1 files changed, 30 insertions, 0 deletions
diff --git a/tests/ui/nll/issue-27282-mutate-before-diverging-arm-3.rs b/tests/ui/nll/issue-27282-mutate-before-diverging-arm-3.rs
new file mode 100644
index 000000000..cff9e963e
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+++ b/tests/ui/nll/issue-27282-mutate-before-diverging-arm-3.rs
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+// This is testing an attempt to corrupt the discriminant of the match
+// arm in a guard, followed by an attempt to continue matching on that
+// corrupted discriminant in the remaining match arms.
+//
+// Basically this is testing that our new NLL feature of emitting a
+// fake read on each match arm is catching cases like this.
+//
+// This case is interesting because a borrow of **x is untracked, because **x is
+// immutable. However, for matches we care that **x refers to the same value
+// until we have chosen a match arm.
+
+struct ForceFnOnce;
+fn main() {
+    let mut x = &mut &Some(&2);
+    let force_fn_once = ForceFnOnce;
+    match **x {
+        None => panic!("unreachable"),
+        Some(&_) if {
+            // ForceFnOnce needed to exploit #27282
+            (|| { *x = &None; drop(force_fn_once); })();
+            //~^ ERROR cannot mutably borrow `x` in match guard [E0510]
+            false
+        } => {}
+        Some(&a) if { // this binds to garbage if we've corrupted discriminant
+            println!("{}", a);
+            panic!()
+        } => {}
+        _ => panic!("unreachable"),
+    }
+}