Add `ScopeAuxiliaryVec`, return MIR+aux via tuple

It's nice to be able to index with a scope-id,
but coherence rules prevent us from implementing
`Index<ScopeId>` for `Vec<ScopeAuxiliary>`, and I'd
prefer that `ScopeAuxiliary` remain in librustc_mir,
just for compilation time reasons.

src/librustc_mir/build/matches/mod.rs

@@ -633,7 +633,7 @@ impl<'a,'tcx> Builder<'a,'tcx> {
             span: span,
         });
         let index = index as u32;
-        let extent = self.scope_auxiliary[var_scope_id.index()].extent;
+        let extent = self.scope_auxiliary[var_scope_id].extent;
         self.schedule_drop(span, extent, &Lvalue::Var(index), var_ty);
         self.var_indices.insert(var_id, index);
 

src/librustc_mir/build/mod.rs

@@ -14,7 +14,7 @@ use rustc::middle::ty::{FnOutput, Ty};
 use rustc::mir::repr::*;
 use rustc_data_structures::fnv::FnvHashMap;
 use rustc_front::hir;
-
+use std::ops::{Index, IndexMut};
 use syntax::ast;
 use syntax::codemap::Span;
 
@@ -33,7 +33,7 @@ pub struct Builder<'a, 'tcx: 'a> {
     // but these are liable to get out of date once optimization
     // begins. They are also hopefully temporary, and will be
     // no longer needed when we adopt graph-based regions.
-    scope_auxiliary: Vec<ScopeAuxiliary>,
+    scope_auxiliary: ScopeAuxiliaryVec,
 
     // the current set of loops; see the `scope` module for more
     // details
@@ -85,9 +85,24 @@ pub struct Location {
     pub statement_index: usize,
 }
 
-pub struct MirAndScopeAuxiliary<'tcx> {
-    pub mir: Mir<'tcx>,
-    pub scope_auxiliary: Vec<ScopeAuxiliary>,
+pub struct ScopeAuxiliaryVec {
+    pub vec: Vec<ScopeAuxiliary>
+}
+
+impl Index<ScopeId> for ScopeAuxiliaryVec {
+    type Output = ScopeAuxiliary;
+
+    #[inline]
+    fn index(&self, index: ScopeId) -> &ScopeAuxiliary {
+        &self.vec[index.index()]
+    }
+}
+
+impl IndexMut<ScopeId> for ScopeAuxiliaryVec {
+    #[inline]
+    fn index_mut(&mut self, index: ScopeId) -> &mut ScopeAuxiliary {
+        &mut self.vec[index.index()]
+    }
 }
 
 ///////////////////////////////////////////////////////////////////////////
@@ -143,7 +158,7 @@ pub fn construct<'a,'tcx>(hir: Cx<'a,'tcx>,
                           argument_extent: CodeExtent,
                           return_ty: FnOutput<'tcx>,
                           ast_block: &'tcx hir::Block)
-                          -> MirAndScopeAuxiliary<'tcx> {
+                          -> (Mir<'tcx>, ScopeAuxiliaryVec) {
     let cfg = CFG { basic_blocks: vec![] };
 
     let mut builder = Builder {
@@ -152,7 +167,7 @@ pub fn construct<'a,'tcx>(hir: Cx<'a,'tcx>,
         fn_span: span,
         scopes: vec![],
         scope_datas: vec![],
-        scope_auxiliary: vec![],
+        scope_auxiliary: ScopeAuxiliaryVec { vec: vec![] },
         loop_scopes: vec![],
         temp_decls: vec![],
         var_decls: vec![],
@@ -188,8 +203,8 @@ pub fn construct<'a,'tcx>(hir: Cx<'a,'tcx>,
                        true
                    }));
 
-    MirAndScopeAuxiliary {
-        mir: Mir {
+    (
+        Mir {
             basic_blocks: builder.cfg.basic_blocks,
             scopes: builder.scope_datas,
             var_decls: builder.var_decls,
@@ -198,8 +213,8 @@ pub fn construct<'a,'tcx>(hir: Cx<'a,'tcx>,
             return_ty: return_ty,
             span: span
         },
-        scope_auxiliary: builder.scope_auxiliary,
-    }
+        builder.scope_auxiliary,
+    )
 }
 
 impl<'a,'tcx> Builder<'a,'tcx> {

src/librustc_mir/build/scope.rs

@@ -257,7 +257,7 @@ impl<'a,'tcx> Builder<'a,'tcx> {
             free: None,
             cached_block: None,
         });
-        self.scope_auxiliary.push(ScopeAuxiliary {
+        self.scope_auxiliary.vec.push(ScopeAuxiliary {
             extent: extent,
             dom: self.cfg.current_location(entry),
             postdoms: vec![]
@@ -279,7 +279,7 @@ impl<'a,'tcx> Builder<'a,'tcx> {
         let scope = self.scopes.pop().unwrap();
         assert_eq!(scope.extent, extent);
         unpack!(block = build_scope_drops(&mut self.cfg, &scope, &self.scopes, block));
-        self.scope_auxiliary[scope.id.index()]
+        self.scope_auxiliary[scope.id]
             .postdoms
             .push(self.cfg.current_location(block));
         block.unit()
@@ -313,7 +313,7 @@ impl<'a,'tcx> Builder<'a,'tcx> {
                 self.cfg.terminate(block, scope.id, span, free);
                 block = next;
             }
-            self.scope_auxiliary[scope.id.index()]
+            self.scope_auxiliary[scope.id]
                 .postdoms
                 .push(self.cfg.current_location(block));
         }

src/librustc_mir/mir_map.rs

@@ -19,7 +19,7 @@
 extern crate syntax;
 extern crate rustc_front;
 
-use build::{self, MirAndScopeAuxiliary};
+use build;
 use rustc::dep_graph::DepNode;
 use rustc::mir::repr::Mir;
 use pretty;
@@ -183,7 +183,7 @@ fn build_mir<'a,'tcx:'a>(cx: Cx<'a,'tcx>,
     let parameter_scope =
         cx.tcx().region_maps.lookup_code_extent(
             CodeExtentData::ParameterScope { fn_id: fn_id, body_id: body.id });
-    let MirAndScopeAuxiliary { mut mir, scope_auxiliary } =
+    let (mut mir, scope_auxiliary) =
         build::construct(cx,
                          span,
                          implicit_arg_tys,

src/librustc_mir/pretty.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use build::{Location, ScopeAuxiliary};
+use build::{Location, ScopeAuxiliaryVec};
 use rustc::mir::repr::*;
 use rustc::middle::ty::{self, TyCtxt};
 use rustc_data_structures::fnv::FnvHashMap;
@@ -39,7 +39,7 @@ pub fn dump_mir<'a, 'tcx>(tcx: &TyCtxt<'tcx>,
                           disambiguator: &Display,
                           node_id: NodeId,
                           mir: &Mir<'tcx>,
-                          auxiliary: Option<&Vec<ScopeAuxiliary>>) {
+                          auxiliary: Option<&ScopeAuxiliaryVec>) {
     let filters = match tcx.sess.opts.debugging_opts.dump_mir {
         None => return,
         Some(ref filters) => filters,
@@ -91,12 +91,12 @@ pub fn write_mir_fn<'tcx>(tcx: &TyCtxt<'tcx>,
                           node_id: NodeId,
                           mir: &Mir<'tcx>,
                           w: &mut Write,
-                          auxiliary: Option<&Vec<ScopeAuxiliary>>)
+                          auxiliary: Option<&ScopeAuxiliaryVec>)
                           -> io::Result<()> {
     // compute scope/entry exit annotations
     let mut annotations = FnvHashMap();
     if let Some(auxiliary) = auxiliary {
-        for (index, auxiliary) in auxiliary.iter().enumerate() {
+        for (index, auxiliary) in auxiliary.vec.iter().enumerate() {
             let scope_id = ScopeId::new(index);
 
             annotations.entry(auxiliary.dom)
@@ -183,7 +183,7 @@ fn comment(tcx: &TyCtxt,
 
 fn write_scope_tree(tcx: &TyCtxt,
                     mir: &Mir,
-                    auxiliary: Option<&Vec<ScopeAuxiliary>>,
+                    auxiliary: Option<&ScopeAuxiliaryVec>,
                     scope_tree: &FnvHashMap<Option<ScopeId>, Vec<ScopeId>>,
                     w: &mut Write,
                     parent: Option<ScopeId>,
@@ -201,7 +201,7 @@ fn write_scope_tree(tcx: &TyCtxt,
         }
 
         if let Some(auxiliary) = auxiliary {
-            let extent = auxiliary[child.index()].extent;
+            let extent = auxiliary[child].extent;
             let data = tcx.region_maps.code_extent_data(extent);
             writeln!(w, "{0:1$}Extent: {2:?}", "", indent, data)?;
         }