openpgp: Mark enum Fingerprint as non-exhaustive.

1 files changed, 10 insertions, 1 deletions

diff --git a/openpgp/src/fingerprint.rs b/openpgp/src/fingerprint.rs
index 7ed623d1..5cc5907e 100644
--- a/openpgp/src/fingerprint.rs
+++ b/openpgp/src/fingerprint.rs
@@ -10,13 +10,20 @@ use quickcheck::{Arbitrary, Gen};
 /// 4880].
 ///
 ///   [Section 12.2 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-12.2
+///
+/// Note: This enum cannot be exhaustively matched to allow future
+/// extensions.
 #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
 pub enum Fingerprint {
     /// 20 byte SHA-1 hash.
     V4([u8;20]),
     /// Used for holding fingerprints that we don't understand.  For
     /// instance, we don't grok v3 fingerprints.
-    Invalid(Box<[u8]>)
+    Invalid(Box<[u8]>),
+
+    /// This marks this enum as non-exhaustive.  Do not use this
+    /// variant.
+    #[doc(hidden)] __Nonexhaustive,
 }
 
 impl fmt::Display for Fingerprint {
@@ -72,6 +79,7 @@ impl Fingerprint {
         match self {
             &Fingerprint::V4(ref fp) => fp,
             &Fingerprint::Invalid(ref fp) => fp,
+            Fingerprint::__Nonexhaustive => unreachable!(),
         }
     }
 
@@ -123,6 +131,7 @@ impl Fingerprint {
         let raw = match self {
             &Fingerprint::V4(ref fp) => &fp[..],
             &Fingerprint::Invalid(ref fp) => &fp[..],
+            Fingerprint::__Nonexhaustive => unreachable!(),
         };
 
         // We currently only handle V4 fingerprints, which look like: