Support add_subdirectory()

1. Update the main CMakeLists.txt
2. Add test project

.github/workflows/build.yml

@@ -48,6 +48,12 @@ jobs:
             cmake --build build/papilio_test_install
             build/papilio_test_install/papilio_test_install
 
+        - name: Test add_subdirectory
+          run: |
+            cmake -GNinja -S test/test_subdir/ -B build/papilio_test_subdir -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=g++-12
+            cmake --build build/papilio_test_subdir
+            build/papilio_test_subdir/papilio_test_subdir
+
     Clang:
         runs-on: ubuntu-22.04
         strategy:

CMakeLists.txt

@@ -38,13 +38,16 @@ endif()
 include(GNUInstallDirs)
 
 add_library(papilio ${papilio_src})
-target_sources(papilio PUBLIC "$<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/natvis/papilio.natvis>")
-target_sources(papilio PUBLIC "$<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/cpp.hint>")
+target_sources(papilio PUBLIC "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/natvis/papilio.natvis>")
+target_sources(papilio PUBLIC "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/cpp.hint>")
 target_include_directories(papilio PUBLIC
-    $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/include>
+    $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
     $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
 )
 
+# Add an ALIAS target for using the library by add_subdirectory()
+add_library(papilio::papilio ALIAS papilio)
+
 # Enable warnings for development
 target_compile_options(papilio PRIVATE
     $<$<CXX_COMPILER_ID:MSVC>:/W4 /WX>

test/test_subdir/CMakeLists.txt

@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.20)
+
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED)
+
+project(papilio_test_subdir LANGUAGES CXX)
+
+add_subdirectory(
+    ../..
+    # Adding a parent directory as a subdirectory needs to specify its binary_dir
+    ${PROJECT_BINARY_DIR}/papilio
+)
+
+add_executable(papilio_test_subdir "test_subdir.cpp")
+target_link_libraries(papilio_test_subdir PRIVATE papilio::papilio)

test/test_subdir/test_subdir.cpp

@@ -0,0 +1,10 @@
+#include <papilio/papilio.hpp>
+
+int main()
+{
+    papilio::println("papilio as submodule");
+    papilio::println();
+    papilio::println("{} {} {}", "hello", 42, 3.14f);
+
+    return 0;
+}