Add a variable to specify language-wide system include directories

Create a `CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES` variable to specify
system include directories for for `<LANG>` compiler command lines.
This plays a role for include directories as the existing
`CMAKE_<LANG>_STANDARD_LIBRARIES` variable does for link libraries.

10 files changed, 66 insertions, 0 deletions

diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index 925b70c..b8c8bea 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -365,6 +365,7 @@ Variables for Languages
    /variable/CMAKE_LANG_SIMULATE_VERSION
    /variable/CMAKE_LANG_SIZEOF_DATA_PTR
    /variable/CMAKE_LANG_SOURCE_FILE_EXTENSIONS
+   /variable/CMAKE_LANG_STANDARD_INCLUDE_DIRECTORIES
    /variable/CMAKE_LANG_STANDARD_LIBRARIES
    /variable/CMAKE_USER_MAKE_RULES_OVERRIDE_LANG
 
diff --git a/Help/release/dev/standard-include-directories.rst b/Help/release/dev/standard-include-directories.rst
new file mode 100644
index 0000000..a03d7db
--- /dev/null
+++ b/Help/release/dev/standard-include-directories.rst
@@ -0,0 +1,6 @@
+standard-include-directories
+----------------------------
+
+* A :variable:`CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES` variable was
+  added for use by toolchain files to specify system include directories
+  to be appended to all compiler command lines.
diff --git a/Help/variable/CMAKE_LANG_STANDARD_INCLUDE_DIRECTORIES.rst b/Help/variable/CMAKE_LANG_STANDARD_INCLUDE_DIRECTORIES.rst
new file mode 100644
index 0000000..c8e3d57
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_STANDARD_INCLUDE_DIRECTORIES.rst
@@ -0,0 +1,14 @@
+CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES
+-----------------------------------------
+
+Include directories to be used for every source file compiled with
+the ``<LANG>`` compiler.  This is meant for specification of system
+include directories needed by the language for the current platform.
+The directories always appear at the end of the include path passed
+to the compiler.
+
+This variable should not be set by project code.  It is meant to be set by
+CMake's platform information modules for the current toolchain, or by a
+toolchain file when used with :variable:`CMAKE_TOOLCHAIN_FILE`.
+
+See also :variable:`CMAKE_<LANG>_STANDARD_LIBRARIES`.
diff --git a/Help/variable/CMAKE_LANG_STANDARD_LIBRARIES.rst b/Help/variable/CMAKE_LANG_STANDARD_LIBRARIES.rst
index ad3b911..ba6df93 100644
--- a/Help/variable/CMAKE_LANG_STANDARD_LIBRARIES.rst
+++ b/Help/variable/CMAKE_LANG_STANDARD_LIBRARIES.rst
@@ -8,3 +8,5 @@ libraries needed by the language for the current platform.
 This variable should not be set by project code.  It is meant to be set by
 CMake's platform information modules for the current toolchain, or by a
 toolchain file when used with :variable:`CMAKE_TOOLCHAIN_FILE`.
+
+See also :variable:`CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES`.
diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index 31fff9f..8859172 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -2415,6 +2415,18 @@ std::vector<std::string> cmGeneratorTarget::GetIncludeDirectories(
 
   cmDeleteAll(linkInterfaceIncludeDirectoriesEntries);
 
+  // Add standard include directories for this language.
+  std::string const standardIncludesVar =
+    "CMAKE_" + lang + "_STANDARD_INCLUDE_DIRECTORIES";
+  std::string const standardIncludes =
+    this->Makefile->GetSafeDefinition(standardIncludesVar);
+  std::vector<std::string>::size_type const before = includes.size();
+  cmSystemTools::ExpandListArgument(standardIncludes, includes);
+  for (std::vector<std::string>::iterator i = includes.begin() + before;
+       i != includes.end(); ++i) {
+    cmSystemTools::ConvertToUnixSlashes(*i);
+  }
+
   return includes;
 }
 
diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index 3f4c22f..ea2842f 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -1385,6 +1385,9 @@ cmGlobalGenerator::CreateQtAutoGeneratorsTargets()
 
 void cmGlobalGenerator::FinalizeTargetCompileInfo()
 {
+  std::vector<std::string> const langs =
+    this->CMakeInstance->GetState()->GetEnabledLanguages();
+
   // Construct per-target generator information.
   for (unsigned int i = 0; i < this->Makefiles.size(); ++i) {
     cmMakefile* mf = this->Makefiles[i];
@@ -1429,6 +1432,23 @@ void cmGlobalGenerator::FinalizeTargetCompileInfo()
         }
       }
     }
+
+    // The standard include directories for each language
+    // should be treated as system include directories.
+    std::set<std::string> standardIncludesSet;
+    for (std::vector<std::string>::const_iterator li = langs.begin();
+         li != langs.end(); ++li) {
+      std::string const standardIncludesVar =
+        "CMAKE_" + *li + "_STANDARD_INCLUDE_DIRECTORIES";
+      std::string const standardIncludesStr =
+        mf->GetSafeDefinition(standardIncludesVar);
+      std::vector<std::string> standardIncludesVec;
+      cmSystemTools::ExpandListArgument(standardIncludesStr,
+                                        standardIncludesVec);
+      standardIncludesSet.insert(standardIncludesVec.begin(),
+                                 standardIncludesVec.end());
+    }
+    mf->AddSystemIncludeDirectories(standardIncludesSet);
   }
 }
 
diff --git a/Tests/IncludeDirectories/CMakeLists.txt b/Tests/IncludeDirectories/CMakeLists.txt
index 9ee1957..523c4f7 100644
--- a/Tests/IncludeDirectories/CMakeLists.txt
+++ b/Tests/IncludeDirectories/CMakeLists.txt
@@ -63,6 +63,7 @@ else()
     PROPERTIES COMPILE_FLAGS "-ITarProp")
 endif()
 
+add_subdirectory(StandardIncludeDirectories)
 add_subdirectory(TargetIncludeDirectories)
 
 set_property(DIRECTORY PROPERTY INCLUDE_DIRECTORIES "${CMAKE_BINARY_DIR}")
diff --git a/Tests/IncludeDirectories/StandardIncludeDirectories/CMakeLists.txt b/Tests/IncludeDirectories/StandardIncludeDirectories/CMakeLists.txt
new file mode 100644
index 0000000..dcbc566
--- /dev/null
+++ b/Tests/IncludeDirectories/StandardIncludeDirectories/CMakeLists.txt
@@ -0,0 +1,5 @@
+# Normally this variable should be set by a platform information module or
+# a toolchain file, but for purposes of this test we simply set it here.
+set(CMAKE_C_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_SOURCE_DIR}/StdDir)
+
+add_executable(StandardIncludeDirectories main.c)
diff --git a/Tests/IncludeDirectories/StandardIncludeDirectories/StdDir/StdIncDir.h b/Tests/IncludeDirectories/StandardIncludeDirectories/StdDir/StdIncDir.h
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/Tests/IncludeDirectories/StandardIncludeDirectories/StdDir/StdIncDir.h
diff --git a/Tests/IncludeDirectories/StandardIncludeDirectories/main.c b/Tests/IncludeDirectories/StandardIncludeDirectories/main.c
new file mode 100644
index 0000000..edfe9ce
--- /dev/null
+++ b/Tests/IncludeDirectories/StandardIncludeDirectories/main.c
@@ -0,0 +1,5 @@
+#include "StdIncDir.h"
+int main()
+{
+  return 0;
+}