Add test for generics with lifetimes

Signed-off-by: Ahmed Abdelraoof <[email protected]>

safe-discriminant/tests/pass/generics_with_lifetimes_enum.rs

@@ -0,0 +1,21 @@
+use safe_discriminant::Discriminant;
+
+// TODO
+// pub enum Foo<'a, T: 'a> will not work
+
+#[derive(Discriminant)]
+#[repr(i64)]
+pub enum Foo<'a, T>
+where
+    T: 'a,
+{
+    A(T) = 1,
+    B(&'a str) = -1,
+}
+
+fn main() {
+    let a = Foo::A(1);
+    let b: Foo<'_, u8> = Foo::B("hello world");
+    assert_eq!(a.discriminant(), 1);
+    assert_eq!(b.discriminant(), -1);
+}