Match binding is assignment

src/librustc/middle/borrowck/gather_loans/mod.rs

@@ -160,16 +160,8 @@ fn gather_loans_in_local(this: &mut GatherLoanCtxt,
             })
         }
         Some(init) => {
-            // Variable declarations with initializers are considered "assigns":
-            let tcx = this.bccx.tcx;
-            pat_util::pat_bindings(tcx.def_map, local.pat, |_, id, span, _| {
-                gather_moves::gather_assignment(this.bccx,
-                                                &this.move_data,
-                                                id,
-                                                span,
-                                                @LpVar(id),
-                                                id);
-            });
+            // Variable declarations with initializers are considered "assigns",
+            // which is handled by `gather_pat`:
             let init_cmt = this.bccx.cat_expr(init);
             this.gather_pat(init_cmt, local.pat, None);
         }
@@ -811,6 +803,17 @@ impl<'a> GatherLoanCtxt<'a> {
         self.bccx.cat_pattern(discr_cmt, root_pat, |cmt, pat| {
             match pat.node {
               ast::PatIdent(bm, _, _) if self.pat_is_binding(pat) => {
+                // Each match binding is effectively an assignment.
+                let tcx = self.bccx.tcx;
+                pat_util::pat_bindings(tcx.def_map, pat, |_, id, span, _| {
+                    gather_moves::gather_assignment(self.bccx,
+                                                    &self.move_data,
+                                                    id,
+                                                    span,
+                                                    @LpVar(id),
+                                                    id);
+                });
+
                 match bm {
                   ast::BindByRef(mutbl) => {
                     // ref x or ref x @ p --- creates a ptr which must

src/test/compile-fail/borrowck-match-binding-is-assignment.rs

@@ -0,0 +1,51 @@
+// Copyright 2012-2014 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.
+
+// Test that immutable pattern bindings cannot be reassigned.
+
+enum E {
+    Foo(int)
+}
+
+struct S {
+    bar: int,
+}
+
+pub fn main() {
+    match 1i {
+        x => {
+            x += 1; //~ ERROR re-assignment of immutable variable `x`
+        }
+    }
+
+    match Foo(1) {
+        Foo(x) => {
+            x += 1; //~ ERROR re-assignment of immutable variable `x`
+        }
+    }
+
+    match S { bar: 1 } {
+        S { bar: x } => {
+            x += 1; //~ ERROR re-assignment of immutable variable `x`
+        }
+    }
+
+    match (1i,) {
+        (x,) => {
+            x += 1; //~ ERROR re-assignment of immutable variable `x`
+        }
+    }
+
+    match [1,2,3] {
+        [x,_,_] => {
+            x += 1; //~ ERROR re-assignment of immutable variable `x`
+        }
+    }
+}