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authorCraig Scott <craig.scott@crascit.com>2022-07-03 04:50:33 (GMT)
committerKitware Robot <kwrobot@kitware.com>2022-07-03 04:50:44 (GMT)
commit2a336d855443d7db601bd79e80fce86726962cd2 (patch)
tree51a21089ba1810b9ad1f1d91570997fb942301ec
parent32014390465669fe4ead629a79447c9996c7dee5 (diff)
parentd185f7c0a8cac19edaea8d54c2a12b51a622731b (diff)
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Merge topic 'doc-LINK_LIBRARY_genex' into release-3.24
d185f7c0a8 Help: Rework $<LINK_LIBRARY>, $<LINK_GROUP> and related docs Acked-by: Kitware Robot <kwrobot@kitware.com> Merge-request: !7413
-rw-r--r--Help/manual/cmake-generator-expressions.7.rst288
-rw-r--r--Help/prop_tgt/LINK_LIBRARY_OVERRIDE.rst69
-rw-r--r--Help/prop_tgt/LINK_LIBRARY_OVERRIDE_LIBRARY.rst50
-rw-r--r--Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE.rst27
-rw-r--r--Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE_SUPPORTED.rst17
-rw-r--r--Help/variable/CMAKE_LANG_LINK_LIBRARY_USING_FEATURE.rst27
-rw-r--r--Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.rst35
-rw-r--r--Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.txt66
-rw-r--r--Help/variable/CMAKE_LINK_GROUP_USING_FEATURE_SUPPORTED.rst13
-rw-r--r--Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.rst34
-rw-r--r--Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.txt140
-rw-r--r--Help/variable/LINK_GROUP_PREDEFINED_FEATURES.txt32
-rw-r--r--Help/variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt158
13 files changed, 502 insertions, 454 deletions
diff --git a/Help/manual/cmake-generator-expressions.7.rst b/Help/manual/cmake-generator-expressions.7.rst
index c871b1b..0a54c1d 100644
--- a/Help/manual/cmake-generator-expressions.7.rst
+++ b/Help/manual/cmake-generator-expressions.7.rst
@@ -1370,229 +1370,237 @@ Output-Related Expressions
.. versionadded:: 3.24
- Manage how libraries are specified during the link step.
- This expression may be used to specify how to link libraries in a target.
- For example:
+ Specify a set of libraries to link to a target, along with a ``feature``
+ which provides details about *how* they should be linked. For example:
.. code-block:: cmake
add_library(lib1 STATIC ...)
add_library(lib2 ...)
- target_link_libraries(lib2 PRIVATE "$<LINK_LIBRARY:load_archive,lib1>")
-
- This specify to use the ``lib1`` target with feature ``load_archive`` for
- linking target ``lib2``. The feature must have be defined by
- :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>` variable or, if
- :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` is false,
- by :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variable.
-
- .. note::
-
- The evaluation of this generator expression will use, for the following
- variables, the values defined at the level of the creation of the target:
-
- * :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED`
- * :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>`
- * :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED`
- * :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>`
-
- This expression can only be used to specify link libraries (i.e. part of
- :command:`link_libraries` or :command:`target_link_libraries` commands and
- :prop_tgt:`LINK_LIBRARIES` or :prop_tgt:`INTERFACE_LINK_LIBRARIES` target
- properties).
+ target_link_libraries(lib2 PRIVATE "$<LINK_LIBRARY:WHOLE_ARCHIVE,lib1>")
- .. note::
-
- If this expression appears in the :prop_tgt:`INTERFACE_LINK_LIBRARIES`
- property of a target, it will be included in the imported target generated
- by :command:`install(EXPORT)` command. It is the responsibility of the
- environment consuming this import to define the link feature used by this
- expression.
+ This specifies that ``lib2`` should link to ``lib1`` and use the
+ ``WHOLE_ARCHIVE`` feature when doing so.
- The ``library-list`` argument can hold CMake targets or external libraries.
- Any CMake target of type :ref:`OBJECT <Object Libraries>` or
- :ref:`INTERFACE <Interface Libraries>` will be ignored by this expression and
- will be handled in the standard way.
+ Feature names are case-sensitive and may only contain letters, numbers and
+ underscores. Feature names defined in all uppercase are reserved for CMake's
+ own built-in features. The pre-defined built-in library features are:
- Each target or external library involved in the link step must have only one
- kind of feature (the absence of feature is also incompatible with any
- feature). For example:
-
- .. code-block:: cmake
-
- add_library(lib1 ...)
+ .. include:: ../variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt
- add_library(lib2 ...)
- target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature1,lib1>")
+ Built-in and custom library features are defined in terms of the following
+ variables:
+
+ * :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED`
+ * :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>`
+ * :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED`
+ * :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>`
+
+ The value used for each of these variables is the value as set at the end of
+ the directory scope in which the target was created. The usage is as follows:
+
+ 1. If the language-specific
+ :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` variable
+ is true, the ``feature`` must be defined by the corresponding
+ :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>` variable.
+ 2. If no language-specific ``feature`` is supported, then the
+ :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` variable must be
+ true and the ``feature`` must be defined by the corresponding
+ :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variable.
+
+ The following limitations should be noted:
+
+ * The ``library-list`` can specify CMake targets or libraries.
+ Any CMake target of type :ref:`OBJECT <Object Libraries>`
+ or :ref:`INTERFACE <Interface Libraries>` will ignore the feature aspect
+ of the expression and instead be linked in the standard way.
+
+ * The ``$<LINK_LIBRARY:...>`` generator expression can only be used to
+ specify link libraries. In practice, this means it can appear in the
+ :prop_tgt:`LINK_LIBRARIES` and :prop_tgt:`INTERFACE_LINK_LIBRARIES`
+ target properties, and be specified in :command:`target_link_libraries`
+ and :command:`link_libraries` commands.
+
+ * If a ``$<LINK_LIBRARY:...>`` generator expression appears in the
+ :prop_tgt:`INTERFACE_LINK_LIBRARIES` property of a target, it will be
+ included in the imported target generated by a :command:`install(EXPORT)`
+ command. It is the responsibility of the environment consuming this
+ import to define the link feature used by this expression.
+
+ * Each target or library involved in the link step must have at most only
+ one kind of library feature. The absence of a feature is also incompatible
+ with all other features. For example:
- add_library(lib3 ...)
- target_link_libraries(lib3 PRIVATE lib1 lib2)
- # an error will be raised here because lib1 has two different features
+ .. code-block:: cmake
- To resolve such incompatibilities, the :prop_tgt:`LINK_LIBRARY_OVERRIDE`
- and :prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>` target properties can be
- used.
+ add_library(lib1 ...)
+ add_library(lib2 ...)
+ add_library(lib3 ...)
- .. note::
+ # lib1 will be associated with feature1
+ target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature1,lib1>")
- This expression does not guarantee that the list of specified libraries
- will be kept grouped. So, to manage constructs like ``start-group`` and
- ``end-group``, as supported by ``GNU ld``, the :genex:`LINK_GROUP`
- generator expression can be used.
+ # lib1 is being linked with no feature here. This conflicts with the
+ # use of feature1 in the line above and would result in an error.
+ target_link_libraries(lib3 PRIVATE lib1 lib2)
- CMake pre-defines some features of general interest:
+ Where it isn't possible to use the same feature throughout a build for a
+ given target or library, the :prop_tgt:`LINK_LIBRARY_OVERRIDE` and
+ :prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>` target properties can be
+ used to resolve such incompatibilities.
- .. include:: ../variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt
+ * The ``$<LINK_LIBRARY:...>`` generator expression does not guarantee
+ that the list of specified targets and libraries will be kept grouped
+ together. To manage constructs like ``--start-group`` and ``--end-group``,
+ as supported by the GNU ``ld`` linker, use the :genex:`LINK_GROUP`
+ generator expression instead.
.. genex:: $<LINK_GROUP:feature,library-list>
.. versionadded:: 3.24
- Manage the grouping of libraries during the link step.
- This expression may be used to specify how to keep groups of libraries during
- the link of a target.
- For example:
+ Specify a group of libraries to link to a target, along with a ``feature``
+ which defines how that group should be linked. For example:
.. code-block:: cmake
add_library(lib1 STATIC ...)
add_library(lib2 ...)
- target_link_libraries(lib2 PRIVATE "$<LINK_GROUP:cross_refs,lib1,external>")
-
- This specify to use the ``lib1`` target and ``external`` library with the
- group feature ``cross_refs`` for linking target ``lib2``. The feature must
- have be defined by :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>`
- variable or, if :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
- is false, by :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>` variable.
+ target_link_libraries(lib2 PRIVATE "$<LINK_GROUP:RESCAN,lib1,external>")
- .. note::
+ This specifies that ``lib2`` should link to ``lib1`` and ``external``, and
+ that both of those two libraries should be included on the linker command
+ line according to the definition of the ``RESCAN`` feature.
- The evaluation of this generator expression will use, for the following
- variables, the values defined at the level of the creation of the target:
+ Feature names are case-sensitive and may only contain letters, numbers and
+ underscores. Feature names defined in all uppercase are reserved for CMake's
+ own built-in features. Currently, there is only one pre-defined built-in
+ group feature:
- * :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
- * :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>`
- * :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
- * :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>`
+ .. include:: ../variable/LINK_GROUP_PREDEFINED_FEATURES.txt
- This expression can only be used to specify link libraries (i.e. part of
- :command:`link_libraries` or :command:`target_link_libraries` commands and
- :prop_tgt:`LINK_LIBRARIES` or :prop_tgt:`INTERFACE_LINK_LIBRARIES` target
- properties).
+ Built-in and custom group features are defined in terms of the following
+ variables:
- .. note::
+ * :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
+ * :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>`
+ * :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
+ * :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>`
- If this expression appears in the :prop_tgt:`INTERFACE_LINK_LIBRARIES`
- property of a target, it will be included in the imported target generated
- by :command:`install(EXPORT)` command. It is the responsibility of the
- environment consuming this import to define the link feature used by this
- expression.
+ The value used for each of these variables is the value as set at the end of
+ the directory scope in which the target was created. The usage is as follows:
- The ``library-list`` argument can hold CMake targets or external libraries.
- Any CMake target of type :ref:`OBJECT <Object Libraries>` or
- :ref:`INTERFACE <Interface Libraries>` will be ignored by this expression and
- will be handled in the standard way.
+ 1. If the language-specific
+ :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED` variable
+ is true, the ``feature`` must be defined by the corresponding
+ :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>` variable.
+ 2. If no language-specific ``feature`` is supported, then the
+ :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED` variable must be
+ true and the ``feature`` must be defined by the corresponding
+ :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>` variable.
- .. note::
+ The ``LINK_GROUP`` generator expression is compatible with the
+ :genex:`LINK_LIBRARY` generator expression. The libraries involved in a
+ group can be specified using the :genex:`LINK_LIBRARY` generator expression.
- This expression is compatible with the :genex:`LINK_LIBRARY` generator
- expression. The libraries involved in a group can be specified using the
- :genex:`LINK_LIBRARY` generator expression.
-
- Each target or external library involved in the link step can be part of
- different groups as far as these groups use the same feature, so mixing
- different group features for the same target or library is forbidden. The
- different groups will be part of the link step.
+ Each target or external library involved in the link step is allowed to be
+ part of multiple groups, but only if all the groups involved specify the
+ same ``feature``. Such groups will not be merged on the linker command line,
+ the individual groups will still be preserved. Mixing different group
+ features for the same target or library is forbidden.
.. code-block:: cmake
add_library(lib1 ...)
add_library(lib2 ...)
-
add_library(lib3 ...)
- target_link_libraries(lib3 PUBLIC "$<LINK_GROUP:feature1,lib1,lib2>")
-
add_library(lib4 ...)
+ add_library(lib5 ...)
+
+ target_link_libraries(lib3 PUBLIC "$<LINK_GROUP:feature1,lib1,lib2>")
target_link_libraries(lib4 PRIVATE "$<LINK_GROUP:feature1,lib1,lib3>")
- # lib4 will be linked with the groups {lib1,lib2} and {lib1,lib3}
+ # lib4 will be linked with the groups {lib1,lib2} and {lib1,lib3}.
+ # Both groups specify the same feature, so this is fine.
- add_library(lib5 ...)
target_link_libraries(lib5 PRIVATE "$<LINK_GROUP:feature2,lib1,lib3>")
- # an error will be raised here because lib1 is part of two groups with
- # different features
+ # An error will be raised here because both lib1 and lib3 are part of two
+ # groups with different features.
When a target or an external library is involved in the link step as part of
- a group and also as standalone, any occurrence of the standalone link item
- will be replaced by the group or groups it belong to.
+ a group and also as not part of any group, any occurrence of the non-group
+ link item will be replaced by the groups it belongs to.
.. code-block:: cmake
add_library(lib1 ...)
add_library(lib2 ...)
-
add_library(lib3 ...)
+ add_library(lib4 ...)
+
target_link_libraries(lib3 PUBLIC lib1)
- add_library(lib4 ...)
target_link_libraries(lib4 PRIVATE lib3 "$<LINK_GROUP:feature1,lib1,lib2>")
# lib4 will only be linked with lib3 and the group {lib1,lib2}
- This example will be "re-written" by CMake in the following form:
+ Because ``lib1`` is part of the group defined for ``lib4``, that group then
+ gets applied back to the use of ``lib1`` for ``lib3``. The end result will
+ be as though the linking relationship for ``lib3`` had been specified as:
.. code-block:: cmake
- add_library(lib1 ...)
- add_library(lib2 ...)
-
- add_library(lib3 ...)
target_link_libraries(lib3 PUBLIC "$<LINK_GROUP:feature1,lib1,lib2>")
- add_library(lib4 ...)
- target_link_libraries(lib4 PRIVATE lib3 "$<LINK_GROUP:feature1,lib1,lib2>")
- # lib4 will only be linked with lib3 and the group {lib1,lib2}
-
- Be aware that the precedence of the group over the standalone link item can
- result in some circular dependency between groups, which will raise an
- error because circular dependencies are not allowed for groups.
+ Be aware that the precedence of the group over the non-group link item can
+ result in circular dependencies between groups. If this occurs, a fatal
+ error is raised because circular dependencies are not allowed for groups.
.. code-block:: cmake
add_library(lib1A ...)
add_library(lib1B ...)
-
add_library(lib2A ...)
add_library(lib2B ...)
+ add_library(lib3 ...)
+ # Non-group linking relationships, these are non-circular so far
target_link_libraries(lib1A PUBLIC lib2A)
target_link_libraries(lib2B PUBLIC lib1B)
- add_library(lib ...)
- target_link_libraries(lib3 PRIVATE "$<LINK_GROUP:feat,lib1A,lib1B>"
- "$<LINK_GROUP:feat,lib2A,lib2B>")
+ # The addition of these groups creates circular dependencies
+ target_link_libraries(lib3 PRIVATE
+ "$<LINK_GROUP:feat,lib1A,lib1B>"
+ "$<LINK_GROUP:feat,lib2A,lib2B>"
+ )
- This example will be "re-written" by CMake in the following form:
+ Because of the groups defined for ``lib3``, the linking relationships for
+ ``lib1A`` and ``lib2B`` effectively get expanded to the equivalent of:
.. code-block:: cmake
- add_library(lib1A ...)
- add_library(lib1B ...)
-
- add_library(lib2A ...)
- add_library(lib2B ...)
-
target_link_libraries(lib1A PUBLIC "$<LINK_GROUP:feat,lib2A,lib2B>")
target_link_libraries(lib2B PUBLIC "$<LINK_GROUP:feat,lib1A,lib1B>")
- add_library(lib ...)
- target_link_libraries(lib3 PRIVATE "$<LINK_GROUP:feat,lib1A,lib1B>"
- "$<LINK_GROUP:feat,lib2A,lib2B>")
+ This creates a circular dependency between groups:
+ ``lib1A --> lib2B --> lib1A``.
- So, we have a circular dependency between groups ``{lib1A,lib1B}`` and
- ``{lib2A,lib2B}``.
+ The following limitations should also be noted:
- CMake pre-defines some features of general interest:
+ * The ``library-list`` can specify CMake targets or libraries.
+ Any CMake target of type :ref:`OBJECT <Object Libraries>`
+ or :ref:`INTERFACE <Interface Libraries>` will ignore the feature aspect
+ of the expression and instead be linked in the standard way.
- .. include:: ../variable/LINK_GROUP_PREDEFINED_FEATURES.txt
+ * The ``$<LINK_GROUP:...>`` generator expression can only be used to
+ specify link libraries. In practice, this means it can appear in the
+ :prop_tgt:`LINK_LIBRARIES` and :prop_tgt:`INTERFACE_LINK_LIBRARIES`
+ target properties, and be specified in :command:`target_link_libraries`
+ and :command:`link_libraries` commands.
+
+ * If a ``$<LINK_GROUP:...>`` generator expression appears in the
+ :prop_tgt:`INTERFACE_LINK_LIBRARIES` property of a target, it will be
+ included in the imported target generated by a :command:`install(EXPORT)`
+ command. It is the responsibility of the environment consuming this
+ import to define the link feature used by this expression.
.. genex:: $<INSTALL_INTERFACE:...>
diff --git a/Help/prop_tgt/LINK_LIBRARY_OVERRIDE.rst b/Help/prop_tgt/LINK_LIBRARY_OVERRIDE.rst
index 81a2a4a..916a7c6 100644
--- a/Help/prop_tgt/LINK_LIBRARY_OVERRIDE.rst
+++ b/Help/prop_tgt/LINK_LIBRARY_OVERRIDE.rst
@@ -3,52 +3,63 @@ LINK_LIBRARY_OVERRIDE
.. versionadded:: 3.24
-To resolve incompatible features introduced by :genex:`LINK_LIBRARY` generator
-expression, this property offers the possibility to override, per ``link-item``
-(``CMake`` target or external library) involved in the link step, any defined
-features with a new one.
+Override the library features associated with libraries from
+:genex:`LINK_LIBRARY` generator expressions. This can be used to resolve
+incompatible library features that result from specifying different features
+for the same library in different :genex:`LINK_LIBRARY` generator expressions.
-This property takes a :ref:`;-list <CMake Language Lists>` of override
-declarations which have the following format:
-
-::
+This property supports overriding multiple libraries and features. It expects
+a :ref:`semicolon-separated list <CMake Language Lists>`, where each list item
+has the following form::
feature[,link-item]*
-For the list of ``link-item`` (``CMake`` target or external library) specified,
-the feature ``feature`` will be used in place of any declared feature. For
-example:
+For each comma-separated ``link-item``, any existing library feature associated
+with it will be ignored for the target this property is set on. The item
+will instead be associated with the specified ``feature``. Each ``link-item``
+can be anything that would be accepted as part of a ``library-list`` in a
+:genex:`LINK_LIBRARY` generator expression.
.. code-block:: cmake
add_library(lib1 ...)
- target_link_libraries(lib1 PUBLIC "$<LINK_LIBRARY:feature1,external>")
-
add_library(lib2 ...)
- target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature2,lib1>")
-
add_library(lib3 ...)
+
+ target_link_libraries(lib1 PUBLIC "$<LINK_LIBRARY:feature1,external>")
+ target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature2,lib1>")
target_link_libraries(lib3 PRIVATE lib1 lib2)
- # Here, lib1 has two different features which prevents to link lib3
- # So, define LINK_LIBRARY_OVERRIDE property to ensure correct link
+
+ # lib1 is associated with both feature2 and no feature. Without any override,
+ # this would result in a fatal error at generation time for lib3.
+ # Define an override to resolve the incompatible feature associations.
set_property(TARGET lib3 PROPERTY LINK_LIBRARY_OVERRIDE "feature2,lib1,external")
- # The lib1 and external will be used with FEATURE2 to link lib3
-It is also possible to override any feature with the pre-defined feature
-``DEFAULT`` to get the standard behavior (i.e. no feature):
+ # lib1 and external will now be associated with feature2 instead when linking lib3
+
+It is also possible to override any feature with the pre-defined ``DEFAULT``
+library feature. This effectively discards any feature for that link item,
+for that target only (``lib3`` in this example):
.. code-block:: cmake
- set_property(TARGET lib3 PROPERTY LINK_LIBRARY_OVERRIDE "DEFAULT,lib1"
- "feature2,external")
- # The lib1 will be used without any feature and external will use feature2 to link lib3
+ # When linking lib3, discard any library feature for lib1, and use feature2 for external
+ set_property(TARGET lib3 PROPERTY LINK_LIBRARY_OVERRIDE
+ "DEFAULT,lib1"
+ "feature2,external"
+ )
+
+The above example also demonstrates how to specify different feature overrides
+for different link items. See the :prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>`
+target property for an alternative way of overriding library features for
+individual libraries, which may be simpler in some cases. If both properties
+are defined and specify an override for the same link item,
+:prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>` takes precedence over
+``LINK_LIBRARY_OVERRIDE``.
Contents of ``LINK_LIBRARY_OVERRIDE`` may use
:manual:`generator expressions <cmake-generator-expressions(7)>`.
-See also :prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>` target property for
-a per linked target oriented approach to override features.
-
-For more information about features, see
-:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>`
-and :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variables.
+For more information about library features, see the
+:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>` and
+:variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variables.
diff --git a/Help/prop_tgt/LINK_LIBRARY_OVERRIDE_LIBRARY.rst b/Help/prop_tgt/LINK_LIBRARY_OVERRIDE_LIBRARY.rst
index 112f614..4d3dd4f 100644
--- a/Help/prop_tgt/LINK_LIBRARY_OVERRIDE_LIBRARY.rst
+++ b/Help/prop_tgt/LINK_LIBRARY_OVERRIDE_LIBRARY.rst
@@ -3,43 +3,49 @@ LINK_LIBRARY_OVERRIDE_<LIBRARY>
.. versionadded:: 3.24
-To resolve incompatible features introduced by :genex:`LINK_LIBRARY` generator
-expression, this property offers the possibility to override, for a
-``link-item`` (``CMake`` target or external library) involved in the link step,
-any defined features with a new one.
+Override the library feature associated with ``<LIBRARY>`` from
+:genex:`LINK_LIBRARY` generator expressions. This can be used to resolve
+incompatible library features that result from specifying different features
+for ``<LIBRARY>`` in different :genex:`LINK_LIBRARY` generator expressions.
-This property takes a ``feature`` name which will be applied to the
-``link-item`` specified by ``<LIBRARY>`` suffix property. For example:
+When set on a target, this property holds a single library feature name, which
+will be applied to ``<LIBRARY>`` when linking that target.
.. code-block:: cmake
add_library(lib1 ...)
- target_link_libraries(lib1 PUBLIC "$<LINK_LIBRARY:feature1,external>")
-
add_library(lib2 ...)
- target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature2,lib1>")
-
add_library(lib3 ...)
+
+ target_link_libraries(lib1 PUBLIC "$<LINK_LIBRARY:feature1,external>")
+ target_link_libraries(lib2 PUBLIC "$<LINK_LIBRARY:feature2,lib1>")
target_link_libraries(lib3 PRIVATE lib1 lib2)
- # Here, lib1 has two different features which prevents to link lib3
- # So, define LINK_LIBRARY_OVERRIDE_lib1 property to ensure correct link
+
+ # lib1 is associated with both feature2 and no feature. Without any override,
+ # this would result in a fatal error at generation time for lib3.
+ # Define an override to resolve the incompatible feature associations.
set_property(TARGET lib3 PROPERTY LINK_LIBRARY_OVERRIDE_lib1 feature2)
- # The lib1 will be used with feature2 to link lib3
-It is also possible to override any feature with the pre-defined feature
-``DEFAULT`` to get the standard behavior (i.e. no feature):
+ # lib1 will now be associated with feature2 instead when linking lib3
+
+It is also possible to override any feature with the pre-defined ``DEFAULT``
+library feature. This effectively discards any feature for that link item,
+for that target only (``lib3`` in this example):
.. code-block:: cmake
+ # When linking lib3, discard any library feature for lib1
set_property(TARGET lib3 PROPERTY LINK_LIBRARY_OVERRIDE_lib1 DEFAULT)
- # The lib1 will be used without any feature to link lib3
+
+See the :prop_tgt:`LINK_LIBRARY_OVERRIDE` target property for an alternative
+way of overriding library features for multiple libraries at once. If both
+properties are defined and specify an override for the same link item,
+``LINK_LIBRARY_OVERRIDE_<LIBRARY>`` takes precedence over
+:prop_tgt:`LINK_LIBRARY_OVERRIDE`.
Contents of ``LINK_LIBRARY_OVERRIDE_<LIBRARY>`` may use
:manual:`generator expressions <cmake-generator-expressions(7)>`.
-This property takes precedence over :prop_tgt:`LINK_LIBRARY_OVERRIDE`
-target property.
-
-For more information about features, see
-:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>`
-and :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variables.
+For more information about library features, see the
+:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>` and
+:variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variables.
diff --git a/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE.rst b/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE.rst
index f2ef843..7c929d0 100644
--- a/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE.rst
+++ b/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE.rst
@@ -3,25 +3,14 @@ CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>
.. versionadded:: 3.24
-This variable defines, for the specified ``<FEATURE>`` and the linker language
-``<LANG>``, the expression expected by the linker when libraries are specified
-using :genex:`LINK_GROUP` generator expression.
+This variable defines how to link a group of libraries for the specified
+``<FEATURE>`` when a :genex:`LINK_GROUP` generator expression is used and
+the link language for the target is ``<LANG>``.
+For this variable to have any effect, the associated
+:variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED` variable
+must be set to true.
-.. note::
-
- * Feature names can contain Latin letters, digits and undercores.
- * Feature names defined in all uppercase are reserved to CMake.
-
-See also the associated variable
-:variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED` and
-:variable:`CMAKE_LINK_GROUP_USING_<FEATURE>` variable for the definition of
-features independent from the link language.
+The :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>` variable should be defined
+instead for features that are independent of the link language.
.. include:: CMAKE_LINK_GROUP_USING_FEATURE.txt
-
-Predefined Features
-^^^^^^^^^^^^^^^^^^^
-
-CMake pre-defines some features of general interest:
-
-.. include:: LINK_GROUP_PREDEFINED_FEATURES.txt
diff --git a/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE_SUPPORTED.rst b/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE_SUPPORTED.rst
index 533eee7..b314c5a 100644
--- a/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE_SUPPORTED.rst
+++ b/Help/variable/CMAKE_LANG_LINK_GROUP_USING_FEATURE_SUPPORTED.rst
@@ -3,11 +3,12 @@ CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED
.. versionadded:: 3.24
-Set to ``TRUE`` if the ``<FEATURE>``, as defined by variable
-:variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>`, is supported for the
-linker language ``<LANG>``.
-
-.. note::
-
- This variable is evaluated before the more generic variable
- :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED`.
+This variable specifies whether the ``<FEATURE>`` is supported for the link
+language ``<LANG>``. If this variable is true, then the ``<FEATURE>`` must
+be defined by :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>`, and the
+more generic :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED` and
+:variable:`CMAKE_LINK_GROUP_USING_<FEATURE>` variables are not used.
+
+If ``CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED`` is false or is not
+set, then the :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED` variable
+will determine whether ``<FEATURE>`` is deemed to be supported.
diff --git a/Help/variable/CMAKE_LANG_LINK_LIBRARY_USING_FEATURE.rst b/Help/variable/CMAKE_LANG_LINK_LIBRARY_USING_FEATURE.rst
index 220ae99..39fcff8 100644
--- a/Help/variable/CMAKE_LANG_LINK_LIBRARY_USING_FEATURE.rst
+++ b/Help/variable/CMAKE_LANG_LINK_LIBRARY_USING_FEATURE.rst
@@ -3,25 +3,14 @@ CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>
.. versionadded:: 3.24
-This variable defines, for the specified ``<FEATURE>`` and the linker language
-``<LANG>``, the expression expected by the linker when libraries are specified
-using :genex:`LINK_LIBRARY` generator expression.
+This variable defines how to link a library or framework for the specified
+``<FEATURE>`` when a :genex:`LINK_LIBRARY` generator expression is used and
+the link language for the target is ``<LANG>``.
+For this variable to have any effect, the associated
+:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` variable
+must be set to true.
-.. note::
-
- * Feature names can contain Latin letters, digits and undercores.
- * Feature names defined in all uppercase are reserved to CMake.
-
-See also the associated variable
-:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` and
-:variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variable for the definition of
-features independent from the link language.
+The :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>` variable should be defined
+instead for features that are independent of the link language.
.. include:: CMAKE_LINK_LIBRARY_USING_FEATURE.txt
-
-Predefined Features
-^^^^^^^^^^^^^^^^^^^
-
-CMake pre-defines some features of general interest:
-
-.. include:: LINK_LIBRARY_PREDEFINED_FEATURES.txt
diff --git a/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.rst b/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.rst
index 692c099..90b7f8b 100644
--- a/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.rst
+++ b/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.rst
@@ -3,31 +3,20 @@ CMAKE_LINK_GROUP_USING_<FEATURE>
.. versionadded:: 3.24
-This variable defines, for the specified ``<FEATURE>``, the expression expected
-by the linker when libraries are specified using :genex:`LINK_GROUP` generator
-expression.
+This variable defines how to link a group of libraries for the specified
+``<FEATURE>`` when a :genex:`LINK_GROUP` generator expression is used.
+Both of the following conditions must be met for this variable to have any
+effect:
-.. note::
+* The associated :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
+ variable must be set to true.
- * Feature names can contain Latin letters, digits and undercores.
- * Feature names defined in all uppercase are reserved to CMake.
+* There is no language-specific definition for the same ``<FEATURE>``.
+ This means :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED`
+ cannot be true for the link language used by the target for which the
+ :genex:`LINK_GROUP` generator expression is evaluated.
-See also the associated variable
-:variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED` and
-:variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>` variable for the definition
-of features dependent from the link language.
-
-This variable will be used by :genex:`LINK_GROUP` generator expression if,
-for the linker language, the variable
-:variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED` is not defined
-and the variable :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED` is
-``TRUE``..
+The :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>` variable should be
+defined instead for features that are dependent on the link language.
.. include:: CMAKE_LINK_GROUP_USING_FEATURE.txt
-
-Predefined Features
-^^^^^^^^^^^^^^^^^^^
-
-CMake pre-defines some features of general interest:
-
-.. include:: LINK_GROUP_PREDEFINED_FEATURES.txt
diff --git a/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.txt b/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.txt
index ecd9cb5..23ea157 100644
--- a/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.txt
+++ b/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE.txt
@@ -1,17 +1,24 @@
+Feature names are case-sensitive and may only contain letters, numbers
+and underscores. Feature names defined in all uppercase are reserved for
+CMake's own built-in features (see `Predefined Features`_ further below).
-It must contain two elements.
+
+Feature Definitions
+^^^^^^^^^^^^^^^^^^^
+
+A group feature definition is a list that contains exactly two elements:
::
<PREFIX> <SUFFIX>
-``<PREFIX>`` and ``<SUFFIX>`` will be used to encapsulate the list of
-libraries.
+On the linker command line, ``<PREFIX>`` will precede the list of libraries
+in the group and ``<SUFFIX>`` will follow after.
-For the elements of this variable, the ``LINKER:`` prefix can be used:
+For the elements of this variable, the ``LINKER:`` prefix can be used.
- .. include:: ../command/LINK_OPTIONS_LINKER.txt
- :start-line: 3
+.. include:: ../command/LINK_OPTIONS_LINKER.txt
+ :start-line: 3
Examples
^^^^^^^^
@@ -19,36 +26,53 @@ Examples
Solving cross-references between two static libraries
"""""""""""""""""""""""""""""""""""""""""""""""""""""
-A common need is the capability to search repeatedly in a group of static
-libraries until no new undefined references are created. This capability is
-offered by different environments but with a specific syntax:
+A project may define two or more static libraries which have circular
+dependencies between them. In order for the linker to resolve all symbols
+at link time, it may need to search repeatedly among the libraries until no
+new undefined references are created. Different linkers use different syntax
+for achieving this. The following example shows how this may be implemented
+for some linkers. Note that this is for illustration purposes only.
+Projects should use the built-in ``RESCAN`` group feature instead
+(see `Predefined Features`_), which provides a more complete and more robust
+implementation of this functionality.
.. code-block:: cmake
set(CMAKE_C_LINK_GROUP_USING_cross_refs_SUPPORTED TRUE)
- if(CMAKE_C_COMPILER_ID STREQUAL "GNU"
- AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
- set(CMAKE_C_LINK_GROUP_USING_cross_refs "LINKER:--start-group"
- "LINKER:--end-group")
- elseif(CMAKE_C_COMPILER_ID STREQUAL "SunPro"
- AND CMAKE_SYSTEM_NAME STREQUAL "SunOS")
- set(CMAKE_C_LINK_GROUP_USING_cross_refs "LINKER:-z,rescan-start"
- "LINKER:-z,rescan-end")
+ if(CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
+ set(CMAKE_C_LINK_GROUP_USING_cross_refs
+ "LINKER:--start-group"
+ "LINKER:--end-group"
+ )
+ elseif(CMAKE_C_COMPILER_ID STREQUAL "SunPro" AND CMAKE_SYSTEM_NAME STREQUAL "SunOS")
+ set(CMAKE_C_LINK_GROUP_USING_cross_refs
+ "LINKER:-z,rescan-start"
+ "LINKER:-z,rescan-end"
+ )
else()
# feature not yet supported for the other environments
set(CMAKE_C_LINK_GROUP_USING_cross_refs_SUPPORTED FALSE)
endif()
add_library(lib1 STATIC ...)
+ add_library(lib2 SHARED ...)
- add_library(lib3 SHARED ...)
if(CMAKE_C_LINK_GROUP_USING_cross_refs_SUPPORTED)
- target_link_libraries(lib3 PRIVATE "$<LINK_GROUP:cross_refs,lib1,external>")
+ target_link_libraries(lib2 PRIVATE "$<LINK_GROUP:cross_refs,lib1,external>")
else()
- target_link_libraries(lib3 PRIVATE lib1 external)
+ target_link_libraries(lib2 PRIVATE lib1 external)
endif()
-CMake will generate the following link expressions:
+CMake will generate the following linker command line fragments when linking
+``lib2``:
* ``GNU``: ``-Wl,--start-group /path/to/lib1.a -lexternal -Wl,--end-group``
* ``SunPro``: ``-Wl,-z,rescan-start /path/to/lib1.a -lexternal -Wl,-z,rescan-end``
+
+
+Predefined Features
+^^^^^^^^^^^^^^^^^^^
+
+The following built-in group features are pre-defined by CMake:
+
+.. include:: LINK_GROUP_PREDEFINED_FEATURES.txt
diff --git a/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE_SUPPORTED.rst b/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE_SUPPORTED.rst
index 318892f..8b4ee6e 100644
--- a/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE_SUPPORTED.rst
+++ b/Help/variable/CMAKE_LINK_GROUP_USING_FEATURE_SUPPORTED.rst
@@ -3,11 +3,10 @@ CMAKE_LINK_GROUP_USING_<FEATURE>_SUPPORTED
.. versionadded:: 3.24
-Set to ``TRUE`` if the ``<FEATURE>``, as defined by variable
-:variable:`CMAKE_LINK_GROUP_USING_<FEATURE>`, is supported regardless the
-linker language.
+This variable specifies whether the ``<FEATURE>`` is supported regardless of
+the link language. If this variable is true, then the ``<FEATURE>`` must
+be defined by :variable:`CMAKE_LINK_GROUP_USING_<FEATURE>`.
-.. note::
-
- This variable is evaluated if, and only if, the variable
- :variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED` is not defined.
+Note that this variable has no effect if
+:variable:`CMAKE_<LANG>_LINK_GROUP_USING_<FEATURE>_SUPPORTED` is true for
+the link language of the target.
diff --git a/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.rst b/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.rst
index 9f1cede..c652733 100644
--- a/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.rst
+++ b/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.rst
@@ -3,31 +3,17 @@ CMAKE_LINK_LIBRARY_USING_<FEATURE>
.. versionadded:: 3.24
-This variable defines, for the specified ``FEATURE``, the expression expected
-by the linker, regardless the linker language, when libraries are specified
-using :genex:`LINK_LIBRARY` generator expression.
+This variable defines how to link a library or framework for the specified
+``<FEATURE>`` when a :genex:`LINK_LIBRARY` generator expression is used.
+Both of the following conditions must be met for this variable to have any
+effect:
-.. note::
+* The associated :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED`
+ variable must be set to true.
- * Feature names can contain Latin letters, digits and undercores.
- * Feature names defined in all uppercase are reserved to CMake.
-
-See also the associated variable
-:variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` and
-:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>` variable for the
-definition of features dependent from the link language.
-
-This variable will be used by :genex:`LINK_LIBRARY` generator expression if,
-for the linker language, the variable
-:variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` is not defined
-and the variable :variable:`CMAKE_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED` is
-``TRUE``.
+* There is no language-specific definition for the same ``<FEATURE>``.
+ This means :variable:`CMAKE_<LANG>_LINK_LIBRARY_USING_<FEATURE>_SUPPORTED`
+ cannot be true for the link language used by the target for which the
+ :genex:`LINK_LIBRARY` generator expression is evaluated.
.. include:: CMAKE_LINK_LIBRARY_USING_FEATURE.txt
-
-Predefined Features
-^^^^^^^^^^^^^^^^^^^
-
-CMake pre-defines some features of general interest:
-
-.. include:: LINK_LIBRARY_PREDEFINED_FEATURES.txt
diff --git a/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.txt b/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.txt
index ec293d3..4b13b7c 100644
--- a/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.txt
+++ b/Help/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.txt
@@ -1,39 +1,58 @@
+Feature names are case-sensitive and may only contain letters, numbers
+and underscores. Feature names defined in all uppercase are reserved for
+CMake's own built-in features (see `Predefined Features`_ further below).
-It can contain one or three elements.
-::
-
- [<PREFIX>] <LIBRARY_EXPRESSION> [<SUFFIX>]
+Feature Definitions
+^^^^^^^^^^^^^^^^^^^
-When ``<PREFIX>`` and/or ``<SUFFIX>`` are specified, they encapsulate the list
-of libraries.
+A library feature definition is a list that contains one or three elements:
-.. note::
+::
- Even if ``<PREFIX>`` and ``<SUFFIX>`` are specified, there is not guarantee
- that the list of specified libraries, as part of :genex:`LINK_LIBRARY`
- generator expression, will be kept grouped. So, constructs like
- ``start-group`` and ``end-group``, as supported by ``GNU ld``, cannot be
- used.
+ [<PREFIX>] <LIBRARY_EXPRESSION> [<SUFFIX>]
-``<LIBRARY_EXPRESSION>`` is used to specify the decoration for each
-library. For that purpose, the patterns ``<LIBRARY>``, ``<LINK_ITEM>``, and
-``<LIB_ITEM>`` are available:
+When ``<PREFIX>`` and ``<SUFFIX>`` are specified, they precede and follow
+respectively the whole list of libraries specified in the
+:genex:`LINK_LIBRARY` expression, not each library item individually.
+There is no guarantee that the list of specified libraries will be kept
+grouped together though, so the ``<PREFIX>`` and ``<SUFFIX>`` may appear
+more than once if the library list is reorganized by CMake to satisfy other
+constraints. This means constructs like ``--start-group`` and ``--end-group``,
+as supported by the GNU ``ld`` linker, cannot be used in this way. The
+:genex:`LINK_GROUP` generator expression should be used instead for such
+constructs.
+
+``<LIBRARY_EXPRESSION>`` is used to specify the pattern for constructing the
+corresponding fragment on the linker command line for each library.
+The following placeholders can be used in the expression:
+
+* ``<LIBRARY>`` is expanded to the full path to the library for CMake targets,
+ or to a platform-specific value based on the item otherwise (the same as
+ ``<LINK_ITEM>`` on Windows, or the library base name for other platforms).
+* ``<LINK_ITEM>`` is expanded to how the library would normally be linked on
+ the linker command line.
+* ``<LIB_ITEM>`` is expanded to the full path to the library for CMake targets,
+ or the item itself exactly as specified in the ``<LIBRARY_EXPRESSION>``
+ otherwise.
+
+In addition to the above, it is possible to have one pattern for paths
+(CMake targets and external libraries specified with file paths) and another
+for other items specified by name only. The ``PATH{}`` and ``NAME{}`` wrappers
+can be used to provide the expansion for those two cases, respectively.
+When wrappers are used, both must be present. For example:
-* ``<LIBRARY>`` is expanded to the library as computed by CMake.
-* ``<LINK_ITEM>`` is expanded to the same expression as if the library was
- specified in the standard way.
-* ``<LIB_ITEM>`` is equivalent to ``<LIBRARY>`` for CMake targets and is
- expanded to the item specified by the user for external libraries.
+.. code-block:: cmake
-Moreover, it is possible to have different decorations for paths (CMake targets
-and external libraries specified with absolute paths) and other items specified
-by name. For that purpose, ``PATH{}`` and ``NAME{}`` wrappers can be used.
+ set(CMAKE_LINK_LIBRARY_USING_weak_library
+ "PATH{-weak_library <LIBRARY>}NAME{LINKER:-weak-l<LIB_ITEM>}"
+ )
-For all three elements of this variable, the ``LINKER:`` prefix can be used:
+For all three elements of this variable (``<PREFIX>``, ``<LIBRARY_EXPRESSION>``,
+and ``<SUFFIX>``), the ``LINKER:`` prefix can be used.
- .. include:: ../command/LINK_OPTIONS_LINKER.txt
- :start-line: 3
+.. include:: ../command/LINK_OPTIONS_LINKER.txt
+ :start-line: 3
Examples
^^^^^^^^
@@ -41,19 +60,24 @@ Examples
Loading a whole static library
""""""""""""""""""""""""""""""
-A common need is the capability to load a whole static library. This capability
-is offered by various environments but with a specific syntax:
+A common need is to prevent the linker from discarding any symbols from a
+static library. Different linkers use different syntax for achieving this.
+The following example shows how this may be implemented for some linkers.
+Note that this is for illustration purposes only. Projects should use the
+built-in ``WHOLE_ARCHIVE`` feature instead (see `Predefined Features`_), which
+provides a more complete and more robust implementation of this functionality.
.. code-block:: cmake
set(CMAKE_C_LINK_LIBRARY_USING_load_archive_SUPPORTED TRUE)
if(CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
set(CMAKE_C_LINK_LIBRARY_USING_load_archive "-force_load <LIB_ITEM>")
- elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU"
- AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
- set(CMAKE_C_LINK_LIBRARY_USING_load_archive "LINKER:--push-state,--whole-archive"
- "<LINK_ITEM>"
- "LINKER:--pop-state")
+ elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
+ set(CMAKE_C_LINK_LIBRARY_USING_load_archive
+ "LINKER:--push-state,--whole-archive"
+ "<LINK_ITEM>"
+ "LINKER:--pop-state"
+ )
elseif(CMAKE_C_COMPILER_ID STREQUAL "MSVC")
set(CMAKE_C_LINK_LIBRARY_USING_load_archive "/WHOLEARCHIVE:<LIBRARY>")
else()
@@ -62,41 +86,45 @@ is offered by various environments but with a specific syntax:
endif()
add_library(lib1 STATIC ...)
-
add_library(lib2 SHARED ...)
+
if(CMAKE_C_LINK_LIBRARY_USING_load_archive_SUPPORTED)
+ # The -force_load Apple linker option requires a file name
+ set(external_lib
+ "$<IF:$<LINK_LANG_AND_ID:C,AppleClang>,libexternal.a,external>"
+ )
target_link_libraries(lib2 PRIVATE
- "$<LINK_LIBRARY:load_archive,lib1,$<IF:$<LINK_LANG_AND_ID:C,Clang>,libexternal.a,external>>")
+ "$<LINK_LIBRARY:load_archive,lib1,${external_lib}>"
+ )
else()
target_link_libraries(lib2 PRIVATE lib1 external)
endif()
CMake will generate the following link expressions:
-* ``Clang``: ``-force_load /path/to/lib1.a -force_load libexternal.a``
-* ``GNU``: ``-Wl,--whole-archive /path/to/lib1.a -lexternal -Wl,--no-whole-archive``
+* ``AppleClang``: ``-force_load /path/to/lib1.a -force_load libexternal.a``
+* ``GNU``: ``-Wl,--push-state,--whole-archive /path/to/lib1.a -lexternal -Wl,--pop-state``
* ``MSVC``: ``/WHOLEARCHIVE:/path/to/lib1.lib /WHOLEARCHIVE:external.lib``
-CMake will ensure, when possible, that ``<PREFIX>`` and ``<SUFFIX>`` are
-not repeated for each library.
-
-In case of ``Clang``, the pattern ``<LIB_ITEM>`` is used because we need to
-specify the library as defined by the user, not the name computed by CMake
-(in that case ``external``).
-
Linking a library as weak
"""""""""""""""""""""""""
-On MacOS, it is possible to link a library in weak mode (the library and all
-references are marked as weak imports), but different flags must be used for a
-library specified by path and by name. This constraint by be solved by using
-``PATH{}`` and ``NAME{}`` wrappers:
+On macOS, it is possible to link a library in weak mode (the library and all
+references are marked as weak imports). Different flags must be used for a
+library specified by file path compared to one specified by name.
+This constraint can be solved using ``PATH{}`` and ``NAME{}`` wrappers.
+Again, the following example shows how this may be implemented for some
+linkers, but it is for illustration purposes only. Projects should use the
+built-in ``WEAK_FRAMEWORK`` or ``WEAK_LIBRARY`` features instead (see
+`Predefined Features`_), which provide more complete and more robust
+implementations of this functionality.
.. code-block:: cmake
if (CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
set(CMAKE_LINK_LIBRARY_USING_weak_library
- "PATH{-weak_library <LIBRARY>}NAME{LINKER:-weak-l<LIB_ITEM>}")
+ "PATH{-weak_library <LIBRARY>}NAME{LINKER:-weak-l<LIB_ITEM>}"
+ )
set(CMAKE_LINK_LIBRARY_USING_weak_library_SUPPORTED TRUE)
endif()
@@ -108,5 +136,15 @@ library specified by path and by name. This constraint by be solved by using
target_link_libraries(main PRIVATE lib external)
endif()
-CMake will generate the following link expression:
-``-weak_library /path/to/lib -Xlinker -weak-lexternal``
+CMake will generate the following linker command line fragment when linking
+``main`` using the ``AppleClang`` toolchain:
+
+``-weak_library /path/to/lib -Xlinker -weak-lexternal``.
+
+
+Predefined Features
+^^^^^^^^^^^^^^^^^^^
+
+The following built-in library features are pre-defined by CMake:
+
+.. include:: LINK_LIBRARY_PREDEFINED_FEATURES.txt
diff --git a/Help/variable/LINK_GROUP_PREDEFINED_FEATURES.txt b/Help/variable/LINK_GROUP_PREDEFINED_FEATURES.txt
index 5f1a11b..557886e 100644
--- a/Help/variable/LINK_GROUP_PREDEFINED_FEATURES.txt
+++ b/Help/variable/LINK_GROUP_PREDEFINED_FEATURES.txt
@@ -1,22 +1,22 @@
-**Circular references with static libraries**
-
-Some linkers are one-pass only so to handle circular references between
-static libraries, the following feature can be used:
-
``RESCAN``
- The specified static libraries are searched repeatedly until no
- new undefined references are created. Normally, an static library is searched
- only once in the order that it is specified on the command line. If a symbol
- in that library is needed to resolve an undefined symbol referred to by an
- object in an library that appears later on the command line, the linker would
- not be able to resolve that reference. By grouping the static libraries, they
- all be searched repeatedly until all possible references are resolved (use
- linker options ``--start-group`` and ``--end-group`` or, on ``SunOS``,
- ``-z rescan-start`` and ``-z rescan-end``).
+ Some linkers are single-pass only. For such linkers, circular references
+ between libraries typically result in unresolved symbols. This feature
+ instructs the linker to search the specified static libraries repeatedly
+ until no new undefined references are created.
+
+ Normally, a static library is searched only once in the order that it is
+ specified on the command line. If a symbol in that library is needed to
+ resolve an undefined symbol referred to by an object in a library that
+ appears later on the command line, the linker would not be able to resolve
+ that reference. By grouping the static libraries with the ``RESCAN``
+ feature, they will all be searched repeatedly until all possible references
+ are resolved. This will use linker options like ``--start-group`` and
+ ``--end-group``, or on SunOS, ``-z rescan-start`` and ``-z rescan-end``.
Using this feature has a significant performance cost. It is best to use it
only when there are unavoidable circular references between two or more
static libraries.
- This feature is available on ``Linux``, ``BSD``, and ``SunOS`` target
- platforms as well as ``Windows`` when ``GNU`` toolchain is used.
+ This feature is available when using toolchains that target Linux, BSD, and
+ SunOS. It can also be used when targeting Windows platforms if the GNU
+ toolchain is used.
diff --git a/Help/variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt b/Help/variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt
index e4fa0ed8..8ae6c57 100644
--- a/Help/variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt
+++ b/Help/variable/LINK_LIBRARY_PREDEFINED_FEATURES.txt
@@ -1,88 +1,96 @@
-**Features available in all environments**
-
``DEFAULT``
- This feature enables default link expression. This is mainly
- useful with :prop_tgt:`LINK_LIBRARY_OVERRIDE` and
+ This feature corresponds to standard linking, essentially equivalent to
+ using no feature at all. It is typically only used with the
+ :prop_tgt:`LINK_LIBRARY_OVERRIDE` and
:prop_tgt:`LINK_LIBRARY_OVERRIDE_<LIBRARY>` target properties.
-**Features available for a subset of environments**
-
``WHOLE_ARCHIVE``
- Force load of all members in a static library.
-
- Target platforms supported: all ``Apple`` variants, ``Linux``, all ``BSD``
- variants, ``SunOS``, ``Windows``, ``CYGWIN``, and ``MSYS``.
-
- Platform-specific notes:
-
- * On Apple platforms, the library must be specified as a CMake target name, a
- library file name (such as ``libfoo.a``), or a library file path (such as
- ``/path/to/libfoo.a``). It cannot be specified as a plain library name
- (such as ``foo``, where ``foo`` is not CMake target), due to a limitation
- in the Apple linker.
- * On Windows platforms, for ``MSVC`` or MSVC-like toolchains, the version
- must be greater than ``1900``.
-
-**Features available in Apple environments**
-
-It is assumed that the linker used is the one provided by `XCode` or is
-compatible with it.
-
-Framework support
+ Force inclusion of all members of a static library. This feature is only
+ supported for the following platforms, with limitations as noted:
+
+ * Linux.
+ * All BSD variants.
+ * SunOS.
+ * All Apple variants. The library must be specified as a CMake target name,
+ a library file name (such as ``libfoo.a``), or a library file path (such as
+ ``/path/to/libfoo.a``). Due to a limitation of the Apple linker, it
+ cannot be specified as a plain library name like ``foo``, where ``foo``
+ is not a CMake target.
+ * Windows. When using a MSVC or MSVC-like toolchain, the MSVC version must
+ be greater than 1900.
+ * Cygwin.
+ * MSYS.
``FRAMEWORK``
- This option tells the linker to search for the specified
- framework (use linker option ``-framework``).
-``NEEDED_FRAMEWORK``
- This is the same as the ``FRAMEWORK`` feature but means
- to really link with the framework even if no symbols are used from it (use
- linker option ``-needed_framework``).
-``REEXPORT_FRAMEWORK``
- This is the same as the ``FRAMEWORK`` feature but
- also specifies that all symbols in that framework should be available to
- clients linking to the library being created (use linker option
- ``-reexport_framework``).
-``WEAK_FRAMEWORK``
- This is the same as the ``FRAMEWORK`` feature but forces
- the framework and all references to it to be marked as weak imports (use
- linker option ``-weak_framework``).
+ This option tells the linker to search for the specified framework using
+ the ``-framework`` linker option. It can only be used on Apple platforms,
+ and only with a linker that understands the option used (i.e. the linker
+ provided with Xcode, or one compatible with it).
+
+ The framework can be specified as a CMake framework target, a bare framework
+ name, or a file path. If a target is given, that target must have the
+ :prop_tgt:`FRAMEWORK` target property set to true. For a file path, if it
+ contains a directory part, that directory will be added as a framework
+ search path.
+
+ .. code-block:: cmake
+
+ add_library(lib SHARED ...)
+ target_link_libraries(lib PRIVATE "$<LINK_LIBRARY:FRAMEWORK,/path/to/my_framework>")
+
+ # The constructed linker command line will contain:
+ # -F/path/to -framework my_framework
+
+ File paths must conform to one of the following patterns (``*`` is a
+ wildcard, and optional parts are shown as ``[...]``):
+
+ * ``[/path/to/]FwName[.framework]``
+ * ``[/path/to/]FwName.framework/FwName``
+ * ``[/path/to/]FwName.framework/Versions/*/FwName``
+
+ Note that CMake recognizes and automatically handles framework targets,
+ even without using the ``$<LINK_LIBRARY:FRAMEWORK,...>`` expression.
+ The generator expression can still be used with a CMake target if the
+ project wants to be explicit about it, but it is not required to do so.
+ The linker command line may have some differences between using the
+ generator expression or not, but the final result should be the same.
+ On the other hand, if a file path is given, CMake will recognize some paths
+ automatically, but not all cases. The project may want to use
+ ``$<LINK_LIBRARY:FRAMEWORK,...>`` for file paths so that the expected
+ behavior is clear.
-Features for framework linking have a special handling in CMake: the
-framework can be specified as a CMake framework target or file path. In the
-first case, the target must have the :prop_tgt:`FRAMEWORK` target property set
-as ``TRUE`` to enable framework handling. In the later case, if the path
-includes a directory part, this one will be specified as framework search path
-at link step.
-
-.. code-block:: cmake
-
- add_library(lib SHARED ...)
- target_link_libraries(lib PRIVATE "$<LINK_LIBRARY:NEEDED_FRAMEWORK,/path/to/my_framework>")
-
- # at link step we will have:
- # -F/path/to -needed_framework my_framework
-
-.. note::
-
- The expected formats for the file path, with optional parts specified as
- ``()?``, are:
+``NEEDED_FRAMEWORK``
+ This is similar to the ``FRAMEWORK`` feature, except it forces the linker
+ to link with the framework even if no symbols are used from it. It uses
+ the ``-needed_framework`` option and has the same linker constraints as
+ ``FRAMEWORK``.
- * (/path/to/)?FwName(.framework)?
- * (/path/to/)?FwName.framework/FwName
- * (/path/to/)?FwName.framework/Versions/\*/FwName
+``REEXPORT_FRAMEWORK``
+ This is similar to the ``FRAMEWORK`` feature, except it tells the linker
+ that the framework should be available to clients linking to the library
+ being created. It uses the ``-reexport_framework`` option and has the
+ same linker constraints as ``FRAMEWORK``.
-Library support
+``WEAK_FRAMEWORK``
+ This is similar to the ``FRAMEWORK`` feature, except it forces the linker
+ to mark the framework and all references to it as weak imports. It uses
+ the ``-weak_framework`` option and has the same linker constraints as
+ ``FRAMEWORK``.
``NEEDED_LIBRARY``
- This is the same as specifying a link item (target or
- library) but means to really link with the item even if no symbols are used
- from it (use linker option ``-needed_library`` or ``-needed-l``).
+ This is similar to the ``NEEDED_FRAMEWORK`` feature, except it is for use
+ with non-framework targets or libraries (Apple platforms only).
+ It uses the ``-needed_library`` or ``-needed-l`` option as appropriate,
+ and has the same linker constraints as ``NEEDED_FRAMEWORK``.
+
``REEXPORT_LIBRARY``
- This is the same as specifying a link item (target or
- library) but also specifies that all symbols in that item should be available
- to clients linking to the library being created (use linker option
- ``-reexport_library`` or ``-reexport-l``).
+ This is similar to the ``REEXPORT_FRAMEWORK`` feature, except it is for use
+ with non-framework targets or libraries (Apple platforms only).
+ It uses the ``-reexport_library`` or ``-reexport-l`` option as appropriate,
+ and has the same linker constraints as ``REEXPORT_FRAMEWORK``.
+
``WEAK_LIBRARY``
- This is the same as specifying a link item (target or
- library) but forces the item and all references to it to be marked as weak
- imports (use linker option ``-weak_library`` or ``-weak-l``).
+ This is similar to the ``WEAK_FRAMEWORK`` feature, except it is for use
+ with non-framework targets or libraries (Apple platforms only).
+ It uses the ``-weak_library`` or ``-weak-l`` option as appropriate,
+ and has the same linker constraints as ``WEAK_FRAMEWORK``.