Add is_ref_for_guard method

src/librustc/mir/mod.rs

@@ -913,6 +913,16 @@ impl<'tcx> LocalDecl<'tcx> {
         }
     }
 
+    /// Returns `true` if this is a reference to a variable bound in a `match`
+    /// expression that is used to access said variable for the guard of the
+    /// match arm.
+    pub fn is_ref_for_guard(&self) -> bool {
+        match self.is_user_variable {
+            Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) => true,
+            _ => false,
+        }
+    }
+
     /// Returns `true` is the local is from a compiler desugaring, e.g.,
     /// `__next` from a `for` loop.
     #[inline]

src/librustc_mir/borrow_check/error_reporting.rs

@@ -180,9 +180,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                                     &including_downcast,
                                 )?;
                             } else if let Place::Base(PlaceBase::Local(local)) = proj.base {
-                                if let Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) =
+                                if self.mir.local_decls[local].is_ref_for_guard() {
-                                    self.mir.local_decls[local].is_user_variable
-                                {
                                     self.append_place_to_string(
                                         &proj.base,
                                         buf,

src/librustc_mir/borrow_check/mutability_errors.rs

@@ -95,12 +95,7 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                     }
                 } else if {
                     if let Place::Base(PlaceBase::Local(local)) = *base {
-                        if let Some(ClearCrossCrate::Set(BindingForm::RefForGuard))
+                        self.mir.local_decls[local].is_ref_for_guard()
-                            = self.mir.local_decls[local].is_user_variable {
-                                true
-                        } else {
-                            false
-                        }
                     } else {
                         false
                     }

src/librustc_mir/build/expr/as_rvalue.rs

@@ -503,13 +503,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 elem: ProjectionElem::Deref,
             }) => {
                 debug_assert!(
-                    if let Some(ClearCrossCrate::Set(BindingForm::RefForGuard)) =
+                    this.local_decls[local].is_ref_for_guard(),
-                        this.local_decls[local].is_user_variable
-                    {
-                        true
-                    } else {
-                        false
-                    },
                     "Unexpected capture place",
                 );
                 this.local_decls[local].mutability