openpgp: Add generic forwards for Policy data structures.neal/policy-forwarders

  - Implement `Policy` for `&dyn Policy`, `Box<T> where T: Policy`,
    `&StandardPolicy` and `&NullPolicy` by implementing a generic
    forwarder.

2 files changed, 123 insertions, 0 deletions

diff --git a/openpgp/NEWS b/openpgp/NEWS
index 3524af4b..1889abf8 100644
--- a/openpgp/NEWS
+++ b/openpgp/NEWS
@@ -3,6 +3,11 @@
 #+TITLE: sequoia-openpgp NEWS – history of user-visible changes
 #+STARTUP: content hidestars
 
+* Changes in 1.20.0
+** Notable fixes
+** New functionality
+   - Implemented Policy for &dyn Policy, Box<T> where T: Policy,
+     &StandardPolicy and &NullPolicy.
 * Changes in 1.19.0
 ** Notable fixes
    - Key4::import_secret_cv25519 will now clamp some bits of the given
diff --git a/openpgp/src/policy.rs b/openpgp/src/policy.rs
index 9ea4fcb2..1e641356 100644
--- a/openpgp/src/policy.rs
+++ b/openpgp/src/policy.rs
@@ -153,6 +153,56 @@ pub trait Policy : fmt::Debug + Send + Sync {
     }
 }
 
+impl Policy for &dyn Policy {
+    fn signature(&self, sig: &Signature, sec: HashAlgoSecurity) -> Result<()> {
+        (*self).signature(sig, sec)
+    }
+
+    fn key(&self, ka: &ValidErasedKeyAmalgamation<key::PublicParts>)
+        -> Result<()>
+    {
+        (*self).key(ka)
+    }
+
+    fn symmetric_algorithm(&self, algo: SymmetricAlgorithm) -> Result<()> {
+        (*self).symmetric_algorithm(algo)
+    }
+
+    fn aead_algorithm(&self, algo: AEADAlgorithm) -> Result<()> {
+        (*self).aead_algorithm(algo)
+    }
+
+    fn packet(&self, packet: &Packet) -> Result<()> {
+        (*self).packet(packet)
+    }
+}
+
+impl<T> Policy for Box<T>
+    where T: Policy
+{
+    fn signature(&self, sig: &Signature, sec: HashAlgoSecurity) -> Result<()> {
+        self.as_ref().signature(sig, sec)
+    }
+
+    fn key(&self, ka: &ValidErasedKeyAmalgamation<key::PublicParts>)
+        -> Result<()>
+    {
+        self.as_ref().key(ka)
+    }
+
+    fn symmetric_algorithm(&self, algo: SymmetricAlgorithm) -> Result<()> {
+        self.as_ref().symmetric_algorithm(algo)
+    }
+
+    fn aead_algorithm(&self, algo: AEADAlgorithm) -> Result<()> {
+        self.as_ref().aead_algorithm(algo)
+    }
+
+    fn packet(&self, packet: &Packet) -> Result<()> {
+        self.as_ref().packet(packet)
+    }
+}
+
 /// Whether the signed data requires a hash algorithm with collision
 /// resistance.
 ///
@@ -1666,6 +1716,30 @@ impl<'a> Policy for StandardPolicy<'a> {
     }
 }
 
+impl<'a> Policy for &StandardPolicy<'a> {
+    fn signature(&self, sig: &Signature, sec: HashAlgoSecurity) -> Result<()> {
+        (*self).signature(sig, sec)
+    }
+
+    fn key(&self, ka: &ValidErasedKeyAmalgamation<key::PublicParts>)
+        -> Result<()>
+    {
+        (*self).key(ka)
+    }
+
+    fn symmetric_algorithm(&self, algo: SymmetricAlgorithm) -> Result<()> {
+        (*self).symmetric_algorithm(algo)
+    }
+
+    fn aead_algorithm(&self, algo: AEADAlgorithm) -> Result<()> {
+        (*self).aead_algorithm(algo)
+    }
+
+    fn packet(&self, packet: &Packet) -> Result<()> {
+        (*self).packet(packet)
+    }
+}
+
 /// Asymmetric encryption algorithms.
 ///
 /// This type is for refining the [`StandardPolicy`] with respect to
@@ -1848,6 +1922,30 @@ impl Policy for NullPolicy {
 
 }
 
+impl Policy for &NullPolicy {
+    fn signature(&self, sig: &Signature, sec: HashAlgoSecurity) -> Result<()> {
+        (*self).signature(sig, sec)
+    }
+
+    fn key(&self, ka: &ValidErasedKeyAmalgamation<key::PublicParts>)
+        -> Result<()>
+    {
+        (*self).key(ka)
+    }
+
+    fn symmetric_algorithm(&self, algo: SymmetricAlgorithm) -> Result<()> {
+        (*self).symmetric_algorithm(algo)
+    }
+
+    fn aead_algorithm(&self, algo: AEADAlgorithm) -> Result<()> {
+        (*self).aead_algorithm(algo)
+    }
+
+    fn packet(&self, packet: &Packet) -> Result<()> {
+        (*self).packet(packet)
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::io::Read;
@@ -3181,4 +3279,24 @@ mod test {
         assert_eq!(p.packet_tag_cutoff(Tag::Signature),
                    Some(Timestamp::Y2007M2.into()));
     }
+
+    #[test]
+    fn policy_blanket_impls() {
+        fn f<T>(_: T) where T: Policy {
+        }
+
+        let p = StandardPolicy::new();
+        f(&p);
+        f(Box::new(&p));
+        f(Box::new(p));
+
+        let p = NullPolicy::new();
+        f(&p);
+        f(Box::new(&p));
+        f(Box::new(p));
+
+        let p: &dyn Policy = &StandardPolicy::new();
+        f(p);
+        f(Box::new(p));
+    }
 }