Use deep fake borrows for deref patterns

2 files changed, 26 insertions, 0 deletions

diff --git a/tests/ui/pattern/deref-patterns/fake_borrows.rs b/tests/ui/pattern/deref-patterns/fake_borrows.rs
new file mode 100644
index 00000000000..35fa9cbf7d8
--- /dev/null
+++ b/tests/ui/pattern/deref-patterns/fake_borrows.rs
@@ -0,0 +1,14 @@
+#![feature(deref_patterns)]
+#![allow(incomplete_features)]
+
+#[rustfmt::skip]
+fn main() {
+    let mut b = Box::new(false);
+    match b {
+        deref!(true) => {}
+        _ if { *b = true; false } => {}
+        //~^ ERROR cannot assign `*b` in match guard
+        deref!(false) => {}
+        _ => {},
+    }
+}
diff --git a/tests/ui/pattern/deref-patterns/fake_borrows.stderr b/tests/ui/pattern/deref-patterns/fake_borrows.stderr
new file mode 100644
index 00000000000..6a591e6416c
--- /dev/null
+++ b/tests/ui/pattern/deref-patterns/fake_borrows.stderr
@@ -0,0 +1,12 @@
+error[E0510]: cannot assign `*b` in match guard
+  --> $DIR/fake_borrows.rs:9:16
+   |
+LL |     match b {
+   |           - value is immutable in match guard
+LL |         deref!(true) => {}
+LL |         _ if { *b = true; false } => {}
+   |                ^^^^^^^^^ cannot assign
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0510`.