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.

src/test/compile-fail/asm-out-read-uninit.rs

@@ -19,7 +19,7 @@ fn foo(x: int) { info!("{}", x); }
 pub fn main() {
     let x: int;
     unsafe {
-        asm!("mov $1, $0" : "=r"(x) : "r"(x)); //~ ERROR use of possibly uninitialized value: `x`
+        asm!("mov $1, $0" : "=r"(x) : "r"(x)); //~ ERROR use of possibly uninitialized variable: `x`
     }
     foo(x);
 }

src/test/compile-fail/borrowck-block-unint.rs

@@ -11,7 +11,7 @@
 fn force(f: ||) { f(); }
 fn main() {
     let x: int;
-    force(|| {
-        info!("{}", x); //~ ERROR capture of possibly uninitialized variable: `x`
+    force(|| {  //~ ERROR capture of possibly uninitialized variable: `x`
+        info!("{}", x);
     });
 }

src/test/compile-fail/borrowck-uninit-in-assignop.rs

@@ -0,0 +1,44 @@
+// 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.
+
+// Tests that the use of uninitialized variable in assignment operator
+// expression is detected.
+
+pub fn main() {
+    let x: int;
+    x += 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x -= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x *= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x /= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x %= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x ^= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x &= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x |= 1; //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x <<= 1;    //~ ERROR use of possibly uninitialized variable: `x`
+
+    let x: int;
+    x >>= 1;    //~ ERROR use of possibly uninitialized variable: `x`
+}

src/test/compile-fail/borrowck-use-in-index-lvalue.rs

@@ -10,6 +10,10 @@
 
 fn test() {
     let w: ~[int];
+    w[5] = 0; //~ ERROR use of possibly uninitialized variable: `w`
+              //~^ ERROR cannot assign to immutable vec content `w[..]`
+
+    let mut w: ~[int];
     w[5] = 0; //~ ERROR use of possibly uninitialized variable: `w`
 }
 

src/test/compile-fail/liveness-unused.rs

@@ -23,6 +23,11 @@ fn f1b(x: &mut int) {
 #[allow(unused_variable)]
 fn f1c(x: int) {}
 
+fn f1d() {
+    let x: int;
+    //~^ ERROR unused variable: `x`
+}
+
 fn f2() {
     let x = 3;
     //~^ ERROR unused variable: `x`