fuzz: rename and improve the Miniscript Script roundtrip target

Parse also key hashes using the Key type. Make this target the first of
the 4 Miniscript fuzz targets in a single `miniscript` file.

Co-authored-by: Pieter Wuille <pieter.wuille@gmail.com>

src/Makefile.test.include

@@ -269,7 +269,7 @@ test_fuzz_fuzz_SOURCES = \
  test/fuzz/locale.cpp \
  test/fuzz/merkleblock.cpp \
  test/fuzz/message.cpp \
- test/fuzz/miniscript_decode.cpp \
+ test/fuzz/miniscript.cpp \
  test/fuzz/minisketch.cpp \
  test/fuzz/muhash.cpp \
  test/fuzz/multiplication_overflow.cpp \

src/test/fuzz/miniscript.cpp

@@ -0,0 +1,70 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <core_io.h>
+#include <hash.h>
+#include <key.h>
+#include <script/miniscript.h>
+#include <script/script.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+#include <util/strencodings.h>
+
+namespace {
+
+//! Context that implements naive conversion from/to script only, for roundtrip testing.
+struct ScriptParserContext {
+    //! For Script roundtrip we never need the key from a key hash.
+    struct Key {
+        bool is_hash;
+        std::vector<unsigned char> data;
+    };
+
+    const std::vector<unsigned char>& ToPKBytes(const Key& key) const
+    {
+        assert(!key.is_hash);
+        return key.data;
+    }
+
+    const std::vector<unsigned char> ToPKHBytes(const Key& key) const
+    {
+        if (key.is_hash) return key.data;
+        const auto h = Hash160(key.data);
+        return {h.begin(), h.end()};
+    }
+
+    template<typename I>
+    std::optional<Key> FromPKBytes(I first, I last) const
+    {
+        Key key;
+        key.data.assign(first, last);
+        key.is_hash = false;
+        return key;
+    }
+
+    template<typename I>
+    std::optional<Key> FromPKHBytes(I first, I last) const
+    {
+        Key key;
+        key.data.assign(first, last);
+        key.is_hash = true;
+        return key;
+    }
+} SCRIPT_PARSER_CONTEXT;
+
+}
+
+/* Fuzz tests that test parsing from a script, and roundtripping via script. */
+FUZZ_TARGET(miniscript_script)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const std::optional<CScript> script = ConsumeDeserializable<CScript>(fuzzed_data_provider);
+    if (!script) return;
+
+    const auto ms = miniscript::FromScript(*script, SCRIPT_PARSER_CONTEXT);
+    if (!ms) return;
+
+    assert(ms->ToScript(SCRIPT_PARSER_CONTEXT) == *script);
+}

src/test/fuzz/miniscript_decode.cpp

@@ -1,71 +0,0 @@
-// Copyright (c) 2022 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#include <core_io.h>
-#include <hash.h>
-#include <key.h>
-#include <script/miniscript.h>
-#include <script/script.h>
-#include <span.h>
-#include <test/fuzz/FuzzedDataProvider.h>
-#include <test/fuzz/fuzz.h>
-#include <test/fuzz/util.h>
-#include <util/strencodings.h>
-
-#include <optional>
-
-using miniscript::operator""_mst;
-
-
-struct Converter {
-    typedef CPubKey Key;
-
-    std::optional<std::string> ToString(const Key& key) const {
-        return HexStr(key);
-    }
-    const std::vector<unsigned char> ToPKBytes(const Key& key) const {
-        return {key.begin(), key.end()};
-    }
-    const std::vector<unsigned char> ToPKHBytes(const Key& key) const {
-        const auto h = Hash160(key);
-        return {h.begin(), h.end()};
-    }
-
-    template<typename I>
-    std::optional<Key> FromString(I first, I last) const {
-        const auto bytes = ParseHex(std::string(first, last));
-        Key key{bytes.begin(), bytes.end()};
-        if (key.IsValid()) return key;
-        return {};
-    }
-    template<typename I>
-    std::optional<Key> FromPKBytes(I first, I last) const {
-        Key key{first, last};
-        if (key.IsValid()) return key;
-        return {};
-    }
-    template<typename I>
-    std::optional<Key> FromPKHBytes(I first, I last) const {
-        return {};
-    }
-};
-
-const Converter CONVERTER;
-
-FUZZ_TARGET(miniscript_decode)
-{
-    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
-    const std::optional<CScript> script = ConsumeDeserializable<CScript>(fuzzed_data_provider);
-    if (!script) return;
-
-    const auto ms = miniscript::FromScript(*script, CONVERTER);
-    if (!ms) return;
-
-    // We can roundtrip it to its string representation.
-    std::string ms_str = *ms->ToString(CONVERTER);
-    assert(*miniscript::FromString(ms_str, CONVERTER) == *ms);
-    // The Script representation must roundtrip since we parsed it this way the first time.
-    const CScript ms_script = ms->ToScript(CONVERTER);
-    assert(ms_script == *script);
-}