cmake_parse_arguments: add KEYWORDS_MISSING_VALUES

Add KEYWORDS_MISSING_VALUES output variable to cmake_parse_arguments() to
allow to detect keywords that received no values.

Fixes: #18706

1 files changed, 11 insertions, 3 deletions

diff --git a/Help/command/cmake_parse_arguments.rst b/Help/command/cmake_parse_arguments.rst
index c8327e2..196d90f 100644
--- a/Help/command/cmake_parse_arguments.rst
+++ b/Help/command/cmake_parse_arguments.rst
@@ -59,6 +59,11 @@ All remaining arguments are collected in a variable
 where recognized. This can be checked afterwards to see
 whether your macro was called with unrecognized parameters.
 
+``<one_value_keywords>`` and ``<multi_value_keywords>`` that where given no
+values at all are collected in a variable ``<prefix>_KEYWORDS_MISSING_VALUES``
+that will be undefined if all keywords received values. This can be checked
+to see if there where keywords without any values given.
+
 As an example here a ``my_install()`` macro, which takes similar arguments
 as the real :command:`install` command:
 
@@ -77,7 +82,7 @@ Assume ``my_install()`` has been called like this:
 
 .. code-block:: cmake
 
-   my_install(TARGETS foo bar DESTINATION bin OPTIONAL blub)
+   my_install(TARGETS foo bar DESTINATION bin OPTIONAL blub CONFIGURATIONS)
 
 After the ``cmake_parse_arguments`` call the macro will have set or undefined
 the following variables::
@@ -89,6 +94,8 @@ the following variables::
    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
 
 You can then continue and process these variables.
 
@@ -97,5 +104,6 @@ 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 and
-``MY_INSTALL_OPTIONAL`` will therefore be set to ``TRUE``.
+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``.