Add tests for generator resume arguments

src/test/ui/generator/retain-resume-ref.rs

@@ -0,0 +1,25 @@
+//! This test ensures that a mutable reference cannot be passed as a resume argument twice.
+
+#![feature(generators, generator_trait)]
+
+use std::marker::Unpin;
+use std::ops::{
+    Generator,
+    GeneratorState::{self, *},
+};
+use std::pin::Pin;
+
+fn main() {
+    let mut thing = String::from("hello");
+
+    let mut gen = |r| {
+        if false {
+            yield r;
+        }
+    };
+
+    let mut gen = Pin::new(&mut gen);
+    gen.as_mut().resume(&mut thing);
+    gen.as_mut().resume(&mut thing);
+    //~^ cannot borrow `thing` as mutable more than once at a time
+}

src/test/ui/generator/retain-resume-ref.stderr

@@ -0,0 +1,13 @@
+error[E0499]: cannot borrow `thing` as mutable more than once at a time
+  --> $DIR/retain-resume-ref.rs:23:25
+   |
+LL |     gen.as_mut().resume(&mut thing);
+   |                         ---------- first mutable borrow occurs here
+LL |     gen.as_mut().resume(&mut thing);
+   |                  ------ ^^^^^^^^^^ second mutable borrow occurs here
+   |                  |
+   |                  first borrow later used by call
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0499`.

src/test/ui/generator/smoke-resume-args.rs

@@ -0,0 +1,97 @@
+// run-pass
+
+#![feature(generators, generator_trait)]
+
+use std::fmt::Debug;
+use std::marker::Unpin;
+use std::ops::{
+    Generator,
+    GeneratorState::{self, *},
+};
+use std::pin::Pin;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+fn drain<G: Generator<R, Yield = Y> + Unpin, R, Y>(
+    gen: &mut G,
+    inout: Vec<(R, GeneratorState<Y, G::Return>)>,
+) where
+    Y: Debug + PartialEq,
+    G::Return: Debug + PartialEq,
+{
+    let mut gen = Pin::new(gen);
+
+    for (input, out) in inout {
+        assert_eq!(gen.as_mut().resume(input), out);
+    }
+}
+
+static DROPS: AtomicUsize = AtomicUsize::new(0);
+
+#[derive(Debug, PartialEq)]
+struct DropMe;
+
+impl Drop for DropMe {
+    fn drop(&mut self) {
+        DROPS.fetch_add(1, Ordering::SeqCst);
+    }
+}
+
+fn expect_drops<T>(expected_drops: usize, f: impl FnOnce() -> T) -> T {
+    DROPS.store(0, Ordering::SeqCst);
+
+    let res = f();
+
+    let actual_drops = DROPS.load(Ordering::SeqCst);
+    assert_eq!(actual_drops, expected_drops);
+    res
+}
+
+fn main() {
+    drain(
+        &mut |mut b| {
+            while b != 0 {
+                b = yield (b + 1);
+            }
+            -1
+        },
+        vec![(1, Yielded(2)), (-45, Yielded(-44)), (500, Yielded(501)), (0, Complete(-1))],
+    );
+
+    expect_drops(2, || drain(&mut |a| yield a, vec![(DropMe, Yielded(DropMe))]));
+
+    expect_drops(6, || {
+        drain(
+            &mut |a| yield yield a,
+            vec![(DropMe, Yielded(DropMe)), (DropMe, Yielded(DropMe)), (DropMe, Complete(DropMe))],
+        )
+    });
+
+    #[allow(unreachable_code)]
+    expect_drops(2, || drain(&mut |a| yield return a, vec![(DropMe, Complete(DropMe))]));
+
+    expect_drops(2, || {
+        drain(
+            &mut |a: DropMe| {
+                if false { yield () } else { a }
+            },
+            vec![(DropMe, Complete(DropMe))],
+        )
+    });
+
+    expect_drops(4, || {
+        drain(
+            #[allow(unused_assignments, unused_variables)]
+            &mut |mut a: DropMe| {
+                a = yield;
+                a = yield;
+                a = yield;
+            },
+            vec![
+                (DropMe, Yielded(())),
+                (DropMe, Yielded(())),
+                (DropMe, Yielded(())),
+                (DropMe, Complete(())),
+            ],
+        )
+    });
+}