Add test for issue-30904

Author: JohnTitor

src/test/ui/unboxed-closures/issue-30904.rs

@@ -0,0 +1,36 @@
+#![feature(fn_traits, unboxed_closures)]
+
+fn test<F: for<'x> FnOnce<(&'x str,)>>(_: F) {}
+
+struct Compose<F,G>(F,G);
+impl<T,F,G> FnOnce<(T,)> for Compose<F,G>
+where F: FnOnce<(T,)>, G: FnOnce<(F::Output,)> {
+    type Output = G::Output;
+    extern "rust-call" fn call_once(self, (x,): (T,)) -> G::Output {
+        (self.1)((self.0)(x))
+    }
+}
+
+struct Str<'a>(&'a str);
+fn mk_str<'a>(s: &'a str) -> Str<'a> { Str(s) }
+
+fn main() {
+    let _: for<'a> fn(&'a str) -> Str<'a> = mk_str;
+    // expected concrete lifetime, found bound lifetime parameter 'a
+    let _: for<'a> fn(&'a str) -> Str<'a> = Str;
+    //~^ ERROR: mismatched types
+
+    test(|_: &str| {});
+    test(mk_str);
+    // expected concrete lifetime, found bound lifetime parameter 'x
+    test(Str); //~ ERROR: type mismatch in function arguments
+
+    test(Compose(|_: &str| {}, |_| {}));
+    test(Compose(mk_str, |_| {}));
+    // internal compiler error: cannot relate bound region:
+    //   ReLateBound(DebruijnIndex { depth: 2 },
+    //     BrNamed(DefId { krate: 0, node: DefIndex(6) => test::'x }, 'x(65)))
+    //<= ReSkolemized(0,
+    //     BrNamed(DefId { krate: 0, node: DefIndex(6) => test::'x }, 'x(65)))
+    test(Compose(Str, |_| {}));
+}

src/test/ui/unboxed-closures/issue-30904.stderr

@@ -0,0 +1,24 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-30904.rs:20:45
+   |
+LL |     let _: for<'a> fn(&'a str) -> Str<'a> = Str;
+   |                                             ^^^ expected concrete lifetime, found bound lifetime parameter 'a
+   |
+   = note: expected type `for<'a> fn(&'a str) -> Str<'a>`
+              found type `fn(&str) -> Str<'_> {Str::<'_>}`
+
+error[E0631]: type mismatch in function arguments
+  --> $DIR/issue-30904.rs:26:10
+   |
+LL | fn test<F: for<'x> FnOnce<(&'x str,)>>(_: F) {}
+   |    ----    -------------------------- required by this bound in `test`
+...
+LL | struct Str<'a>(&'a str);
+   | ------------------------ found signature of `fn(&str) -> _`
+...
+LL |     test(Str);
+   |          ^^^ expected signature of `for<'x> fn(&'x str) -> _`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.