test: improves tapscript unit tests

This commit creates new test utilities for future Taproot script
tests within script_tests.json. The key features of this commit are the
addition of three new tags: `#SCRIPT#`, `#CONTROLBLOCK#`, and
`#TAPROOTOUTPUT#`. These tags streamline the test creation process by
eliminating the need to manually generate these components outside the
test suite.

* `#SCRIPT#`: Parses Tapscript and outputs a byte string of opcodes.
* `#CONTROLBLOCK#`: Automatically generates the control block for a given
Taproot output.
* `#TAPROOTOUTPUT#`: Generates the final Taproot scriptPubKey.

Update src/test/script_tests.cpp

Co-authored-by: Jan B <608446+janb84@users.noreply.github.com>

src/test/data/script_tests.json

@@ -2610,6 +2610,63 @@
 [["645168", 0.00000001], "0x22 0x0020f913eacf2e38a5d6fc3a8311d72ae704cb83866350a984dd3e5eb76d2a8c28e8", "HASH160 0x14 0xdbb7d1c0a56b7a9c423300c8cca6e6e065baf1dc EQUAL", "P2SH,WITNESS", "UNBALANCED_CONDITIONAL"],
 [["645168", 0.00000001], "0x22 0x0020f913eacf2e38a5d6fc3a8311d72ae704cb83866350a984dd3e5eb76d2a8c28e8", "HASH160 0x14 0xdbb7d1c0a56b7a9c423300c8cca6e6e065baf1dc EQUAL", "P2SH,WITNESS,MINIMALIF", "UNBALANCED_CONDITIONAL"],
 
+["Tapscript tests"],
+[
+    [
+        "1ffe1234567890",
+        "00",
+        "#SCRIPT# HASH256 DUP SHA1 DROP DUP DROP TOALTSTACK HASH256 DUP DROP TOALTSTACK FROMALTSTACK",
+        "#CONTROLBLOCK#",
+        0.00000001
+    ],
+    "",
+    "0x51 0x20 #TAPROOTOUTPUT#",
+    "P2SH,WITNESS,TAPROOT",
+    "OK",
+    "TAPSCRIPT Tests testing tapscript with many different op codes including ALTSTACK interactions"
+],
+[
+    [
+        "abcdef",
+        "#SCRIPT# 1 IF SHA256 ENDIF SIZE SWAP DROP 32 EQUAL",
+        "#CONTROLBLOCK#",
+        0.00000001
+    ],
+    "",
+    "0x51 0x20 #TAPROOTOUTPUT#",
+    "P2SH,WITNESS,TAPROOT",
+    "OK",
+    "TAPSCRIPT Test IF conditional when true"
+],
+[
+    [
+        "abcdef",
+        "#SCRIPT# 0 IF SHA256 ENDIF SIZE SWAP DROP 32 EQUAL",
+        "#CONTROLBLOCK#",
+        0.00000001
+    ],
+    "",
+    "0x51 0x20 #TAPROOTOUTPUT#",
+    "P2SH,WITNESS,TAPROOT",
+    "EVAL_FALSE",
+    "TAPSCRIPT Test IF conditional when false"
+],
+[
+    [
+        "aa",
+        "bb",
+        "cc",
+        "#SCRIPT# EQUAL IF DROP DROP ENDIF",
+        "#CONTROLBLOCK#",
+        0.00000001
+    ],
+    "",
+    "0x51 0x20 #TAPROOTOUTPUT#",
+    "P2SH,WITNESS,TAPROOT",
+    "OK",
+    "TAPSCRIPT Test that DROP operations do not execute inside of a false IF conditional"
+],
+
 ["NULLFAIL should cover all signatures and signatures only"],
 ["0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0", "0x01 0x14 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0x01 0x14 CHECKMULTISIG NOT", "DERSIG", "OK", "BIP66 and NULLFAIL-compliant"],
 ["0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0", "0x01 0x14 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0x01 0x14 CHECKMULTISIG NOT", "DERSIG,NULLFAIL", "OK", "BIP66 and NULLFAIL-compliant"],

src/test/script_tests.cpp

@@ -916,21 +916,38 @@ BOOST_AUTO_TEST_CASE(script_json_test)
     // amount (nValue) to use in the crediting tx
     UniValue tests = read_json(json_tests::script_tests);
 
+    const KeyData keys;
     for (unsigned int idx = 0; idx < tests.size(); idx++) {
         const UniValue& test = tests[idx];
         std::string strTest = test.write();
         CScriptWitness witness;
+        TaprootBuilder taprootBuilder;
         CAmount nValue = 0;
         unsigned int pos = 0;
         if (test.size() > 0 && test[pos].isArray()) {
             unsigned int i=0;
             for (i = 0; i < test[pos].size()-1; i++) {
                 auto element = test[pos][i].get_str();
-                const auto witness_value{TryParseHex<unsigned char>(element)};
+                // We use #SCRIPT# to flag a non-hex script that we can read using ParseScript
-                if (!witness_value.has_value()) {
+                // Taproot script must be third from the last element in witness stack
-                    BOOST_ERROR("Bad witness in test: " << strTest << " witness is not hex: " << element);
+                static const std::string SCRIPT_FLAG{"#SCRIPT#"};
+                if (element.starts_with(SCRIPT_FLAG)) {
+                    CScript script = ParseScript(element.substr(SCRIPT_FLAG.size()));
+                    witness.stack.push_back(ToByteVector(script));
+                } else if (element == "#CONTROLBLOCK#") {
+                    // Taproot script control block - second from the last element in witness stack
+                    // If #CONTROLBLOCK# we auto-generate the control block
+                    taprootBuilder.Add(/*depth=*/0, witness.stack.back(), TAPROOT_LEAF_TAPSCRIPT, /*track=*/true);
+                    taprootBuilder.Finalize(XOnlyPubKey(keys.key0.GetPubKey()));
+                    auto controlblocks = taprootBuilder.GetSpendData().scripts[{witness.stack.back(), TAPROOT_LEAF_TAPSCRIPT}];
+                    witness.stack.push_back(*(controlblocks.begin()));
+                } else {
+                    const auto witness_value{TryParseHex<unsigned char>(element)};
+                    if (!witness_value.has_value()) {
+                        BOOST_ERROR("Bad witness in test: " << strTest << " witness is not hex: " << element);
+                    }
+                    witness.stack.push_back(witness_value.value());
                 }
-                witness.stack.push_back(witness_value.value());
             }
             nValue = AmountFromValue(test[pos][i]);
             pos++;
@@ -945,7 +962,14 @@ BOOST_AUTO_TEST_CASE(script_json_test)
         std::string scriptSigString = test[pos++].get_str();
         CScript scriptSig = ParseScript(scriptSigString);
         std::string scriptPubKeyString = test[pos++].get_str();
-        CScript scriptPubKey = ParseScript(scriptPubKeyString);
+        CScript scriptPubKey;
+        // If requested, auto-generate the taproot output
+        if (scriptPubKeyString == "0x51 0x20 #TAPROOTOUTPUT#") {
+            BOOST_CHECK_MESSAGE(taprootBuilder.IsComplete(), "Failed to autogenerate Tapscript output key");
+            scriptPubKey = CScript() << OP_1 << ToByteVector(taprootBuilder.GetOutput());
+        } else {
+            scriptPubKey = ParseScript(scriptPubKeyString);
+        }
         unsigned int scriptflags = ParseScriptFlags(test[pos++].get_str());
         int scriptError = ParseScriptError(test[pos++].get_str());