Tweak so that no configuration change is needed

... for existing integrations (like FB's buck integration) to keep compiling

CMakeLists.txt

@@ -512,18 +512,11 @@ include(CxxFlags)
 get_cxx_std_flags(CMAKE_REQUIRED_FLAGS)
 
 CHECK_CXX_SOURCE_COMPILES("
-template< typename F >
-int apply(F f) {
-  return f();
-}
-
 struct test {
   test() : value_(0) {}
 
   int lambda() {
-    return apply([=]() {
-      return value_;
-    });
+    return [=,this]() { return value_; }();
   }
 
   int value_;
@@ -533,17 +526,14 @@ int main() {
   test t;
   return t.lambda();
 }
-" HAVE_IMPLICIT_THIS_LAMBDA_CAPTURE
+" USE_EXPLICIT_CAPTURE_THIS
 )
 
 unset(CMAKE_REQUIRED_FLAGS)
 
-if(HAVE_IMPLICIT_THIS_LAMBDA_CAPTURE)
-  set(ROCKSDB_THIS_LAMBDA_CAPTURE "=")
-else()
-  set(ROCKSDB_THIS_LAMBDA_CAPTURE "=, this")
+if(USE_EXPLICIT_CAPTURE_THIS)
+  add_definitions(-DROCKSDB_EXPLICIT_CAPTURE_THIS)
 endif()
-add_definitions(-DROCKSDB_THIS_LAMBDA_CAPTURE=${ROCKSDB_THIS_LAMBDA_CAPTURE})
 
 
 include_directories(${PROJECT_SOURCE_DIR})

build_tools/build_detect_platform

@@ -702,12 +702,12 @@ EOF
 fi
 
 
-$CXX $PLATFORM_CXXFLAGS $COMMON_FLAGS -x c++ - -o /dev/null 2>/dev/null <<EOF
+$CXX $PLATFORM_CXXFLAGS $COMMON_FLAGS -Werror -x c++ - -o /dev/null 2>/dev/null <<EOF
 struct test {
   test() : value_(0) {}
-  
+
   int lambda() {
-    return [=]() { return value_; }();
+    return [=,this]() { return value_; }();
   }
 
   int value_;
@@ -719,9 +719,7 @@ int main() {
 }
 EOF
 if [ "$?" = 0 ]; then
-  COMMON_FLAGS="$COMMON_FLAGS -DROCKSDB_THIS_LAMBDA_CAPTURE=\"=\""
-else
-  COMMON_FLAGS="$COMMON_FLAGS -DROCKSDB_THIS_LAMBDA_CAPTURE=\"=, this\""
+  COMMON_FLAGS="$COMMON_FLAGS -DROCKSDB_EXPLICIT_CAPTURE_THIS"
 fi
 
 if [ "$FBCODE_BUILD" != "true" -a "$PLATFORM" = OS_LINUX ]; then

cmake/modules/CxxFlags.cmake

@@ -1,7 +1,7 @@
-macro(get_cxx_std_flags FLAGS_VARIABLE)
-  if( CMAKE_CXX_STANDARD_REQUIRED )
-    set(${FLAGS_VARIABLE} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION})
-  else()
-    set(${FLAGS_VARIABLE} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_EXTENSION_COMPILE_OPTION})
-  endif()
-endmacro()
+macro(get_cxx_std_flags FLAGS_VARIABLE)
+  if( CMAKE_CXX_STANDARD_REQUIRED )
+    set(${FLAGS_VARIABLE} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION})
+  else()
+    set(${FLAGS_VARIABLE} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_EXTENSION_COMPILE_OPTION})
+  endif()
+endmacro()

db/log_reader.cc

@@ -15,7 +15,7 @@
 #include "test_util/sync_point.h"
 #include "util/coding.h"
 #include "util/crc32c.h"
-#include "util/util.h"
+#include "port/lang.h"
 
 namespace ROCKSDB_NAMESPACE {
 namespace log {

db/memtable.cc

@@ -36,7 +36,7 @@
 #include "util/autovector.h"
 #include "util/coding.h"
 #include "util/mutexlock.h"
-#include "util/util.h"
+#include "port/lang.h"
 
 namespace ROCKSDB_NAMESPACE {
 

db/write_batch.cc

@@ -59,7 +59,7 @@
 #include "util/coding.h"
 #include "util/duplicate_detector.h"
 #include "util/string_util.h"
-#include "util/util.h"
+#include "port/lang.h"
 
 namespace ROCKSDB_NAMESPACE {
 

include/rocksdb/file_system.h

@@ -105,7 +105,7 @@ struct FileOptions : EnvOptions {
 
   FileOptions(const FileOptions& opts)
     : EnvOptions(opts), io_options(opts.io_options) {}
-  
+
   FileOptions& operator=(const FileOptions& opts) = default;
 };
 

memory/concurrent_arena.h

@@ -13,6 +13,7 @@
 #include <utility>
 #include "memory/allocator.h"
 #include "memory/arena.h"
+#include "port/lang.h"
 #include "port/likely.h"
 #include "util/core_local.h"
 #include "util/mutexlock.h"

util/util.h → port/lang.h

@@ -14,3 +14,10 @@
 #define FALLTHROUGH_INTENDED do {} while (0)
 #endif
 #endif
+
+#if defined(ROCKSDB_EXPLICIT_CAPTURE_THIS) || __cplusplus >= 202002L
+// C++20 deprecates implicit capture of 'this' in [=]
+#define ROCKSDB_THIS_LAMBDA_CAPTURE =, this
+#else
+#define ROCKSDB_THIS_LAMBDA_CAPTURE =
+#endif

table/block_based/block_based_table_builder.cc

@@ -21,6 +21,7 @@
 
 #include "db/dbformat.h"
 #include "index_builder.h"
+#include "port/lang.h"
 
 #include "rocksdb/cache.h"
 #include "rocksdb/comparator.h"

table/block_based/block_based_table_reader.cc

@@ -58,7 +58,7 @@
 #include "util/crc32c.h"
 #include "util/stop_watch.h"
 #include "util/string_util.h"
-#include "util/util.h"
+#include "port/lang.h"
 #include "util/xxhash.h"
 
 namespace ROCKSDB_NAMESPACE {

third-party/folly/folly/synchronization/Baton.h

@@ -16,6 +16,12 @@
 #include <folly/synchronization/WaitOptions.h>
 #include <folly/synchronization/detail/Spin.h>
 
+#ifdef ROCKSDB_EXPLICIT_CAPTURE_THIS
+#define ROCKSDB_THIS_LAMBDA_CAPTURE =,this
+#else
+#define ROCKSDB_THIS_LAMBDA_CAPTURE =
+#endif
+
 namespace folly {
 
 /// A Baton allows a thread to block once and be awoken. Captures a

util/crc32c.cc

@@ -16,7 +16,7 @@
 #include <wmmintrin.h>
 #endif
 #include "util/coding.h"
-#include "util/util.h"
+#include "port/lang.h"
 
 #include "util/crc32c_arm64.h"
 

util/hash.cc

@@ -10,7 +10,7 @@
 #include <string.h>
 #include "util/coding.h"
 #include "util/hash.h"
-#include "util/util.h"
+#include "port/lang.h"
 #include "util/xxhash.h"
 
 namespace ROCKSDB_NAMESPACE {

util/murmurhash.cc

@@ -10,7 +10,7 @@
   is under the MIT license.
 */
 #include "murmurhash.h"
-#include "util/util.h"
+#include "port/lang.h"
 
 #if defined(__x86_64__)
 

util/xxhash.cc

@@ -126,7 +126,7 @@ static void* XXH_memcpy(void* dest, const void* src, size_t size) { return memcp
 #include "xxhash.h"
 
 /* BEGIN RocksDB customizations */
-#include "util/util.h" /* for FALLTHROUGH_INTENDED, inserted as appropriate */
+#include "port/lang.h" /* for FALLTHROUGH_INTENDED, inserted as appropriate */
 /* END RocksDB customizations */
 
 /* *************************************