[SYCL] Emit an error on attempt to compile in less than C++17 mode (#6678)

Author: romanovvlad

sycl/doc/PreprocessorMacros.md

@@ -34,10 +34,6 @@ This file describes macros that have effect on SYCL compiler and run-time.
   Disables all deprecation warnings in SYCL runtime headers, including SYCL
   1.2.1 deprecations.
 
-- **SYCL_DISABLE_CPP_VERSION_CHECK_WARNING**
-
-  Disables a message which warns about unsupported C++ version.
-
 - **SYCL_FALLBACK_ASSERT**
 
   Defining as non-zero enables the fallback assert feature even on devices

sycl/include/sycl/detail/defines_elementary.hpp

@@ -105,16 +105,5 @@
 #define __SYCL_WARNING(msg) __pragma(message(msg))
 #endif // __GNUC__
 
-#if !defined(SYCL_DISABLE_CPP_VERSION_CHECK_WARNING) && __cplusplus < 201703L
-
-#if defined(_MSC_VER) && !defined(__clang__)
-__SYCL_WARNING("DPCPP does not support C++ version earlier than C++17. Some "
-               "features might not be available.")
-#else
-// This is the only way to emit a warning from system headers using clang, it
-// cannot be wrapped by a macro(__pragma warning doesn't work in system
-// headers). The solution is borrowed from libcxx.
-#warning: DPCPP does not support C++ version earlier than C++17. Some features might not be available.
-#endif
-
-#endif
+static_assert(__cplusplus >= 201703L,
+              "DPCPP does not support C++ version earlier than C++17.");

sycl/test/basic_tests/stdcpp_compat.cpp

@@ -1,5 +1,4 @@
 // RUN: %clangxx -std=c++14 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify=expected,cxx14 %s -c -o %t.out
-// RUN: %clangxx -std=c++14 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out -DSYCL_DISABLE_CPP_VERSION_CHECK_WARNING=1
 // RUN: %clangxx -std=c++14 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify=cxx14,warning_extension,expected %s -c -o %t.out
 // RUN: %clangxx -std=c++17 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
 // RUN: %clangxx -std=c++20 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
@@ -10,13 +9,15 @@
 
 #include <sycl/sycl.hpp>
 
-// cxx14-warning@* {{DPCPP does not support C++ version earlier than C++17. Some features might not be available.}}
+// clang-format off
+// cxx14-error@* {{static assertion failed due to requirement '201402L >= 201703L'}}
 //
 // The next warning is not emitted in device compilation for some reason
 // warning_extension-warning@* 0-1 {{#warning is a C++2b extension}}
 //
 // The next warning is emitted for windows only
 // expected-warning@* 0-1 {{Alignment of class vec is not in accordance with SYCL specification requirements, a limitation of the MSVC compiler(Error C2719).Requested alignment applied, limited at 64.}}
+// clang-format on
 
 class KernelName1;