Explaining CMake's BUNDLE_EXTENSION for Bundle and Framework Creation

What it is

• It's primarily used on macOS and iOS platforms.
• BUNDLE_EXTENSION is a target property in CMake that specifies the file extension used for creating bundles, frameworks, or macOS application bundles.

Default Values

• The default behavior depends on the specific target type:
  • BUNDLE: ".bundle"
  • FRAMEWORK: ".framework"
  • MACOSX_BUNDLE: ".app"

Customization

• This allows you to tailor the extension to your bundle's specific needs or the requirements of the host application that will use it.
• You can override these defaults using the set_target_properties command in your CMakeLists.txt file.

Example

set(MY_BUNDLE_NAME my_special_bundle)
add_bundle(${MY_BUNDLE_NAME} SRCS source1.cpp source2.cpp)

# Change the extension to ".plugin"
set_target_properties(${MY_BUNDLE_NAME} PROPERTIES BUNDLE_EXTENSION ".plugin")

In this example, the bundle named my_special_bundle will be created with a .plugin extension instead of the default .bundle.

• Creating plugins that require a specific extension (e.g., .so for shared libraries on Linux).
• Specifying a custom extension for compatibility with a particular host application.

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Customizing a Framework Extension

set(MY_FRAMEWORK_NAME my_custom_framework)
add_library(${MY_FRAMEWORK_NAME} SHARED framework1.cpp framework2.cpp)

# Set the framework type for macOS
set_target_properties(${MY_FRAMEWORK_NAME} PROPERTIES MACOSX_FRAMEWORK TRUE)

# Change the extension to ".fx"
set_target_properties(${MY_FRAMEWORK_NAME} PROPERTIES BUNDLE_EXTENSION ".fx")

This code creates a shared library named my_custom_framework with a .fx extension instead of the default .framework. This might be useful if the framework needs to be compatible with a specific host application that uses .fx for its frameworks.

Creating a Plugin with Specific Extension

set(MY_PLUGIN_NAME my_special_plugin)
add_library(${MY_PLUGIN_NAME} SHARED plugin1.cpp plugin2.cpp)

# Change the extension to ".so" (common for Linux plugins)
set_target_properties(${MY_PLUGIN_NAME} PROPERTIES BUNDLE_EXTENSION ".so")

This code creates a shared library named my_special_plugin with a .so extension. This is a common extension for plugins on Linux systems.

Customizing a macOS Application Extension (Open Feature Request)

set(MY_APP_NAME my_special_app)
add_executable(${MY_APP_NAME} main.cpp)
set_target_properties(${MY_APP_NAME} PROPERTIES MACOSX_BUNDLE TRUE)

# Change the extension to ".myapp" (assuming future support)
set_target_properties(${MY_APP_NAME} PROPERTIES BUNDLE_EXTENSION ".myapp")

This code (assuming future support) would create a macOS application named my_special_app with a .myapp extension instead of the default .app.

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Renaming After CMake Generation

• You can write a post-build script (e.g., using Bash on Linux/macOS or PowerShell on Windows) that renames the generated file to your desired extension.
• CMake generates the bundle/framework/application with the default extension.

Example (Bash script, assuming Linux/macOS)

# Get the target name and path (modify as needed for your target)
target_name="my_special_bundle"
target_dir="${CMAKE_CURRENT_BINARY_DIR}/${target_name}"

# Check if the target exists
if [ -d "${target_dir}" ]; then
  # Rename the bundle file (assuming default '.bundle' extension)
  mv "${target_dir}" "${target_dir}.plugin"  # Change '.plugin' to your desired extension
  echo "Renamed bundle to ${target_dir}.plugin"
fi

Using Custom Build Commands (Limited Use)

• However, this approach can be less portable and more complex to maintain across different platforms.
• In some cases, you might be able to use custom build commands within CMake to create the bundle structure and files with your desired extension.

Considering Alternative Packaging Tools

• If your project has complex bundling requirements or needs to support a wider range of platforms, you might explore using dedicated packaging tools like:
  • Platform-specific tools (e.g., pkgconfig on Linux, Xcodebuild on macOS)
  • Language-specific packaging systems (e.g., npm for Node.js modules, pip for Python packages)

These tools often have more flexibility in specifying extensions and managing bundle contents.

Choosing the Right Approach

The best approach depends on your specific needs and project complexity.

• If you need more control over the bundle structure or have complex packaging requirements, consider alternative packaging tools.
• For simple extension customization, renaming the generated file might suffice.