test for issue rust-lang#77175

src/test/ui/lifetimes/issue-77175.rs

@@ -0,0 +1,19 @@
+#[deny(single_use_lifetimes)]
+// edition:2018
+// check-pass
+
+// Prior to the fix, the compiler complained that the 'a lifetime was only used
+// once. This was obviously wrong since the lifetime is used twice: For the s3
+// parameter and the return type. The issue was caused by the compiler
+// desugaring the async function into a generator that uses only a single
+// lifetime, which then the validator complained about becauase of the
+// single_use_lifetimes constraints.
+async fn bar<'a>(s1: String, s2: &'_ str, s3: &'a str) -> &'a str {
+    s3
+}
+
+fn foo<'a>(s1: String, s2: &'_ str, s3: &'a str) -> &'a str {
+    s3
+}
+
+fn main() {}