1 files changed, 67 insertions, 0 deletions
diff --git a/src/test/ui/nll/issue-57100.rs b/src/test/ui/nll/issue-57100.rs
new file mode 100644
index 000000000..f15929334
--- /dev/null
+++ b/src/test/ui/nll/issue-57100.rs
@@ -0,0 +1,67 @@
+#![allow(unused)]
+
+
+// This tests the error messages for borrows of union fields when the unions are embedded in other
+// structs or unions.
+
+#[derive(Clone, Copy, Default)]
+struct Leaf {
+    l1_u8: u8,
+    l2_u8: u8,
+}
+
+#[derive(Clone, Copy)]
+union First {
+    f1_leaf: Leaf,
+    f2_leaf: Leaf,
+    f3_union: Second,
+}
+
+#[derive(Clone, Copy)]
+union Second {
+    s1_leaf: Leaf,
+    s2_leaf: Leaf,
+}
+
+struct Root {
+    r1_u8: u8,
+    r2_union: First,
+}
+
+// Borrow a different field of the nested union.
+fn nested_union() {
+    unsafe {
+        let mut r = Root {
+            r1_u8: 3,
+            r2_union: First { f3_union: Second { s2_leaf: Leaf { l1_u8: 8, l2_u8: 4 } } }
+        };
+
+        let mref = &mut r.r2_union.f3_union.s1_leaf.l1_u8;
+        //                                  ^^^^^^^
+        *mref = 22;
+        let nref = &r.r2_union.f3_union.s2_leaf.l1_u8;
+        //                              ^^^^^^^
+        //~^^ ERROR cannot borrow `r.r2_union.f3_union` (via `r.r2_union.f3_union.s2_leaf.l1_u8`) as immutable because it is also borrowed as mutable (via `r.r2_union.f3_union.s1_leaf.l1_u8`) [E0502]
+        println!("{} {}", mref, nref)
+    }
+}
+
+// Borrow a different field of the first union.
+fn first_union() {
+    unsafe {
+        let mut r = Root {
+            r1_u8: 3,
+            r2_union: First { f3_union: Second { s2_leaf: Leaf { l1_u8: 8, l2_u8: 4 } } }
+        };
+
+        let mref = &mut r.r2_union.f2_leaf.l1_u8;
+        //                         ^^^^^^^
+        *mref = 22;
+        let nref = &r.r2_union.f1_leaf.l1_u8;
+        //                     ^^^^^^^
+        //~^^ ERROR cannot borrow `r.r2_union` (via `r.r2_union.f1_leaf.l1_u8`) as immutable because it is also borrowed as mutable (via `r.r2_union.f2_leaf.l1_u8`) [E0502]
+        println!("{} {}", mref, nref)
+    }
+}
+
+fn main() {}