insert(closure_def_id, freevar_list);
         });
 
         let body_owner_def_id = self.tcx.hir().body_owner_def_id(body.id());
@@ -176,7 +187,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             self.param_env,
             region_scope_tree,
             &self.tables.borrow(),
-        ).consume_body(body);
+        )
+        .consume_body(body);
 
         if let Some(closure_substs) = infer_kind {
             // Unify the (as yet unbound) type variable in the closure
@@ -250,9 +262,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     let var_hir_id = tcx.hir().node_to_hir_id(var_node_id);
                     let freevar_ty = self.node_ty(var_hir_id);
                     let upvar_id = ty::UpvarId {
-                        var_path: ty::UpvarPath {
-                            hir_id: var_hir_id,
-                        },
+                        var_path: ty::UpvarPath { hir_id: var_hir_id },
                         closure_expr_id: LocalDefId::from_def_id(closure_def_index),
                     };
                     let capture = self.tables.borrow().upvar_capture(upvar_id);
@@ -272,7 +282,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             },
                         ),
                     }
-                }).collect()
+                })
+                .collect()
         })
     }
 }