docs: add docstrings for TxBuilder

bdk-ffi/src/bdk.udl

@@ -676,51 +676,143 @@ dictionary Condition {
   LockTime? timelock;
 };
 
+/// A `TxBuilder` is created by calling `build_tx` or `build_fee_bump` on a wallet. After assigning it, you set options on it
+/// until finally calling `finish` to consume the builder and generate the transaction.
 interface TxBuilder {
   constructor();
 
+  /// Fill-in the `PSBT_GLOBAL_XPUB` field with the extended keys contained in both the external and internal
+  /// descriptors.
+  ///
+  /// This is useful for offline signers that take part to a multisig. Some hardware wallets like BitBox and ColdCard
+  /// are known to require this.
   TxBuilder add_global_xpubs();
 
+  /// Add a recipient to the internal list of recipients.
   TxBuilder add_recipient([ByRef] Script script, Amount amount);
 
+  /// Replace the recipients already added with a new list of recipients.
   TxBuilder set_recipients(sequence<ScriptAmount> recipients);
 
+  /// Add a utxo to the internal list of unspendable utxos.
+  ///
+  /// It’s important to note that the "must-be-spent" utxos added with `TxBuilder::add_utxo` have priority over this.
   TxBuilder add_unspendable(OutPoint unspendable);
 
+  /// Replace the internal list of unspendable utxos with a new list.
+  ///
+  /// It’s important to note that the "must-be-spent" utxos added with `TxBuilder::add_utxo` have priority over these.
   TxBuilder unspendable(sequence<OutPoint> unspendable);
 
+  /// Add a utxo to the internal list of utxos that must be spent.
+  ///
+  /// These have priority over the "unspendable" utxos, meaning that if a utxo is present both in the "utxos" and the
+  /// "unspendable" list, it will be spent.
   TxBuilder add_utxo(OutPoint outpoint);
 
+  /// The TxBuilder::policy_path is a complex API. See the Rust docs for complete information: https://docs.rs/bdk_wallet/latest/bdk_wallet/struct.TxBuilder.html#method.policy_path
   TxBuilder policy_path(record<string, sequence<u64>> policy_path, KeychainKind keychain);
 
+  /// Set a specific `ChangeSpendPolicy`. See `TxBuilder::do_not_spend_change` and `TxBuilder::only_spend_change` for
+  /// some shortcuts. This method assumes the presence of an internal keychain, otherwise it has no effect.
   TxBuilder change_policy(ChangeSpendPolicy change_policy);
 
+  /// Do not spend change outputs.
+  ///
+  /// This effectively adds all the change outputs to the "unspendable" list. See `TxBuilder::unspendable`. This method
+  /// assumes the presence of an internal keychain, otherwise it has no effect.
   TxBuilder do_not_spend_change();
 
+  /// Only spend change outputs.
+  ///
+  /// This effectively adds all the non-change outputs to the "unspendable" list. See `TxBuilder::unspendable`. This
+  /// method assumes the presence of an internal keychain, otherwise it has no effect.
   TxBuilder only_spend_change();
 
+  /// Only spend utxos added by `TxBuilder::add_utxo`.
+  ///
+  /// The wallet will not add additional utxos to the transaction even if they are needed to make the transaction valid.
   TxBuilder manually_selected_only();
 
+  /// Set a custom fee rate.
+  ///
+  /// This method sets the mining fee paid by the transaction as a rate on its size. This means that the total fee paid
+  /// is equal to fee_rate times the size of the transaction. Default is 1 sat/vB in accordance with Bitcoin Core’s
+  /// default relay policy.
+  ///
+  /// Note that this is really a minimum feerate – it’s possible to overshoot it slightly since adding a change output
+  /// to drain the remaining excess might not be viable.
   TxBuilder fee_rate([ByRef] FeeRate fee_rate);
 
+  /// Set an absolute fee The `fee_absolute` method refers to the absolute transaction fee in `Amount`. If anyone sets
+  /// both the `fee_absolute` method and the `fee_rate` method, the `FeePolicy` enum will be set by whichever method was
+  /// called last, as the `FeeRate` and `FeeAmount` are mutually exclusive.
+  ///
+  /// Note that this is really a minimum absolute fee – it’s possible to overshoot it slightly since adding a change output to drain the remaining excess might not be viable.
   TxBuilder fee_absolute(Amount fee);
 
+  /// Spend all the available inputs. This respects filters like `TxBuilder::unspendable` and the change policy.
   TxBuilder drain_wallet();
 
+  /// Sets the address to drain excess coins to.
+  ///
+  /// Usually, when there are excess coins they are sent to a change address generated by the wallet. This option
+  /// replaces the usual change address with an arbitrary script_pubkey of your choosing. Just as with a change output,
+  /// if the drain output is not needed (the excess coins are too small) it will not be included in the resulting
+  /// transaction. The only difference is that it is valid to use `drain_to` without setting any ordinary recipients
+  /// with `add_recipient` (but it is perfectly fine to add recipients as well).
+  ///
+  /// If you choose not to set any recipients, you should provide the utxos that the transaction should spend via
+  /// `add_utxos`. `drain_to` is very useful for draining all the coins in a wallet with `drain_wallet` to a single
+  /// address.
   TxBuilder drain_to([ByRef] Script script);
 
+  /// Set an exact `nSequence` value.
+  ///
+  /// This can cause conflicts if the wallet’s descriptors contain an "older" (`OP_CSV`) operator and the given
+  /// `nsequence` is lower than the CSV value.
   TxBuilder set_exact_sequence(u32 nsequence);
 
+  /// Add data as an output using `OP_RETURN`.
   TxBuilder add_data(sequence<u8> data);
 
+  /// Set the current blockchain height.
+  ///
+  /// This will be used to:
+  ///
+  /// 1. Set the `nLockTime` for preventing fee sniping. Note: This will be ignored if you manually specify a
+  /// `nlocktime` using `TxBuilder::nlocktime`.
+  ///
+  /// 2. Decide whether coinbase outputs are mature or not. If the coinbase outputs are not mature at `current_height`,
+  /// we ignore them in the coin selection. If you want to create a transaction that spends immature coinbase inputs,
+  /// manually add them using `TxBuilder::add_utxos`.
+  /// In both cases, if you don’t provide a current height, we use the last sync height.
   TxBuilder current_height(u32 height);
 
+  /// Use a specific nLockTime while creating the transaction.
+  ///
+  /// This can cause conflicts if the wallet’s descriptors contain an "after" (`OP_CLTV`) operator.
   TxBuilder nlocktime(LockTime locktime);
 
+  /// Set whether or not the dust limit is checked.
+  ///
+  /// Note: by avoiding a dust limit check you may end up with a transaction that is non-standard.
   TxBuilder allow_dust(boolean allow_dust);
 
+  /// Build a transaction with a specific version.
+  ///
+  /// The version should always be greater than 0 and greater than 1 if the wallet’s descriptors contain an "older"
+  /// (`OP_CSV`) operator.
   TxBuilder version(i32 version);
 
+  /// Finish building the transaction.
+  ///
+  /// Uses the thread-local random number generator (rng).
+  ///
+  /// Returns a new `Psbt` per BIP174.
+  ///
+  /// WARNING: To avoid change address reuse you must persist the changes resulting from one or more calls to this
+  /// method before closing the wallet. See `Wallet::reveal_next_address`.
   [Throws=CreateTxError]
   Psbt finish([ByRef] Wallet wallet);
 };