add Location::START const

Author: nikomatsakis

src/librustc/mir/mod.rs

@@ -1978,6 +1978,11 @@ impl fmt::Debug for Location {
 }
 
 impl Location {
+    pub const START: Location = Location {
+        block: START_BLOCK,
+        statement_index: 0,
+    };
+
     /// Returns the location immediately after this one within the enclosing block.
     ///
     /// Note that if this location represents a terminator, then the

src/librustc_mir/borrow_check/nll/type_check/input_output.rs

@@ -112,7 +112,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                 let anon_defn_ty = anon_defn_ty.subst(tcx, anon_decl.substs);
                 let anon_defn_ty = renumber::renumber_regions(
                     cx.infcx,
-                    TyContext::Location(start_position),
+                    TyContext::Location(Location::START),
                     &anon_defn_ty,
                 );
                 debug!(
@@ -134,7 +134,7 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
         }).unwrap_or_else(|terr| {
                 span_mirbug!(
                     self,
-                    start_position,
+                    Location::START,
                     "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
                     output_ty,
                     mir_output_ty,

src/librustc_mir/transform/elaborate_drops.rs

@@ -550,7 +550,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
     }
 
     fn drop_flags_on_init(&mut self) {
-        let loc = Location { block: START_BLOCK, statement_index: 0 };
+        let loc = Location::START;
         let span = self.patch.source_info_for_location(self.mir, loc).span;
         let false_ = self.constant_bool(span, false);
         for flag in self.drop_flags.values() {
@@ -576,7 +576,7 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
     }
 
     fn drop_flags_for_args(&mut self) {
-        let loc = Location { block: START_BLOCK, statement_index: 0 };
+        let loc = Location::START;
         dataflow::drop_flag_effects_for_function_entry(
             self.tcx, self.mir, self.env, |path, ds| {
                 self.set_drop_flag(loc, path, ds);