Initial work on targets discovery with global var

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+project(toplevel LANGUAGES C)
+
+add_subdirectory(libraries)
+
+set(ALL_MY_PROJECT_TARGETS "" CACHE INTERNAL "Global list")
+
+# Function to recursively collect all targets
+function(get_all_project_targets _target_list_var _current_dir)
+    # Get targets defined directly in the current directory
+    get_property(_targets_in_dir DIRECTORY "${_current_dir}" PROPERTY BUILDSYSTEM_TARGETS)
+	message("_targets_in_dir: ${_targets_in_dir}")
+	list(APPEND _ALL_MY_PROJECT_TARGETS ${ALL_MY_PROJECT_TARGETS} ${_targets_in_dir})
+	set(ALL_MY_PROJECT_TARGETS ${_ALL_MY_PROJECT_TARGETS} "" CACHE INTERNAL "")
+	message("ALL_MY_PROJECT_TARGETS: ${ALL_MY_PROJECT_TARGETS}")
+
+    # Get subdirectories of the current directory
+    get_property(_subdirs DIRECTORY "${_current_dir}" PROPERTY SUBDIRECTORIES)
+    foreach(_subdir IN LISTS _subdirs)
+        # Recursively call for each subdirectory
+		message("_subdir: ${_subdir}")
+        get_all_project_targets(${_target_list_var} "${_subdir}")
+    endforeach()
+endfunction()
+
+# Call the function from the top-level CMakeLists.txt
+get_all_project_targets(ALL_MY_PROJECT_TARGETS "${CMAKE_CURRENT_SOURCE_DIR}")
+
+# Print the list of all targets
+message("All CMake Targets in this project:")
+foreach(target_name IN LISTS ALL_MY_PROJECT_TARGETS)
+    message("- ${target_name}")
+endforeach()
+
+# Do stuff
+add_executable(${PROJECT_NAME}-exe main.c)
+target_link_libraries(${PROJECT_NAME}-exe library_a-lib library_b-lib)

Makefile

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+run: build
+	cmake --build build
+build:
+	cmake -S . -B $@
+clean:
+	rm -Rf build

libraries/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+
+add_subdirectory(library_a)
+add_subdirectory(library_b)

libraries/library_a/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+project(library_a LANGUAGES C)
+
+add_library(${PROJECT_NAME}-lib OBJECT library_a.c)

libraries/library_a/library_a.c

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+#include <stdio.h>
+int library_a(void)
+{
+	printf("%s\n", __func__);
+	return 0;
+}

libraries/library_b/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+project(library_b LANGUAGES C)
+
+add_library(${PROJECT_NAME}-lib OBJECT library_b.c)

libraries/library_b/library_b.c

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+#include <stdio.h>
+
+int library_b(void)
+{
+	printf("%s\n", __func__);
+	return 0;
+}

main.c

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+#include <stdio.h>
+
+int library_a(void);
+int library_b(void);
+
+int main(void)
+{
+	printf("%s\n", __func__);
+	library_a();
+	library_b();
+	return 0;
+}