borrowck: classify expressions as assignees, uses or both

- Repurposes `MoveData.assignee_ids` to mean only `=` but not `+=`, so
  that borrowck effectively classifies all expressions into assignees,
  uses or both.
- Removes two `span_err` in liveness analysis, which are now borrowck's
  responsibilities.

Closes #12527.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/test/compile-fail/borrowck-while-cond.rs b/src/test/compile-fail/borrowck-while-cond.rs
new file mode 100644
index 00000000000..27d42d666ea
--- /dev/null
+++ b/src/test/compile-fail/borrowck-while-cond.rs
@@ -0,0 +1,14 @@
+// Copyright 2012 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 x: bool;
+    while x { } //~ ERROR use of possibly uninitialized variable: `x`
+}