Add test for issue-51798

src/test/ui/issues/auxiliary/issue-51798.rs

@@ -0,0 +1,3 @@
+#![crate_type = "lib"]
+
+pub fn vec() -> Vec<u8> { vec![] }

src/test/ui/issues/issue-51798.rs

@@ -0,0 +1,14 @@
+// edition:2018
+// aux-build:issue-51798.rs
+// check-pass
+
+extern crate issue_51798;
+
+mod server {
+    fn f() {
+        let mut v = issue_51798::vec();
+        v.clear();
+    }
+}
+
+fn main() {}