CMake/Help/command/add_custom_target.rst

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add_custom_target
-----------------
Add a target with no output so it will always be built.
::
add_custom_target(Name [ALL] [command1 [args1...]]
[COMMAND command2 [args2...] ...]
[DEPENDS depend depend depend ... ]
Add an option for explicit BYPRODUCTS of custom commands (#14963) A common idiom in CMake-based build systems is to have custom commands that generate files not listed explicitly as outputs so that these files do not have to be newer than the inputs. The file modification times of such "byproducts" are updated only when their content changes. Then other build rules can depend on the byproducts explicitly so that their dependents rebuild when the content of the original byproducts really does change. This "undeclared byproduct" approach is necessary for Makefile, VS, and Xcode build tools because if a byproduct were listed as an output of a rule then the rule would always rerun when the input is newer than the byproduct but the byproduct may never be updated. Ninja solves this problem by offering a 'restat' feature to check whether an output was really modified after running a rule and tracking the fact that it is up to date separately from its timestamp. However, Ninja also stats all dependencies up front and will only restat files that are listed as outputs of rules with the 'restat' option enabled. Therefore an undeclared byproduct that does not exist at the start of the build will be considered missing and the build will fail even if other dependencies would cause the byproduct to be available before its dependents build. CMake works around this limitation by adding 'phony' build rules for custom command dependencies in the build tree that do not have any explicit specification of what produces them. This is not optimal because it prevents Ninja from reporting an error when an input to a rule really is missing. A better approach is to allow projects to explicitly specify the byproducts of their custom commands so that no phony rules are needed for them. In order to work with the non-Ninja generators, the byproducts must be known separately from the outputs. Add a new "BYPRODUCTS" option to the add_custom_command and add_custom_target commands to specify byproducts explicitly. Teach the Ninja generator to specify byproducts as outputs of the custom commands. In the case of POST_BUILD, PRE_LINK, and PRE_BUILD events on targets that link, the byproducts must be specified as outputs of the link rule that runs the commands. Activate 'restat' for such rules so that Ninja knows it needs to check the byproducts, but not for link rules that have no byproducts.
2014-11-14 02:54:52 +03:00
[BYPRODUCTS [files...]]
[WORKING_DIRECTORY dir]
[COMMENT comment]
[VERBATIM] [USES_TERMINAL]
[SOURCES src1 [src2...]])
Adds a target with the given name that executes the given commands.
The target has no output file and is *always considered out of date*
even if the commands try to create a file with the name of the target.
Use the :command:`add_custom_command` command to generate a file with
dependencies. By default nothing depends on the custom target. Use
the :command:`add_dependencies` command to add dependencies to or
from other targets.
The options are:
``ALL``
Indicate that this target should be added to the default build
target so that it will be run every time (the command cannot be
called ``ALL``).
Add an option for explicit BYPRODUCTS of custom commands (#14963) A common idiom in CMake-based build systems is to have custom commands that generate files not listed explicitly as outputs so that these files do not have to be newer than the inputs. The file modification times of such "byproducts" are updated only when their content changes. Then other build rules can depend on the byproducts explicitly so that their dependents rebuild when the content of the original byproducts really does change. This "undeclared byproduct" approach is necessary for Makefile, VS, and Xcode build tools because if a byproduct were listed as an output of a rule then the rule would always rerun when the input is newer than the byproduct but the byproduct may never be updated. Ninja solves this problem by offering a 'restat' feature to check whether an output was really modified after running a rule and tracking the fact that it is up to date separately from its timestamp. However, Ninja also stats all dependencies up front and will only restat files that are listed as outputs of rules with the 'restat' option enabled. Therefore an undeclared byproduct that does not exist at the start of the build will be considered missing and the build will fail even if other dependencies would cause the byproduct to be available before its dependents build. CMake works around this limitation by adding 'phony' build rules for custom command dependencies in the build tree that do not have any explicit specification of what produces them. This is not optimal because it prevents Ninja from reporting an error when an input to a rule really is missing. A better approach is to allow projects to explicitly specify the byproducts of their custom commands so that no phony rules are needed for them. In order to work with the non-Ninja generators, the byproducts must be known separately from the outputs. Add a new "BYPRODUCTS" option to the add_custom_command and add_custom_target commands to specify byproducts explicitly. Teach the Ninja generator to specify byproducts as outputs of the custom commands. In the case of POST_BUILD, PRE_LINK, and PRE_BUILD events on targets that link, the byproducts must be specified as outputs of the link rule that runs the commands. Activate 'restat' for such rules so that Ninja knows it needs to check the byproducts, but not for link rules that have no byproducts.
2014-11-14 02:54:52 +03:00
``BYPRODUCTS``
Specify the files the command is expected to produce but whose
modification time may or may not be updated on subsequent builds.
If a byproduct name is a relative path it will be interpreted
relative to the build tree directory corresponding to the
current source directory.
Each byproduct file will be marked with the :prop_sf:`GENERATED`
source file property automatically.
Explicit specification of byproducts is supported by the
:generator:`Ninja` generator to tell the ``ninja`` build tool
how to regenerate byproducts when they are missing. It is
also useful when other build rules (e.g. custom commands)
depend on the byproducts. Ninja requires a build rule for any
generated file on which another rule depends even if there are
order-only dependencies to ensure the byproducts will be
available before their dependents build.
The ``BYPRODUCTS`` option is ignored on non-Ninja generators
except to mark byproducts ``GENERATED``.
``COMMAND``
Specify the command-line(s) to execute at build time.
If more than one ``COMMAND`` is specified they will be executed in order,
but *not* necessarily composed into a stateful shell or batch script.
(To run a full script, use the :command:`configure_file` command or the
:command:`file(GENERATE)` command to create it, and then specify
a ``COMMAND`` to launch it.)
If ``COMMAND`` specifies an executable target (created by the
:command:`add_executable` command) it will automatically be replaced
by the location of the executable created at build time.
Additionally a target-level dependency will be added so that the
executable target will be built before this custom target.
Arguments to ``COMMAND`` may use
:manual:`generator expressions <cmake-generator-expressions(7)>`.
References to target names in generator expressions imply target-level
dependencies.
The command and arguments are optional and if not specified an empty
target will be created.
``COMMENT``
Display the given message before the commands are executed at
build time.
``DEPENDS``
Reference files and outputs of custom commands created with
:command:`add_custom_command` command calls in the same directory
(``CMakeLists.txt`` file). They will be brought up to date when
the target is built.
Use the :command:`add_dependencies` command to add dependencies
on other targets.
``SOURCES``
Specify additional source files to be included in the custom target.
Specified source files will be added to IDE project files for
convenience in editing even if they have no build rules.
``VERBATIM``
All arguments to the commands will be escaped properly for the
build tool so that the invoked command receives each argument
unchanged. Note that one level of escapes is still used by the
CMake language processor before ``add_custom_target`` even sees
the arguments. Use of ``VERBATIM`` is recommended as it enables
correct behavior. When ``VERBATIM`` is not given the behavior
is platform specific because there is no protection of
tool-specific special characters.
``USES_TERMINAL``
The command will be given direct access to the terminal if possible.
With the :generator:`Ninja` generator, this places the command in
the ``console`` pool.
``WORKING_DIRECTORY``
Execute the command with the given current working directory.
If it is a relative path it will be interpreted relative to the
build tree directory corresponding to the current source directory.