♻️ Refactor CMake structure and replace submodules with FetchContent

.github/codecov.yml

@@ -1,5 +1,4 @@
 ignore:
-  - "extern/**/*"
   - "**/python"
   - "test/**/*"
 

.github/dependabot.yml

@@ -1,16 +1,5 @@
 version: 2
 updates:
-  - package-ecosystem: "gitsubmodule"
-    directory: "/"
-    groups:
-      submodules:
-        patterns:
-          - "*"
-    schedule:
-      interval: "monthly"
-      time: "06:00"
-      timezone: "Europe/Vienna"
-
   - package-ecosystem: "github-actions"
     directory: "/"
     groups:

.pre-commit-config.yaml

@@ -92,8 +92,6 @@ repos:
     hooks:
       - id: cmake-format
         additional_dependencies: [pyyaml]
-      - id: cmake-lint
-        additional_dependencies: [pyyaml]
 
   # Format configuration files with prettier
   - repo: https://github.com/pre-commit/mirrors-prettier

.readthedocs.yaml

@@ -1,9 +1,5 @@
 version: 2
 
-submodules:
-  include: all
-  recursive: true
-
 build:
   os: ubuntu-22.04
   tools:

CMakeLists.txt

@@ -6,28 +6,25 @@ project(
   LANGUAGES CXX
   DESCRIPTION "MQT Core - The Backbone of the Munich Quantum Toolkit")
 
-# this is to create aliases and maintain backwards compatibility
-set(OLD_PROJECT_NAME "qfr")
-
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 
 include(cmake/StandardProjectSettings.cmake)
 include(cmake/PreventInSourceBuilds.cmake)
-include(cmake/CheckSubmodule.cmake)
 include(cmake/PackageAddTest.cmake)
 include(cmake/Cache.cmake)
 
+option(BUILD_MQT_CORE_TESTS "Also build tests for the MQT Core project" ON)
+option(BUILD_MQT_CORE_BENCHMARKS "Also build benchmarks for the MQT Core project")
 option(BUILD_MQT_CORE_BINDINGS "Build the MQT Core Python bindings" OFF)
+
 if(BUILD_MQT_CORE_BINDINGS)
   # ensure that the BINDINGS option is set
   set(BINDINGS
       ON
       CACHE BOOL "Enable settings related to Python bindings" FORCE)
-  # cmake-lint: disable=C0103
   set(Python_FIND_VIRTUALENV
       FIRST
       CACHE STRING "Give precedence to virtualenvs when searching for Python")
-  # cmake-lint: disable=C0103
   set(Python_ARTIFACTS_INTERACTIVE
       ON
       CACHE BOOL "Prevent multiple searches for Python and instead cache the results.")
@@ -60,27 +57,18 @@ if(NOT TARGET project_options)
   enable_sanitizers(project_options)
 endif()
 
-check_submodule_present(json)
-check_submodule_present(pybind11_json)
-check_submodule_present(boost/config)
-check_submodule_present(boost/multiprecision)
+include(cmake/ExternalDependencies.cmake)
 
 # add main library code
 add_subdirectory(src)
 
 # add test code
-option(BUILD_MQT_CORE_TESTS "Also build tests for the MQT Core project" ON)
 if(BUILD_MQT_CORE_TESTS)
-  check_submodule_present(googletest)
   enable_testing()
   include(GoogleTest)
   add_subdirectory(test)
 endif()
 
-option(BUILD_MQT_CORE_BENCHMARKS "Also build benchmarks for the MQT Core project")
 if(BUILD_MQT_CORE_BENCHMARKS)
-  check_submodule_present(googletest)
-  enable_testing()
-  include(GoogleTest)
   add_subdirectory(eval)
 endif()

README.md

@@ -74,6 +74,15 @@ MQT Core encompasses:
 Building (and running) is continuously tested under Linux, MacOS, and Windows using the [latest available system versions for GitHub Actions](https://github.com/actions/runner-images).
 However, the implementation should be compatible with any current C++ compiler supporting C++17 and a minimum CMake version of 3.19.
 
+MQT Core relies on some external dependencies:
+
+- [nlohmann/json](https://github.com/nlohmann/json): A JSON library for modern C++.
+- [boost/multiprecision](https://github.com/boostorg/multiprecision): A library for multiprecision arithmetic (used in the ZX package).
+- [google/googletest](https://github.com/google/googletest): A testing framework for C++ (only used in tests).
+- [pybind/pybind11_json](https://github.com/pybind/pybind11_json): Using nlohmann::json with pybind11 (only used for creating the Python bindings).
+
+CMake will automatically look for installed versions of these libraries. If it does not find them, they will be fetched automatically at configure time via the [FetchContent](https://cmake.org/cmake/help/latest/module/FetchContent.html) module (check out the documentation for more information on how to customize this behavior).
+
 It is recommended (although not required) to have [GraphViz](https://www.graphviz.org) installed for visualization purposes.
 
 If you want to use the ZX library, it is recommended (although not strictly necessary) to have [GMP](https://gmplib.org/) installed in your system.

cmake/ExternalDependencies.cmake

@@ -0,0 +1,142 @@
+# Declare all external dependencies and make sure that they are available.
+
+include(FetchContent)
+set(FETCH_PACKAGES "")
+
+# A macro to declare a dependency that takes into account the different CMake versions and the
+# features that they make available. In particular: - CMake 3.24 introduced the `FIND_PACKAGE_ARGS`
+# option to `FetchContent` which allows to combine `FetchContent_Declare` and `find_package` in a
+# single call. - CMake 3.25 introduced the `SYSTEM` option to `FetchContent_Declare` which marks the
+# dependency as a system dependency. This is useful to avoid compiler warnings from external header
+# only libraries. - CMake 3.28 introduced the `EXCLUDE_FROM_ALL` option to `FetchContent_Declare`
+# which allows to exclude all targets from the dependency from the `all` target.
+macro(DECLARE_DEPENDENCY)
+  cmake_parse_arguments(DEPENDENCY "SYSTEM;EXCLUDE_FROM_ALL" "NAME;URL;MD5;MIN_VERSION;ALT_NAME" ""
+                        ${ARGN})
+  set(ADDITIONAL_OPTIONS "")
+  if(DEPENDENCY_SYSTEM AND CMAKE_VERSION VERSION_GREATER_EQUAL 3.25)
+    list(APPEND ADDITIONAL_OPTIONS SYSTEM)
+  endif()
+  if(DEPENDENCY_EXCLUDE_FROM_ALL AND CMAKE_VERSION VERSION_GREATER_EQUAL 3.28)
+    list(APPEND ADDITIONAL_OPTIONS EXCLUDE_FROM_ALL)
+  endif()
+  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.28)
+    FetchContent_Declare(
+      ${DEPENDENCY_NAME}
+      URL ${DEPENDENCY_URL}
+      URL_MD5 ${DEPENDENCY_MD5}
+      ${ADDITIONAL_OPTIONS} FIND_PACKAGE_ARGS ${DEPENDENCY_MIN_VERSION} NAMES
+      ${DEPENDENCY_ALT_NAME})
+    list(APPEND FETCH_PACKAGES ${DEPENDENCY_NAME})
+  elseif(CMAKE_VERSION VERSION_GREATER_EQUAL 3.25)
+    FetchContent_Declare(
+      ${DEPENDENCY_NAME}
+      URL ${DEPENDENCY_URL}
+      URL_MD5 ${DEPENDENCY_MD5}
+      ${ADDITIONAL_OPTIONS} FIND_PACKAGE_ARGS ${DEPENDENCY_MIN_VERSION} NAMES
+      ${DEPENDENCY_ALT_NAME})
+    list(APPEND FETCH_PACKAGES ${DEPENDENCY_NAME})
+  elseif(CMAKE_VERSION VERSION_GREATER_EQUAL 3.24)
+    FetchContent_Declare(
+      ${DEPENDENCY_NAME}
+      URL ${DEPENDENCY_URL}
+      URL_MD5 ${DEPENDENCY_MD5}
+      ${ADDITIONAL_OPTIONS} FIND_PACKAGE_ARGS ${DEPENDENCY_MIN_VERSION} NAMES
+      ${DEPENDENCY_ALT_NAME})
+    list(APPEND FETCH_PACKAGES ${DEPENDENCY_NAME})
+  else()
+    # try to get the system installed version
+    find_package(${DEPENDENCY_NAME} ${DEPENDENCY_MIN_VERSION} QUIET NAMES ${DEPENDENCY_ALT_NAME})
+    if(NOT ${DEPENDENCY_NAME}_FOUND)
+      FetchContent_Declare(
+        ${DEPENDENCY_NAME}
+        URL ${DEPENDENCY_URL}
+        URL_MD5 ${DEPENDENCY_MD5})
+      list(APPEND FETCH_PACKAGES ${DEPENDENCY_NAME})
+    endif()
+  endif()
+endmacro()
+
+set(JSON_BuildTests
+    OFF
+    CACHE INTERNAL "")
+set(JSON_MultipleHeaders
+    OFF
+    CACHE INTERNAL "")
+declare_dependency(
+  NAME
+  nlohmann_json
+  URL
+  https://github.com/nlohmann/json/releases/download/v3.11.3/json.tar.xz
+  MD5
+  c23a33f04786d85c29fda8d16b5f0efd
+  MIN_VERSION
+  3.11.3
+  SYSTEM
+  EXCLUDE_FROM_ALL)
+
+set(BOOST_MP_STANDALONE
+    ON
+    CACHE INTERNAL "Use standalone boost multiprecision")
+declare_dependency(
+  NAME
+  boost_multiprecision
+  URL
+  https://github.com/boostorg/multiprecision/archive/refs/tags/Boost_1_84_0.tar.gz
+  MD5
+  b829378c90f4b268c79a796025c43eee
+  MIN_VERSION
+  1.74.0
+  ALT_NAME
+  Boost
+  SYSTEM
+  EXCLUDE_FROM_ALL)
+
+if(BUILD_MQT_CORE_TESTS)
+  set(gtest_force_shared_crt
+      ON
+      CACHE BOOL "" FORCE)
+  set(FP_ARGS 1.14.0 NAMES GTest)
+  declare_dependency(
+    NAME
+    googletest
+    URL
+    https://github.com/google/googletest/archive/refs/tags/v1.14.0.tar.gz
+    MD5
+    c8340a482851ef6a3fe618a082304cfc
+    MIN_VERSION
+    1.14.0
+    ALT_NAME
+    GTest
+    SYSTEM
+    EXCLUDE_FROM_ALL)
+endif()
+
+if(BINDINGS)
+  if(NOT SKBUILD)
+    # Manually detect the installed pybind11 package and import it into CMake.
+    execute_process(
+      COMMAND "${Python_EXECUTABLE}" -m pybind11 --cmakedir
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      OUTPUT_VARIABLE pybind11_DIR)
+    list(APPEND CMAKE_PREFIX_PATH "${pybind11_DIR}")
+  endif()
+
+  # add pybind11 library
+  find_package(pybind11 CONFIG REQUIRED)
+
+  declare_dependency(
+    NAME
+    pybind11_json
+    URL
+    https://github.com/pybind/pybind11_json/archive/refs/tags/0.2.13.tar.gz
+    MD5
+    93ebbea2bb69f71febe0f83c8f88ced2
+    MIN_VERSION
+    0.2.13
+    SYSTEM
+    EXCLUDE_FROM_ALL)
+endif()
+
+# Make all declared dependencies available.
+FetchContent_MakeAvailable(${FETCH_PACKAGES})

docs/DevelopmentGuide.md

@@ -9,14 +9,9 @@ Ready to contribute to the project? Here is how to set up a local development en
 2. Clone your fork locally
 
    ```console
-   $ git clone [email protected]:your_name_here/mqt-core --recursive
+   $ git clone [email protected]:your_name_here/mqt-core.git
    ```
 
-   :::{warning}
-   The {code}`--recursive` flag is required to also clone all the required submodules.
-   If you happen to forget passing the flag on your initial clone, you can initialize all the submodules by executing {code}`git submodule update --init --recursive` in the main project directory.
-   :::
-
 3. Change into the project directory
 
    ```console