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Merge topic 'doc-cmake_parse_arguments-prefix'

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2000abe74f Help: Recommend good prefixes for cmake_parse_arguments,  expand example
bb37d0e1a5 Help: Improve grammar and wording for cmake_parse_arguments

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !9788
This commit is contained in:
Craig Scott
2024-09-03 22:26:12 +00:00
committed by Kitware Robot
parent b69cd358d5 2000abe74f
commit c9a8a7400a
1 changed files with 103 additions and 46 deletions
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149
Help/command/cmake_parse_arguments.rst
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@@ -20,48 +20,49 @@ It processes the arguments given to that macro or function,
and defines a set of variables which hold the values of the
respective options.
The first signature reads processes arguments passed in the ``<args>...``.
The first signature reads arguments passed in the ``<args>...``.
This may be used in either a :command:`macro` or a :command:`function`.
.. versionadded:: 3.7
The ``PARSE_ARGV`` signature is only for use in a :command:`function`
body. In this case the arguments that are parsed come from the
body. In this case, the arguments that are parsed come from the
``ARGV#`` variables of the calling function. The parsing starts with
the ``<N>``-th argument, where ``<N>`` is an unsigned integer.
This allows for the values to have special characters like ``;`` in them.
The ``<options>`` argument contains all options for the respective macro,
i.e. keywords which can be used when calling the macro without any value
following, like e.g. the ``OPTIONAL`` keyword of the :command:`install`
command.
The ``<options>`` argument contains all options for the respective function
or macro. These are keywords that have no value following them, like the
``OPTIONAL`` keyword of the :command:`install` command.
The ``<one_value_keywords>`` argument contains all keywords for this macro
which are followed by one value, like e.g. ``DESTINATION`` keyword of the
:command:`install` command.
The ``<one_value_keywords>`` argument contains all keywords for this function
or macro which are followed by one value, like the ``DESTINATION`` keyword of
the :command:`install` command.
The ``<multi_value_keywords>`` argument contains all keywords for this
macro which can be followed by more than one value, like e.g. the
function or macro which can be followed by more than one value, like the
``TARGETS`` or ``FILES`` keywords of the :command:`install` command.
.. versionchanged:: 3.5
All keywords shall be unique. I.e. every keyword shall only be specified
once in either ``<options>``, ``<one_value_keywords>`` or
All keywords must be unique. Each keyword can only be specified
once in any of the ``<options>``, ``<one_value_keywords>``, or
``<multi_value_keywords>``. A warning will be emitted if uniqueness is
violated.
When done, ``cmake_parse_arguments`` will consider for each of the
keywords listed in ``<options>``, ``<one_value_keywords>`` and
``<multi_value_keywords>`` a variable composed of the given ``<prefix>``
followed by ``"_"`` and the name of the respective keyword. These
variables will then hold the respective value from the argument list
or be undefined if the associated option could not be found.
For the ``<options>`` keywords, these will always be defined,
to ``TRUE`` or ``FALSE``, whether the option is in the argument list or not.
keywords listed in ``<options>``, ``<one_value_keywords>``, and
``<multi_value_keywords>``, a variable composed of the given ``<prefix>``
followed by ``"_"`` and the name of the respective keyword. For
``<one_value_keywords>`` and ``<multi_value_keywords>``, these variables
will then hold the respective value(s) from the argument list, or be undefined
if the associated keyword was not given (policy :policy:`CMP0174` can also
affect the behavior for ``<one_value_keywords>``). For the ``<options>``
keywords, these variables will always be defined, and they will be set to
``TRUE`` if the keyword is present, or ``FALSE`` if it is not.
All remaining arguments are collected in a variable
``<prefix>_UNPARSED_ARGUMENTS`` that will be undefined if all arguments
were recognized. This can be checked afterwards to see
whether your macro was called with unrecognized parameters.
whether your macro or function was called with unrecognized parameters.
.. versionadded:: 3.15
``<one_value_keywords>`` and ``<multi_value_keywords>`` that were given no
@@ -75,9 +76,42 @@ whether your macro was called with unrecognized parameters.
policy :policy:`CMP0174` controls whether a corresponding
``<prefix>_<keyword>`` variable is defined or not.
Choose a ``<prefix>`` carefully to avoid clashing with existing variable names.
When used inside a function, it is usually suitable to use the prefix ``arg``.
There is a very strong convention that all keywords are fully uppercase, so
this prefix results in variables of the form ``arg_SOME_KEYWORD``. This makes
the code more readable, and it minimizes the chance of clashing with cache
variables, which also have a strong convention of being all uppercase.
Consider the following example macro, ``my_install()``, which takes similar
arguments to the real :command:`install` command:
.. code-block:: cmake
function(my_install)
set(options OPTIONAL FAST)
set(oneValueArgs DESTINATION RENAME)
set(multiValueArgs TARGETS CONFIGURATIONS)
cmake_parse_arguments(PARSE_ARGV 0 arg
"${options}" "${oneValueArgs}" "${multiValueArgs}"
)
# The above will set or unset variables with the following names:
# arg_OPTIONAL
# arg_FAST
# arg_DESTINATION
# arg_RENAME
# arg_TARGETS
# arg_CONFIGURATIONS
#
# The following will also be set or unset:
# arg_UNPARSED_ARGUMENTS
# arg_KEYWORDS_MISSING_VALUES
When used inside a macro, ``arg`` might not be a suitable prefix because the
code will affect the calling scope. If another macro also called in the same
scope were to use ``arg`` in its own call to ``cmake_parse_arguments()``,
and if there are any common keywords between the two macros, the later call's
variables can overwrite or remove those of the earlier macro's call.
Therefore, it is advisable to incorporate something unique from the macro name
in the ``<prefix>``, such as ``arg_lowercase_macro_name``.
.. code-block:: cmake
@@ -85,40 +119,63 @@ arguments to the real :command:`install` command:
set(options OPTIONAL FAST)
set(oneValueArgs DESTINATION RENAME)
set(multiValueArgs TARGETS CONFIGURATIONS)
cmake_parse_arguments(MY_INSTALL "${options}" "${oneValueArgs}"
"${multiValueArgs}" ${ARGN} )
cmake_parse_arguments(arg_my_install
"${options}" "${oneValueArgs}" "${multiValueArgs}"
${ARGN}
)
# ...
endmacro()
Assume ``my_install()`` has been called like this:
macro(my_special_install)
# NOTE: Has the same keywords as my_install()
set(options OPTIONAL FAST)
set(oneValueArgs DESTINATION RENAME)
set(multiValueArgs TARGETS CONFIGURATIONS)
cmake_parse_arguments(arg_my_special_install
"${options}" "${oneValueArgs}" "${multiValueArgs}"
${ARGN}
)
# ...
endmacro()
Suppose the above macros are called one after the other, like so:
.. code-block:: cmake
my_install(TARGETS foo bar DESTINATION bin OPTIONAL blub CONFIGURATIONS)
my_special_install(TARGETS barry DESTINATION sbin RENAME FAST)
After the ``cmake_parse_arguments`` call the macro will have set or undefined
the following variables::
After these two calls, the following describes the variables that will be
set or unset::
MY_INSTALL_OPTIONAL = TRUE
MY_INSTALL_FAST = FALSE # was not used in call to my_install
MY_INSTALL_DESTINATION = "bin"
MY_INSTALL_RENAME <UNDEFINED> # was not used
MY_INSTALL_TARGETS = "foo;bar"
MY_INSTALL_CONFIGURATIONS <UNDEFINED> # was not used
MY_INSTALL_UNPARSED_ARGUMENTS = "blub" # nothing expected after "OPTIONAL"
MY_INSTALL_KEYWORDS_MISSING_VALUES = "CONFIGURATIONS"
# No value for "CONFIGURATIONS" given
arg_my_install_OPTIONAL = TRUE
arg_my_install_FAST = FALSE # was not present in call to my_install
arg_my_install_DESTINATION = "bin"
arg_my_install_RENAME <UNSET> # was not present
arg_my_install_TARGETS = "foo;bar"
arg_my_install_CONFIGURATIONS <UNSET> # was not present
arg_my_install_UNPARSED_ARGUMENTS = "blub" # nothing expected after "OPTIONAL"
arg_my_install_KEYWORDS_MISSING_VALUES = "CONFIGURATIONS" # value was missing
You can then continue and process these variables.
arg_my_special_install_OPTIONAL = FALSE # was not present
arg_my_special_install_FAST = TRUE
arg_my_special_install_DESTINATION = "sbin"
arg_my_special_install_RENAME <UNSET> # value was missing
arg_my_special_install_TARGETS = "barry"
arg_my_special_install_CONFIGURATIONS <UNSET> # was not present
arg_my_special_install_UNPARSED_ARGUMENTS <UNSET>
arg_my_special_install_KEYWORDS_MISSING_VALUES = "RENAME"
Keywords terminate lists of values, e.g. if directly after a
``one_value_keyword`` another recognized keyword follows, this is
interpreted as the beginning of the new option. E.g.
``my_install(TARGETS foo DESTINATION OPTIONAL)`` would result in
``MY_INSTALL_DESTINATION`` set to ``"OPTIONAL"``, but as ``OPTIONAL``
is a keyword itself ``MY_INSTALL_DESTINATION`` will be empty (but added
to ``MY_INSTALL_KEYWORDS_MISSING_VALUES``) and ``MY_INSTALL_OPTIONAL`` will
therefore be set to ``TRUE``.
Keywords terminate lists of values. If a keyword is given directly after a
``<one_value_keyword>``, that preceding ``<one_value_keyword>`` receives no
value and the keyword is added to the ``<prefix>_KEYWORDS_MISSING_VALUES``
variable. In the above example, the call to ``my_special_install()`` contains
the ``RENAME`` keyword immediately followed by the ``FAST`` keyword.
In this case, ``FAST`` terminates processing of the ``RENAME`` keyword.
``arg_my_special_install_FAST`` is set to ``TRUE``,
``arg_my_special_install_RENAME`` is unset, and
``arg_my_special_install_KEYWORDS_MISSING_VALUES`` contains the value
``RENAME``.
See Also
^^^^^^^^