Merge bitcoin/bitcoin#25827: descriptor: check if rawtr has only one key.

416ceb8661 descriptor: check if `rawtr` has only one key. (w0xlt)

Pull request description:

  If I understand `rawtr` descriptor correctly, it should only allow `rawtr(KEY)`, not `rawtr(KEY1, KEY2, ...)` or other concatenations.

  On master branch, `rawtr(KEY1, KEY2, ...)` will produce the `rawtr(KEY1)` descriptor ignoring the `KEY2, ...` with no error messages or warnings.

  For example, the code below will print `rawtr(tprv8ZgxMBicQKsPefef2Doobbq3xTCaVTHcDn6me82KSXY1vY9AJAWD5u7SDM4XGLfc4EoXRMFrJKpp6HNmQWA3FTMRQeEmMJYJ9RPqe9ne2hU/*)#lx9qryfh`
  for the supposedly invalid descriptor
  `rawtr(tprv8ZgxMBicQKsPefef2Doobbq3xTCaVTHcDn6me82KSXY1vY9AJAWD5u7SDM4XGLfc4EoXRMFrJKpp6HNmQWA3FTMRQeEmMJYJ9RPqe9ne2hU/*, tprv8ZgxMBicQKsPezQ2KGArMRovTEbCGxaLgBgaVcTvEx8mby8ogX2bgC4HBapH4yMwrz2FpoCuA17eocuUVMgEP6fnm83YpwSDTFrumw42bny/*)`
  ```python
          self.nodes[1].createwallet(wallet_name="rawtr_multi", descriptors=True, blank=True)
          rawtr_multi = self.nodes[1].get_wallet_rpc("rawtr_multi")
          rawtr_multi_desc = "rawtr(tprv8ZgxMBicQKsPefef2Doobbq3xTCaVTHcDn6me82KSXY1vY9AJAWD5u7SDM4XGLfc4EoXRMFrJKpp6HNmQWA3FTMRQeEmMJYJ9RPqe9ne2hU/*, tprv8ZgxMBicQKsPezQ2KGArMRovTEbCGxaLgBgaVcTvEx8mby8ogX2bgC4HBapH4yMwrz2FpoCuA17eocuUVMgEP6fnm83YpwSDTFrumw42bny/*)#uv78hkt0"
          result = rawtr_multi.importdescriptors([{"desc": rawtr_multi_desc, "active": True, "timestamp": "now"}])

          print(rawtr_multi.listdescriptors(True))
  ```

  This PR adds a check that prevents `rawtr` descriptors from being created if more than one key is entered, shows an error message, and adds a test for this case.

ACKs for top commit:
  achow101:
    ACK 416ceb8661
  sipa:
    ACK 416ceb8661

Tree-SHA512: a2009e91f1bca6ee79cc68f65811caa6a21fc8b80acd8dc58e283f424b41fe53b0db7ce3693b1c7e2184ff571e6d1fbb9f5ccde89b65d3026726f3393c492044

src/script/descriptor.cpp

@@ -1472,6 +1472,10 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
     }
     if (ctx == ParseScriptContext::TOP && Func("rawtr", expr)) {
         auto arg = Expr(expr);
+        if (expr.size()) {
+            error = strprintf("rawtr(): only one key expected.");
+            return nullptr;
+        }
         auto output_key = ParsePubkey(key_exp_index, arg, ParseScriptContext::P2TR, out, error);
         if (!output_key) return nullptr;
         ++key_exp_index;

src/test/descriptor_tests.cpp

@@ -464,6 +464,31 @@ Check("sh(wsh(multi(20,KzoAz5CanayRKex3fSLQ2BwJpN7U52gZvxMyk78nDMHuqrUxuSJy,KwGN
     CheckUnparsable("", "raw(asdf)", "Raw script is not hex"); // Invalid script
     CheckUnparsable("", "raw(Ü)#00000000", "Invalid characters in payload"); // Invalid chars
 
+    Check(
+        "rawtr(xprv9vHkqa6EV4sPZHYqZznhT2NPtPCjKuDKGY38FBWLvgaDx45zo9WQRUT3dKYnjwih2yJD9mkrocEZXo1ex8G81dwSM1fwqWpWkeS3v86pgKt/86'/1'/0'/1/*)#a5gn3t7k",
+        "rawtr(xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/86'/1'/0'/1/*)#4ur3xhft",
+        "",
+        "rawtr([5a61ff8e/86'/1'/0']xpub6DtZpc9PRL2B6pwoNGysmHAaBofDmWv5S6KQEKKGPKhf5fV62ywDtSziSApYVK3JnYY5KUSgiCwiXW5wtd8z7LNBxT9Mu5sEro8itdGfTeA/1/*)#llheyd9x",
+        RANGE | HARDENED | XONLY_KEYS,
+        {{"51205172af752f057d543ce8e4a6f8dcf15548ec6be44041bfa93b72e191cfc8c1ee"}, {"51201b66f20b86f700c945ecb9ad9b0ad1662b73084e2bfea48bee02126350b8a5b1"}, {"512063e70f66d815218abcc2306aa930aaca07c5cde73b75127eb27b5e8c16b58a25"}},
+        OutputType::BECH32M,
+        {{0x80000056, 0x80000001, 0x80000000, 1, 0}, {0x80000056, 0x80000001, 0x80000000, 1, 1}, {0x80000056, 0x80000001, 0x80000000, 1, 2}});
+
+
+    Check(
+        "rawtr(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1)",
+        "rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd)",
+        "rawtr(L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1)",
+        "rawtr(a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd)",
+        SIGNABLE | XONLY_KEYS,
+        {{"5120a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd"}},
+        OutputType::BECH32M);
+
+    CheckUnparsable(
+        "",
+        "rawtr(xpub68FQ9imX6mCWacw6eNRjaa8q8ynnHmUd5i7MVR51ZMPP5JycyfVHSLQVFPHMYiTybWJnSBL2tCBpy6aJTR2DYrshWYfwAxs8SosGXd66d8/*, xpub69Mvq3QMipdvnd9hAyeTnT5jrkcBuLErV212nsGf3qr7JPWysc9HnNhCsazdzj1etSx28hPSE8D7DnceFbNdw4Kg8SyRfjE2HFLv1P8TSGc/*)",
+        "rawtr(): only one key expected.");
+
     // A 2of4 but using a direct push rather than OP_2
     CScript nonminimalmultisig;
     CKey keys[4];