Disallow unreachable as well

Cargo.toml

@@ -31,6 +31,7 @@ rust_2018_idioms = "deny"
 
 [lints.clippy]
 panic = "deny"
+unreachable = "deny"
 expect_used = "deny"
 unwrap_used = "deny"
 mem_forget = "deny"

src/megolm/inbound_group_session.rs

@@ -182,6 +182,7 @@ impl InboundGroupSession {
         //
         // After that we compare the raw ratchet bytes in constant time.
 
+        #[allow(clippy::unreachable)]
         if self.config != other.config || self.signing_key != other.signing_key {
             // Short circuit if session configs differ or the signing keys
             // differ. This is comparing public key material.

src/megolm/ratchet.rs

@@ -109,22 +109,24 @@ struct RatchetParts<'a> {
 
 impl<'a> RatchetParts<'a> {
     fn update(&'a mut self, from: usize, to: usize) {
+        #[allow(clippy::unreachable)]
         let from = match from {
             0 => &self.r_0,
             1 => &self.r_1,
             2 => &self.r_2,
             3 => &self.r_3,
-            _ => unreachable!(),
+            _ => unreachable!("We only have 4 ratchet parts"),
         };
 
         let result = from.hash(ADVANCEMENT_SEEDS[to]);
 
+        #[allow(clippy::unreachable)]
         let to = match to {
             0 => &mut self.r_0,
             1 => &mut self.r_1,
             2 => &mut self.r_2,
             3 => &mut self.r_3,
-            _ => unreachable!(),
+            _ => unreachable!("We only have 4 ratchet parts"),
         };
 
         to.update(&result.into_bytes());