walletrpc: add PsbtCoinSelect option to FundPsbt

lnrpc/walletrpc/walletkit_grpc.pb.go

@@ -218,15 +218,25 @@ type WalletKitClient interface {
 	LabelTransaction(ctx context.Context, in *LabelTransactionRequest, opts ...grpc.CallOption) (*LabelTransactionResponse, error)
 	// lncli: `wallet psbt fund`
 	// FundPsbt creates a fully populated PSBT that contains enough inputs to fund
-	// the outputs specified in the template. There are two ways of specifying a
-	// template: Either by passing in a PSBT with at least one output declared or
-	// by passing in a raw TxTemplate message.
+	// the outputs specified in the template. There are three ways a user can
+	// specify what we call the template (a list of inputs and outputs to use in
+	// the PSBT): Either as a PSBT packet directly with no coin selection (using
+	// the legacy "psbt" field), a PSBT with advanced coin selection support (using
+	// the new "coin_select" field) or as a raw RPC message (using the "raw"
+	// field).
+	// The legacy "psbt" and "raw" modes, the following restrictions apply:
+	// 1. If there are no inputs specified in the template, coin selection is
+	// performed automatically.
+	// 2. If the template does contain any inputs, it is assumed that full
+	// coin selection happened externally and no additional inputs are added. If
+	// the specified inputs aren't enough to fund the outputs with the given fee
+	// rate, an error is returned.
 	//
-	// If there are no inputs specified in the template, coin selection is
-	// performed automatically. If the template does contain any inputs, it is
-	// assumed that full coin selection happened externally and no additional
-	// inputs are added. If the specified inputs aren't enough to fund the outputs
-	// with the given fee rate, an error is returned.
+	// The new "coin_select" mode does not have these restrictions and allows the
+	// user to specify a PSBT with inputs and outputs and still perform coin
+	// selection on top of that.
+	// For all modes this RPC requires any inputs that are specified to be locked
+	// by the user (if they belong to this node in the first place).
 	//
 	// After either selecting or verifying the inputs, all input UTXOs are locked
 	// with an internal app ID.
@@ -716,15 +726,25 @@ type WalletKitServer interface {
 	LabelTransaction(context.Context, *LabelTransactionRequest) (*LabelTransactionResponse, error)
 	// lncli: `wallet psbt fund`
 	// FundPsbt creates a fully populated PSBT that contains enough inputs to fund
-	// the outputs specified in the template. There are two ways of specifying a
-	// template: Either by passing in a PSBT with at least one output declared or
-	// by passing in a raw TxTemplate message.
+	// the outputs specified in the template. There are three ways a user can
+	// specify what we call the template (a list of inputs and outputs to use in
+	// the PSBT): Either as a PSBT packet directly with no coin selection (using
+	// the legacy "psbt" field), a PSBT with advanced coin selection support (using
+	// the new "coin_select" field) or as a raw RPC message (using the "raw"
+	// field).
+	// The legacy "psbt" and "raw" modes, the following restrictions apply:
+	// 1. If there are no inputs specified in the template, coin selection is
+	// performed automatically.
+	// 2. If the template does contain any inputs, it is assumed that full
+	// coin selection happened externally and no additional inputs are added. If
+	// the specified inputs aren't enough to fund the outputs with the given fee
+	// rate, an error is returned.
 	//
-	// If there are no inputs specified in the template, coin selection is
-	// performed automatically. If the template does contain any inputs, it is
-	// assumed that full coin selection happened externally and no additional
-	// inputs are added. If the specified inputs aren't enough to fund the outputs
-	// with the given fee rate, an error is returned.
+	// The new "coin_select" mode does not have these restrictions and allows the
+	// user to specify a PSBT with inputs and outputs and still perform coin
+	// selection on top of that.
+	// For all modes this RPC requires any inputs that are specified to be locked
+	// by the user (if they belong to this node in the first place).
 	//
 	// After either selecting or verifying the inputs, all input UTXOs are locked
 	// with an internal app ID.