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+A closure or generator was constructed that references its own type.
+
+Erroneous code example:
+
+```compile_fail,E0644
+fn fix<F>(f: &F)
+  where F: Fn(&F)
+{
+    f(&f);
+}
+
+fn main() {
+    fix(&|y| {
+        // Here, when `x` is called, the parameter `y` is equal to `x`.
+    });
+}
+```
+
+Rust does not permit a closure to directly reference its own type,
+either through an argument (as in the example above) or by capturing
+itself through its environment. This restriction helps keep closure
+inference tractable.
+
+The easiest fix is to rewrite your closure into a top-level function,
+or into a method. In some cases, you may also be able to have your
+closure call itself by capturing a `&Fn()` object or `fn()` pointer
+that refers to itself. That is permitting, since the closure would be
+invoking itself via a virtual call, and hence does not directly
+reference its own *type*.