[docs] add doxygen comments to wallet code

Co-authored-by: Xekyo <murch@murch.one>

src/wallet/coinselection.h

@@ -15,6 +15,7 @@ static constexpr CAmount MIN_CHANGE{COIN / 100};
 //! final minimum change amount after paying for fees
 static const CAmount MIN_FINAL_CHANGE = MIN_CHANGE/2;
 
+/** A UTXO under consideration for use in funding a new transaction. */
 class CInputCoin {
 public:
  CInputCoin(const CTransactionRef& tx, unsigned int i)
@@ -56,31 +57,58 @@ class CInputCoin {
  }
 };
 
+/** Parameters for filtering which OutputGroups we may use in coin selection.
+ * We start by being very selective and requiring multiple confirmations and
+ * then get more permissive if we cannot fund the transaction. */
 struct CoinEligibilityFilter
 {
+ /** Minimum number of confirmations for outputs that we sent to ourselves.
+ * We may use unconfirmed UTXOs sent from ourselves, e.g. change outputs. */
  const int conf_mine;
+ /** Minimum number of confirmations for outputs received from a different
+ * wallet. We never spend unconfirmed foreign outputs as we cannot rely on these funds yet. */
  const int conf_theirs;
+ /** Maximum number of unconfirmed ancestors aggregated across all UTXOs in an OutputGroup. */
  const uint64_t max_ancestors;
+ /** Maximum number of descendants that a single UTXO in the OutputGroup may have. */
  const uint64_t max_descendants;
- const bool m_include_partial_groups{false}; //! Include partial destination groups when avoid_reuse and there are full groups
+ /** When avoid_reuse=true and there are full groups (OUTPUT_GROUP_MAX_ENTRIES), whether or not to use any partial groups.*/
+ const bool m_include_partial_groups{false};
 
  CoinEligibilityFilter(int conf_mine, int conf_theirs, uint64_t max_ancestors) : conf_mine(conf_mine), conf_theirs(conf_theirs), max_ancestors(max_ancestors), max_descendants(max_ancestors) {}
  CoinEligibilityFilter(int conf_mine, int conf_theirs, uint64_t max_ancestors, uint64_t max_descendants) : conf_mine(conf_mine), conf_theirs(conf_theirs), max_ancestors(max_ancestors), max_descendants(max_descendants) {}
  CoinEligibilityFilter(int conf_mine, int conf_theirs, uint64_t max_ancestors, uint64_t max_descendants, bool include_partial) : conf_mine(conf_mine), conf_theirs(conf_theirs), max_ancestors(max_ancestors), max_descendants(max_descendants), m_include_partial_groups(include_partial) {}
 };
 
+/** A group of UTXOs paid to the same output script. */
 struct OutputGroup
 {
+ /** The list of UTXOs contained in this output group. */
  std::vector<CInputCoin> m_outputs;
+ /** Whether the UTXOs were sent by the wallet to itself. This is relevant because we may want at
+ * least a certain number of confirmations on UTXOs received from outside wallets while trusting
+ * our own UTXOs more. */
  bool m_from_me{true};
+ /** The total value of the UTXOs in sum. */
  CAmount m_value{0};
+ /** The minimum number of confirmations the UTXOs in the group have. Unconfirmed is 0. */
  int m_depth{999};
+ /** The aggregated count of unconfirmed ancestors of all UTXOs in this
+ * group. Not deduplicated and may overestimate when ancestors are shared. */
  size_t m_ancestors{0};
+ /** The maximum count of descendants of a single UTXO in this output group. */
  size_t m_descendants{0};
+ /** The value of the UTXOs after deducting the cost of spending them at the effective feerate. */
  CAmount effective_value{0};
+ /** The fee to spend these UTXOs at the effective feerate. */
  CAmount fee{0};
+ /** The target feerate of the transaction we're trying to build. */
  CFeeRate m_effective_feerate{0};
+ /** The fee to spend these UTXOs at the long term feerate. */
  CAmount long_term_fee{0};
+ /** The feerate for spending a created change output eventually (i.e. not urgently, and thus at
+ * a lower feerate). Calculated using long term fee estimate. This is used to decide whether
+ * it could be economical to create a change output. */
  CFeeRate m_long_term_feerate{0};
 
  OutputGroup() {}

src/wallet/wallet.h

@@ -564,7 +564,15 @@ class COutput
 {
 public:
  const CWalletTx *tx;
+
+ /** Index in tx->vout. */
  int i;
+
+ /**
+ * Depth in block chain.
+ * If > 0: the tx is on chain and has this many confirmations.
+ * If = 0: the tx is waiting confirmation.
+ * If < 0: a conflicting tx is on chain and has this many confirmations. */
  int nDepth;
 
  /** Pre-computed estimated size of this output as a fully-signed input in a transaction. Can be -1 if it could not be calculated */
@@ -604,17 +612,30 @@ class COutput
  }
 };
 
+/** Parameters for one iteration of Coin Selection. */
 struct CoinSelectionParams
 {
+ /** Toggles use of Branch and Bound instead of Knapsack solver. */
  bool use_bnb = true;
+ /** Size of a change output in bytes, determined by the output type. */
  size_t change_output_size = 0;
+ /** Size of the input to spend a change output in virtual bytes. */
  size_t change_spend_size = 0;
+ /** The targeted feerate of the transaction being built. */
  CFeeRate m_effective_feerate;
+ /** The feerate estimate used to estimate an upper bound on what should be sufficient to spend
+ * the change output sometime in the future. */
  CFeeRate m_long_term_feerate;
+ /** If the cost to spend a change output at the discard feerate exceeds its value, drop it to fees. */
  CFeeRate m_discard_feerate;
+ /** Size of the transaction before coin selection, consisting of the header and recipient
+ * output(s), excluding the inputs and change output(s). */
  size_t tx_noinputs_size = 0;
  /** Indicate that we are subtracting the fee from outputs */
  bool m_subtract_fee_outputs = false;
+ /** When true, always spend all (up to OUTPUT_GROUP_MAX_ENTRIES) or none of the outputs
+ * associated with the same address. This helps reduce privacy leaks resulting from address
+ * reuse. Dust outputs are not eligible to be added to output groups and thus not considered. */
  bool m_avoid_partial_spends = false;
 
  CoinSelectionParams(bool use_bnb, size_t change_output_size, size_t change_spend_size, CFeeRate effective_feerate,
@@ -652,7 +673,10 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
  //! the current wallet version: clients below this version are not able to load the wallet
  int nWalletVersion GUARDED_BY(cs_wallet){FEATURE_BASE};
 
+ /** The next scheduled rebroadcast of wallet transactions. */
  int64_t nNextResend = 0;
+ /** Whether this wallet will submit newly created transactions to the node's mempool and
+ * prompt rebroadcasts (see ResendWalletTransactions()). */
  bool fBroadcastTransactions = false;
  // Local time that the tip block was received. Used to schedule wallet rebroadcasts.
  std::atomic<int64_t> m_best_block_time {0};
@@ -694,6 +718,7 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
  * Should be called with non-zero block_hash and posInBlock if this is for a transaction that is included in a block. */
  void SyncTransaction(const CTransactionRef& tx, CWalletTx::Confirmation confirm, bool update_tx = true) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
+ /** WalletFlags set on this wallet. */
  std::atomic<uint64_t> m_wallet_flags{0};
 
  bool SetAddressBookWithDB(WalletBatch& batch, const CTxDestination& address, const std::string& strName, const std::string& strPurpose);
@@ -753,8 +778,11 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
 
  /**
  * Select a set of coins such that nValueRet >= nTargetValue and at least
- * all coins from coinControl are selected; Never select unconfirmed coins
- * if they are not ours
+ * all coins from coin_control are selected; never select unconfirmed coins if they are not ours
+ * param@[out] setCoinsRet Populated with inputs including pre-selected inputs from
+ * coin_control and Coin Selection if successful.
+ * param@[out] nValueRet Total value of selected coins including pre-selected ones
+ * from coin_control and Coin Selection if successful.
  */
  bool SelectCoins(const std::vector<COutput>& vAvailableCoins, const CAmount& nTargetValue, std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet,
  const CCoinControl& coin_control, CoinSelectionParams& coin_selection_params, bool& bnb_used) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
@@ -788,6 +816,8 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
  /** Interface to assert chain access */
  bool HaveChain() const { return m_chain ? true : false; }
 
+ /** Map from txid to CWalletTx for all transactions this wallet is
+ * interested in, including received and sent transactions. */
  std::map<uint256, CWalletTx> mapWallet GUARDED_BY(cs_wallet);
 
  typedef std::multimap<int64_t, CWalletTx*> TxItems;
@@ -799,6 +829,10 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
  std::map<CTxDestination, CAddressBookData> m_address_book GUARDED_BY(cs_wallet);
  const CAddressBookData* FindAddressBookEntry(const CTxDestination&, bool allow_change = false) const EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
 
+ /** Set of Coins owned by this wallet that we won't try to spend from. A
+ * Coin may be locked if it has already been used to fund a transaction
+ * that hasn't confirmed yet. We wouldn't consider the Coin spent already,
+ * but also shouldn't try to use it again. */
  std::set<COutPoint> setLockedCoins GUARDED_BY(cs_wallet);
 
  /** Registered interfaces::Chain::Notifications handler. */
@@ -833,6 +867,11 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
  * small change; This method is stochastic for some inputs and upon
  * completion the coin set and corresponding actual target value is
  * assembled
+ * param@[in] coins Set of UTXOs to consider. These will be categorized into
+ * OutputGroups and filtered using eligibility_filter before
+ * selecting coins.
+ * param@[out] setCoinsRet Populated with the coins selected if successful.
+ * param@[out] nValueRet Used to return the total value of selected coins.
  */
  bool SelectCoinsMinConf(const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, std::vector<COutput> coins,
  std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet, const CoinSelectionParams& coin_selection_params, bool& bnb_used) const;
@@ -1015,6 +1054,8 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
 
  CFeeRate m_pay_tx_fee{DEFAULT_PAY_TX_FEE};
  unsigned int m_confirm_target{DEFAULT_TX_CONFIRM_TARGET};
+ /** Allow Coin Selection to pick unconfirmed UTXOs that were sent from our own wallet if it
+ * cannot fund the transaction otherwise. */
  bool m_spend_zero_conf_change{DEFAULT_SPEND_ZEROCONF_CHANGE};
  bool m_signal_rbf{DEFAULT_WALLET_RBF};
  bool m_allow_fallback_fee{true}; //!< will be false if -fallbackfee=0
@@ -1025,7 +1066,12 @@ class CWallet final : public WalletStorage, public interfaces::Chain::Notificati
  * Override with -fallbackfee
  */
  CFeeRate m_fallback_fee{DEFAULT_FALLBACK_FEE};
+
+ /** If the cost to spend a change output at this feerate is greater than the value of the
+ * output itself, just drop it to fees. */
  CFeeRate m_discard_rate{DEFAULT_DISCARD_FEE};
+
+ /** The maximum fee amount we're willing to pay to prioritize partial spend avoidance. */
  CAmount m_max_aps_fee{DEFAULT_MAX_AVOIDPARTIALSPEND_FEE}; //!< note: this is absolute fee, not fee rate
  OutputType m_default_address_type{DEFAULT_ADDRESS_TYPE};
  /**