Add a test for rust-lang#2630

Closes rust-lang#2630.

Author: topecongiro

tests/source/fn-simple.rs

@@ -64,3 +64,6 @@ mod foo {
 pub(crate) fn init() {}
 
 crate fn init() {}
+
+// #2630
+fn make_map<T, F: (Fn(&T) -> String)>(records: &Vec<T>, key_fn: F) -> HashMap<String, usize> {}

tests/target/fn-simple.rs

@@ -105,3 +105,6 @@ mod foo {
 pub(crate) fn init() {}
 
 crate fn init() {}
+
+// #2630
+fn make_map<T, F: Fn(&T) -> String>(records: &Vec<T>, key_fn: F) -> HashMap<String, usize> {}