Help: Revise target_link_libraries command documentation
Organize the documentation into subsections to separate the signatures. Refactor the discussion of allowed link items into bullet points and expand into more detail on each.
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Brad King
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target_link_libraries
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---------------------
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Link a target to given libraries.
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.. only:: html
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.. contents::
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Specify libraries or flags to use when linking a given target and/or
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its dependents. :ref:`Usage requirements <Target Usage Requirements>`
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from linked library targets will be propagated. Usage requirements
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of a target's dependencies affect compilation of its own sources.
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Overview
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^^^^^^^^
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This command has several signatures as detailed in subsections below.
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All of them have the general form::
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target_link_libraries(<target> ... <item>... ...)
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The named ``<target>`` must have been created in the current directory by
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a command such as :command:`add_executable` or :command:`add_library`.
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Repeated calls for the same ``<target>`` append items in the order called.
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Each ``<item>`` may be:
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* **A library target name**: The generated link line will have the
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full path to the linkable library file associated with the target.
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The buildsystem will have a dependency to re-link ``<target>`` if
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the library file changes.
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The named target must be created by :command:`add_library` within
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the project or as an :ref:`IMPORTED library <Imported Targets>`.
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If it is created within the project an ordering dependency will
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automatically be added in the build system to make sure the named
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library target is up-to-date before the ``<target>`` links.
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* **A full path to a library file**: The generated link line will
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normally preserve the full path to the file. However, there are
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some cases where CMake must ask the linker to search for the library
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(e.g. ``/usr/lib/libfoo.so`` becomes ``-lfoo``), such as when it
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appears in a system library directory that the compiler front-end
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may replace with an alternative. Either way, the buildsystem will
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have a dependency to re-link ``<target>`` if the library file changes.
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If the library file is in a Mac OSX framework, the ``Headers`` directory
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of the framework will also be processed as a
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:ref:`usage requirement <Target Usage Requirements>`. This has the same
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effect as passing the framework directory as an include directory.
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* **A plain library name**: The generated link line will ask the linker
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to search for the library (e.g. ``foo`` becomes ``-lfoo`` or ``foo.lib``).
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* **A link flag**: Item names starting with ``-``, but not ``-l`` or
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``-framework``, are treated as linker flags. Note that such flags will
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be treated like any other library link item for purposes of transitive
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dependencies, so they are generally safe to specify only as private link
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items that will not propagate to dependents.
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* A ``debug``, ``optimized``, or ``general`` keyword immediately followed
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by another ``<item>``. The item following such a keyword will be used
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only for the corresponding build configuration. The ``debug`` keyword
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corresponds to the ``Debug`` configuration (or to configurations named
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in the :prop_gbl:`DEBUG_CONFIGURATIONS` global property if it is set).
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The ``optimized`` keyword corresponds to all other configurations. The
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``general`` keyword corresponds to all configurations, and is purely
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optional. Higher granularity may be achieved for per-configuration
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rules by creating and linking to
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:ref:`IMPORTED library targets <Imported Targets>`.
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Items containing ``::``, such as ``Foo::Bar``, are assumed to be
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:ref:`IMPORTED <Imported Targets>` or :ref:`ALIAS <Alias Targets>` library
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target names and will cause an error if no such target exists.
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See policy :policy:`CMP0028`.
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Arguments to ``target_link_libraries`` may use "generator expressions"
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with the syntax ``$<...>``. Note however, that generator expressions
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will not be used in OLD handling of :policy:`CMP0003` or :policy:`CMP0004`.
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See the :manual:`cmake-generator-expressions(7)` manual for available
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expressions. See the :manual:`cmake-buildsystem(7)` manual for more on
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defining buildsystem properties.
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Libraries for a Target and/or its Dependents
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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::
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target_link_libraries(<target> [item1 [item2 [...]]]
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[[debug|optimized|general] <item>] ...)
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target_link_libraries(<target>
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<PRIVATE|PUBLIC|INTERFACE> <item>...
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[<PRIVATE|PUBLIC|INTERFACE> <item>...]...)
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Specify libraries or flags to use when linking a given target. The
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named ``<target>`` must have been created in the current directory by a
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command such as :command:`add_executable` or :command:`add_library`. The
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remaining arguments specify library names or flags. Repeated calls for
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the same ``<target>`` append items in the order called.
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The ``PUBLIC``, ``PRIVATE`` and ``INTERFACE`` keywords can be used to
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specify both the link dependencies and the link interface in one command.
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Libraries and targets following ``PUBLIC`` are linked to, and are made
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part of the link interface. Libraries and targets following ``PRIVATE``
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are linked to, but are not made part of the link interface. Libraries
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following ``INTERFACE`` are appended to the link interface and are not
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used for linking ``<target>``.
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If a library name matches that of another target in the project a
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dependency will automatically be added in the build system to make sure
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the library being linked is up-to-date before the target links. Item names
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starting with ``-``, but not ``-l`` or ``-framework``, are treated as
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linker flags. Note that such flags will be treated like any other library
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link item for purposes of transitive dependencies, so they are generally
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safe to specify only as private link items that will not propagate to
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dependents of ``<target>``.
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Libraries for both a Target and its Dependents
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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A ``debug``, ``optimized``, or ``general`` keyword indicates that the
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library immediately following it is to be used only for the
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corresponding build configuration. The ``debug`` keyword corresponds to
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the Debug configuration (or to configurations named in the
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:prop_gbl:`DEBUG_CONFIGURATIONS` global property if it is set). The
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``optimized`` keyword corresponds to all other configurations. The
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``general`` keyword corresponds to all configurations, and is purely
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optional (assumed if omitted). Higher granularity may be achieved for
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per-configuration rules by creating and linking to
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:ref:`IMPORTED library targets <Imported Targets>`.
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::
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target_link_libraries(<target> <item>...)
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Library dependencies are transitive by default with this signature.
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When this target is linked into another target then the libraries
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@ -45,37 +114,34 @@ by setting the property directly. When :policy:`CMP0022` is not set to
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of this command may set the property making any libraries linked
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exclusively by this signature private.
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CMake will also propagate :ref:`usage requirements <Target Usage Requirements>`
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from linked library targets. Usage requirements of dependencies affect
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compilation of sources in the ``<target>``.
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If an ``<item>`` is a library in a Mac OX framework, the ``Headers``
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directory of the framework will also be processed as a
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:ref:`usage requirement <Target Usage Requirements>`. This has the same
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effect as passing the framework directory as an include directory.
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--------------------------------------------------------------------------
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Libraries for a Target and/or its Dependents (Legacy)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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::
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target_link_libraries(<target>
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<PRIVATE|PUBLIC|INTERFACE> <lib> ...
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[<PRIVATE|PUBLIC|INTERFACE> <lib> ... ] ...])
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<LINK_PRIVATE|LINK_PUBLIC> <lib>...
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[<LINK_PRIVATE|LINK_PUBLIC> <lib>...]...)
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The ``PUBLIC``, ``PRIVATE`` and ``INTERFACE`` keywords can be used to
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specify both the link dependencies and the link interface in one command.
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Libraries and targets following ``PUBLIC`` are linked to, and are made
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part of the link interface. Libraries and targets following ``PRIVATE``
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are linked to, but are not made part of the link interface. Libraries
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following ``INTERFACE`` are appended to the link interface and are not
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used for linking ``<target>``.
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The ``LINK_PUBLIC`` and ``LINK_PRIVATE`` modes can be used to specify both
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the link dependencies and the link interface in one command.
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--------------------------------------------------------------------------
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This signature is for compatibility only. Prefer the ``PUBLIC`` or
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``PRIVATE`` keywords instead.
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Libraries and targets following ``LINK_PUBLIC`` are linked to, and are
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made part of the :prop_tgt:`INTERFACE_LINK_LIBRARIES`. If policy
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:policy:`CMP0022` is not ``NEW``, they are also made part of the
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:prop_tgt:`LINK_INTERFACE_LIBRARIES`. Libraries and targets following
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``LINK_PRIVATE`` are linked to, but are not made part of the
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:prop_tgt:`INTERFACE_LINK_LIBRARIES` (or :prop_tgt:`LINK_INTERFACE_LIBRARIES`).
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Libraries for Dependents Only (Legacy)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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::
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target_link_libraries(<target> LINK_INTERFACE_LIBRARIES
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[[debug|optimized|general] <lib>] ...)
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target_link_libraries(<target> LINK_INTERFACE_LIBRARIES <item>...)
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The ``LINK_INTERFACE_LIBRARIES`` mode appends the libraries to the
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:prop_tgt:`INTERFACE_LINK_LIBRARIES` target property instead of using them
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@ -99,28 +165,8 @@ is not ``NEW``, they are also appended to the
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``general`` (or without any keyword) are treated as if specified for both
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``debug`` and ``optimized``.
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--------------------------------------------------------------------------
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::
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target_link_libraries(<target>
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<LINK_PRIVATE|LINK_PUBLIC>
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[[debug|optimized|general] <lib>] ...
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[<LINK_PRIVATE|LINK_PUBLIC>
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[[debug|optimized|general] <lib>] ...])
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The ``LINK_PUBLIC`` and ``LINK_PRIVATE`` modes can be used to specify both
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the link dependencies and the link interface in one command.
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This signature is for compatibility only. Prefer the ``PUBLIC`` or
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``PRIVATE`` keywords instead.
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Libraries and targets following ``LINK_PUBLIC`` are linked to, and are
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made part of the :prop_tgt:`INTERFACE_LINK_LIBRARIES`. If policy
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:policy:`CMP0022` is not ``NEW``, they are also made part of the
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:prop_tgt:`LINK_INTERFACE_LIBRARIES`. Libraries and targets following
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``LINK_PRIVATE`` are linked to, but are not made part of the
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:prop_tgt:`INTERFACE_LINK_LIBRARIES` (or :prop_tgt:`LINK_INTERFACE_LIBRARIES`).
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Cyclic Dependencies of Static Libraries
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The library dependency graph is normally acyclic (a DAG), but in the case
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of mutually-dependent ``STATIC`` libraries CMake allows the graph to
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@ -139,17 +185,11 @@ For example, the code
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links ``main`` to ``A B A B``. While one repetition is usually
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sufficient, pathological object file and symbol arrangements can require
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more. One may handle such cases by manually repeating the component in
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the last ``target_link_libraries`` call. However, if two archives are
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really so interdependent they should probably be combined into a single
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archive.
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Arguments to target_link_libraries may use "generator expressions"
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with the syntax ``$<...>``. Note however, that generator expressions
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will not be used in OLD handling of :policy:`CMP0003` or :policy:`CMP0004`.
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See the :manual:`cmake-generator-expressions(7)` manual for available
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expressions. See the :manual:`cmake-buildsystem(7)` manual for more on
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defining buildsystem properties.
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more. One may handle such cases by using the
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:prop_tgt:`LINK_INTERFACE_MULTIPLICITY` target property or by manually
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repeating the component in the last ``target_link_libraries`` call.
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However, if two archives are really so interdependent they should probably
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be combined into a single archive, perhaps by using :ref:`Object Libraries`.
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Creating Relocatable Packages
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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