Evaluate borrow and struct expressions in `into`

This fixes some ordering problems around assignment expressions.

4 files changed, 73 insertions, 6 deletions

diff --git a/src/test/ui/borrowck/borrowck-init-in-fru.stderr b/src/test/ui/borrowck/borrowck-init-in-fru.stderr
index a4c042d1c12..f01afe1466a 100644
--- a/src/test/ui/borrowck/borrowck-init-in-fru.stderr
+++ b/src/test/ui/borrowck/borrowck-init-in-fru.stderr
@@ -1,8 +1,8 @@
 error[E0381]: use of possibly-uninitialized variable: `origin`
-  --> $DIR/borrowck-init-in-fru.rs:9:5
+  --> $DIR/borrowck-init-in-fru.rs:9:14
    |
 LL |     origin = Point { x: 10, ..origin };
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ use of possibly-uninitialized `origin.y`
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^ use of possibly-uninitialized `origin.y`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/mir/mir_assign_eval_order.rs b/src/test/ui/mir/mir_assign_eval_order.rs
new file mode 100644
index 00000000000..1594421b0b1
--- /dev/null
+++ b/src/test/ui/mir/mir_assign_eval_order.rs
@@ -0,0 +1,67 @@
+// Test evaluation order of assignment expressions is right to left.
+
+// run-pass
+
+// We would previously not finish evaluating borrow and FRU expressions before
+// starting on the LHS
+
+struct S(i32);
+
+fn evaluate_reborrow_before_assign() {
+    let mut x = &1;
+    let y = &mut &2;
+    let z = &3;
+    // There's an implicit reborrow of `x` on the right-hand side of the
+    // assignement. Note that writing an explicit reborrow would not show this
+    // bug, as now there would be two reborrows on the right-hand side and at
+    // least one of them would happen before the left-hand side is evaluated.
+    *{ x = z; &mut *y } = x;
+    assert_eq!(*x, 3);
+    assert_eq!(**y, 1);             // y should be assigned the original value of `x`.
+}
+
+fn evaluate_mut_reborrow_before_assign() {
+    let mut x = &mut 1;
+    let y = &mut &mut 2;
+    let z = &mut 3;
+    *{ x = z; &mut *y } = x;
+    assert_eq!(*x, 3);
+    assert_eq!(**y, 1);            // y should be assigned the original value of `x`.
+}
+
+// We should evaluate `x[2]` and borrow the value out *before* evaluating the
+// LHS and changing its value.
+fn evaluate_ref_to_temp_before_assign_slice() {
+    let mut x = &[S(0), S(1), S(2)][..];
+    let y = &mut &S(7);
+    *{ x = &[S(3), S(4), S(5)]; &mut *y } = &x[2];
+    assert_eq!(2, y.0);
+    assert_eq!(5, x[2].0);
+}
+
+// We should evaluate `x[2]` and copy the value out *before* evaluating the LHS
+// and changing its value.
+fn evaluate_fru_to_temp_before_assign_slice() {
+    let mut x = &[S(0), S(1), S(2)][..];
+    let y = &mut S(7);
+    *{ x = &[S(3), S(4), S(5)]; &mut *y } = S { ..x[2] };
+    assert_eq!(2, y.0);
+    assert_eq!(5, x[2].0);
+}
+
+// We should evaluate `*x` and copy the value out *before* evaluating the LHS
+// and dropping `x`.
+fn evaluate_fru_to_temp_before_assign_box() {
+    let x = Box::new(S(0));
+    let y = &mut S(1);
+    *{ drop(x); &mut *y } = S { ..*x };
+    assert_eq!(0, y.0);
+}
+
+fn main() {
+    evaluate_reborrow_before_assign();
+    evaluate_mut_reborrow_before_assign();
+    evaluate_ref_to_temp_before_assign_slice();
+    evaluate_fru_to_temp_before_assign_slice();
+    evaluate_fru_to_temp_before_assign_box();
+}
diff --git a/src/test/ui/nll/issue-52534-2.stderr b/src/test/ui/nll/issue-52534-2.stderr
index dd8a87f7e29..cef4aba0240 100644
--- a/src/test/ui/nll/issue-52534-2.stderr
+++ b/src/test/ui/nll/issue-52534-2.stderr
@@ -1,8 +1,8 @@
 error[E0597]: `x` does not live long enough
-  --> $DIR/issue-52534-2.rs:6:9
+  --> $DIR/issue-52534-2.rs:6:13
    |
 LL |         y = &x
-   |         ^^^^^^ borrowed value does not live long enough
+   |             ^^ borrowed value does not live long enough
 LL |
 LL |     }
    |     - `x` dropped here while still borrowed
diff --git a/src/test/ui/span/issue-36537.stderr b/src/test/ui/span/issue-36537.stderr
index edb804e850e..0939584380a 100644
--- a/src/test/ui/span/issue-36537.stderr
+++ b/src/test/ui/span/issue-36537.stderr
@@ -1,8 +1,8 @@
 error[E0597]: `a` does not live long enough
-  --> $DIR/issue-36537.rs:5:9
+  --> $DIR/issue-36537.rs:5:13
    |
 LL |         p = &a;
-   |         ^^^^^^ borrowed value does not live long enough
+   |             ^^ borrowed value does not live long enough
 ...
 LL |     }
    |     - `a` dropped here while still borrowed