Merge bitcoin#31540: refactor: std::span compat fixes

fa494a1 refactor: Specify const in std::span constructor, where needed (MarcoFalke)
faaf480 Allow std::span in stream serialization (MarcoFalke)
faa5391 refactor: test: Return std::span from StringBytes (MarcoFalke)
fa86223 refactor: Avoid passing span iterators when data pointers are expected (MarcoFalke)
faae6fa refactor: Simplify SpanPopBack (MarcoFalke)
facc4f1 refactor: Replace fwd-decl with proper include (MarcoFalke)
fac3a78 refactor: Avoid needless, unsafe c-style cast (MarcoFalke)

Pull request description:

  The `std::span` type is already used in some parts of the codebase, and in most contexts can implicitly convert to and from `Span`. However, the two types are not identical in behavior and trying to use one over the other can result in compile failures in some contexts.

  Fix all those issues by allowing either `Span` or `std::span` in any part of the codebase.

  All of the changes are also required for the scripted-diff to replace `Span` with `std::span` in bitcoin#31519

ACKs for top commit:
  sipa:
    utACK fa494a1
  fjahr:
    Code review ACK fa494a1
  achow101:
    ACK fa494a1
  theuni:
    utACK fa494a1.
  adamandrews1:
    utACK bitcoin@fa494a1

Tree-SHA512: 9440941823e884ff5d7ac161f58b9a0704d8e803b4c91c400bdb5f58f898e4637d63ae627cfc7330e98a721fc38285a04641175aa18d991bd35f8b69ed1d74c4

src/base58.cpp

@@ -139,7 +139,7 @@ std::string EncodeBase58Check(Span<const unsigned char> input)
     // add 4-byte hash check to the end
     std::vector<unsigned char> vch(input.begin(), input.end());
     uint256 hash = Hash(vch);
-    vch.insert(vch.end(), (unsigned char*)&hash, (unsigned char*)&hash + 4);
+    vch.insert(vch.end(), hash.data(), hash.data() + 4);
     return EncodeBase58(vch);
 }
 

src/script/miniscript.h

@@ -1798,7 +1798,7 @@ inline NodeRef<Key> Parse(Span<const char> in, const Ctx& ctx)
         // Get threshold
         int next_comma = FindNextChar(in, ',');
         if (next_comma < 1) return false;
-        const auto k_to_integral{ToIntegral<int64_t>(std::string_view(in.begin(), next_comma))};
+        const auto k_to_integral{ToIntegral<int64_t>(std::string_view(in.data(), next_comma))};
         if (!k_to_integral.has_value()) return false;
         const int64_t k{k_to_integral.value()};
         in = in.subspan(next_comma + 1);
@@ -1954,15 +1954,15 @@ inline NodeRef<Key> Parse(Span<const char> in, const Ctx& ctx)
             } else if (Const("after(", in)) {
                 int arg_size = FindNextChar(in, ')');
                 if (arg_size < 1) return {};
-                const auto num{ToIntegral<int64_t>(std::string_view(in.begin(), arg_size))};
+                const auto num{ToIntegral<int64_t>(std::string_view(in.data(), arg_size))};
                 if (!num.has_value() || *num < 1 || *num >= 0x80000000L) return {};
                 constructed.push_back(MakeNodeRef<Key>(internal::NoDupCheck{}, ctx.MsContext(), Fragment::AFTER, *num));
                 in = in.subspan(arg_size + 1);
                 script_size += 1 + (*num > 16) + (*num > 0x7f) + (*num > 0x7fff) + (*num > 0x7fffff);
             } else if (Const("older(", in)) {
                 int arg_size = FindNextChar(in, ')');
                 if (arg_size < 1) return {};
-                const auto num{ToIntegral<int64_t>(std::string_view(in.begin(), arg_size))};
+                const auto num{ToIntegral<int64_t>(std::string_view(in.data(), arg_size))};
                 if (!num.has_value() || *num < 1 || *num >= 0x80000000L) return {};
                 constructed.push_back(MakeNodeRef<Key>(internal::NoDupCheck{}, ctx.MsContext(), Fragment::OLDER, *num));
                 in = in.subspan(arg_size + 1);
@@ -1974,7 +1974,7 @@ inline NodeRef<Key> Parse(Span<const char> in, const Ctx& ctx)
             } else if (Const("thresh(", in)) {
                 int next_comma = FindNextChar(in, ',');
                 if (next_comma < 1) return {};
-                const auto k{ToIntegral<int64_t>(std::string_view(in.begin(), next_comma))};
+                const auto k{ToIntegral<int64_t>(std::string_view(in.data(), next_comma))};
                 if (!k.has_value() || *k < 1) return {};
                 in = in.subspan(next_comma + 1);
                 // n = 1 here because we read the first WRAPPED_EXPR before reaching THRESH

src/script/solver.h

@@ -10,14 +10,14 @@
 
 #include <attributes.h>
 #include <script/script.h>
+#include <span.h>
 
 #include <string>
 #include <optional>
 #include <utility>
 #include <vector>
 
 class CPubKey;
-template <typename C> class Span;
 
 enum class TxoutType {
     NONSTANDARD,

src/serialize.h

@@ -264,6 +264,7 @@ 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, BasicByte B, int N> void Serialize(Stream& s, const B (&a)[N]) { s.write(MakeByteSpan(a)); }
 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, std::size_t N> void Serialize(Stream& s, std::span<B, N> span) { s.write(std::as_bytes(span)); }
 template <typename Stream, BasicByte B> void Serialize(Stream& s, Span<B> span) { s.write(AsBytes(span)); }
 
 template <typename Stream, CharNotInt8 V> void Unserialize(Stream&, V) = delete; // char serialization forbidden. Use uint8_t or int8_t
@@ -278,6 +279,7 @@ 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, BasicByte B, int N> void Unserialize(Stream& s, B (&a)[N]) { s.read(MakeWritableByteSpan(a)); }
 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, std::size_t N> void Unserialize(Stream& s, std::span<B, N> span) { s.read(std::as_writable_bytes(span)); }
 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); }

src/span.h

@@ -248,9 +248,8 @@ template <typename T>
 T& SpanPopBack(Span<T>& span)
 {
     size_t size = span.size();
-    ASSERT_IF_DEBUG(size > 0);
-    T& back = span[size - 1];
-    span = Span<T>(span.data(), size - 1);
+    T& back = span.back();
+    span = span.first(size - 1);
     return back;
 }
 

src/streams.h

@@ -79,7 +79,7 @@ class VectorWriter
             memcpy(vchData.data() + nPos, src.data(), nOverwrite);
         }
         if (nOverwrite < src.size()) {
-            vchData.insert(vchData.end(), UCharCast(src.data()) + nOverwrite, UCharCast(src.end()));
+            vchData.insert(vchData.end(), UCharCast(src.data()) + nOverwrite, UCharCast(src.data() + src.size()));
         }
         nPos += src.size();
     }

src/test/script_tests.cpp

@@ -1700,9 +1700,8 @@ BOOST_AUTO_TEST_CASE(bip341_keypath_test_vectors)
             BOOST_CHECK_EQUAL(HexStr(sighash), input["intermediary"]["sigHash"].get_str());
 
             // To verify the sigmsg, hash the expected sigmsg, and compare it with the (expected) sighash.
-            BOOST_CHECK_EQUAL(HexStr((HashWriter{HASHER_TAPSIGHASH} << Span{ParseHex(input["intermediary"]["sigMsg"].get_str())}).GetSHA256()), input["intermediary"]["sigHash"].get_str());
+            BOOST_CHECK_EQUAL(HexStr((HashWriter{HASHER_TAPSIGHASH} << std::span<const uint8_t>{ParseHex(input["intermediary"]["sigMsg"].get_str())}).GetSHA256()), input["intermediary"]["sigHash"].get_str());
         }
-
     }
 }
 

src/test/serialize_tests.cpp

@@ -304,7 +304,7 @@ class Base
         if (s.template GetParams<BaseFormat>().m_base_format == BaseFormat::RAW) {
             s << m_base_data;
         } else {
-            s << Span{HexStr(Span{&m_base_data, 1})};
+            s << std::span<const char>{HexStr(Span{&m_base_data, 1})};
         }
     }
 

src/test/util/net.h

@@ -12,6 +12,7 @@
 #include <netaddress.h>
 #include <node/connection_types.h>
 #include <node/eviction.h>
+#include <span.h>
 #include <sync.h>
 #include <util/sock.h>
 
@@ -28,9 +29,6 @@
 
 class FastRandomContext;
 
-template <typename C>
-class Span;
-
 struct ConnmanTestMsg : public CConnman {
     using CConnman::CConnman;
 

src/util/hasher.h

@@ -8,13 +8,12 @@
 #include <crypto/common.h>
 #include <crypto/siphash.h>
 #include <primitives/transaction.h>
+#include <span.h>
 #include <uint256.h>
 
 #include <cstdint>
 #include <cstring>
 
-template <typename C> class Span;
-
 class SaltedTxidHasher
 {
 private:

src/wallet/test/db_tests.cpp

@@ -34,9 +34,9 @@ inline std::ostream& operator<<(std::ostream& os, const std::pair<const Serializ
 
 namespace wallet {
 
-static Span<const std::byte> StringBytes(std::string_view str)
+inline std::span<const std::byte> StringBytes(std::string_view str)
 {
-    return AsBytes<const char>({str.data(), str.size()});
+    return std::as_bytes(std::span{str});
 }
 
 static SerializeData StringData(std::string_view str)