zcash_client_backend: Factor out input source traits from WalletRead

Prior to this change, it's necessary to implement the entirety of the
`WalletRead` trait in order to be able to use the input selection
functionality provided by `zcash_client_backend::data_api::input_selection`.
This change factors out the minimal operations required for transaction
proposal construction to better reflect the principle of least authority
and make the input selection code reusable in more contexts.

In order to minimize the operations of the newly-created `InputSource`
and `ShieldingSource` traits, this change also removes the
`min_confirmations` field from transaction proposals, in favor of
storing explicit target and anchor heights. This has the effect of
limiting the lifetime of transaction proposals to `PRUNING_DEPTH -
min_confirmations` blocks.

.github/workflows/ci.yml

@@ -162,7 +162,7 @@ jobs:
       - run: cargo fetch
       # Requires #![deny(rustdoc::broken_intra_doc_links)] in crates.
       - name: Check intra-doc links
-        run: cargo doc --all --document-private-items
+        run: cargo doc --all --all-features --document-private-items
 
   fmt:
     name: Rustfmt

Cargo.toml

@@ -39,7 +39,7 @@ zcash_proofs = { version = "0.13", path = "zcash_proofs", default-features = fal
 ff = "0.13"
 group = "0.13"
 incrementalmerkletree = "0.5"
-shardtree = "0.1"
+shardtree = "0.2"
 
 # Payment protocols
 # - Sapling

zcash_client_backend/CHANGELOG.md

@@ -8,10 +8,16 @@ and this library adheres to Rust's notion of
 ## [Unreleased]
 
 ### Added
-- `zcash_client_backend::data_api::wallet::propose_standard_transfer_to_address`
+- `zcash_client_backend::data_api`:
+  - `TransparentInputSource`
+  - `SaplingInputSource`
+  - `wallet::propose_standard_transfer_to_address`
+  - `wallet::input_selection::SaplingInputs`
+  - `wallet::input_selection::ShieldingSelector` has been
+    factored out from the `InputSelector` trait to separate out transparent
+    functionality and move it behind the `transparent-inputs` feature flag.
 - `zcash_client_backend::fees::standard`
 - `zcash_client_backend::wallet`:
-  - `input_selection::Proposal::min_confirmations`
   - `ReceivedSaplingNote::from_parts`
   - `ReceivedSaplingNote::{txid, output_index, diversifier, rseed, note_commitment_tree_position}`
 
@@ -39,7 +45,7 @@ and this library adheres to Rust's notion of
   - `wallet::create_proposed_transaction` now takes its `proposal` argument
     by reference instead of as an owned value.
   - `wallet::create_proposed_transaction` no longer takes a `min_confirmations`
-    argument. Instead, `min_confirmations` is stored in the `Proposal`
+    argument. Instead, it uses the anchor height from its `proposal` argument.
   - `wallet::create_spend_to_address` now takes an additional
     `change_memo` argument.
   - The error type of `wallet::create_spend_to_address` has been changed to use
@@ -51,6 +57,39 @@ and this library adheres to Rust's notion of
     - `wallet::create_spend_to_address`
     - `wallet::shield_transparent_funds`
     - `wallet::spend`
+  - In order to support better reusability for input selection code, two new
+    traits have been factored out from `WalletRead`:
+    - `zcash_client_backend::data_api::TransparentInputSource`
+    - `zcash_client_backend::data_api::SaplingInputSource`
+  - `wallet::input_selection::InputSelector::propose_shielding`,
+    has been moved out to the newly-created `ShieldingSelector` trait.
+    - `ShieldingSelector::propose_shielding` has been altered such that it takes
+      an explicit `target_height` in order to minimize the capabilities that the
+      `data_api::TransparentInputSource` trait must expose. Also, it now takes its
+      `min_confirmations` argument as `u32` instead of `NonZeroU32`.
+  - The `wallet::input_selection::InputSelector::DataSource`
+    associated type has been renamed to `InputSource`.
+  - The signature of `wallet:input_selection::InputSelector::propose_transaction` 
+    has been altered such that it longer takes `min_confirmations` as an
+    argument, instead taking explicit `target_height` and `anchor_height`
+    arguments. This helps to minimize the set of capabilities that the
+    `data_api::SaplingInputSource` must expose.
+  - `WalletRead::get_checkpoint_depth` has been removed without replacement. This
+    is no longer needed given the change to use the stored anchor height for transaction
+    proposal execution.
+  - `wallet::{propose_shielding, shield_transparent_funds}` now takes their
+    `min_confirmations` arguments as `u32` rather than a `NonZeroU32` to permit
+    implmentations to enable zero-conf shielding.
+  - `wallet::create_proposed_transaction` now forces implementations to ignore
+    the database identifiers for its contained notes by universally quantifying
+    the `NoteRef` type parameter.
+  - `wallet::input_selection::Proposal::sapling_inputs` now returns type
+    `Option<&SaplingInputs>`.
+  - `wallet::input_selection::Proposal::min_anchor_height` has been removed in
+    favor of storing this value in `SaplingInputs`.
+  - `wallet::input_selection::GreedyInputSelector` now has relaxed requirements
+    for its `InputSource` associated type.
+
 - `zcash_client_backend::fees`:
   - `ChangeValue::Sapling` is now a structured variant. In addition to the
     existing change value, it now also carries an optional memo to be associated
@@ -92,8 +131,12 @@ and this library adheres to Rust's notion of
 
 ### Removed
 - `zcash_client_backend::data_api::WalletRead::is_valid_account_extfvk` has been
-  removed; it was unused in the ECC mobile wallet SDKs and has been superseded by 
+  removed; it was unused in the ECC mobile wallet SDKs and has been superseded by
   `get_account_for_ufvk`.
+- `zcash_client_backend::data_api::WalletRead::get_spendable_sapling_notes` has been
+  removed without replacement as it was unused, and its functionality will be
+  fully reproduced by `SaplingInputSource::select_spendable_sapling_notes` in a future
+  change.
 
 ## [0.10.0] - 2023-09-25
 

zcash_client_backend/Cargo.toml

@@ -30,6 +30,7 @@ zcash_primitives.workspace = true
 # (Breaking upgrades to these require a breaking upgrade to this crate.)
 # - Data Access API
 time = "0.3.22"
+nonempty.workspace = true
 
 # - Encodings
 base64.workspace = true
@@ -87,6 +88,7 @@ gumdrop = "0.8"
 jubjub.workspace = true
 proptest.workspace = true
 rand_core.workspace = true
+shardtree = { workspace = true, features = ["test-dependencies"] }
 zcash_proofs.workspace = true
 zcash_address = { workspace = true, features = ["test-dependencies"] }