Fix wasm build. (#11708)

Author: trivialfis

CMakeLists.txt

@@ -253,7 +253,9 @@ if(FORCE_COLORED_OUTPUT AND (CMAKE_GENERATOR STREQUAL "Ninja") AND
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fdiagnostics-color=always")
 endif()
 
-find_package(Threads REQUIRED)
+if(NOT (CMAKE_SYSTEM_NAME STREQUAL "Emscripten"))
+  find_package(Threads REQUIRED)
+endif()
 
 # -- OpenMP
 include(cmake/FindOpenMPMacOS.cmake)

cmake/Utils.cmake

@@ -261,10 +261,12 @@ endmacro()
 
 # handles dependencies
 macro(xgboost_target_link_libraries target)
-  if(BUILD_STATIC_LIB)
-    target_link_libraries(${target} PUBLIC Threads::Threads ${CMAKE_THREAD_LIBS_INIT})
-  else()
-    target_link_libraries(${target} PRIVATE Threads::Threads ${CMAKE_THREAD_LIBS_INIT})
+  if(NOT (CMAKE_SYSTEM_NAME STREQUAL "Emscripten"))
+    if(BUILD_STATIC_LIB)
+      target_link_libraries(${target} PUBLIC Threads::Threads ${CMAKE_THREAD_LIBS_INIT})
+    else()
+      target_link_libraries(${target} PRIVATE Threads::Threads ${CMAKE_THREAD_LIBS_INIT})
+    endif()
   endif()
 
   if(USE_OPENMP)

src/c_api/c_api.cc

@@ -1579,7 +1579,9 @@ XGB_DLL int XGBoosterLoadModelFromBuffer(BoosterHandle handle, const void *buf,
   API_BEGIN();
   CHECK_HANDLE();
   xgboost_CHECK_C_ARG_PTR(buf);
-  auto buffer = common::Span<char const>{static_cast<char const *>(buf), len};
+  using CharT = std::add_const_t<char>;
+  using IdxType = common::Span<CharT>::index_type;
+  auto buffer = common::Span{static_cast<CharT *>(buf), static_cast<IdxType>(len)};
   // Don't warn, we have to guess the format with buffer input.
   auto in = DispatchModelType(buffer, "", false);
   common::MemoryFixSizeBuffer fs((void *)buf, len);  // NOLINT(*)

src/common/threading_utils.h

@@ -267,7 +267,7 @@ void ParallelFor1d(Index size, std::int32_t n_threads, Func&& fn) {
   static_assert(std::is_void_v<std::invoke_result_t<Func, common::Range1d>>);
   auto const n_blocks = DivRoundUp(size, kBlockOfRowsSize);
   common::ParallelFor(n_blocks, n_threads, [&](auto block_id) {
-    auto const block_beg = block_id * kBlockOfRowsSize;
+    std::size_t const block_beg = block_id * kBlockOfRowsSize;
     auto const block_size = std::min(static_cast<std::size_t>(size - block_beg), kBlockOfRowsSize);
     fn(common::Range1d{block_beg, block_beg + block_size});
   });