openpgp: Use non_exhaustive attribute.

  - Fixes #563
  - With an MSRV >= 1.40.0, we can use #[non_exhaustive], as mentioned
    in #406.
  - This is also a clippy lint:
    https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive

7 files changed, 6 insertions, 45 deletions

diff --git a/openpgp/src/crypto/backend/cng/ecdh.rs b/openpgp/src/crypto/backend/cng/ecdh.rs
index a9118a87..b8f38577 100644
--- a/openpgp/src/crypto/backend/cng/ecdh.rs
+++ b/openpgp/src/crypto/backend/cng/ecdh.rs
@@ -142,8 +142,6 @@ where
         // N/A
         Curve::Unknown(_) | Curve::Ed25519 =>
             Err(Error::UnsupportedEllipticCurve(curve.clone()).into()),
-
-        Curve::__Nonexhaustive => unreachable!(),
     }
 }
 
diff --git a/openpgp/src/crypto/backend/nettle/ecdh.rs b/openpgp/src/crypto/backend/nettle/ecdh.rs
index 29e3d448..93d22a07 100644
--- a/openpgp/src/crypto/backend/nettle/ecdh.rs
+++ b/openpgp/src/crypto/backend/nettle/ecdh.rs
@@ -109,8 +109,6 @@ pub fn encrypt<R>(recipient: &Key<key::PublicParts, R>,
             // N/A
             Curve::Unknown(_) | Curve::Ed25519 =>
                 Err(Error::UnsupportedEllipticCurve(curve.clone()).into()),
-
-            Curve::__Nonexhaustive => unreachable!(),
         }
     } else {
         Err(Error::InvalidArgument("Expected an ECDHPublicKey".into()).into())
diff --git a/openpgp/src/crypto/backend/nettle/hash.rs b/openpgp/src/crypto/backend/nettle/hash.rs
index b4600b14..bf1d9cb5 100644
--- a/openpgp/src/crypto/backend/nettle/hash.rs
+++ b/openpgp/src/crypto/backend/nettle/hash.rs
@@ -29,7 +29,6 @@ impl HashAlgorithm {
             HashAlgorithm::MD5 => true,
             HashAlgorithm::Private(_) => false,
             HashAlgorithm::Unknown(_) => false,
-            HashAlgorithm::__Nonexhaustive => unreachable!(),
         }
     }
 
@@ -60,7 +59,6 @@ impl HashAlgorithm {
             HashAlgorithm::RipeMD => Ok(Box::new(Ripemd160::default())),
             HashAlgorithm::Private(_) | HashAlgorithm::Unknown(_) =>
                 Err(Error::UnsupportedHashAlgorithm(self).into()),
-            HashAlgorithm::__Nonexhaustive => unreachable!(),
         }
     }
 
@@ -78,7 +76,6 @@ impl HashAlgorithm {
             HashAlgorithm::RipeMD => Ok(rsa::ASN1_OID_RIPEMD160),
             HashAlgorithm::Private(_) | HashAlgorithm::Unknown(_) =>
                 Err(Error::UnsupportedHashAlgorithm(self).into()),
-            HashAlgorithm::__Nonexhaustive => unreachable!(),
         }
     }
 }
diff --git a/openpgp/src/crypto/backend/nettle/symmetric.rs b/openpgp/src/crypto/backend/nettle/symmetric.rs
index 4883a5a1..f25bcd7e 100644
--- a/openpgp/src/crypto/backend/nettle/symmetric.rs
+++ b/openpgp/src/crypto/backend/nettle/symmetric.rs
@@ -58,7 +58,6 @@ impl SymmetricAlgorithm {
                 => true,
             Unencrypted | IDEA | Private(_) | Unknown(_)
                 => false,
-            __Nonexhaustive => unreachable!(),
         }
     }
 
@@ -246,4 +245,4 @@ impl SymmetricAlgorithm {
             _ => Err(Error::UnsupportedSymmetricAlgorithm(self).into()),
         }
     }
-}
\ No newline at end of file
+}
diff --git a/openpgp/src/crypto/hash.rs b/openpgp/src/crypto/hash.rs
index 82add847..c7a8b248 100644
--- a/openpgp/src/crypto/hash.rs
+++ b/openpgp/src/crypto/hash.rs
@@ -305,7 +305,6 @@ impl Hash for Signature {
     fn hash(&self, hash: &mut Context) {
         match self {
             Signature::V4(sig) => sig.hash(hash),
-            Signature::__Nonexhaustive => unreachable!(),
         }
     }
 }
diff --git a/openpgp/src/crypto/mpi.rs b/openpgp/src/crypto/mpi.rs
index 3918a4c2..8f9cfb2a 100644
--- a/openpgp/src/crypto/mpi.rs
+++ b/openpgp/src/crypto/mpi.rs
@@ -434,6 +434,7 @@ impl fmt::Debug for ProtectedMPI {
 ///
 /// Note: This enum cannot be exhaustively matched to allow future
 /// extensions.
+#[non_exhaustive]
 #[derive(Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub enum PublicKey {
     /// RSA public key.
@@ -501,10 +502,6 @@ pub enum PublicKey {
         /// Any data that failed to parse.
         rest: Box<[u8]>,
     },
-
-    /// This marks this enum as non-exhaustive.  Do not use this
-    /// variant.
-    #[doc(hidden)] __Nonexhaustive,
 }
 
 impl PublicKey {
@@ -528,7 +525,6 @@ impl PublicKey {
             &ECDSA { ref curve,.. } => curve.bits(),
             &ECDH { ref curve,.. } => curve.bits(),
             &Unknown { .. } => None,
-            __Nonexhaustive => unreachable!(),
         }
     }
 
@@ -544,7 +540,6 @@ impl PublicKey {
             ECDSA { .. } => Some(PublicKeyAlgorithm::ECDSA),
             ECDH { .. } => Some(PublicKeyAlgorithm::ECDH),
             Unknown { .. } => None,
-            __Nonexhaustive => unreachable!(),
         }
     }
 }
@@ -614,6 +609,7 @@ impl Arbitrary for PublicKey {
 // Deriving Hash here is okay: PartialEq is manually implemented to
 // ensure that secrets are compared in constant-time.
 #[allow(clippy::derive_hash_xor_eq)]
+#[non_exhaustive]
 #[derive(Clone, Hash)]
 pub enum SecretKeyMaterial {
     /// RSA secret key.
@@ -665,10 +661,6 @@ pub enum SecretKeyMaterial {
         /// Any data that failed to parse.
         rest: Protected,
     },
-
-    /// This marks this enum as non-exhaustive.  Do not use this
-    /// variant.
-    #[doc(hidden)] __Nonexhaustive,
 }
 
 impl fmt::Debug for SecretKeyMaterial {
@@ -689,7 +681,6 @@ impl fmt::Debug for SecretKeyMaterial {
                     write!(f, "ECDH {{ scalar: {:?} }}", scalar),
                 &SecretKeyMaterial::Unknown{ ref mpis, ref rest } =>
                     write!(f, "Unknown {{ mips: {:?}, rest: {:?} }}", mpis, rest),
-                SecretKeyMaterial::__Nonexhaustive => unreachable!(),
             }
         } else {
             match self {
@@ -707,7 +698,6 @@ impl fmt::Debug for SecretKeyMaterial {
                     f.write_str("ECDH { <Redacted> }"),
                 &SecretKeyMaterial::Unknown{ .. } =>
                     f.write_str("Unknown { <Redacted> }"),
-                SecretKeyMaterial::__Nonexhaustive => unreachable!(),
             }
         }
     }
@@ -726,7 +716,6 @@ impl PartialOrd for SecretKeyMaterial {
                 &SecretKeyMaterial::ECDSA{ .. } => 4,
                 &SecretKeyMaterial::ECDH{ .. } => 5,
                 &SecretKeyMaterial::Unknown{ .. } => 6,
-                SecretKeyMaterial::__Nonexhaustive => unreachable!(),
             }
         }
 
@@ -812,7 +801,6 @@ impl SecretKeyMaterial {
             ECDSA { .. } => Some(PublicKeyAlgorithm::ECDSA),
             ECDH { .. } => Some(PublicKeyAlgorithm::ECDH),
             Unknown { .. } => None,
-            __Nonexhaustive => unreachable!(),
         }
     }
 }
@@ -889,6 +877,7 @@ impl Default for SecretKeyChecksum {
 ///
 /// Note: This enum cannot be exhaustively matched to allow future
 /// extensions.
+#[non_exhaustive]
 #[derive(Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub enum Ciphertext {
     /// RSA ciphertext.
@@ -920,10 +909,6 @@ pub enum Ciphertext {
         /// Any data that failed to parse.
         rest: Box<[u8]>,
     },
-
-    /// This marks this enum as non-exhaustive.  Do not use this
-    /// variant.
-    #[doc(hidden)] __Nonexhaustive,
 }
 
 impl Ciphertext {
@@ -940,7 +925,6 @@ impl Ciphertext {
             &ElGamal { .. } => Some(PublicKeyAlgorithm::ElGamalEncrypt),
             &ECDH { .. } => Some(PublicKeyAlgorithm::ECDH),
             &Unknown { .. } => None,
-            __Nonexhaustive => unreachable!(),
         }
     }
 }
@@ -986,6 +970,7 @@ impl Arbitrary for Ciphertext {
 ///
 /// Note: This enum cannot be exhaustively matched to allow future
 /// extensions.
+#[non_exhaustive]
 #[derive(Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub enum Signature {
     /// RSA signature.
@@ -1033,10 +1018,6 @@ pub enum Signature {
         /// Any data that failed to parse.
         rest: Box<[u8]>,
     },
-
-    /// This marks this enum as non-exhaustive.  Do not use this
-    /// variant.
-    #[doc(hidden)] __Nonexhaustive,
 }
 
 impl Hash for Signature {
@@ -1111,7 +1092,6 @@ mod tests {
                     PublicKey::parse(ECDH, cur).unwrap(),
 
                 PublicKey::Unknown { .. } => unreachable!(),
-                PublicKey::__Nonexhaustive => unreachable!(),
             };
 
             pk == pk_
@@ -1162,7 +1142,6 @@ mod tests {
                     SecretKeyMaterial::parse(ElGamalEncrypt, cur).unwrap(),
 
                 SecretKeyMaterial::Unknown { .. } => unreachable!(),
-                SecretKeyMaterial::__Nonexhaustive => unreachable!(),
             };
 
             sk == sk_
@@ -1188,7 +1167,6 @@ mod tests {
                     Ciphertext::parse(ECDH, cur).unwrap(),
 
                 Ciphertext::Unknown { .. } => unreachable!(),
-                Ciphertext::__Nonexhaustive => unreachable!(),
             };
 
             ct == ct_
@@ -1218,7 +1196,6 @@ mod tests {
                     Signature::parse(ECDSA, cur).unwrap(),
 
                 Signature::Unknown { .. } => unreachable!(),
-                Signature::__Nonexhaustive => unreachable!(),
             };
 
             sig == sig_
diff --git a/openpgp/src/crypto/s2k.rs b/openpgp/src/crypto/s2k.rs
index 67198a0e..4eee84d8 100644
--- a/openpgp/src/crypto/s2k.rs
+++ b/openpgp/src/crypto/s2k.rs
@@ -33,6 +33,7 @@ use rand::Rng;
 ///
 /// Note: This enum cannot be exhaustively matched to allow future
 /// extensions.
+#[non_exhaustive]
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub enum S2K {
     /// Repeatently hashes the password with a public `salt` value.
@@ -111,10 +112,6 @@ pub enum S2K {
         /// packet is serialized again, it is written out.
         parameters: Option<Box<[u8]>>,
     },
-
-    /// This marks this enum as non-exhaustive.  Do not use this
-    /// variant.
-    #[doc(hidden)] __Nonexhaustive,
 }
 
 impl Default for S2K {
@@ -229,7 +226,6 @@ impl S2K {
                         }
                         S2K::Unknown { .. } | &S2K::Private { .. } =>
                             unreachable!(),
-                        S2K::__Nonexhaustive => unreachable!(),
                     }
 
                     hash.digest(data);
@@ -241,7 +237,6 @@ impl S2K {
             S2K::Unknown { tag, .. } | S2K::Private { tag, .. } =>
                 Err(Error::MalformedPacket(
                         format!("Unknown S2K type {:#x}", tag)).into()),
-            S2K::__Nonexhaustive => unreachable!(),
         }
     }
 
@@ -251,7 +246,6 @@ impl S2K {
         #[allow(deprecated)]
         match self {
             Simple { .. } | Salted { .. } | Iterated { .. } => true,
-            __Nonexhaustive => unreachable!(),
             _ => false,
         }
     }
@@ -367,7 +361,6 @@ impl fmt::Display for S2K {
                 } else {
                     write!(f, "Unknown S2K {}", tag)
                 },
-            S2K::__Nonexhaustive => unreachable!(),
         }
     }
 }