From 7b953283ce41429f67d76bf7f9ada0a064bf06c1 Mon Sep 17 00:00:00 2001
From: Kris Nuttycombe <kris@nutty.land>
Date: Mon, 16 Aug 2021 13:48:37 -0600
Subject: [PATCH] Add blanket implementation of Hashable for
 incrementalmerkletree::Hashable + HashSer

---
 zcash_primitives/src/merkle_tree.rs           | 41 ++++++++++++++++++-
 .../src/merkle_tree/incremental.rs            | 13 +-----
 zcash_primitives/src/sapling.rs               | 32 +--------------
 3 files changed, 43 insertions(+), 43 deletions(-)

diff --git a/zcash_primitives/src/merkle_tree.rs b/zcash_primitives/src/merkle_tree.rs
index 06ce149e5..b196c33e5 100644
--- a/zcash_primitives/src/merkle_tree.rs
+++ b/zcash_primitives/src/merkle_tree.rs
@@ -1,7 +1,7 @@
 //! Implementation of a Merkle tree of commitments used to prove the existence of notes.
 
 use byteorder::{LittleEndian, ReadBytesExt};
-use incrementalmerkletree::bridgetree;
+use incrementalmerkletree::{self, bridgetree, Altitude};
 use std::collections::VecDeque;
 use std::io::{self, Read, Write};
 
@@ -29,6 +29,45 @@ pub trait Hashable: Clone + Copy {
     fn empty_root(_: usize) -> Self;
 }
 
+/// A hashable node within a Merkle tree.
+pub trait HashSer {
+    /// Parses a node from the given byte source.
+    fn read<R: Read>(reader: R) -> io::Result<Self>
+    where
+        Self: Sized;
+
+    /// Serializes this node.
+    fn write<W: Write>(&self, writer: W) -> io::Result<()>;
+}
+
+impl<T> Hashable for T where T: incrementalmerkletree::Hashable + HashSer + Copy {
+    /// Parses a node from the given byte source.
+    fn read<R: Read>(reader: R) -> io::Result<Self> {
+        <Self as HashSer>::read(reader)
+    }
+
+    /// Serializes this node.
+    fn write<W: Write>(&self, writer: W) -> io::Result<()> {
+        <Self as HashSer>::write(self, writer)
+    }
+
+    /// Returns the parent node within the tree of the two given nodes.
+    fn combine(alt: usize, lhs: &Self, rhs: &Self) -> Self {
+        <Self as incrementalmerkletree::Hashable>::combine(Altitude::from(alt as u8), lhs, rhs)
+    }
+
+    /// Returns a blank leaf node.
+    fn blank() -> Self {
+        <Self as incrementalmerkletree::Hashable>::empty_leaf()
+    }
+
+    /// Returns the empty root for the given depth.
+    fn empty_root(alt: usize) -> Self {
+        <Self as incrementalmerkletree::Hashable>::empty_root(Altitude::from(alt as u8))
+    }
+}
+
+
 struct PathFiller<Node: Hashable> {
     queue: VecDeque<Node>,
 }
diff --git a/zcash_primitives/src/merkle_tree/incremental.rs b/zcash_primitives/src/merkle_tree/incremental.rs
index a7fb65685..33a014b0d 100644
--- a/zcash_primitives/src/merkle_tree/incremental.rs
+++ b/zcash_primitives/src/merkle_tree/incremental.rs
@@ -13,22 +13,11 @@ use incrementalmerkletree::{
 };
 use orchard::tree::MerkleCrhOrchardOutput;
 
-use super::CommitmentTree;
+use super::{CommitmentTree, HashSer};
 use crate::serialize::{Optional, Vector};
 
 pub const SER_V1: u8 = 1;
 
-/// A hashable node within a Merkle tree.
-pub trait HashSer {
-    /// Parses a node from the given byte source.
-    fn read<R: Read>(reader: R) -> io::Result<Self>
-    where
-        Self: Sized;
-
-    /// Serializes this node.
-    fn write<W: Write>(&self, writer: W) -> io::Result<()>;
-}
-
 pub fn read_frontier_v0<H: Hashable + super::Hashable, R: Read>(
     mut reader: R,
 ) -> io::Result<Frontier<H, 32>> {
diff --git a/zcash_primitives/src/sapling.rs b/zcash_primitives/src/sapling.rs
index 44087f78a..3ab9c84e4 100644
--- a/zcash_primitives/src/sapling.rs
+++ b/zcash_primitives/src/sapling.rs
@@ -23,7 +23,7 @@ use subtle::{Choice, ConstantTimeEq};
 
 use crate::{
     constants::{self, SPENDING_KEY_GENERATOR},
-    merkle_tree::Hashable,
+    merkle_tree::{Hashable, HashSer},
     transaction::components::amount::MAX_MONEY,
 };
 
@@ -83,34 +83,6 @@ impl Node {
     }
 }
 
-impl Hashable for Node {
-    fn read<R: Read>(mut reader: R) -> io::Result<Self> {
-        let mut repr = [0u8; 32];
-        reader.read_exact(&mut repr)?;
-        Ok(Node::new(repr))
-    }
-
-    fn write<W: Write>(&self, mut writer: W) -> io::Result<()> {
-        writer.write_all(self.repr.as_ref())
-    }
-
-    fn combine(depth: usize, lhs: &Self, rhs: &Self) -> Self {
-        Node {
-            repr: merkle_hash(depth, &lhs.repr, &rhs.repr),
-        }
-    }
-
-    fn blank() -> Self {
-        Node {
-            repr: Note::uncommitted().to_repr(),
-        }
-    }
-
-    fn empty_root(depth: usize) -> Self {
-        EMPTY_ROOTS[depth]
-    }
-}
-
 impl incrementalmerkletree::Hashable for Node {
     fn empty_leaf() -> Self {
         Node {
@@ -129,7 +101,7 @@ impl incrementalmerkletree::Hashable for Node {
     }
 }
 
-impl crate::merkle_tree::incremental::HashSer for Node {
+impl HashSer for Node {
     fn read<R: Read>(mut reader: R) -> io::Result<Self> {
         let mut repr = [0u8; 32];
         reader.read_exact(&mut repr)?;