Consider the case of a MMR with one entry, and a new entry is being
added. Both of these values are quite unique, they are at the same time
the root and only leaf of their corresponding tree. Currently this
representation is not supported by the [MerkleStore], so the leaves are
not in it. Once the two values are merged, they both become leaves of a
new tree under the new parent, and the existing validation didn't permit
that promotion from happening.
This lifts the validation, and changes the method to clarify that not
only `root` are being merged, by arbitrary nodes of a tree (leafs,
internal, or roots), with arbitrary mixing of each.
Prior to this commit, MerkleStore allowed the creation of Sparse Merkle
tree only with the maximum depth of 63. However, this doesn't fit the
Tiered Sparse Merkle tree requirements, as it will contain trees of
depth 16.
This commit adds the `depth` argument to the MerkleStore methods that
will create Sparse Merkle trees.
The path returned by `EmptySubtreeRoots` starts at the root, and goes to
the leaf. The MerkleStore constructor assumed the other direction, so
the parent/child hashes were reversed.
This fixes the bug and adds a test.
Returning tuples is often confusing as they don't convey meaning and it
should be used only when there is no possible ambiguity.
For `MerkleStore`, we had a couple of tuples being returned, and reading
the implementation was required in order to distinguish if they were
leaf values or computed roots.
This commit introduces two containers that will self-document these
returns: `RootPath` and `ValuePath`. It will also update `set_node` to
return both the new root & the new path, so we can prevent duplicated
traversals downstream when updating a node (one to update, the second to
fetch the new path/root).
The store builds the path from root to leaf, this updates the code to
return a path from leaf to root, as it is done by the other structures.
This also added custom error for missing root.
