Fix somes warning when compiling with Visual Studio 2019 on x64 target

[gvollant]

In visual studio 2019 x64 target, pointer size and size_t are 64 bits and int are 32 bits
This commit uses size_t for buffer size

[gvollant]

These warning fixes are simple.
I don't understand why it's no "mergeable"

gillesvollant@gv-w81x64:/mnt/w$ diff -c /mnt/n/amalib_external_lib_cache/protobuf-cpp-3.14.0_static_bld_gcc_ltofull/src/google/protobuf/parse_context.h /mnt/y/protobu
f/src/google/protobuf/parse_context.h
*** /mnt/n/amalib_external_lib_cache/protobuf-cpp-3.14.0_static_bld_gcc_ltofull/src/google/protobuf/parse_context.h     2020-11-13 23:55:22.000000000 +0100
--- /mnt/y/protobuf/src/google/protobuf/parse_context.h 2020-12-15 14:33:50.510179200 +0100
***************
*** 208,214 ****
    bool DoneWithCheck(const char** ptr, int d) {
      GOOGLE_DCHECK(*ptr);
      if (PROTOBUF_PREDICT_TRUE(*ptr < limit_end_)) return false;
!     int overrun = *ptr - buffer_end_;
      GOOGLE_DCHECK_LE(overrun, kSlopBytes);  // Guaranteed by parse loop.
      if (overrun ==
          limit_) {  //  No need to flip buffers if we ended on a limit.
--- 208,214 ----
    bool DoneWithCheck(const char** ptr, int d) {
      GOOGLE_DCHECK(*ptr);
      if (PROTOBUF_PREDICT_TRUE(*ptr < limit_end_)) return false;
!     size_t overrun = *ptr - buffer_end_;
      GOOGLE_DCHECK_LE(overrun, kSlopBytes);  // Guaranteed by parse loop.
      if (overrun ==
          limit_) {  //  No need to flip buffers if we ended on a limit.
***************
*** 217,223 ****
        if (overrun > 0 && next_chunk_ == nullptr) *ptr = nullptr;
        return true;
      }
!     auto res = DoneFallback(overrun, d);
      *ptr = res.first;
      return res.second;
    }
--- 217,223 ----
        if (overrun > 0 && next_chunk_ == nullptr) *ptr = nullptr;
        return true;
      }
!     auto res = DoneFallback(static_cast<int>(overrun), d);
      *ptr = res.first;
      return res.second;
    }
***************
*** 347,353 ****
    const char* AppendUntilEnd(const char* ptr, const A& append) {
      if (ptr - buffer_end_ > limit_) return nullptr;
      while (limit_ > kSlopBytes) {
!       int chunk_size = buffer_end_ + kSlopBytes - ptr;
        GOOGLE_DCHECK_GE(chunk_size, 0);
        append(ptr, chunk_size);
        ptr = Next();
--- 347,353 ----
    const char* AppendUntilEnd(const char* ptr, const A& append) {
      if (ptr - buffer_end_ > limit_) return nullptr;
      while (limit_ > kSlopBytes) {
!       size_t chunk_size = buffer_end_ + kSlopBytes - ptr;
        GOOGLE_DCHECK_GE(chunk_size, 0);
        append(ptr, chunk_size);
        ptr = Next();
***************
*** 428,434 ****
  template <uint32 tag>
  bool ExpectTag(const char* ptr) {
    if (tag < 128) {
!     return *ptr == tag;
    } else {
      static_assert(tag < 128 * 128, "We only expect tags for 1 or 2 bytes");
      char buf[2] = {static_cast<char>(tag | 0x80), static_cast<char>(tag >> 7)};
--- 428,434 ----
  template <uint32 tag>
  bool ExpectTag(const char* ptr) {
    if (tag < 128) {
!     return *ptr == static_cast<char>(tag);
    } else {
      static_assert(tag < 128 * 128, "We only expect tags for 1 or 2 bytes");
      char buf[2] = {static_cast<char>(tag | 0x80), static_cast<char>(tag >> 7)};

[gvollant]

@coryan @acozzette
hello, do you known if I need a specific procedure to get this pull request reviewed?

regards,gilles

[acozzette]

I believe this has to be a signed type because overrun can be negative. Maybe std::ptrdiff_t would be the right type.

[coryan]

Consider: auto overrun = *ptr - buffer_end_;

[gvollant]

finally, I made a new commit with
int overrun = static_cast<int>(*ptr - buffer_end_);

overrun is used for compare with limit_ (which is int) and as first argument of DoneFallback (which expect int).

[acozzette]

Thanks, @gvollant.