From 7c05fcbce35fa6b363612f1b6114ebed17881c8f Mon Sep 17 00:00:00 2001
From: Kris Nuttycombe <kris@nutty.land>
Date: Fri, 30 Aug 2024 14:30:16 -0600
Subject: [PATCH] Add unstable
 `UnifiedFullViewingKey::from_sapling_extended_full_viewing_key`

---
 zcash_keys/CHANGELOG.md    |  2 ++
 zcash_keys/src/encoding.rs | 10 ++++++++++
 zcash_keys/src/keys.rs     | 23 +++++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/zcash_keys/CHANGELOG.md b/zcash_keys/CHANGELOG.md
index e7454fb178..df5dc795e3 100644
--- a/zcash_keys/CHANGELOG.md
+++ b/zcash_keys/CHANGELOG.md
@@ -8,6 +8,8 @@ and this library adheres to Rust's notion of
 
 ### Added
 - `zcash_keys::encoding::decode_extfvk_with_network`
+- `impl std::error::Error for DecodingError`
+- `impl std::error::Error for Bech32DecodeError`
 
 ## [0.3.0] - 2024-08-19
 ### Notable changes
diff --git a/zcash_keys/src/encoding.rs b/zcash_keys/src/encoding.rs
index f53931f7da..894103a04b 100644
--- a/zcash_keys/src/encoding.rs
+++ b/zcash_keys/src/encoding.rs
@@ -66,6 +66,16 @@ impl fmt::Display for Bech32DecodeError {
     }
 }
 
+#[cfg(feature = "sapling")]
+impl std::error::Error for Bech32DecodeError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match &self {
+            Bech32DecodeError::Bech32Error(e) => Some(e),
+            _ => None,
+        }
+    }
+}
+
 #[cfg(feature = "sapling")]
 fn bech32_decode<T, F>(hrp: &str, s: &str, read: F) -> Result<T, Bech32DecodeError>
 where
diff --git a/zcash_keys/src/keys.rs b/zcash_keys/src/keys.rs
index f1f8d6eb6c..86f0587459 100644
--- a/zcash_keys/src/keys.rs
+++ b/zcash_keys/src/keys.rs
@@ -37,6 +37,9 @@ use {
 #[cfg(feature = "orchard")]
 use orchard::{self, keys::Scope};
 
+#[cfg(all(feature = "sapling", feature = "unstable"))]
+use ::sapling::zip32::ExtendedFullViewingKey;
+
 #[cfg(feature = "sapling")]
 pub mod sapling {
     pub use sapling::zip32::{
@@ -176,6 +179,8 @@ impl std::fmt::Display for DecodingError {
     }
 }
 
+impl std::error::Error for DecodingError {}
+
 #[cfg(feature = "unstable")]
 impl Era {
     /// Returns the unique identifier for the era.
@@ -674,6 +679,24 @@ impl UnifiedFullViewingKey {
             vec![],
         )
     }
+
+    #[cfg(all(feature = "sapling", feature = "unstable"))]
+    pub fn from_sapling_extended_full_viewing_key(
+        sapling: ExtendedFullViewingKey,
+    ) -> Result<UnifiedFullViewingKey, DerivationError> {
+        Self::from_checked_parts(
+            #[cfg(feature = "transparent-inputs")]
+            None,
+            #[cfg(feature = "sapling")]
+            Some(sapling.to_diversifiable_full_viewing_key()),
+            #[cfg(feature = "orchard")]
+            None,
+            // We don't currently allow constructing new UFVKs with unknown items, but we store
+            // this to allow parsing such UFVKs.
+            vec![],
+        )
+    }
+
     /// Construct a UFVK from its constituent parts, after verifying that UIVK derivation can
     /// succeed.
     fn from_checked_parts(