test: Use string_view for json_tests

This avoids a static constructor of the global std::string, and rules
out possibly expensive and implicit copies of the string completely.

cmake/script/GenerateHeaderFromJson.cmake

@@ -5,10 +5,10 @@
 file(READ ${JSON_SOURCE_PATH} hex_content HEX)
 string(REGEX MATCHALL "([A-Za-z0-9][A-Za-z0-9])" bytes "${hex_content}")
 
-file(WRITE ${HEADER_PATH} "#include <string>\n")
+file(WRITE ${HEADER_PATH} "#include <string_view>\n")
 file(APPEND ${HEADER_PATH} "namespace json_tests{\n")
 get_filename_component(json_source_basename ${JSON_SOURCE_PATH} NAME_WE)
-file(APPEND ${HEADER_PATH} "static const std::string ${json_source_basename}{\n")
+file(APPEND ${HEADER_PATH} "inline constexpr char detail_${json_source_basename}_bytes[]{\n")
 
 set(i 0)
 foreach(byte ${bytes})
@@ -21,4 +21,6 @@ foreach(byte ${bytes})
   endif()
 endforeach()
 
-file(APPEND ${HEADER_PATH} "\n};};")
+file(APPEND ${HEADER_PATH} "\n};\n")
+file(APPEND ${HEADER_PATH} "inline constexpr std::string_view ${json_source_basename}{std::begin(detail_${json_source_basename}_bytes), std::end(detail_${json_source_basename}_bytes)};")
+file(APPEND ${HEADER_PATH} "\n}")

src/test/util/json.cpp

@@ -1,15 +1,15 @@
-// Copyright (c) 2023 The Bitcoin Core developers
+// Copyright (c) 2023-present 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 <test/util/json.h>
 
-#include <string>
+#include <univalue.h>
 #include <util/check.h>
 
-#include <univalue.h>
+#include <string_view>
 
-UniValue read_json(const std::string& jsondata)
+UniValue read_json(std::string_view jsondata)
 {
     UniValue v;
     Assert(v.read(jsondata) && v.isArray());

src/test/util/json.h

@@ -1,14 +1,14 @@
-// Copyright (c) 2023 The Bitcoin Core developers
+// Copyright (c) 2023-present The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #ifndef BITCOIN_TEST_UTIL_JSON_H
 #define BITCOIN_TEST_UTIL_JSON_H
 
-#include <string>
-
 #include <univalue.h>
 
-UniValue read_json(const std::string& jsondata);
+#include <string_view>
+
+UniValue read_json(std::string_view jsondata);
 
 #endif // BITCOIN_TEST_UTIL_JSON_H