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CMP0154
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-------
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.. versionadded:: 3.28
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Generated files are private by default in targets using :ref:`file sets`.
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CMake 3.27 and below assume that any file generated as an output or byproduct
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of :command:`add_custom_command` or :command:`add_custom_target` may be a
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public header file meant for inclusion by dependents' source files. This
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requires :ref:`Ninja Generators` to add conservative order-only dependencies
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that prevent a target's source files from compiling before custom commands
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from the target's dependencies are finished, even if those custom commands
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only produce sources private to their own target.
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:ref:`File Sets`, introduced by CMake 3.23, provide a way to express the
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visibility of generated header files. CMake 3.28 and above prefer to
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assume that, in targets using file sets, generated files are private to
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their own target by default. Generated public headers must be specified
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as members of a ``PUBLIC`` (or ``INTERFACE``) ``FILE_SET``, typically of
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type ``HEADERS``. With this information, :ref:`Ninja Generators` may omit
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the above-mentioned conservative dependencies and produce more efficient
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build graphs.
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Additionally, if the custom command's output is a member of a file set of type
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``CXX_MODULES``, it will additionally not be required to exist before
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compiling other sources in the same target. Since these files should not be
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included at compile time directly, they may not be implicitly required to
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exist for other compilation rules.
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This policy provides compatibility for projects using file sets in targets
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with generated header files that have not been updated. Such projects
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should be updated to express generated public headers in a file set.
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For example:
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.. code-block:: cmake
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add_custom_command(
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OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/foo.h
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...
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)
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target_sources(foo
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PUBLIC FILE_SET HEADERS
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BASE_DIRS ${CMAKE_CURRENT_BINARY_DIR}
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FILES ${CMAKE_CURRENT_BINARY_DIR}/foo.h
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)
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The ``OLD`` behavior for this policy is to assume generated files are
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public, even in targets using file sets, and for :ref:`Ninja Generators`
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to produce conservative build graphs. The ``NEW`` behavior for this
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policy is to assume generated files are private in targets using file sets,
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and for :ref:`Ninja Generators` to produce more efficient build graphs.
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.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.28
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.. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
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.. include:: STANDARD_ADVICE.txt
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.. include:: DEPRECATED.txt
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