Alternatives to FindSWIG for SWIG Integration

Purpose

• Optionally, checks for support for specific target languages (introduced in CMake 3.18).
• Determines the version of the found SWIG executable.
• Locates an installed version of the Simplified Wrapper and Interface Generator (SWIG) on your system.

Location

• The FindSWIG.cmake module is typically part of the standard CMake distribution. You can usually find it in a directory like /usr/share/cmake-3.<version>/Modules (replace <version> with your actual CMake version number).

Functionality

1. Inclusion
   It's included in your project's CMakeLists.txt file using the find_package command:

   find_package(SWIG REQUIRED 3.0)  # Find SWIG with minimum version 3.0
   

2. Searching
   The module searches for the SWIG executable in common locations on your system, relying on system environment variables and default installation paths.

3. Information Gathering
   If SWIG is found, the module sets the following variables:

   • SWIG_FOUND: Boolean indicating if SWIG was found (TRUE) or not (FALSE).
   • SWIG_EXECUTABLE: Path to the SWIG executable.
   • SWIG_DIR: Installation directory of SWIG (often containing libraries and headers).
   • SWIG_VERSION: Version number of the found SWIG executable.
   • SWIG_<lang>_FOUND (introduced in CMake 3.18): Boolean variables for each requested target language (e.g., python_FOUND, java_FOUND), indicating whether SWIG supports generating bindings for that language.

Example Usage

find_package(SWIG REQUIRED 2.0 COMPONENTS python)  # Find SWIG 2.0 or later with Python support

if (SWIG_FOUND)
  message("SWIG found: ${SWIG_EXECUTABLE}")
  message("SWIG version: ${SWIG_VERSION}")

  # Use SWIG to generate Python bindings...
endif()

Key Points

• The OPTIONAL_COMPONENTS argument (also introduced in CMake 3.18) lets you check for support for optional target languages without making it a requirement.
• The COMPONENTS argument (available since CMake 3.18) allows you to specify required target languages.
• The REQUIRED keyword in find_package ensures that CMake fails if SWIG cannot be found, halting the build process.

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Example 1: Basic Usage with Python Bindings

This example finds SWIG (version 2.0 or later) and ensures it has Python support for generating Python bindings:

find_package(SWIG REQUIRED 2.0 COMPONENTS python)

if (SWIG_FOUND)
  message("SWIG found: ${SWIG_EXECUTABLE}")
  message("SWIG version: ${SWIG_VERSION}")

  # Define your SWIG interface file
  set(SWIG_INTERFACE_FILE my_library.i)

  # Use SWIG to generate Python bindings
  swig_add_module(my_python_module python ${SWIG_INTERFACE_FILE})
  target_link_libraries(my_python_module my_library)  # Link your C++ library

  # (Optional) Install the Python module
  install(TARGETS my_python_module DESTINATION lib/python3.X  # Adjust path for your Python version
          RUNTIME DESTINATION ${CMAKE_INSTALL_PREFIX}/bin)
endif()

1. The code finds SWIG with the REQUIRED keyword and minimum version 2.0.
2. The COMPONENTS python argument verifies Python support.
3. It defines the SWIG_INTERFACE_FILE containing the SWIG interface declarations.
4. The swig_add_module command creates a Python module named my_python_module.
5. The target_link_libraries command links your C++ library (my_library) to the Python module.
6. The optional install command installs the Python module and its runtime component.

Example 2: Checking for Optional Language Support (CMake 3.18 or later)

This example finds SWIG and checks if it can generate bindings for both Python and Java:

find_package(SWIG REQUIRED 3.18)  # Requires CMake 3.18 or later

if (SWIG_FOUND)
  message("SWIG found: ${SWIG_EXECUTABLE}")
  message("SWIG version: ${SWIG_VERSION}")

  if (SWIG_PYTHON_FOUND)
    message("SWIG supports generating Python bindings.")
  else()
    message("SWIG does not support Python bindings (optional).")
  endif()

  if (SWIG_JAVA_FOUND)
    message("SWIG supports generating Java bindings.")
  else()
    message("SWIG does not support Java bindings (optional).")
  endif()
endif()

1. This code requires CMake 3.18 or later for the SWIG_<lang>_FOUND variables.
2. It checks for SWIG_PYTHON_FOUND and SWIG_JAVA_FOUND to see if the found SWIG supports Python and Java, respectively.
3. These variables indicate optional language support, not a requirement.

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Manual Configuration

• This approach doesn't leverage CMake's package finding capabilities and requires manual setup.
• If your project has a small build footprint and only requires a specific SWIG version, you can manually set environment variables:
  • SWIG_EXECUTABLE: Path to your SWIG executable.
  • SWIG_DIR: Installation directory of SWIG (optional, for header/library locations).

Custom Find Module

• It offers more flexibility but requires more effort to maintain.
• This involves writing CMake code to search for SWIG in custom locations and setting appropriate variables.
• If you have specific requirements beyond FindSWIG, you can create a custom CMake module to locate and configure SWIG.

Package Manager Integration

• This approach depends on your chosen package manager and its support for SWIG.
• You can leverage the package managers' find modules or mechanisms to locate and link to SWIG during your project's build.
• If your project uses a package manager like Vcpkg, Conan, or Spack, these tools might have packages for SWIG and provide CMake integration.

Build System Integration

• Consult your build system's documentation for details.
• If you're not using CMake as your primary build system, your build system itself might have mechanisms for finding and integrating with SWIG.

• Desired level of automation and maintainability
• Build system and package manager usage
• Specific SWIG requirements
• Project complexity