# CMake 3.16 Release Notes

Changes made since CMake 3.15 include the following.

## New Features

### Languages

- CMake learned to support the Objective C (`OBJC`) and Objective C++ (`OBJCXX`) languages. They may be enabled via the `project()` and `enable_language()` commands. When `OBJC` or `OBJCXX` is enabled, source files with the `.m` or `.mm`, respectively, will be compiled as Objective C or C++. Otherwise they will be treated as plain C++ sources as they were before.

### Compilers

- The `Clang` compiler is now supported on `Solaris`.

### Platforms

- On AIX, executables using the `ENABLE_EXPORTS` target property now produce a linker import file with a `.imp` extension in addition to the executable file. Plugins (created via `add_library()` with the `MODULE` option) that use `target_link_libraries()` to link to the executable for its symbols are now linked using the import file. The `install(TARGETS)` command now installs the import file as an `ARCHIVE` artifact.

- On AIX, runtime linking is no longer enabled by default. CMake provides the linker enough information to resolve all symbols up front. One may manually enable runtime linking for shared libraries and/or loadable modules by adding `-Wl,-G` to their link flags (e.g. in the `CMAKE_SHARED_LINKER_FLAGS` or `CMAKE_MODULE_LINKER_FLAGS` variable). One may manually enable runtime linking for executables by adding `-Wl,-brtl` to their link flags (e.g. in the `CMAKE_EXE_LINKER_FLAGS` variable).

### Command-Line

- `cmake(1)` `-E` now supports `true` and `false` commands, which do nothing while returning exit codes of 0 and 1, respectively.

- `cmake(1)` gained a `--trace-redirect=<file>` command line option that can be used to redirect `--trace` output to a file instead of `stderr`.

- The `cmake(1)` `--loglevel` command line option has been renamed to `--log-level` to make it consistent with the naming of other command line options. The `--loglevel` option is still supported to preserve backward compatibility.

### Commands

- The `add_test()` command learned the option `COMMAND_EXPAND_LISTS` which causes lists in the `COMMAND` argument to be expanded, including lists created by generator expressions.

- The `file()` command learned a new sub-command, `GET_RUNTIME_DEPENDENCIES`, which allows you to recursively get the list of libraries linked by an executable or library. This sub-command is intended as a replacement for `GetPrerequisites`.

- The `find_file()`, `find_library()`, `find_path()`, `find_package()`, and `find_program()` commands have learned to check the following variables to control the default behavior for groups of search locations:

  - `CMAKE_FIND_USE_PACKAGE_ROOT_PATH` - Controls the default behavior of searching the `<PackageName>_ROOT` variables.

  - `CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH` - Controls the default behavior of searching the CMake-specific environment variables.

  - `CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH` - Controls the default behavior of searching the standard system environment variables.

  - `CMAKE_FIND_USE_CMAKE_PATH` - Controls the default behavior of searching the CMake-specific cache variables.

  - `CMAKE_FIND_USE_CMAKE_SYSTEM_PATH` - Controls the default behavior of searching the platform-specific CMake variables.

- The `find_package()` command has learned to check the `CMAKE_FIND_USE_PACKAGE_REGISTRY` variable to control the default behavior of searching the CMake user package registry and to check the `CMAKE_FIND_USE_SYSTEM_PACKAGE_REGISTRY` variable to control the default behavior of searching the CMake system package registry.

- The `message()` command learned indentation control with the new `CMAKE_MESSAGE_INDENT` variable.

- The `target_precompile_headers()` command was added to specify a list of headers to precompile for faster compilation times.

### Variables

- The `CMAKE_CUDA_RESOLVE_DEVICE_SYMBOLS` variable has been introduced to optionally initialize the `CUDA_RESOLVE_DEVICE_SYMBOLS` target property.

- The `CMAKE_ECLIPSE_RESOURCE_ENCODING` variable was added to specify the resource encoding for the the `Eclipse CDT4` extra generator.

- The `CMAKE_UNITY_BUILD` variable was added to initialize the `UNITY_BUILD` target property to tell generators to batch include source files for faster compilation times.

### Properties

- The `BUILD_RPATH` and `INSTALL_RPATH` target properties now support `generator expressions`.

- The `INSTALL_REMOVE_ENVIRONMENT_RPATH` target property was added to remove compiler-defined `RPATH` entries from a target. This property is initialized by the `CMAKE_INSTALL_REMOVE_ENVIRONMENT_RPATH` variable.

- The `PRECOMPILE_HEADERS` target property was added to specify a list of headers to precompile for faster compilation times. Set it using the `target_precompile_headers()` command.

- The `UNITY_BUILD` target property was added to tell generators to batch include source files for faster compilation times.

- The `VS_CONFIGURATION_TYPE` target property now supports `generator expressions`.

- The `VS_DPI_AWARE` target property was added to tell Visual Studio Generators to set the `EnableDpiAwareness` property in `.vcxproj` files.

- The `XCODE_SCHEME_DEBUG_DOCUMENT_VERSIONING` target property was added to tell the `Xcode` generator to set the value of the `Allow debugging when using document Versions Browser` schema option.

### Modules

- The `FindDoxygen` module `doxygen_add_docs()` command gained a new `USE_STAMP_FILE` option. When this option present, the custom target created by the command will only re-run Doxygen if any of the source files have changed since the last successful run.

- The `FindGnuTLS` module now provides an imported target.

- The `FindPackageHandleStandardArgs` module `find_package_handle_standard_args()` command gained a new `REASON_FAILURE_MESSAGE` option to specify a message giving the reason for the failure.

- The `FindPkgConfig` module `pkg_search_module()` command now defines a `<prefix>_MODULE_NAME` result variable containing the first matching module name.

- The `FindPython3` and `FindPython` modules gained options to control which `ABIs` will be searched.

- The `FindPython3`, `FindPython2`, and `FindPython` modules now support direct specification of artifacts via cache entries.

### Autogen

- When using `AUTOMOC`, the new `CMAKE_AUTOMOC_PATH_PREFIX` variable or `AUTOMOC_PATH_PREFIX` target property may be enabled to generate the `-p` path prefix option for `moc`. This ensures that `moc` output files are identical on different build setups (given, that the headers compiled by `moc` are in an `include directory`). Also it ensures that `moc` output files will compile correctly when the source and/or build directory is a symbolic link.

### CTest

- `ctest(1)` now has the ability to schedule tests based on resource requirements for each test. See Resource Allocation for details.

- A new test property, `SKIP_REGULAR_EXPRESSION`, has been added. This property is similar to `FAIL_REGULAR_EXPRESSION` and `PASS_REGULAR_EXPRESSION`, but with the same meaning as `SKIP_RETURN_CODE`. This is useful, for example, in cases where the user has no control over the return code of the test. For example, in Catch2, the return value is the number of assertion failed, therefore it is impossible to use it for `SKIP_RETURN_CODE`.

### CPack

- `cpack(1)` learned support for multiple configurations for `-C` option.

- The `CPack DEB Generator` is now able to format generic text (usually used as the description for multiple CPack generators) according to the Debian Policy Manual. See the `CPACK_PACKAGE_DESCRIPTION_FILE` and `CPACK_DEBIAN_<COMPONENT>_DESCRIPTION` variables.

- The `CPack Archive Generator` learned to generate `.tar.zst` packages with Zstandard compression.

## Deprecated and Removed Features

- An explicit deprecation diagnostic was added for policy `CMP0067` (`CMP0066` and below were already deprecated). The `cmake-policies(7)` manual explains that the OLD behaviors of all policies are deprecated and that projects should port to the NEW behaviors.

- The `CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY` variable has been deprecated. Use the `CMAKE_FIND_USE_PACKAGE_REGISTRY` variable instead.

- The `GetPrerequisites` module has been deprecated, as it has been superseded by `file(GET_RUNTIME_DEPENDENCIES)`.

- The `CPACK_INSTALL_SCRIPT` variable has been deprecated in favor of the new, more accurately named `CPACK_INSTALL_SCRIPTS` variable.

## Other Changes

- The `cmake(1)` `-C <initial-cache>` option now evaluates the initial cache script with `CMAKE_SOURCE_DIR` and `CMAKE_BINARY_DIR` set to the top-level source and build trees.

- The `cmake(1)` `-E remove_directory` command-line tool, when given the path to a symlink to a directory, now removes just the symlink. It no longer removes content of the linked directory.

- The `ctest(1)` `--build-makeprogram` command-line option now specifies the make program used when configuring a project with the `Ninja` generator or the Makefile Generators.

- The `ExternalProject` module `ExternalProject_Add()` command has been updated so that `GIT_SUBMODULES ""` initializes no submodules. See policy `CMP0097`.

- The `FindGTest` module has been updated to recognize MSVC build trees generated by GTest 1.8.1.

- The `project()` command no longer strips leading zeros in version components. See policy `CMP0096`.

- The Qt Compressed Help file is now named `CMake.qch`, which no longer contains the release version in the file name. When CMake is upgraded in-place, the name and location of this file will remain constant. Tools such as IDEs, help viewers, etc. should now be able to refer to this file at a fixed location that remains valid across CMake upgrades.

- `RPATH` entries are properly escaped in the generated CMake scripts used for installation. See policy `CMP0095`.

- When using `CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS` on Windows the auto-generated exports are now updated only when the object files providing the symbols are updated.

## Updates

Changes made since CMake 3.16.0 include the following.

### 3.16.2

- CMake 3.16.0 and 3.16.1 processed `.hh` files with `AUTOMOC`. This was a behavior change from CMake 3.15 and below that can break existing projects, so it has been reverted as of 3.16.2.

### 3.16.5

- The `FindPython`, `FindPython2`, and `FindPython3` modules no longer create cache entries for `Python{,2,3}_LIBRARY_RELEASE` and `Python{,2,3}_LIBRARY_DEBUG`. Those values are always computed from other results and so should not be cached. The entries were created by CMake 3.16.0 through 3.16.4 but were always `FORCE`-set and could not be meaningfully edited by users.

  Additionally, the modules no longer expose their internal `_Python*` cache entries publicly. CMake 3.16.0 through 3.16.4 accidentally made them visible as advanced cache entries.

### 3.16.7

- Selection of the Objective C or C++ compiler now considers the `CC` or `CXX` environment variable if the `OBJC` or `OBJCXX` environment variable is not set.

- The `FindPkgConfig` module now extracts include directories prefixed with `-isystem` into the `*_INCLUDE_DIRS` variables and `INTERFACE_INCLUDE_DIRECTORIES` target properties. Previously they would be places in `*_CFLAGS_OTHER` variables and `INTERFACE_COMPILE_OPTIONS` target properties.

### 3.16.9

- The default value of `CMAKE_AUTOMOC_PATH_PREFIX` was changed to `OFF` because this feature can break existing projects that have identically named header files in different include directories. This restores compatibility with behavior of CMake 3.15 and below.