test: assert CScript allocation characteristics

Verifies that script types are correctly allocated using prevector's direct or indirect storage based on their size:

Direct allocated script types (size ≤ 28 bytes):
* OP_RETURN (small)
* P2WPKH
* P2SH
* P2PKH

Indirect allocated script types (size > 28 bytes):
* P2WSH
* P2TR
* P2PK
* MULTISIG (small)

This test provides a baseline for verifying changes to prevector's inline capacity.

The `CHECK_SCRIPT_STATIC_SIZE` and `CHECK_SCRIPT_DYNAMIC_SIZE` macros were added to differentiate the two cases - while preserving the correct source code line in case of failure.

src/test/script_tests.cpp

@@ -1151,6 +1151,107 @@ BOOST_AUTO_TEST_CASE(script_CHECKMULTISIG23)
     BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_INVALID_STACK_OPERATION, ScriptErrorString(err));
 }
 
+/** Return the TxoutType of a script without exposing Solver details. */
+static TxoutType GetTxoutType(const CScript& output_script)
+{
+    std::vector<std::vector<uint8_t>> unused;
+    return Solver(output_script, unused);
+}
+
+#define CHECK_SCRIPT_STATIC_SIZE(script, expected_size)                   \
+    do {                                                                  \
+        BOOST_CHECK_EQUAL((script).size(), (expected_size));              \
+        BOOST_CHECK_EQUAL((script).capacity(), CScriptBase::STATIC_SIZE); \
+        BOOST_CHECK_EQUAL((script).allocated_memory(), 0);                \
+    } while (0)
+
+#define CHECK_SCRIPT_DYNAMIC_SIZE(script, expected_size, expected_extra)                 \
+    do {                                                                 \
+        BOOST_CHECK_EQUAL((script).size(), (expected_size));             \
+        BOOST_CHECK_EQUAL((script).capacity(), (expected_extra));         \
+        BOOST_CHECK_EQUAL((script).allocated_memory(), (expected_extra)); \
+    } while (0)
+
+BOOST_AUTO_TEST_CASE(script_size_and_capacity_test)
+{
+    BOOST_CHECK_EQUAL(sizeof(CompressedScript), 40);
+    BOOST_CHECK_EQUAL(sizeof(CScriptBase), 32);
+    BOOST_CHECK_NE(sizeof(CScriptBase), sizeof(prevector<CScriptBase::STATIC_SIZE + 1, uint8_t>)); // CScriptBase size should be set to avoid wasting space in padding
+    BOOST_CHECK_EQUAL(sizeof(CScript), 32);
+    BOOST_CHECK_EQUAL(sizeof(CTxOut), 40);
+
+    CKey dummy_key;
+    dummy_key.MakeNewKey(/*fCompressed=*/true);
+    const CPubKey dummy_pubkey{dummy_key.GetPubKey()};
+
+    // Small OP_RETURN has direct allocation
+    {
+        const auto script{CScript() << OP_RETURN << std::vector<uint8_t>(10, 0xaa)};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::NULL_DATA);
+        CHECK_SCRIPT_STATIC_SIZE(script, 12);
+    }
+
+    // P2WPKH has direct allocation
+    {
+        const auto script{GetScriptForDestination(WitnessV0KeyHash{PKHash{dummy_pubkey}})};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::WITNESS_V0_KEYHASH);
+        CHECK_SCRIPT_STATIC_SIZE(script, 22);
+    }
+
+    // P2SH has direct allocation
+    {
+        const auto script{GetScriptForDestination(ScriptHash{CScript{} << OP_TRUE})};
+        BOOST_CHECK(script.IsPayToScriptHash());
+        CHECK_SCRIPT_STATIC_SIZE(script, 23);
+    }
+
+    // P2PKH has direct allocation
+    {
+        const auto script{GetScriptForDestination(PKHash{dummy_pubkey})};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::PUBKEYHASH);
+        CHECK_SCRIPT_STATIC_SIZE(script, 25);
+    }
+
+    // P2WSH needs extra allocation
+    {
+        const auto script{GetScriptForDestination(WitnessV0ScriptHash{CScript{} << OP_TRUE})};
+        BOOST_CHECK(script.IsPayToWitnessScriptHash());
+        CHECK_SCRIPT_DYNAMIC_SIZE(script, 34, 34);
+    }
+
+    // P2TR needs extra allocation
+    {
+        const auto script{GetScriptForDestination(WitnessV1Taproot{XOnlyPubKey{dummy_pubkey}})};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::WITNESS_V1_TAPROOT);
+        CHECK_SCRIPT_DYNAMIC_SIZE(script, 34, 34);
+    }
+
+    // Compressed P2PK needs extra allocation
+    {
+        const auto script{GetScriptForRawPubKey(dummy_pubkey)};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::PUBKEY);
+        CHECK_SCRIPT_DYNAMIC_SIZE(script, 35, 35);
+    }
+
+    // Uncompressed P2PK needs extra allocation
+    {
+        CKey uncompressed_key;
+        uncompressed_key.MakeNewKey(/*fCompressed=*/false);
+        const CPubKey uncompressed_pubkey{uncompressed_key.GetPubKey()};
+
+        const auto script{GetScriptForRawPubKey(uncompressed_pubkey)};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::PUBKEY);
+        CHECK_SCRIPT_DYNAMIC_SIZE(script, 67, 67);
+    }
+
+    // Bare multisig needs extra allocation
+    {
+        const auto script{GetScriptForMultisig(1, std::vector{2, dummy_pubkey})};
+        BOOST_CHECK_EQUAL(GetTxoutType(script), TxoutType::MULTISIG);
+        CHECK_SCRIPT_DYNAMIC_SIZE(script, 71, 103);
+    }
+}
+
 /* Wrapper around ProduceSignature to combine two scriptsigs */
 SignatureData CombineSignatures(const CTxOut& txout, const CMutableTransaction& tx, const SignatureData& scriptSig1, const SignatureData& scriptSig2)
 {