Merge #16378: The ultimate send RPC

92326d89766155a792254d30a9962251b8fc7799 [rpc] add send method (Sjors Provoost)
2c2a1445dc9d22c9d729b8301c8b3f54195bcfcf [rpc] add snake case aliases for transaction methods (Sjors Provoost)
1bc8d0fd5906bc9637d513cd193a1f47ad94da28 [rpc] walletcreatefundedpsbt: allow inputs to be null (Sjors Provoost)

Pull request description:

  `walletcreatefundedpsbt` has some interesting features that `sendtoaddress` and `sendmany` don't have:
  * manual coin selection
  * outputting a PSBT (it was controversial to add this, see #18201)
  * create a transaction without adding to wallet (which leads to broadcasting, unless `-walletbroadcast=0`)

  At the same time `walletcreatefundedpsbt` can't broadcast a transaction, which is inconvenient for simple use cases.

  This PR introduces a new `send` RPC method which creates a PSBT, signs it if possible and adds it to the wallet by default. If it can't sign all inputs, it outputs a PSBT. If `add_to_wallet` is set to `false` it will return the transaction in both PSBT and hex format.

  Because it uses a PSBT internally, it will much easier to add hardware wallet support to this method (see #16546).

  For `bitcoin-cli` users, it tries to keep the simplest use case easy to use:

  ```sh
  bitcoin-cli -regtest send '{"ADDRESS": 0.1}' 1 sat/b
  ```

  This paves the way for deprecating `sendtoaddress` and `sendmany` though there's no rush. The only missing feature compared to these older methods is adding labels to a destination address.

  Depends on:
  - [x] #16377 (`[rpc] don't automatically append inputs in walletcreatefundedpsbt`)
  - [x] #11413 (`[wallet] [rpc] sendtoaddress/sendmany: Add explicit feerate option`)
  - [x] #18244 (`[rpc] have lockUnspents also lock manually selected coins`)

ACKs for top commit:
  meshcollider:
    Light re-utACK 92326d89766155a792254d30a9962251b8fc7799
  achow101:
    ACK 92326d89766155a792254d30a9962251b8fc7799 Reviewed code and test, ran tests.
  kallewoof:
    utACK 92326d89766155a792254d30a9962251b8fc7799

Tree-SHA512: 7552ef1b193d4c06e381c44932fdb0d54f64383e4c7d6b988f49d059c7d4bba45ce6aa7813e03df86360ad9dad6f3010eb76ee7da480551742d5fd98c2251c0f

1 files changed, 5 insertions, 0 deletions

diff --git a/doc/release-notes-16378.md b/doc/release-notes-16378.md
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+RPC
+---
+- A new `send` RPC with similar syntax to `walletcreatefundedpsbt`, including
+  support for coin selection and a custom fee rate. Using the new `send` method
+  is encouraged: `sendmany` and `sendtoaddress` may be deprecated in a future release.