Features: Add COMPILE_FEATURES generator expression.

Allow setting build properties based on the features available
for a target.  The availability of features is determined at
generate-time by evaluating the link implementation.

Ensure that the <LANG>_STANDARD determined while evaluating
COMPILE_FEATURES in the link implementation is not lower than that
provided by the INTERFACE of the link implementation.  This is
similar to handling of transitive properties such as
POSITION_INDEPENDENT_CODE.

2 files changed, 35 insertions, 0 deletions

diff --git a/Tests/CompileFeatures/CMakeLists.txt b/Tests/CompileFeatures/CMakeLists.txt
index 0e1e6c9..7a8a975 100644
--- a/Tests/CompileFeatures/CMakeLists.txt
+++ b/Tests/CompileFeatures/CMakeLists.txt
@@ -83,3 +83,17 @@ set_property(TARGET iface
 )
 add_executable(IfaceCompileFeatures main.cpp)
 target_link_libraries(IfaceCompileFeatures iface)
+
+add_executable(CompileFeaturesGenex genex_test.cpp)
+set_property(TARGET CompileFeaturesGenex PROPERTY CXX_STANDARD 11)
+target_compile_definitions(CompileFeaturesGenex PRIVATE HAVE_OVERRIDE_CONTROL=$<COMPILE_FEATURES:cxx_final,cxx_override>)
+
+add_executable(CompileFeaturesGenex2 genex_test.cpp)
+target_compile_features(CompileFeaturesGenex2 PRIVATE cxx_constexpr)
+target_compile_definitions(CompileFeaturesGenex2 PRIVATE HAVE_OVERRIDE_CONTROL=$<COMPILE_FEATURES:cxx_final,cxx_override>)
+
+add_library(noexcept_iface INTERFACE)
+target_compile_features(noexcept_iface INTERFACE cxx_noexcept)
+add_executable(CompileFeaturesGenex3 genex_test.cpp)
+target_link_libraries(CompileFeaturesGenex3 PRIVATE noexcept_iface)
+target_compile_definitions(CompileFeaturesGenex3 PRIVATE HAVE_OVERRIDE_CONTROL=$<COMPILE_FEATURES:cxx_final,cxx_override>)
diff --git a/Tests/CompileFeatures/genex_test.cpp b/Tests/CompileFeatures/genex_test.cpp
new file mode 100644
index 0000000..ca38883
--- /dev/null
+++ b/Tests/CompileFeatures/genex_test.cpp
@@ -0,0 +1,21 @@
+
+#if !HAVE_OVERRIDE_CONTROL
+#error "Expect override control feature"
+#else
+
+struct A
+{
+  virtual int getA() { return 7; }
+};
+
+struct B final : A
+{
+  int getA() override { return 42; }
+};
+
+#endif
+
+int main()
+{
+
+}