Promote Refs to constants instead of static

Author: spastorino

src/librustc/mir/interpret/queries.rs

@@ -36,11 +36,16 @@ impl<'tcx> TyCtxt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         def_id: DefId,
         substs: SubstsRef<'tcx>,
+        promoted: Option<mir::Promoted>,
         span: Option<Span>,
     ) -> ConstEvalResult<'tcx> {
         let instance = ty::Instance::resolve(self, param_env, def_id, substs);
         if let Some(instance) = instance {
-            self.const_eval_instance(param_env, instance, span)
+            if let Some(promoted) = promoted {
+                self.const_eval_promoted(instance, promoted)
+            } else {
+                self.const_eval_instance(param_env, instance, span)
+            }
         } else {
             Err(ErrorHandled::TooGeneric)
         }

src/librustc/mir/mod.rs

@@ -166,6 +166,16 @@ pub struct Body<'tcx> {
 
     /// A span representing this MIR, for error reporting.
     pub span: Span,
+
+    /// The user may be writing e.g. &[(SOME_CELL, 42)][i].1 and this would get promoted, because
+    /// we'd statically know that no thing with interior mutability will ever be available to the
+    /// user without some serious unsafe code.  Now this means that our promoted is actually
+    /// &[(SOME_CELL, 42)] and the MIR using it will do the &promoted[i].1 projection because the
+    /// index may be a runtime value. Such a promoted value is illegal because it has reachable
+    /// interior mutability. This flag just makes this situation very obvious where the previous
+    /// implementation without the flag hid this situation silently.
+    /// FIXME(oli-obk): rewrite the promoted during promotion to eliminate the cell components.
+    pub ignore_interior_mut_in_const_validation: bool,
 }
 
 impl<'tcx> Body<'tcx> {
@@ -202,6 +212,7 @@ impl<'tcx> Body<'tcx> {
             spread_arg: None,
             var_debug_info,
             span,
+            ignore_interior_mut_in_const_validation: false,
             control_flow_destroyed,
         }
     }