Use EverInit instead of MaybeInit to determine initialization

Author: KiChjang

src/librustc_mir/borrow_check/mod.rs

@@ -1810,9 +1810,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 }
             }
             Reservation(WriteKind::Move)
+            | Write(WriteKind::Move)
             | Reservation(WriteKind::StorageDeadOrDrop)
             | Reservation(WriteKind::MutableBorrow(BorrowKind::Shared))
-            | Write(WriteKind::Move)
             | Write(WriteKind::StorageDeadOrDrop)
             | Write(WriteKind::MutableBorrow(BorrowKind::Shared)) => {
                 if let Err(_place_err) = self.is_mutable(place, is_local_mutation_allowed) {
@@ -1851,8 +1851,11 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     // mutated, then it is justified to be annotated with the `mut`
                     // keyword, since the mutation may be a possible reassignment.
                     let mpi = self.move_data.rev_lookup.find_local(*local);
-                    if flow_state.inits.contains(&mpi) {
-                        self.used_mut.insert(*local);
+                    let ii = &self.move_data.init_path_map[mpi];
+                    for index in ii {
+                        if flow_state.ever_inits.contains(index) {
+                            self.used_mut.insert(*local);
+                        }
                     }
                 }
             }

src/test/run-pass/nll/issue-50461-used-mut-from-moves.rs

@@ -0,0 +1,25 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(nll)]
+#![deny(unused_mut)]
+
+struct Foo {
+    pub value: i32
+}
+
+fn use_foo_mut(mut foo: Foo) {
+    foo = foo;
+    println!("{}", foo.value);
+}
+
+fn main() {
+    use_foo_mut(Foo { value: 413 });
+}