feat: implement Eq for Ipld

Implement the `Eq` trait for the `Ipld` enum. NaN floats are never equal
to another. Though in the Ipld Data model they are forbidden. This means
that we can implement `Eq` for it.

As it's currently not strictly enforced that an `Ipld::Float` does not
contain a NaN, we make at least sure that in case we would encounter it,
that it is treated as equal.

For more information about the dicussion about this topic, see
ipld/libipld#171.

src/ipld.rs

@@ -34,7 +34,7 @@ impl fmt::Display for IndexError {
 impl std::error::Error for IndexError {}
 
 /// Ipld
-#[derive(Clone, PartialEq)]
+#[derive(Clone)]
 pub enum Ipld {
     /// Represents the absence of a value or the value undefined.
     Null,
@@ -86,6 +86,31 @@ impl fmt::Debug for Ipld {
     }
 }
 
+/// NaN floats are forbidden in the IPLD Data Model, but we do not enforce it. So in case such a
+/// value is introduced accidentally, make sure that it still compares as equal. This allows us
+/// to implement `Eq` for `Ipld`.
+impl PartialEq for Ipld {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (Self::Null, Self::Null) => true,
+            (Self::Bool(self_value), Self::Bool(other_value)) => self_value == other_value,
+            (Self::Integer(self_value), Self::Integer(other_value)) => self_value == other_value,
+            (Self::Float(self_value), Self::Float(other_value)) => {
+                // Treat two NaNs as being equal.
+                self_value == other_value || self_value.is_nan() && other_value.is_nan()
+            }
+            (Self::String(self_value), Self::String(other_value)) => self_value == other_value,
+            (Self::Bytes(self_value), Self::Bytes(other_value)) => self_value == other_value,
+            (Self::List(self_value), Self::List(other_value)) => self_value == other_value,
+            (Self::Map(self_value), Self::Map(other_value)) => self_value == other_value,
+            (Self::Link(self_value), Self::Link(other_value)) => self_value == other_value,
+            _ => false,
+        }
+    }
+}
+
+impl Eq for Ipld {}
+
 /// IPLD Kind information without the actual value.
 ///
 /// Sometimes it's useful to know the kind of an Ipld object without the actual value, e.g. for
@@ -363,4 +388,12 @@ mod tests {
         let ipld = Ipld::Map(map);
         assert_eq!(ipld.get("a").unwrap(), Some(&Ipld::Integer(0)));
     }
+
+    // NaN floats are forbidden in the IPLD Data Model, but still make sure they are treated as
+    // equal in case they accidentally end up there.
+    #[test]
+    fn test_partial_eq_nan() {
+        let invalid_ipld = Ipld::Float(f64::NAN);
+        assert_eq!(invalid_ipld, invalid_ipld);
+    }
 }