Introduce build-time generated config.hpp file

Both meson and CMake build detect support for std::optional<T> or its
experimental equivalent.

5 files changed, 41 insertions, 4 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea07846..73d9df2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,7 +6,7 @@
 # The meson/ninja build should be preferred in all other cases.
 #
 cmake_minimum_required(VERSION 3.10)
-project(libdjinterop VERSION 0.11.0)
+project(libdjinterop VERSION 0.12.0)
 
 # Require C++17
 set(CMAKE_CXX_STANDARD 17)
@@ -18,6 +18,14 @@ find_package(SQLite3 3.11.0 REQUIRED)
 # Require zlib >= 1.2.8
 find_package(ZLIB 1.2.8 REQUIRED)
 
+# Generate config.hpp based on build-time environment.
+include(CheckIncludeFileCXX)
+CHECK_INCLUDE_FILE_CXX(optional DJINTEROP_STD_OPTIONAL)
+CHECK_INCLUDE_FILE_CXX(experimental/optional DJINTEROP_STD_EXPERIMENTAL_OPTIONAL)
+configure_file(
+    include/djinterop/config.hpp.in
+    include/djinterop/config.hpp)
+
 add_library(
     djinterop
     src/djinterop/enginelibrary/el_crate_impl.cpp
@@ -50,6 +58,7 @@ target_include_directories(
     ${SQLite3_INCLUDE_DIRS}
     ${ZLIB_INCLUDE_DIRS}
     ext/sqlite_modern_cpp
+    ${CMAKE_CURRENT_BINARY_DIR}/include
     include src)
 
 target_link_libraries(
@@ -60,7 +69,7 @@ target_link_libraries(
 install(TARGETS djinterop DESTINATION lib)
 install(FILES
     include/djinterop/album_art.hpp
-    include/djinterop/config.hpp
+    ${CMAKE_CURRENT_BINARY_DIR}/include/djinterop/config.hpp
     include/djinterop/crate.hpp
     include/djinterop/database.hpp
     include/djinterop/djinterop.hpp
diff --git a/include/djinterop/config.hpp b/include/djinterop/config.hpp.in
index 97260cc..b558501 100644
--- a/include/djinterop/config.hpp
+++ b/include/djinterop/config.hpp.in
@@ -46,4 +46,10 @@
 #endif  // DJINTEROP_SOURCE
 #define DJINTEROP_LOCAL DJINTEROP_SYMBOL_LOCAL
 
+// Symbols defined after this point represent the environment at the time
+// that this library was built.  The environment when this library is used must
+// be compatible in order to use the library successfully.
+#cmakedefine DJINTEROP_STD_OPTIONAL
+#cmakedefine DJINTEROP_STD_EXPERIMENTAL_OPTIONAL
+
 #endif  // DJINTEROP_CONFIG_HPP
diff --git a/include/djinterop/meson.build b/include/djinterop/meson.build
new file mode 100644
index 0000000..c43a0b2
--- /dev/null
+++ b/include/djinterop/meson.build
@@ -0,0 +1,20 @@
+# Generate config file based on build-time feature detection.
+# Note that most build configuration for public headers is handled in the
+# parent build file; this file exists solely because the `output` parameter
+# of configure_file() does not, at the time of writing (meson 0.55.0), support
+# writing the output file to a different directory.
+conf_data = configuration_data()
+if cpp_compiler.has_header('optional')
+    conf_data.set10('DJINTEROP_STD_OPTIONAL', true)
+endif
+if cpp_compiler.has_header('experimental/optional')
+    conf_data.set10('DJINTEROP_STD_EXPERIMENTAL_OPTIONAL', true)
+endif
+configure_file(
+    input: 'config.hpp.in',
+    output: 'config.hpp',
+    configuration: conf_data,
+    format: 'cmake',
+    install_dir: get_option('includedir') + '/djinterop'
+)
+
diff --git a/include/meson.build b/include/meson.build
index ee89840..f43c8e8 100644
--- a/include/meson.build
+++ b/include/meson.build
@@ -1,6 +1,8 @@
+# Used only to generate config.hpp in the nested include dir.
+subdir('djinterop')
+
 djinterop_header_files = [
     'djinterop/album_art.hpp',
-    'djinterop/config.hpp',
     'djinterop/crate.hpp',
     'djinterop/database.hpp',
     'djinterop/djinterop.hpp',
diff --git a/meson.build b/meson.build
index e34ffcb..575e12f 100644
--- a/meson.build
+++ b/meson.build
@@ -1,7 +1,7 @@
 project(
     'djinterop',
     'cpp', 'c',
-    version: '0.11.0',
+    version: '0.12.0',
     license: 'LGPL-3.0',
     default_options: ['cpp_std=c++17', 'default_library=both'])