tests: adjust some `augmented-assignment*` tests

- `tests/ui/augmented-assignment-feature-gate-cross.rs`:
  - This was *originally* to feature-gate overloaded OpAssign
    cross-crate, but now let's keep it as a smoke test.
  - Renamed as `augmented-assignment-cross-crate.rs`.
  - Relocated under `tests/ui/binop/`.
-  `tests/ui/augmented-assignments.rs`:
  - Documented test intent.
  - Moved under `tests/ui/borrowck/`.
- `tests/ui/augmented-assignment-rpass.rs`:
  - Renamed to drop the `-rpass` suffix, since this was leftover from
    when `run-pass` test suite was a thing.
  - Moved under `tests/ui/binop/`.

2 files changed, 57 insertions, 0 deletions

diff --git a/tests/ui/borrowck/augmented-assignments.rs b/tests/ui/borrowck/augmented-assignments.rs
new file mode 100644
index 00000000000..d717dcc7935
--- /dev/null
+++ b/tests/ui/borrowck/augmented-assignments.rs
@@ -0,0 +1,31 @@
+//! Check that overloaded compound assignment operators respect usual borrowck rules and emit
+//! reasonable diagnostics.
+
+use std::ops::AddAssign;
+
+#[derive(Clone)]
+struct Int(i32);
+
+impl AddAssign for Int {
+    fn add_assign(&mut self, _: Int) {
+        unimplemented!()
+    }
+}
+
+fn main() {
+    let mut x = Int(1); //~ NOTE binding `x` declared here
+    x
+    //~^ NOTE borrow of `x` occurs here
+    +=
+    x;
+    //~^ ERROR cannot move out of `x` because it is borrowed
+    //~| NOTE move out of `x` occurs here
+
+    let y = Int(2);
+    //~^ HELP consider changing this to be mutable
+    //~| SUGGESTION mut
+    y   //~ ERROR cannot borrow `y` as mutable, as it is not declared as mutable
+        //~| NOTE cannot borrow as mutable
+    +=
+    Int(1);
+}
diff --git a/tests/ui/borrowck/augmented-assignments.stderr b/tests/ui/borrowck/augmented-assignments.stderr
new file mode 100644
index 00000000000..4b945cd998a
--- /dev/null
+++ b/tests/ui/borrowck/augmented-assignments.stderr
@@ -0,0 +1,26 @@
+error[E0505]: cannot move out of `x` because it is borrowed
+  --> $DIR/augmented-assignments.rs:20:5
+   |
+LL |     let mut x = Int(1);
+   |         ----- binding `x` declared here
+LL |     x
+   |     - borrow of `x` occurs here
+...
+LL |     x;
+   |     ^ move out of `x` occurs here
+
+error[E0596]: cannot borrow `y` as mutable, as it is not declared as mutable
+  --> $DIR/augmented-assignments.rs:27:5
+   |
+LL |     y
+   |     ^ cannot borrow as mutable
+   |
+help: consider changing this to be mutable
+   |
+LL |     let mut y = Int(2);
+   |         +++
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0505, E0596.
+For more information about an error, try `rustc --explain E0505`.