Generate the c++xx standard features instead of skipping them

The features are reused in qtdeclarative (and maybe somewhere else
too), so they should be present. We can still map the conditions
to proper CMake compile feature tests.

Change-Id: I4d307d29d4d293cc23ab005b195ea346087c7162
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>
Reviewed-by: Qt CMake Build Bot
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

configure.cmake

@@ -15,6 +15,27 @@ qt_find_package(Libudev PROVIDED_TARGETS PkgConfig::Libudev)
 
 #### Tests
 
+# c++2a
+qt_config_compile_test(cxx2a
+    LABEL "C++2a support"
+"#if __cplusplus > 201703L
+// Compiler claims to support experimental C++2a, trust it
+#else
+#  error __cplusplus must be > 201703L (the value for C++17)
+#endif
+
+
+int main(int argc, char **argv)
+{
+    (void)argc; (void)argv;
+    /* BEGIN TEST: */
+
+    /* END TEST: */
+    return 0;
+}
+"# FIXME: qmake: CONFIG += c++11 c++14 c++1z c++2a
+)
+
 # precompile_header
 qt_config_compile_test(precompile_header
     LABEL "precompiled header support"
@@ -245,9 +266,25 @@ qt_feature("framework" PUBLIC
 qt_feature_definition("framework" "QT_MAC_FRAMEWORK_BUILD")
 qt_feature("largefile"
     LABEL "Large file support"
-    CONDITION NOT ANDROID AND NOT INTEGRITY AND NOT WINRT
+    CONDITION NOT ANDROID AND NOT INTEGRITY AND NOT WINRT AND NOT rtems
 )
 qt_feature_definition("largefile" "QT_LARGEFILE_SUPPORT" VALUE "64")
+qt_feature("cxx11" PUBLIC
+    LABEL "C++11"
+)
+qt_feature("cxx14" PUBLIC
+    LABEL "C++14"
+    CONDITION QT_FEATURE_cxx11 AND $<COMPILE_FEATURES:cxx_std_14>
+)
+qt_feature("cxx1z" PUBLIC
+    LABEL "C++17"
+    CONDITION QT_FEATURE_cxx14 AND $<COMPILE_FEATURES:cxx_std_17>
+)
+qt_feature("cxx2a" PUBLIC
+    LABEL "C++2a"
+    AUTODETECT OFF
+    CONDITION QT_FEATURE_cxx1z AND TEST_cxx2a
+)
 qt_feature("reduce_exports" PRIVATE
     LABEL "Reduce amount of exported symbols"
     CONDITION NOT WIN32 AND CMAKE_CXX_COMPILE_OPTIONS_VISIBILITY

util/cmake/configurejson2cmake.py

@@ -615,13 +615,7 @@ def parseFeature(ctx, feature, data, cm_fh):
         'alloc_malloc_h': None,
         'alloc_stdlib_h': None,
         'build_all': None,
-        'c++11': None,   # C and C++ versions
         'c11': None,
-        'c++14': None,
-        'c++1y': None,
-        'c++1z': None,
-        # FIXME: used in qtdeclarative, drop when we require C++14
-        'cxx14_make_unique': None,
         'c89': None,
         'c99': None,
         'ccache': None,

util/cmake/helper.py

@@ -302,7 +302,10 @@ def find_library_info_for_target(targetName: str) -> typing.Optional[LibraryMapp
 
 
 def featureName(input: str) -> str:
-    return re.sub(r'[^a-zA-Z0-9_]', '_', input)
+    replacement_char = '_'
+    if input.startswith('c++'):
+        replacement_char = 'x'
+    return re.sub(r'[^a-zA-Z0-9_]', replacement_char, input)
 
 
 def map_qt_library(lib: str) -> str: