From 911d205b1fab7cb0b84e1768c1744d89bd2c5c27 Mon Sep 17 00:00:00 2001
From: Chris Gregory <czipperz@gmail.com>
Date: Sat, 1 Jun 2019 18:42:59 -0500
Subject: [PATCH] On TerminatorKind::DropAndReplace still handle unused_mut
 correctly

---
 src/librustc_mir/borrow_check/used_muts.rs | 44 +++++++++++-----------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/src/librustc_mir/borrow_check/used_muts.rs b/src/librustc_mir/borrow_check/used_muts.rs
index abfc2f9466c..2334bd33694 100644
--- a/src/librustc_mir/borrow_check/used_muts.rs
+++ b/src/librustc_mir/borrow_check/used_muts.rs
@@ -52,6 +52,24 @@ struct GatherUsedMutsVisitor<'visit, 'cx: 'visit, 'gcx: 'tcx, 'tcx: 'cx> {
     mbcx: &'visit mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
 }
 
+impl<'visit, 'cx, 'gcx, 'tcx> GatherUsedMutsVisitor<'visit, 'cx, 'gcx, 'tcx> {
+    fn remove_never_initialized_mut_locals(into: &Place) {
+        // Remove any locals that we found were initialized from the
+        // `never_initialized_mut_locals` set. At the end, the only remaining locals will
+        // be those that were never initialized - we will consider those as being used as
+        // they will either have been removed by unreachable code optimizations; or linted
+        // as unused variables.
+        if let Some(local) = into.base_local() {
+            debug!(
+                "visit_statement: statement={:?} local={:?} \
+                 never_initialized_mut_locals={:?}",
+                statement, local, self.never_initialized_mut_locals
+            );
+            let _ = self.never_initialized_mut_locals.remove(&local);
+        }
+    }
+}
+
 impl<'visit, 'cx, 'gcx, 'tcx> Visitor<'tcx> for GatherUsedMutsVisitor<'visit, 'cx, 'gcx, 'tcx> {
     fn visit_terminator_kind(
         &mut self,
@@ -61,14 +79,10 @@ impl<'visit, 'cx, 'gcx, 'tcx> Visitor<'tcx> for GatherUsedMutsVisitor<'visit, 'c
         debug!("visit_terminator_kind: kind={:?}", kind);
         match &kind {
             TerminatorKind::Call { destination: Some((into, _)), .. } => {
-                if let Some(local) = into.base_local() {
-                    debug!(
-                        "visit_terminator_kind: kind={:?} local={:?} \
-                         never_initialized_mut_locals={:?}",
-                        kind, local, self.never_initialized_mut_locals
-                    );
-                    let _ = self.never_initialized_mut_locals.remove(&local);
-                }
+                self.remove_never_initialized_mut_locals(&into);
+            },
+            TerminatorKind::DropAndReplace { location, .. } => {
+                self.remove_never_initialized_mut_locals(&location);
             },
             _ => {},
         }
@@ -81,19 +95,7 @@ impl<'visit, 'cx, 'gcx, 'tcx> Visitor<'tcx> for GatherUsedMutsVisitor<'visit, 'c
     ) {
         match &statement.kind {
             StatementKind::Assign(into, _) => {
-                // Remove any locals that we found were initialized from the
-                // `never_initialized_mut_locals` set. At the end, the only remaining locals will
-                // be those that were never initialized - we will consider those as being used as
-                // they will either have been removed by unreachable code optimizations; or linted
-                // as unused variables.
-                if let Some(local) = into.base_local() {
-                    debug!(
-                        "visit_statement: statement={:?} local={:?} \
-                         never_initialized_mut_locals={:?}",
-                        statement, local, self.never_initialized_mut_locals
-                    );
-                    let _ = self.never_initialized_mut_locals.remove(&local);
-                }
+                self.remove_never_initialized_mut_locals(into);
             },
             _ => {},
         }