Switch to building the swift package and cocoa binaries as c++20

Author: tgoyne

CHANGELOG.md

@@ -20,7 +20,7 @@
 -----------
 
 ### Internals
-* None.
+* Switch to building the Swift package and Cocoa binaries as C++20 ([PR #7802](https://github.com/realm/realm-core/pull/7802)).
 
 ----------------------------------------------
 

CMakeLists.txt

@@ -34,7 +34,9 @@ endif()
 set(PROJECT_VERSION ${DEP_VERSION})
 
 # Project-wide build flags
-set(CMAKE_CXX_STANDARD 17)
+if (NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 17)
+endif()
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 

Package.swift

@@ -565,5 +565,5 @@ let package = Package(
                 .headerSearchPath("../"),
             ] + cxxSettings) as [CXXSetting]),
     ],
-    cxxLanguageStandard: .cxx17
+    cxxLanguageStandard: .cxx20
 )

tools/cmake/xcode.toolchain.cmake

@@ -31,3 +31,4 @@ set(CMAKE_XCODE_ATTRIBUTE_TVOS_DEPLOYMENT_TARGET "12.0")
 
 set(REALM_ENABLE_ASSERTIONS ON CACHE BOOL "Enable release assertions")
 set(REALM_XCODE_TOOLCHAIN TRUE)
+set(CMAKE_CXX_STANDARD 20)