[cmake] Adding options for INSTALL and TEST (#964)

* [cmake] Adding GSL_INSTALL option

Not all consumers of GSL automatically want to have this install logic.

It's good practice to gate install logic behind an option.
For an example look at magic_enum:
https://github.com/Neargye/magic_enum/blob/master/CMakeLists.txt

If the client wants to install GSL they still can. But they should ask
for it by overriding GSL_INSTALL.

* Update cmake/guidelineSupportLibrary.cmake

added nl@eof

* Update CMakeLists.txt

* Update CMakeLists.txt

Co-authored-by: Juan Ramos <juanr0911@gmail.com>
Co-authored-by: Jordan Maples [MSFT] <49793787+JordanMaples@users.noreply.github.com>

3 files changed, 74 insertions, 48 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7ad13f7..bb66444 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,10 +3,10 @@ cmake_minimum_required(VERSION 3.1.3...3.16)
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/")
 include(guidelineSupportLibrary)
 
-project(GSL VERSION 3.1.0 LANGUAGES CXX)
-
-# Use GNUInstallDirs to provide the right locations on all platforms
-include(GNUInstallDirs)
+project(GSL
+    VERSION 3.1.0
+    LANGUAGES CXX
+)
 
 # Creates a library GSL which is an interface (header files only)
 add_library(GSL INTERFACE)
@@ -25,6 +25,10 @@ if (CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
     set(GSL_STANDALONE_PROJECT ON)
 endif()
 
+### Project options
+option(GSL_INSTALL "Generate and install GSL target" ${GSL_STANDALONE_PROJECT})
+option(GSL_TEST "Build and perform GSL tests" ${GSL_STANDALONE_PROJECT})
+
 # This GSL implementation generally assumes a platform that implements C++14 support.
 set(gsl_min_cxx_standard "14")
 
@@ -34,58 +38,21 @@ else()
     gsl_client_set_cxx_standard(${gsl_min_cxx_standard})
 endif()
 
-# add include folders to the library and targets that consume it
-# the SYSTEM keyword suppresses warnings for users of the library
-if(GSL_STANDALONE_PROJECT)
-    target_include_directories(GSL INTERFACE
-        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
-    )
-else()
-    target_include_directories(GSL SYSTEM INTERFACE
-        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
-    )
-endif()
+# Setup the include directory
+gsl_target_include_directories(${GSL_STANDALONE_PROJECT})
 
 # Add natvis file
 gsl_add_native_visualizer_support()
 
-install(TARGETS GSL EXPORT Microsoft.GSLConfig)
-install(
-    DIRECTORY include/gsl
-    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
-)
-# Make library importable by other projects
-install(EXPORT Microsoft.GSLConfig NAMESPACE Microsoft.GSL:: DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
-export(TARGETS GSL NAMESPACE Microsoft.GSL:: FILE Microsoft.GSLConfig.cmake)
+# Add packaging support
+gsl_create_packaging_file()
 
-# Add find_package() versioning support. The version for
-# generated Microsoft.GSLConfigVersion.cmake will be used from
-# last project() command. The version's compatibility is set between all
-# minor versions (as it was in prev. GSL releases).
-include(CMakePackageConfigHelpers)
-if(${CMAKE_VERSION} VERSION_LESS "3.14.0")
-    write_basic_package_version_file(
-        ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake
-        COMPATIBILITY SameMajorVersion
-    )
-else()
-    write_basic_package_version_file(
-        ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake
-        COMPATIBILITY SameMajorVersion
-        ARCH_INDEPENDENT
-    )
+if (GSL_INSTALL)
+    # Setup install/export logic
+    gsl_install_logic()
 endif()
-install(FILES ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
 
-option(GSL_TEST "Generate tests." ${GSL_STANDALONE_PROJECT})
 if (GSL_TEST)
     enable_testing()
-    if(IOS)
-        add_compile_definitions(
-            GTEST_HAS_DEATH_TEST=1
-        )
-    endif()
     add_subdirectory(tests)
 endif()
diff --git a/cmake/guidelineSupportLibrary.cmake b/cmake/guidelineSupportLibrary.cmake
index 39d8920..2e72100 100644
--- a/cmake/guidelineSupportLibrary.cmake
+++ b/cmake/guidelineSupportLibrary.cmake
@@ -9,6 +9,9 @@ if (DEFINED guideline_support_library_include_guard)
 endif()
 set(guideline_support_library_include_guard ON)
 
+# Neccessary for 'write_basic_package_version_file'
+include(CMakePackageConfigHelpers)
+
 function(gsl_set_default_cxx_standard min_cxx_standard)
     set(GSL_CXX_STANDARD "${min_cxx_standard}" CACHE STRING "Use c++ standard")
 
@@ -75,3 +78,55 @@ function(gsl_add_native_visualizer_support)
         endif()
     endif()
 endfunction()
+
+function(gsl_target_include_directories is_standalone)
+    # Add include folders to the library and targets that consume it
+    # the SYSTEM keyword suppresses warnings for users of the library
+    if(${is_standalone})
+        target_include_directories(GSL INTERFACE
+            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+            $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+        )
+    else()
+        target_include_directories(GSL SYSTEM INTERFACE
+            $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+            $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+        )
+    endif()
+endfunction()
+
+function(gsl_install_logic)
+    # Use GNUInstallDirs to provide the right locations on all platforms
+    # NOTE: Including GNUInstallDirs automatically executes logic
+    include(GNUInstallDirs)
+
+    install(TARGETS GSL EXPORT Microsoft.GSLConfig)
+    install(
+        DIRECTORY include/gsl
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    )
+    # Make library importable by other projects
+    install(EXPORT Microsoft.GSLConfig NAMESPACE Microsoft.GSL:: DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
+    export(TARGETS GSL NAMESPACE Microsoft.GSL:: FILE Microsoft.GSLConfig.cmake)
+
+    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/Microsoft.GSL)
+endfunction()
+
+# Add find_package() versioning support. The version for
+# generated Microsoft.GSLConfigVersion.cmake will be used from
+# last project() command. The version's compatibility is set between all
+# minor versions (as it was in prev. GSL releases).
+function(gsl_create_packaging_file)
+    if(${CMAKE_VERSION} VERSION_LESS "3.14.0")
+        write_basic_package_version_file(
+            ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake
+            COMPATIBILITY SameMajorVersion
+        )
+    else()
+        write_basic_package_version_file(
+            ${CMAKE_CURRENT_BINARY_DIR}/Microsoft.GSLConfigVersion.cmake
+            COMPATIBILITY SameMajorVersion
+            ARCH_INDEPENDENT
+        )
+    endif()
+endfunction()
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 2e7c2dc..1c7b03e 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -10,6 +10,10 @@ find_package(Git REQUIRED QUIET)
 # will make visual studio generated project group files
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
+if(IOS)
+  add_compile_definitions(GTEST_HAS_DEATH_TEST=1)
+endif()
+
 pkg_search_module(GTestMain gtest_main)
 if (NOT GTestMain_FOUND)
     configure_file(CMakeLists.txt.in googletest-download/CMakeLists.txt)