cmake: compact generated data headers

Change the raw and json data generators to emit concatenated byte
string literals instead of per-element initializer lists.

Add MakeByteArray in span.h so raw headers stay compact while
still exposing the same compile-time byte spans.

The hash checks added in the previous commit keep the embedded fixture
contents pinned while this commit only changes their C++ representation.

Co-authored-by: Fabian Jahr <fjahr@protonmail.com>

Author: l0rinc

cmake/script/GenerateHeaderFromJson.cmake

@@ -5,18 +5,23 @@
 cmake_path(GET JSON_SOURCE_PATH STEM json_source_basename)
 
 file(READ ${JSON_SOURCE_PATH} hex_content HEX)
-string(REGEX REPLACE "................" "\\0\n" formatted_bytes "${hex_content}")
-string(REGEX REPLACE "[^\n][^\n]" "'\\\\x\\0'," formatted_bytes "${formatted_bytes}")
+string(REGEX REPLACE "................................................................" "\\0\n" formatted_bytes "${hex_content}")
+string(REGEX REPLACE "[^\n][^\n]" "\\\\x\\0" formatted_bytes "${formatted_bytes}")
+if(formatted_bytes STREQUAL "")
+  set(formatted_bytes "\"\"")
+else()
+  string(REGEX REPLACE "([^\n]+)" "\"\\1\"" formatted_bytes "${formatted_bytes}")
+endif()
 
 set(header_content
 "#include <string_view>
 
 namespace json_tests {
-inline constexpr char detail_${json_source_basename}_bytes[] {
+inline constexpr char detail_${json_source_basename}_bytes[] =
 ${formatted_bytes}
-};
+;
 
-inline constexpr std::string_view ${json_source_basename}{std::begin(detail_${json_source_basename}_bytes), std::end(detail_${json_source_basename}_bytes)};
+inline constexpr std::string_view ${json_source_basename}{detail_${json_source_basename}_bytes, sizeof(detail_${json_source_basename}_bytes) - 1};
 }
 ")
 file(WRITE ${HEADER_PATH} "${header_content}")

cmake/script/GenerateHeaderFromRaw.cmake

@@ -5,18 +5,22 @@
 cmake_path(GET RAW_SOURCE_PATH STEM raw_source_basename)
 
 file(READ ${RAW_SOURCE_PATH} hex_content HEX)
-string(REGEX REPLACE "................" "\\0\n" formatted_bytes "${hex_content}")
-string(REGEX REPLACE "[^\n][^\n]" "std::byte{0x\\0}," formatted_bytes "${formatted_bytes}")
+string(REGEX REPLACE "................................................................" "\\0\n" formatted_bytes "${hex_content}")
+string(REGEX REPLACE "[^\n][^\n]" "\\\\x\\0" formatted_bytes "${formatted_bytes}")
+if(formatted_bytes STREQUAL "")
+  set(formatted_bytes "\"\"")
+else()
+  string(REGEX REPLACE "([^\n]+)" "\"\\1\"" formatted_bytes "${formatted_bytes}")
+endif()
 
 set(header_content
-"#include <cstddef>
-#include <span>
+"#include <span.h>
 
 namespace ${RAW_NAMESPACE} {
-inline constexpr std::byte detail_${raw_source_basename}_raw[] {
+inline constexpr auto detail_${raw_source_basename}_raw{MakeByteArray(
 ${formatted_bytes}
-};
+)};
 
-inline constexpr std::span ${raw_source_basename}{detail_${raw_source_basename}_raw};
+inline constexpr auto ${raw_source_basename}{std::span{detail_${raw_source_basename}_raw}.first<detail_${raw_source_basename}_raw.size() - 1>()};
 }")
 file(WRITE ${HEADER_PATH} "${header_content}")

src/span.h

@@ -5,6 +5,8 @@
 #ifndef BITCOIN_SPAN_H
 #define BITCOIN_SPAN_H
 
+#include <array>
+#include <bit>
 #include <cassert>
 #include <cstddef>
 #include <span>
@@ -80,6 +82,12 @@ T& SpanPopBack(std::span<T>& span)
     return back;
 }
 
+template <size_t N>
+consteval auto MakeByteArray(const char (&bytes)[N])
+{
+    return std::bit_cast<std::array<std::byte, N>>(std::to_array(bytes));
+}
+
 template <typename V>
 auto MakeByteSpan(const V& v) noexcept
 {