Add regression test for issue 229

Author: dtolnay

tests/ui/lifetime-defined-here.rs

@@ -0,0 +1,23 @@
+use async_trait::async_trait;
+
+#[async_trait]
+trait Foo {
+    async fn bar(&self, x: &str, y: &'_ str) -> &'static str;
+}
+
+struct S(String);
+
+#[async_trait]
+impl Foo for S {
+    async fn bar(&self, x: &str, y: &'_ str) -> &'static str {
+        if false {
+            &self.0
+        } else if false {
+            x
+        } else {
+            y
+        }
+    }
+}
+
+fn main() {}

tests/ui/lifetime-defined-here.stderr

@@ -0,0 +1,25 @@
+error: lifetime may not live long enough
+  --> tests/ui/lifetime-defined-here.rs:12:49
+   |
+12 |     async fn bar(&self, x: &str, y: &'_ str) -> &'static str {
+   |     ----- lifetime `'life0` defined here        ^^^^^^^^^^^^ type annotation requires that `'life0` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> tests/ui/lifetime-defined-here.rs:12:49
+   |
+12 |     async fn bar(&self, x: &str, y: &'_ str) -> &'static str {
+   |     ----- lifetime `'life1` defined here        ^^^^^^^^^^^^ type annotation requires that `'life1` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> tests/ui/lifetime-defined-here.rs:12:49
+   |
+12 |     async fn bar(&self, x: &str, y: &'_ str) -> &'static str {
+   |                                      --         ^^^^^^^^^^^^ type annotation requires that `'life2` must outlive `'static`
+   |                                      |
+   |                                      lifetime `'life2` defined here
+
+help: the following changes may resolve your lifetime errors
+  |
+  = help: replace `'life0` with `'static`
+  = help: replace `'life1` with `'static`
+  = help: replace `'life2` with `'static`