CMake/Help/policy/CMP0174.rst

CMP0174
-------

.. versionadded:: 3.31

:command:`cmake_parse_arguments(PARSE_ARGV)` defines a variable for an empty
string after a single-value keyword.

One of the main reasons for using the ``PARSE_ARGV`` form of the
:command:`cmake_parse_arguments` command is to more robustly handle corner
cases related to empty values.  The non-``PARSE_ARGV`` form doesn't preserve
empty arguments, but the ``PARSE_ARGV`` form does.  For each single-value
keyword given, a variable should be defined if the keyword is present, even
if it is followed by an empty string.

Prior to CMake 3.31, no variable would be defined if the value given after a
single-value keyword was an empty string.  This meant the code could not detect
the difference between the keyword not being given, and it being given but with
an empty value, except by iterating over all the arguments and checking if the
keyword is present.

For the ``OLD`` behavior of this policy,
:command:`cmake_parse_arguments(PARSE_ARGV)` does not define a variable for a
single-value keyword followed by an empty string, or followed by no value at
all.

For the ``NEW`` behavior, :command:`cmake_parse_arguments(PARSE_ARGV)` always
defines a variable for each keyword given in the arguments, even a single-value
keyword with an empty string as its value or no value at all.  With the
``NEW`` behavior, the code can robustly check if a single-value keyword was
given using just ``if(DEFINED <prefix>_<keyword>)``.

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.31
.. |WARNS_OR_DOES_NOT_WARN| replace:: warns
.. include:: STANDARD_ADVICE.txt

.. include:: DEPRECATED.txt