Merge bitcoin/bitcoin#25858: psbt: Only include PSBT_OUT_TAP_TREE when the output has a script path

9e386afb67bf8fa71b72f730da1695eeb11828cd tests: Test that PSBT_OUT_TAP_TREE is included correctly (Andrew Chow)
30ff25cf37eec4b09ab40424eb5d6a4a80410955 psbt: Only include m_tap_tree if it has scripts (Andrew Chow)
0577d423adda8e719d7611d03355680c8fbacab8 psbt: Change m_tap_tree to store just the tuples (Andrew Chow)
22c051ca70bae73e0430b05fb9d879591df27699 tests: Test that PSBT_OUT_TAP_TREE is combined correctly (Andrew Chow)
7df6e1bb77a96eac4fbcba424bbe780636b86650 psbt: Fix merging of m_tap_tree (Andrew Chow)
0652dc53b291bd295caff4093ec2854fd4b34645 [BugFix]: Do not allow deserializing PSBT with empty PSBT_OUT_TAP_TREE (Jeremy Rubin)

Pull request description:

  PSBT_OUT_TAP_TREE should not be included for outputs that do not have such a tree. This should be disallowed during parsing, as well as prior to serialization when the field is populated during updating.

  Also added some test cases.

  Alternative to #25856

ACKs for top commit:
  instagibbs:
    ACK https://github.com/bitcoin/bitcoin/pull/25858/commits/9e386afb67bf8fa71b72f730da1695eeb11828cd
  darosior:
    ACK 9e386afb67bf8fa71b72f730da1695eeb11828cd

Tree-SHA512: ce5c02a69752d176dbd967c1e8d30129b1905c8f186aeeef034576c1de82059271a1ee846bd040f5be4e66bb77ba711dcf14ac1e597c5707d7e7e2293f6cfefb

3 files changed, 33 insertions, 2 deletions

diff --git a/test/functional/data/rpc_psbt.json b/test/functional/data/rpc_psbt.json
index 657faebffc..3127350872 100644
--- a/test/functional/data/rpc_psbt.json
+++ b/test/functional/data/rpc_psbt.json
@@ -44,6 +44,10 @@
         [
             "cHNidP8BAKOro2MDAwMDA5ggCAAA////CQAtAAD+///1AAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJAAAAAAAAAAAAAAAAAAAAAAAAAD+///1Zm9ybmV3nWx1Y2vmelLmegAAAAAAAAAAAAAAAAAAAAMKAwMDAwMDAwMDAwMACvMBA3FkAAAAAAAAAAAABAAlAAAAAAAAACEWDQ0zDQ0NDQ0NDQ0NCwEAAH9/f39/fwMAAABNo6P///kAAA==",
             "Input Taproot BIP32 keypath has an invalid length"
+        ],
+        [
+            "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",
+            "Output Taproot tree must not be empty"
         ]
     ],
     "valid" : [
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 4583ca25cf..1fe3b21542 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -27,6 +27,7 @@ from test_framework.psbt import (
     PSBT_IN_SHA256,
     PSBT_IN_HASH160,
     PSBT_IN_HASH256,
+    PSBT_OUT_TAP_TREE,
 )
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
@@ -779,9 +780,18 @@ class PSBTTest(BitcoinTestFramework):
             self.generate(self.nodes[0], 1)
             self.nodes[0].importdescriptors([{"desc": descsum_create("tr({})".format(privkey)), "timestamp":"now"}])
 
-            psbt = watchonly.sendall([wallet.getnewaddress()])["psbt"]
+            psbt = watchonly.sendall([wallet.getnewaddress(), addr])["psbt"]
             psbt = self.nodes[0].walletprocesspsbt(psbt)["psbt"]
-            self.nodes[0].sendrawtransaction(self.nodes[0].finalizepsbt(psbt)["hex"])
+            txid = self.nodes[0].sendrawtransaction(self.nodes[0].finalizepsbt(psbt)["hex"])
+            vout = find_vout_for_address(self.nodes[0], txid, addr)
+
+            # Make sure tap tree is in psbt
+            parsed_psbt = PSBT.from_base64(psbt)
+            assert_greater_than(len(parsed_psbt.o[vout].map[PSBT_OUT_TAP_TREE]), 0)
+            assert "taproot_tree" in self.nodes[0].decodepsbt(psbt)["outputs"][vout]
+            parsed_psbt.make_blank()
+            comb_psbt = self.nodes[0].combinepsbt([psbt, parsed_psbt.to_base64()])
+            assert_equal(comb_psbt, psbt)
 
             self.log.info("Test that walletprocesspsbt both updates and signs a non-updated psbt containing Taproot inputs")
             addr = self.nodes[0].getnewaddress("", "bech32m")
@@ -793,6 +803,14 @@ class PSBTTest(BitcoinTestFramework):
             self.nodes[0].sendrawtransaction(rawtx)
             self.generate(self.nodes[0], 1)
 
+            # Make sure tap tree is not in psbt
+            parsed_psbt = PSBT.from_base64(psbt)
+            assert PSBT_OUT_TAP_TREE not in parsed_psbt.o[0].map
+            assert "taproot_tree" not in self.nodes[0].decodepsbt(psbt)["outputs"][0]
+            parsed_psbt.make_blank()
+            comb_psbt = self.nodes[0].combinepsbt([psbt, parsed_psbt.to_base64()])
+            assert_equal(comb_psbt, psbt)
+
         self.log.info("Test decoding PSBT with per-input preimage types")
         # note that the decodepsbt RPC doesn't check whether preimages and hashes match
         hash_ripemd160, preimage_ripemd160 = random_bytes(20), random_bytes(50)
diff --git a/test/functional/test_framework/psbt.py b/test/functional/test_framework/psbt.py
index 68945e7e84..3a5b4ec74d 100644
--- a/test/functional/test_framework/psbt.py
+++ b/test/functional/test_framework/psbt.py
@@ -123,6 +123,15 @@ class PSBT:
         psbt = [x.serialize() for x in [self.g] + self.i + self.o]
         return b"psbt\xff" + b"".join(psbt)
 
+    def make_blank(self):
+        """
+        Remove all fields except for PSBT_GLOBAL_UNSIGNED_TX
+        """
+        for m in self.i + self.o:
+            m.map.clear()
+
+        self.g = PSBTMap(map={0: self.g.map[0]})
+
     def to_base64(self):
         return base64.b64encode(self.serialize()).decode("utf8")