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.

15 files changed, 129 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()
+{
+
+}
diff --git a/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle-result.txt b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle-stderr.txt b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle-stderr.txt
new file mode 100644
index 0000000..a584d7d
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle-stderr.txt
@@ -0,0 +1,7 @@
+CMake Error in CMakeLists.txt:
+  The COMPILE_FEATURES property of target "empty1" was evaluated when
+  computing the link implementation, and the "CXX_STANDARD" was "98" for that
+  computation.  Computing the COMPILE_FEATURES based on the link
+  implementation resulted in a higher "CXX_STANDARD" "11".  This is not
+  permitted.  The COMPILE_FEATURES may not both depend on and be depended on
+  by the link implementation.
diff --git a/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle.cmake b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle.cmake
new file mode 100644
index 0000000..9d56bc0
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycle.cmake
@@ -0,0 +1,15 @@
+
+add_library(empty1 empty.cpp)
+
+add_library(empty2 INTERFACE)
+add_library(empty3 INTERFACE)
+target_compile_features(empty3 INTERFACE cxx_constexpr)
+
+target_link_libraries(empty1
+  # When starting, $<COMPILE_FEATURES:cxx_final> is '0', so 'freeze' the
+  # CXX_STANDARD at 98 during computation.
+  $<$<COMPILE_FEATURES:cxx_final>:empty2>
+  # This would add cxx_constexpr, but that would require CXX_STANDARD = 11,
+  # which is not allowed after freeze.  Report an error.
+  empty3
+)
diff --git a/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved-result.txt b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved-result.txt
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved-result.txt
@@ -0,0 +1 @@
+0
diff --git a/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved-stderr.txt b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved-stderr.txt
new file mode 100644
index 0000000..10f3293
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved-stderr.txt
@@ -0,0 +1 @@
+^$
diff --git a/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved.cmake b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved.cmake
new file mode 100644
index 0000000..0df548b
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/LinkImplementationFeatureCycleSolved.cmake
@@ -0,0 +1,14 @@
+
+add_library(empty1 empty.cpp)
+
+add_library(empty2 INTERFACE)
+add_library(empty3 INTERFACE)
+target_compile_features(empty3 INTERFACE cxx_constexpr)
+
+target_link_libraries(empty1
+  $<$<COMPILE_FEATURES:cxx_final>:empty2>
+  empty3
+)
+# This, or populating the COMPILE_FEATURES property with a feature in the
+# same standard as cxx_final, solves the cycle above.
+set_property(TARGET empty1 PROPERTY CXX_STANDARD 11)
diff --git a/Tests/RunCMake/CompileFeatures/NonValidTarget1-result.txt b/Tests/RunCMake/CompileFeatures/NonValidTarget1-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/NonValidTarget1-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/CompileFeatures/NonValidTarget1-stderr.txt b/Tests/RunCMake/CompileFeatures/NonValidTarget1-stderr.txt
new file mode 100644
index 0000000..7f3b43b
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/NonValidTarget1-stderr.txt
@@ -0,0 +1,9 @@
+CMake Error at NonValidTarget1.cmake:[0-9]+ \(add_custom_command\):
+  Error evaluating generator expression:
+
+    \$<COMPILE_FEATURES:cxx_final>
+
+  \$<COMPILE_FEATURE> may only be used with binary targets.  It may not be
+  used with add_custom_command or add_custom_target.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/CompileFeatures/NonValidTarget1.cmake b/Tests/RunCMake/CompileFeatures/NonValidTarget1.cmake
new file mode 100644
index 0000000..c6707c1
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/NonValidTarget1.cmake
@@ -0,0 +1,17 @@
+
+set(genexvar $<COMPILE_FEATURES:cxx_final>)
+
+if (HAVE_FINAL)
+  set(expected_result 1)
+else()
+  set(expected_result 0)
+endif()
+
+add_custom_command(OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/copied_file${HAVE_FINAL}.cpp"
+  COMMAND "${CMAKE_COMMAND}" -E copy "${CMAKE_CURRENT_SOURCE_DIR}/empty.cpp" "${CMAKE_CURRENT_BINARY_DIR}/copied_file${genexvar}.cpp"
+)
+
+add_library(empty "${CMAKE_CURRENT_BINARY_DIR}/copied_file${genexvar}.cpp")
+if (HAVE_FINAL)
+  target_compile_features(empty PRIVATE cxx_final)
+endif()
diff --git a/Tests/RunCMake/CompileFeatures/NonValidTarget2-result.txt b/Tests/RunCMake/CompileFeatures/NonValidTarget2-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/NonValidTarget2-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/CompileFeatures/NonValidTarget2-stderr.txt b/Tests/RunCMake/CompileFeatures/NonValidTarget2-stderr.txt
new file mode 100644
index 0000000..635150c
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/NonValidTarget2-stderr.txt
@@ -0,0 +1,9 @@
+CMake Error at NonValidTarget2.cmake:4 \(add_custom_target\):
+  Error evaluating generator expression:
+
+    \$<COMPILE_FEATURES:cxx_final>
+
+  \$<COMPILE_FEATURE> may only be used with binary targets.  It may not be
+  used with add_custom_command or add_custom_target.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)
diff --git a/Tests/RunCMake/CompileFeatures/NonValidTarget2.cmake b/Tests/RunCMake/CompileFeatures/NonValidTarget2.cmake
new file mode 100644
index 0000000..eb84692
--- /dev/null
+++ b/Tests/RunCMake/CompileFeatures/NonValidTarget2.cmake
@@ -0,0 +1,8 @@
+
+set(genexvar $<COMPILE_FEATURES:cxx_final>)
+
+add_custom_target(copy_target
+  COMMAND "${CMAKE_COMMAND}" -E copy "${CMAKE_CURRENT_SOURCE_DIR}/empty.cpp" "${CMAKE_CURRENT_BINARY_DIR}/copied_file${genexvar}.txt"
+)
+
+add_library(empty "${CMAKE_CURRENT_BINARY_DIR}/copied_file${genexvar}.cpp")
diff --git a/Tests/RunCMake/CompileFeatures/RunCMakeTest.cmake b/Tests/RunCMake/CompileFeatures/RunCMakeTest.cmake
index a23d44f..1892a5c 100644
--- a/Tests/RunCMake/CompileFeatures/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CompileFeatures/RunCMakeTest.cmake
@@ -26,6 +26,16 @@ endif()
 if (NOT CXX_FEATURES)
   run_cmake(NoSupportedCxxFeatures)
   run_cmake(NoSupportedCxxFeaturesGenex)
+else()
+  run_cmake(LinkImplementationFeatureCycle)
+  run_cmake(LinkImplementationFeatureCycleSolved)
+
+  if (";${CXX_FEATURES};" MATCHES ";cxx_final;")
+    set(RunCMake_TEST_OPTIONS "-DHAVE_FINAL=1")
+  endif()
+  run_cmake(NonValidTarget1)
+  run_cmake(NonValidTarget2)
+  unset(RunCMake_TEST_OPTIONS)
 endif()
 
 foreach(standard 98 11)