refactor: Print verbose serialize compiler error messages

Author: MarcoFalke

Diff for: src/.clang-format

@@ -43,5 +43,7 @@ SpacesInAngles:  false
 SpacesInContainerLiterals: true
 SpacesInCStyleCastParentheses: false
 SpacesInParentheses: false
+BreakBeforeConceptDeclarations: Always
+RequiresExpressionIndentation: OuterScope
 Standard: c++20
 UseTab:          Never

Diff for: src/serialize.h

@@ -273,8 +273,8 @@ template<typename Stream> inline void Serialize(Stream& s, int64_t a ) { ser_wri
 template<typename Stream> inline void Serialize(Stream& s, uint64_t a) { ser_writedata64(s, a); }
 template<typename Stream, int N> inline void Serialize(Stream& s, const char (&a)[N]) { s.write(MakeByteSpan(a)); }
 template<typename Stream, int N> inline void Serialize(Stream& s, const unsigned char (&a)[N]) { s.write(MakeByteSpan(a)); }
-template <typename Stream, typename B, std::size_t N> void Serialize(Stream& s, const std::array<B, N>& a) { (void)/* force byte-type */UCharCast(a.data()); s.write(MakeByteSpan(a)); }
-template <typename Stream, typename B> void Serialize(Stream& s, Span<B> span) { (void)/* force byte-type */UCharCast(span.data()); s.write(AsBytes(span)); }
+template <typename Stream, BasicByte B, std::size_t N> void Serialize(Stream& s, const std::array<B, N>& a) { s.write(MakeByteSpan(a)); }
+template <typename Stream, BasicByte B> void Serialize(Stream& s, Span<B> span) { s.write(AsBytes(span)); }
 
 #ifndef CHAR_EQUALS_INT8
 template <typename Stream> void Unserialize(Stream&, char) = delete; // char serialization forbidden. Use uint8_t or int8_t
@@ -290,8 +290,8 @@ template<typename Stream> inline void Unserialize(Stream& s, int64_t& a ) { a =
 template<typename Stream> inline void Unserialize(Stream& s, uint64_t& a) { a = ser_readdata64(s); }
 template<typename Stream, int N> inline void Unserialize(Stream& s, char (&a)[N]) { s.read(MakeWritableByteSpan(a)); }
 template<typename Stream, int N> inline void Unserialize(Stream& s, unsigned char (&a)[N]) { s.read(MakeWritableByteSpan(a)); }
-template <typename Stream, typename B, std::size_t N> void Unserialize(Stream& s, std::array<B, N>& a) { (void)/* force byte-type */UCharCast(a.data()); s.read(MakeWritableByteSpan(a)); }
-template <typename Stream, typename B> void Unserialize(Stream& s, Span<B> span) { (void)/* force byte-type */UCharCast(span.data()); s.read(AsWritableBytes(span)); }
+template <typename Stream, BasicByte B, std::size_t N> void Unserialize(Stream& s, std::array<B, N>& a) { s.read(MakeWritableByteSpan(a)); }
+template <typename Stream, BasicByte B> void Unserialize(Stream& s, Span<B> span) { s.read(AsWritableBytes(span)); }
 
 template <typename Stream> inline void Serialize(Stream& s, bool a) { uint8_t f = a; ser_writedata8(s, f); }
 template <typename Stream> inline void Unserialize(Stream& s, bool& a) { uint8_t f = ser_readdata8(s); a = f; }
@@ -755,18 +755,23 @@ template<typename Stream, typename T> void Serialize(Stream& os, const std::uniq
 template<typename Stream, typename T> void Unserialize(Stream& os, std::unique_ptr<const T>& p);
 
 
-
 /**
  * If none of the specialized versions above matched, default to calling member function.
  */
-template<typename Stream, typename T>
-inline void Serialize(Stream& os, const T& a)
+template <class T, class Stream>
+concept Serializable = requires(T a, Stream s) { a.Serialize(s); };
+template <typename Stream, typename T>
+    requires Serializable<T, Stream>
+void Serialize(Stream& os, const T& a)
 {
     a.Serialize(os);
 }
 
-template<typename Stream, typename T>
-inline void Unserialize(Stream& is, T&& a)
+template <class T, class Stream>
+concept Unserializable = requires(T a, Stream s) { a.Unserialize(s); };
+template <typename Stream, typename T>
+    requires Unserializable<T, Stream>
+void Unserialize(Stream& is, T&& a)
 {
     a.Unserialize(is);
 }

Diff for: src/span.h

@@ -5,6 +5,10 @@
 #ifndef BGL_SPAN_H
 #define BGL_SPAN_H
 
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <span>
 #include <type_traits>
 #include <cstddef>
 #include <algorithm>
@@ -288,13 +292,11 @@ Span<std::byte> MakeWritableByteSpan(V&& v) noexcept
     return AsWritableBytes(Span{std::forward<V>(v)});
 }
 
-// Helper functions to safely cast to unsigned char pointers.
-inline unsigned char* UCharCast(char* c) { return (unsigned char*)c; }
-inline unsigned char* UCharCast(unsigned char* c) { return c; }
-inline unsigned char* UCharCast(std::byte* c) { return (unsigned char*)c; }
 inline const unsigned char* UCharCast(const char* c) { return (unsigned char*)c; }
 inline const unsigned char* UCharCast(const unsigned char* c) { return c; }
-inline const unsigned char* UCharCast(const std::byte* c) { return reinterpret_cast<const unsigned char*>(c); }
+// Helper concept for the basic byte types.
+template <typename B>
+concept BasicByte = requires { UCharCast(std::span<B>{}.data()); };
 
 // Helper function to safely convert a Span to a Span<[const] unsigned char>.
 template <typename T> constexpr auto UCharSpanCast(Span<T> s) -> Span<typename std::remove_pointer<decltype(UCharCast(s.data()))>::type> { return {UCharCast(s.data()), s.size()}; }