Merge pull request zcash#34 from nuttycom/add_changelog

Add changelog

CHANGELOG.md

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+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to Rust's notion of
+[Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+- `incrementalmerkletree`:
+  - `Tree::get_witnessed_leaf`, to allow a user to query for the leaf value of
+    witnessed leaves by their position in the tree.
+  - `Tree::witnessed_positions`, to allow a user to query for all positions that
+    have been witnessed.
+  - `Tree::garbage_collect`, to prune checkpoint and removed witness information 
+    that is no longer reachable by rewinds of the tree.
+- `incrementalmerkletree::bridgetree`:
+  - `NonEmptyFrontier::current_leaf`
+  - `BridgeTree::from_frontier`
+  - `BridgeTree::check_consistency`
+
+### Changed
+
+- `incrementalmerkletree`:
+  - The `Tree` trait has substantial changes in this release. Hashes are no longer used
+    in identifying nodes when generating authentication paths and removing witnesses;
+    instead, these operations now use position information exclusively.
+  - `Tree::authentication_path` and `Tree::remove_witness` have both been changed to only
+    take a `position` parameter, instead of both the leaf value and the position.
+  - `Tree::current_leaf` and `Tree::witness` have both been changed to only return the leaf
+    value, instead of both the leaf value and the position.
+- `incrementalmerkletree::bridgetree`:
+  - The type of `BridgeTree::saved` and `Checkpoint::forgotten` have been changed from 
+    `BTreeMap<(Position, H), usize>` to `BTreeMap<Position, usize>`. This change
+    is also reflected in the rturn type of the `BridgeTree::witnessed_indices` method.
+  - The `Checkpoint` type is no longer parameterized by `H`.
+  - `BridgeTree::bridges` has been split into two parts: 
+    - `BridgeTree::prior_bridges` now tracks past bridges not including the current frontier.
+    - `BridgeTree::current_bridge` now tracks current mutable frontier.
+  - The signature of `BridgeTree::from_parts` has been modified to reflect these changes.
+
+### Removed
+- `incrementalmerkletree`:
+  - `Tree::is_witnessed` (use `Tree::get_witnessed_leaf(...).is_some()` instead).
+  - The recording / playback infrastructure, which was unused and added
+    unnecessary complexity:
+    - The `Tree::Recording` associated type.
+    - `Tree::{recording, play}`
+    - `Recording`
+- `Tree::is_witnessed` has been removed (use `Tree::get_witnessed_leaf(...).is_some()`
+  instead).
+
+### Fixed
+
+- A bug in `BridgeTree::garbage_collect` that caused garbage collection to in some 
+  cases incorrectly rewrite checkpointed bridge lengths, resulting in a condition 
+  where a rewind could panic after a GC operation.
+
+## [0.3.0-beta.1] - 2022-03-22
+
+### Added
+- `incrementalmerkletree`:
+  - New trait impls
+    - `impl From<Position> for usize`
+    - `impl Add<usize> for Position`
+    - `impl AddAssign<usize> for Position`
+    - `impl TryFrom<u64> for Position`
+    - `impl Hash for Position`
+  - New trait methods:
+    - `Tree::current_leaf`, which returns the position of the latest note
+      appended to the tree along with the leaf value, if any.
+    - `Tree::current_position`, which returns the position of the latest note
+      appended to the tree, if any.
+    - `Tree::is_witnessed`, which returns a boolean value indicating whether a
+      leaf value has been marked for later construction of an authentication
+      path at a specified position in the tree.
+- `incrementalmerkletree::bridgetree`:
+  - `MerkleBridge::position`, which returns the position of the tip of the
+    frontier.
+  - `MerkleBridge::current_leaf`, which returns the leaf value most recently
+    appended to the frontier.
+  - `Leaf::value`, which returns the value of the leaf by reference.
+  - `impl {PartialEq, Eq} for {AuthFragment, MerkleBridge, BridgeTreeError}`
+  - Various constructor and accessor methods for `Checkpoint` to facilitate
+    serialization:
+    - `Checkpoint::{from_parts, at_length}`
+    - `Checkpoint::{bridges_len, is_witnessed, forgotten}`
+    - `Checkpoint::rewrite_indices`
+  - `BridgeTree::witnessed_indices`
+  - `BridgeTree::garbage_collect`, which prunes data for removed witnesses and
+    inaccessable checkpoints beyond the max rewind depth.
+
+### Changed
+- `incrementalmerkletree`:
+  - `Position` now wraps a `usize` rather than a `u64`, affecting its layout (as
+    exposed by `repr(transparent)`).
+  - The following methods now take an additional `Position` argument to support
+    cases where leaf values may appear at multiple positions in the tree:
+    - `Tree::authentication_path`
+    - `Tree::remove_witness`
+  - `Tree::witness` now returns a tuple of the witnessed position and leaf hash,
+    or `None` if the tree is empty, instead of a boolean value.
+- `incrementalmerkletree::bridgetree`:
+  - Most `MerkleBridge` methods now require `H: Ord`.
+  - Changed the return type of `MerkleBridge::auth_fragments` from 
+    `HashMap<usize, AuthFragment>` to `BTreeMap<Position, AuthFragment>`; the
+    `saved` argument to `BridgeTree::from_parts` is similarly altered.
+  - `MerkleBridge::successor` now takes a boolean argument for tracking the most
+    recently appended leaf, instead of the previous `cur_idx` argument.
+  - `Checkpoint` is now a struct, rather than an enum type, and contains
+    information about witnessed nodes that have been marked for removal since the
+    last checkpoint.
+  - `BridgeTree` now requires an `Ord` constraint for its leaf type, rather than a
+    `Hash` constraint.
+
+### Removed
+- `incrementalmerkletree`:
+  - `Position::increment`
+  - `impl TryFrom<Position> for usize` (use the `From` impl instead).
+- `incrementalmerkletree::bridgetree`:
+  - `Leaf::into_value` (use `Leaf::value` instead).
+  - `MerkleBridge::leaf_value` (use `MerkleBridge::current_leaf` instead).
+  - `H: Clone` bound on `NonEmptyFrontier::<H>::leaf_value`.
+  - `BridgeTree::witnessable_leaves` (use `BridgeTree::witnessed_indices` instead).
+
+## [0.2.0] - 2022-03-22
+
+v0.2.0 is essentially a complete rewrite relative to v0.1.0, and should be considered
+the first usable release.  
+
+## [0.1.0] - 2021-06-23
+Initial release!