Keep old 2G downgrade analyzer

lib/src/analysis/util.rs

@@ -1,7 +1,34 @@
+
+/// Unpacks a pattern, or returns None.
+///
+/// # Examples
+/// Suppose you've got some highly nested enum:
+/// ```
+/// enum Foo {
+///     A(Bar),
+///     B,
+/// }
+///
+/// enum Baz {
+///     C(Bang)
+/// }
+///
+/// struct Bang;
+/// ```
+///
+/// You can use `unpack!` to unroll it like this:
+/// ```
+/// fn get_bang(foo: Foo) -> Option<Bang> {
+///     unpack!(Foo::A(bar) = foo);
+///     unpack!(Baz::C(bang) = bar);
+///     bang
+/// }
+/// ```
 macro_rules! unpack {
     ($pat:pat = $val:expr) => {
         let $pat = $val else { return None; };
     };
 }
 
+// this is apparently how you make a macro publicly usable from this module
 pub(crate) use unpack;