From a9c7a415763563e394e469ac88e5f6665b7b1a86 Mon Sep 17 00:00:00 2001
From: Luqman Aden <laden@csclub.uwaterloo.ca>
Date: Tue, 5 Jul 2016 17:18:22 -0400
Subject: [PATCH] Make match discriminant reassignment check more accurate.

---
 src/librustc_trans/_match.rs     | 27 +++++++++++++++++----------
 src/test/run-pass/issue-27021.rs | 21 +++++++++++++++++++++
 2 files changed, 38 insertions(+), 10 deletions(-)
 create mode 100644 src/test/run-pass/issue-27021.rs

diff --git a/src/librustc_trans/_match.rs b/src/librustc_trans/_match.rs
index 3ef6e29a6f8..10af326be26 100644
--- a/src/librustc_trans/_match.rs
+++ b/src/librustc_trans/_match.rs
@@ -1495,20 +1495,27 @@ impl<'tcx> euv::Delegate<'tcx> for ReassignmentChecker {
     fn decl_without_init(&mut self, _: ast::NodeId, _: Span) {}
 
     fn mutate(&mut self, _: ast::NodeId, _: Span, cmt: mc::cmt, _: euv::MutateMode) {
+        let cmt_id = |cmt: &mc::cmt| match cmt.cat {
+            Categorization::Upvar(mc::Upvar { id: ty::UpvarId { var_id: vid, ..}, ..}) |
+            Categorization::Local(vid) => Some(vid),
+            Categorization::Interior(ref base_cmt, mc::InteriorField(_)) => Some(base_cmt.id),
+            _ => None
+        };
         match cmt.cat {
             Categorization::Upvar(mc::Upvar { id: ty::UpvarId { var_id: vid, .. }, .. }) |
             Categorization::Local(vid) => self.reassigned |= self.node == vid,
-            Categorization::Interior(ref base_cmt, mc::InteriorField(field)) => {
-                match base_cmt.cat {
-                    Categorization::Upvar(mc::Upvar { id: ty::UpvarId { var_id: vid, .. }, .. }) |
-                    Categorization::Local(vid) => {
-                        self.reassigned |= self.node == vid &&
-                            (self.field.is_none() || Some(field) == self.field)
-                    },
-                    _ => {}
+            ref cat => {
+                let mut cat = cat;
+                while let &Categorization::Interior(ref base_cmt, mc::InteriorField(field)) = cat {
+                    if let Some(vid) = cmt_id(base_cmt) {
+                        if self.node == vid && (self.field.is_none() || self.field == Some(field)) {
+                            self.reassigned = true;
+                            return;
+                        }
+                    }
+                    cat = &base_cmt.cat;
                 }
-            },
-            _ => {}
+            }
         }
     }
 }
diff --git a/src/test/run-pass/issue-27021.rs b/src/test/run-pass/issue-27021.rs
new file mode 100644
index 00000000000..eb7d529f0ad
--- /dev/null
+++ b/src/test/run-pass/issue-27021.rs
@@ -0,0 +1,21 @@
+// 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.
+
+fn main() {
+    let mut c = (1, (1, "".to_owned()));
+    match c {
+        c2 => { (c.1).0 = 2; assert_eq!((c2.1).0, 1); }
+    }
+
+    let mut c = (1, (1, (1, "".to_owned())));
+    match c.1 {
+        c2 => { ((c.1).1).0 = 3; assert_eq!((c2.1).0, 1); }
+    }
+}