From fe29cd0a3d1ebff0d90f3e4ebc929f944863be4c Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Mon, 5 Nov 2018 15:24:25 +0100
Subject: [PATCH] Add `ui/borrowck/borrowck-closures-mut-of-mut.rs`.

This is a variant of `ui/borrowck/borrowck-closures-mut-of-imm.rs`
that I used to help identify what changes I needed to make to the
latter file in order to recover its instances of E0524 under NLL.

(Basically this test includes the changes you'd need to make to
`ui/borrowck/borrowck-closures-mut-of-imm.rs` in order to get rid of
occurrences of E0596. And then I realized that one needs to add
invocations of the closures in order to properly extend the mutable
reborrows in a manner such that NLL will roughly match AST-borrowck.)
---
 .../borrowck-closures-mut-of-mut.nll.stderr   | 18 +++++++++++++++++
 .../borrowck/borrowck-closures-mut-of-mut.rs  | 20 +++++++++++++++++++
 .../borrowck-closures-mut-of-mut.stderr       | 18 +++++++++++++++++
 3 files changed, 56 insertions(+)
 create mode 100644 src/test/ui/borrowck/borrowck-closures-mut-of-mut.nll.stderr
 create mode 100644 src/test/ui/borrowck/borrowck-closures-mut-of-mut.rs
 create mode 100644 src/test/ui/borrowck/borrowck-closures-mut-of-mut.stderr

diff --git a/src/test/ui/borrowck/borrowck-closures-mut-of-mut.nll.stderr b/src/test/ui/borrowck/borrowck-closures-mut-of-mut.nll.stderr
new file mode 100644
index 00000000000..18f95f232cd
--- /dev/null
+++ b/src/test/ui/borrowck/borrowck-closures-mut-of-mut.nll.stderr
@@ -0,0 +1,18 @@
+error[E0524]: two closures require unique access to `x` at the same time
+  --> $DIR/borrowck-closures-mut-of-mut.rs:14:18
+   |
+LL |     let mut c1 = || set(&mut *x);
+   |                  --           - first borrow occurs due to use of `x` in closure
+   |                  |
+   |                  first closure is constructed here
+LL |     let mut c2 = || set(&mut *x);
+   |                  ^^           - second borrow occurs due to use of `x` in closure
+   |                  |
+   |                  second closure is constructed here
+LL |     //~^ ERROR two closures require unique access to `x` at the same time
+LL |     c2(); c1();
+   |           -- first borrow later used here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0524`.
diff --git a/src/test/ui/borrowck/borrowck-closures-mut-of-mut.rs b/src/test/ui/borrowck/borrowck-closures-mut-of-mut.rs
new file mode 100644
index 00000000000..50c6f2c585e
--- /dev/null
+++ b/src/test/ui/borrowck/borrowck-closures-mut-of-mut.rs
@@ -0,0 +1,20 @@
+// Tests that two closures cannot simultaneously both have mutable
+// access to the variable. Related to issue #6801.
+
+fn get(x: &isize) -> isize {
+    *x
+}
+
+fn set(x: &mut isize) {
+    *x = 4;
+}
+
+fn a(x: &mut isize) {
+    let mut c1 = || set(&mut *x);
+    let mut c2 = || set(&mut *x);
+    //~^ ERROR two closures require unique access to `x` at the same time
+    c2(); c1();
+}
+
+fn main() {
+}
diff --git a/src/test/ui/borrowck/borrowck-closures-mut-of-mut.stderr b/src/test/ui/borrowck/borrowck-closures-mut-of-mut.stderr
new file mode 100644
index 00000000000..2c5587710a1
--- /dev/null
+++ b/src/test/ui/borrowck/borrowck-closures-mut-of-mut.stderr
@@ -0,0 +1,18 @@
+error[E0524]: two closures require unique access to `x` at the same time
+  --> $DIR/borrowck-closures-mut-of-mut.rs:14:18
+   |
+LL |     let mut c1 = || set(&mut *x);
+   |                  --           - previous borrow occurs due to use of `x` in closure
+   |                  |
+   |                  first closure is constructed here
+LL |     let mut c2 = || set(&mut *x);
+   |                  ^^           - borrow occurs due to use of `x` in closure
+   |                  |
+   |                  second closure is constructed here
+...
+LL | }
+   | - borrow from first closure ends here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0524`.