1 files changed, 123 insertions, 0 deletions
diff --git a/src/test/ui/dropck/dropck-eyepatch.rs b/src/test/ui/dropck/dropck-eyepatch.rs
new file mode 100644
index 000000000..ec1c68561
--- /dev/null
+++ b/src/test/ui/dropck/dropck-eyepatch.rs
@@ -0,0 +1,123 @@
+#![feature(dropck_eyepatch)]
+
+// The point of this test is to illustrate that the `#[may_dangle]`
+// attribute specifically allows, in the context of a type
+// implementing `Drop`, a generic parameter to be instantiated with a
+// lifetime that does not strictly outlive the owning type itself.
+//
+// Here we test that only the expected errors are issued.
+//
+// The illustration is made concrete by comparison with two variations
+// on the type with `#[may_dangle]`:
+//
+//   1. an analogous type that does not implement `Drop` (and thus
+//      should exhibit maximal flexibility with respect to dropck), and
+//
+//   2. an analogous type that does not use `#[may_dangle]` (and thus
+//      should exhibit the standard limitations imposed by dropck.
+//
+// The types in this file follow a pattern, {D,P,S}{t,r}, where:
+//
+// - D means "I implement Drop"
+//
+// - P means "I implement Drop but guarantee my (first) parameter is
+//     pure, i.e., not accessed from the destructor"; no other parameters
+//     are pure.
+//
+// - S means "I do not implement Drop"
+//
+// - t suffix is used when the first generic is a type
+//
+// - r suffix is used when the first generic is a lifetime.
+
+use std::fmt;
+
+struct Dt<A: fmt::Debug>(&'static str, A);
+struct Dr<'a, B:'a+fmt::Debug>(&'static str, &'a B);
+struct Pt<A,B: fmt::Debug>(&'static str, A, B);
+struct Pr<'a, 'b, B:'a+'b+fmt::Debug>(&'static str, &'a B, &'b B);
+struct St<A: fmt::Debug>(&'static str, A);
+struct Sr<'a, B:'a+fmt::Debug>(&'static str, &'a B);
+
+impl<A: fmt::Debug> Drop for Dt<A> {
+    fn drop(&mut self) { println!("drop {} {:?}", self.0, self.1); }
+}
+impl<'a, B: fmt::Debug> Drop for Dr<'a, B> {
+    fn drop(&mut self) { println!("drop {} {:?}", self.0, self.1); }
+}
+unsafe impl<#[may_dangle] A, B: fmt::Debug> Drop for Pt<A, B> {
+    // (unsafe to access self.1  due to #[may_dangle] on A)
+    fn drop(&mut self) { println!("drop {} {:?}", self.0, self.2); }
+}
+unsafe impl<#[may_dangle] 'a, 'b, B: fmt::Debug> Drop for Pr<'a, 'b, B> {
+    // (unsafe to access self.1 due to #[may_dangle] on 'a)
+    fn drop(&mut self) { println!("drop {} {:?}", self.0, self.2); }
+}
+
+
+fn main() {
+    use std::cell::Cell;
+
+    // We use separate blocks with separate variable to prevent the error
+    // messages from being deduplicated.
+
+    {
+        let c_long;
+        let (mut dt, mut dr): (Dt<_>, Dr<_>);
+        c_long = Cell::new(1);
+
+        // No error: sufficiently long-lived state can be referenced in dtors
+        dt = Dt("dt", &c_long);
+        dr = Dr("dr", &c_long);
+    }
+
+    {
+        let (c, mut dt, mut dr): (Cell<_>, Dt<_>, Dr<_>);
+        c = Cell::new(1);
+
+        // No Error: destructor order precisely modelled
+        dt = Dt("dt", &c);
+        dr = Dr("dr", &c);
+    }
+
+    {
+        let (mut dt, mut dr, c_shortest): (Dt<_>, Dr<_>, Cell<_>);
+        c_shortest = Cell::new(1);
+
+        // Error: `c_shortest` dies too soon for the references in dtors to be valid.
+        dt = Dt("dt", &c_shortest);
+        //~^ ERROR `c_shortest` does not live long enough
+        dr = Dr("dr", &c_shortest);
+    }
+
+    {
+        let c_long;
+        let (mut pt, mut pr, c_shortest): (Pt<_, _>, Pr<_>, Cell<_>);
+        c_long = Cell::new(1);
+        c_shortest = Cell::new(1);
+
+        // No error: Drop impl asserts .1 (A and &'a _) are not accessed
+        pt = Pt("pt", &c_shortest, &c_long);
+        pr = Pr("pr", &c_shortest, &c_long);
+    }
+
+    {
+        let c_long;
+        let (mut pt, mut pr, c_shortest): (Pt<_, _>, Pr<_>, Cell<_>);
+        c_long = Cell::new(1);
+        c_shortest = Cell::new(1);
+        // Error: Drop impl's assertion does not apply to `B` nor `&'b _`
+        pt = Pt("pt", &c_long, &c_shortest);
+        //~^ ERROR `c_shortest` does not live long enough
+        pr = Pr("pr", &c_long, &c_shortest);
+    }
+
+    {
+        let (st, sr, c_shortest): (St<_>, Sr<_>, Cell<_>);
+        c_shortest = Cell::new(1);
+        // No error: St and Sr have no destructor.
+        st = St("st", &c_shortest);
+        sr = Sr("sr", &c_shortest);
+    }
+}
+fn use_imm<T>(_: &T) { }