From b041a79f267d61b01bd339f6f01e48bcdf2a56ab Mon Sep 17 00:00:00 2001
From: memoryruins <memoryruinsmusic@gmail.com>
Date: Fri, 12 Oct 2018 12:43:13 -0400
Subject: [PATCH] Add test for issue #52240

Closes #52240
---
 src/test/ui/issues/issue-52240.rs     | 16 ++++++++++++++++
 src/test/ui/issues/issue-52240.stderr |  9 +++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 src/test/ui/issues/issue-52240.rs
 create mode 100644 src/test/ui/issues/issue-52240.stderr

diff --git a/src/test/ui/issues/issue-52240.rs b/src/test/ui/issues/issue-52240.rs
new file mode 100644
index 00000000000..9ac7e9905da
--- /dev/null
+++ b/src/test/ui/issues/issue-52240.rs
@@ -0,0 +1,16 @@
+// issue-52240: Can turn immutable into mut with `ref mut`
+
+enum Foo {
+    Bar(i32),
+}
+
+fn main() {
+    let arr = vec!(Foo::Bar(0));
+    if let (Some(Foo::Bar(ref mut val)), _) = (&arr.get(0), 0) {
+        //~^ ERROR cannot borrow field of immutable binding as mutable
+        *val = 9001;
+    }
+    match arr[0] {
+        Foo::Bar(ref s) => println!("{}", s)
+    }
+}
diff --git a/src/test/ui/issues/issue-52240.stderr b/src/test/ui/issues/issue-52240.stderr
new file mode 100644
index 00000000000..c2c2524816d
--- /dev/null
+++ b/src/test/ui/issues/issue-52240.stderr
@@ -0,0 +1,9 @@
+error[E0596]: cannot borrow field of immutable binding as mutable
+  --> $DIR/issue-52240.rs:9:27
+   |
+LL |     if let (Some(Foo::Bar(ref mut val)), _) = (&arr.get(0), 0) {
+   |                           ^^^^^^^^^^^ cannot mutably borrow field of immutable binding
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.