openpgp: Allow HashSet with mutable key type.

  - Closes #578.
  - Generally, types used as keys of HashSets should not have interior
    mutability. We believe this case to be safe, however.
  - https://rust-lang.github.io/rust-clippy/master/index.html#mutable_key_type

1 files changed, 5 insertions, 0 deletions

diff --git a/openpgp/src/packet/signature.rs b/openpgp/src/packet/signature.rs
index b5760d03..ff941f4d 100644
--- a/openpgp/src/packet/signature.rs
+++ b/openpgp/src/packet/signature.rs
@@ -2175,6 +2175,11 @@ impl crate::packet::Signature {
         }
 
         // Collect subpackets keeping track of the size.
+        #[allow(clippy::mutable_key_type)]
+        // In general, the keys of a HashSet should not have interior mutability.
+        // This particular use should be safe:  The hash set is only constructed
+        // for the merge, we own all objects we put into the set, and we don't
+        // modify them while they are in the set.
         let mut acc = std::collections::HashSet::new();
         let mut size = 0;