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Understanding CMake_XCODE_ATTRIBUTE_an-attribute for Xcode Project Settings


Purpose

  • It allows you to directly set attributes of targets within the generated Xcode project file.
  • It's a variable used with the CMake generator for Xcode projects.

How it Works

    • You specify the variable name as CMAKE_XCODE_ATTRIBUTE_<an-attribute>, where <an-attribute> is the actual Xcode target attribute you want to modify.
    • You assign the desired value to this variable.

  2. Xcode Project Generation

    • When CMake generates the Xcode project using the Xcode generator, it looks for variables with this naming convention.
    • For each such variable encountered, it sets the corresponding attribute in the target properties of the generated project file.

Important Points

  • Potential Issues
    • Overriding CMake's default behavior can lead to unexpected results or break the project if not done carefully.
    • It's essential to understand the specific Xcode target attribute you're modifying and its implications.
  • Limited Use Cases
    • It's intended for low-level control over the Xcode project configuration.
    • Use it only when CMake's built-in mechanisms for managing Xcode project settings are insufficient.
  • Availability
    Introduced in CMake version 3.1.

Example

set(CMAKE_XCODE_ATTRIBUTE_DEAD_CODE_STRIPPING YES)
target_link_libraries(MyTarget PRIVATE MyLibrary)

Alternatives

  • Consider using the XCODE_ATTRIBUTE_<an-attribute> target property for more specific control over individual targets within your project.
  • If possible, leverage CMake's higher-level target properties or commands to configure Xcode project settings. This ensures better integration with CMake's project model.

In Summary


Setting a Global Attribute

This example sets the ONLY_ACTIVE_ARCH attribute to YES for all targets in the project:

set(CMAKE_XCODE_ATTRIBUTE_ONLY_ACTIVE_ARCH YES)

Setting an Attribute for a Specific Target

This example sets the ENABLE_BITCODE attribute to NO for the target named MyExecutable:

set_target_properties(MyExecutable PROPERTIES XCODE_ATTRIBUTE_ENABLE_BITCODE NO)

Using Generator Expressions (Advanced)

This example shows how to use generator expressions with CMAKE_XCODE_ATTRIBUTE_an_attribute to set the VALID_ARCHS attribute based on the current build configuration:

if(CMAKE_BUILD_TYPE STREQUAL "Debug")
  set(CMAKE_XCODE_ATTRIBUTE_VALID_ARCHS "x86_64")
else()
  set(CMAKE_XCODE_ATTRIBUTE_VALID_ARCHS "arm64;x86_64")
endif()
  • Consider alternative approaches using CMake's built-in mechanisms whenever possible for better project management and consistency.
  • Use these examples as a guide, but always refer to the official Xcode target attribute documentation for specific attribute names and valid values.

Higher-Level Target Properties

  • CMake provides built-in target properties that map to common Xcode project settings. These properties offer a cleaner and more maintainable way to configure your project.

Example

Instead of using CMAKE_XCODE_ATTRIBUTE_DEAD_CODE_STRIPPING, you can use the XCODE_ATTRIBUTE_DEAD_CODE_STRIPPING target property:

target_link_libraries(MyTarget PRIVATE MyLibrary)
set_target_properties(MyTarget PROPERTIES XCODE_ATTRIBUTE_DEAD_CODE_STRIPPING YES)

Xcode-Specific Generator Expressions

  • CMake offers generator expressions specifically for Xcode projects. These expressions allow you to set settings conditionally based on build configurations, platforms, or other factors.

Example

Instead of using a complex CMAKE_XCODE_ATTRIBUTE_an-attribute setup for VALID_ARCHS, you can leverage generator expressions:

set_target_properties(MyExecutable PROPERTIES XCODE_ATTRIBUTE_VALID_ARCHS
    $<CONFIG:Debug>="x86_64"
    $<CONFIG:Release>="arm64;x86_64")

Custom Xcode Project Modification (Advanced)

  • This approach requires a deeper understanding of Xcode project files and should be used as a last resort due to potential maintenance challenges.
  • In rare cases where the above options aren't sufficient, you can use CMake's configure_file command to modify the generated Xcode project file after it's been created.
  • Reserve CMAKE_XCODE_ATTRIBUTE_an-attribute for low-level tweaks that aren't well-supported by existing CMake mechanisms.
  • For most use cases, it's recommended to prioritize higher-level target properties and generator expressions as they offer better integration with CMake's project model and make your project configuration more transparent.