From 48d70a160418156e8ae912fe9cf74c9e589b9e37 Mon Sep 17 00:00:00 2001
From: "Kenneth Benzie (Benie)" <k.benzie83@gmail.com>
Date: Fri, 8 Jun 2018 10:45:19 +0100
Subject: [PATCH] Play nice with CMake add_subdirectory

Enable use of `tl::optional<T>` purely as a library with CMake's
`add_subdirectory`. The default configuration works are before.

* `OPTIONAL_ENABLE_TESTS` make building tests optional, enabled by default
* `OPTIONAL_ENABLE_DOCS` make building documentation optional, enabled by default
---
 CMakeLists.txt | 73 +++++++++++++++++++++++++++-----------------------
 1 file changed, 40 insertions(+), 33 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9bd2ff9..970a76c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,42 +2,49 @@ cmake_minimum_required(VERSION 3.0)
 
 project(optional)
 
-# Prepare "Catch" library for other executables
-set(CATCH_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/test)
-add_library(Catch INTERFACE)
-target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
-
-# Make test executable
-set(TEST_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/tests/main.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/noexcept.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/make_optional.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/in_place.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/relops.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/observers.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/extensions.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/constexpr.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/constructors.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/assignment.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/bases.cpp
-                 ${CMAKE_CURRENT_SOURCE_DIR}/tests/nullopt.cpp)
-
-add_executable(tests ${TEST_SOURCES})
+option(OPTIONAL_ENABLE_TESTS "Enable tests." ON)
+option(OPTIONAL_ENABLE_DOCS "Enable documentation." ON)
 
 add_library(optional INTERFACE)
-target_sources(optional INTERFACE ${CMAKE_SOURCE_DIR}/tl/optional.hpp)
-target_include_directories(optional INTERFACE ${CMAKE_SOURCE_DIR}/tl)
+target_sources(optional INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/tl/optional.hpp)
+target_include_directories(optional INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/tl)
 
-target_link_libraries(tests Catch optional)
+if(OPTIONAL_ENABLE_TESTS)
+  # Prepare "Catch" library for other executables
+  set(CATCH_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/test)
+  add_library(Catch INTERFACE)
+  target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
 
-set(CXXSTD 14 CACHE STRING "C++ standard to use, default C++14")
-set_property(TARGET tests PROPERTY CXX_STANDARD ${CXXSTD})
+  # Make test executable
+  set(TEST_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/tests/main.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/noexcept.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/make_optional.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/in_place.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/relops.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/observers.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/extensions.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/constexpr.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/constructors.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/assignment.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/bases.cpp
+                   ${CMAKE_CURRENT_SOURCE_DIR}/tests/nullopt.cpp)
 
-find_package(standardese) # find standardese after installation
+  add_executable(tests ${TEST_SOURCES})
 
-# generates a custom target that will run standardese to generate the documentation
-if (standardese_FOUND)
-standardese_generate(optional
-                     INCLUDE_DIRECTORY tl
-                     CONFIG ${CMAKE_SOURCE_DIR}/standardese.config
-                     INPUT tl/optional.hpp)
-endif ()
+  target_link_libraries(tests Catch optional)
+
+  set(CXXSTD 14 CACHE STRING "C++ standard to use, default C++14")
+  set_property(TARGET tests PROPERTY CXX_STANDARD ${CXXSTD})
+endif()
+
+if(OPTIONAL_ENABLE_DOCS)
+  find_package(standardese) # find standardese after installation
+
+  # generates a custom target that will run standardese to generate the documentation
+  if(standardese_FOUND)
+    standardese_generate(optional
+                         INCLUDE_DIRECTORY tl
+                         CONFIG ${CMAKE_CURRENT_SOURCE_DIR}/standardese.config
+                         INPUT tl/optional.hpp)
+  endif()
+endif()