borrowck-migrate-to-nll: use rust-lang#38899 for testing.

src/test/ui/borrowck/borrowck-migrate-to-nll.edition.stderr

@@ -1,14 +1,14 @@
-warning[E0507]: cannot move out of `foo` in pattern guard
-  --> $DIR/borrowck-migrate-to-nll.rs:26:18
+warning[E0502]: cannot borrow `*block.current` as immutable because it is also borrowed as mutable
+  --> $DIR/borrowck-migrate-to-nll.rs:28:21
    |
-LL |                 (|| { let bar = foo; bar.take() })();
-   |                  ^^             ---
-   |                  |              |
-   |                  |              move occurs because `foo` has type `&mut std::option::Option<&i32>`, which does not implement the `Copy` trait
-   |                  |              move occurs due to use in closure
-   |                  move out of `foo` occurs here
+LL |     let x = &mut block;
+   |             ---------- mutable borrow occurs here
+LL |     let p: &'a u8 = &*block.current;
+   |                     ^^^^^^^^^^^^^^^ immutable borrow occurs here
+LL |     // (use `x` and `p` so enabling NLL doesn't assign overly short lifetimes)
+LL |     drop(x);
+   |          - mutable borrow later used here
    |
-   = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
    = note: for more information, try `rustc --explain E0729`

src/test/ui/borrowck/borrowck-migrate-to-nll.rs

@@ -1,4 +1,4 @@
-// This is a test of the borrowck migrate mode. It leverages #27282, a
+// This is a test of the borrowck migrate mode. It leverages #38899, a
 // bug that is fixed by NLL: this code is (unsoundly) accepted by
 // AST-borrowck, but is correctly rejected by the NLL borrowck.
 //
@@ -18,15 +18,17 @@
 //[zflag] run-pass
 //[edition] run-pass
 
-fn main() {
-    match Some(&4) {
-        None => {},
-        ref mut foo
-            if {
-                (|| { let bar = foo; bar.take() })();
-                false
-            } => {},
-        Some(ref _s) => println!("Note this arm is bogus; the `Some` became `None` in the guard."),
-        _ => println!("Here is some supposedly unreachable code."),
-    }
+pub struct Block<'a> {
+    current: &'a u8,
+    unrelated: &'a u8,
 }
+
+fn bump<'a>(mut block: &mut Block<'a>) {
+    let x = &mut block;
+    let p: &'a u8 = &*block.current;
+    // (use `x` and `p` so enabling NLL doesn't assign overly short lifetimes)
+    drop(x);
+    drop(p);
+}
+
+fn main() {}

src/test/ui/borrowck/borrowck-migrate-to-nll.zflag.stderr

@@ -1,14 +1,14 @@
-warning[E0507]: cannot move out of `foo` in pattern guard
-  --> $DIR/borrowck-migrate-to-nll.rs:26:18
+warning[E0502]: cannot borrow `*block.current` as immutable because it is also borrowed as mutable
+  --> $DIR/borrowck-migrate-to-nll.rs:28:21
    |
-LL |                 (|| { let bar = foo; bar.take() })();
-   |                  ^^             ---
-   |                  |              |
-   |                  |              move occurs because `foo` has type `&mut std::option::Option<&i32>`, which does not implement the `Copy` trait
-   |                  |              move occurs due to use in closure
-   |                  move out of `foo` occurs here
+LL |     let x = &mut block;
+   |             ---------- mutable borrow occurs here
+LL |     let p: &'a u8 = &*block.current;
+   |                     ^^^^^^^^^^^^^^^ immutable borrow occurs here
+LL |     // (use `x` and `p` so enabling NLL doesn't assign overly short lifetimes)
+LL |     drop(x);
+   |          - mutable borrow later used here
    |
-   = note: variables bound in patterns cannot be moved from until after the end of the pattern guard
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
    = note: for more information, try `rustc --explain E0729`