Cmake: Documenting cmake script

[LecrisUT]

I am sorry if this is already implemented, but I couldn't see it in the issues or the list of supported languages.

---

Description

Being able to generate xml and html documentation for cmake entities. These would be particularly useful with sphinx+breathe and moderncmakedomain

Details

A minimal documentation that would be helpful for the user documentation:

• macro() and function(): positional arguments, named arguments (from cmake_parsed_arguments), and expected variables (set from the parent when function/macro is called)
• option() and set(CACHE): type, default, helper string
• target: type, aliases, exported name, generated object (library and binary) if any
• install(COMPONENT): component, installed items
• install(FILES): files, destination
• export(TARGET) (part of target above)
• find_package(COMPONENT): component, target file

Additionally I think these are helpful for the developer documentation:

• add_custom_command(): output files/target, commands, comment
• add_custom_target(): target, commands, comment
• include(): location (e.g. my_helper.cmake)

[albert-github]

When I understand it correctly you want to be able to document cmake files and present them in a way doxygen does.

There is no default support for these kind of files in doxygen, you probably can get some good results using a filter and translate the cmake files to something doxygen understands (like C++ code), with settings like INPUT_FILTER etc. this might be possible.

[LecrisUT]

When I understand it correctly you want to be able to document cmake files and present them in a way doxygen does.

Indeed that's the case. We cannot map all of the cmake entities to C++ ones, but if we can define other custom entities in doxygen, maybe we can find some abstract way of building them. At least all of the definition syntax is statically defined, so it should be possible to connect the doxygen comments above a add_custom_command() for example.

[albert-github]

Maybe you could give an example with the results you got so far and the problems you still encounter i.e.:

• attach a, small, self contained example (source+configuration file in a, compressed, tar or zip file) that allows us to see and reproduce the problem? Please don't add external links as they might not be persistent.
• specify the full doxygen version used (doxygen -v).

[LecrisUT]

Ok, I will make a small example project to mock-up these, but conceptually here is a short snippet of what I am referring to, just so we can confirm we are on the same page:

### This is a description of `my_function`
### 
### @param _inp1 A positional argument
### @param VAR2 A named argument
function(my_function _inp1)
  cmake_parse_arguments(ARGS "" "VAR2" "" ${ARGN})
  ...
endfunction()

[albert-github]

(Just some nitpicking)

1. The : should not be present in the @param statement for the argument name
2. VAR2 is not an argument of the function

[LecrisUT]

2. VAR2 is not an argument of the function

Actually that's the thing about cmake. VAR2 is an argument of my_function because it is called via:

my_function(${positional_argument} VAR2 ${named_argument}) 

Initially I think it is ok if these are passed manually because these need to be parsed, e.g. finding the cmake_parse_arguments() expanding any definitions defined from set(), etc. It might be possible to use cmake-file-api to retrieve these, but I haven't researched this.

[albert-github]

When I'm not mistaken the @param VAR2 will throw a warning as doxygen doesn't know about the argument VAR2 but it will show in the documentation.

[LecrisUT]

Well, I've tried to to trick doxygen to parse it as a different language, and unsurprisingly it failed spectacularly:

Input file

Filename: test.cmake

### This is a description of `my_function`
###
### @param _inp1 A positional argument
### @param VAR2 A named argument
/// This is a description of `my_function`
///
/// @param _inp1 A positional argument
/// @param VAR2 A named argument
function(my_function _inp1)
	cmake_parse_arguments(ARGS "" "VAR2" "" ${ARGN})
endfunction()

Doxyfile (Relevant parts)

GENERATE_XML = YES
INPUT                  = cmake/test.cmake
EXTENSION_MAPPING      = cmake=c++

Generated xml

<?xml version='1.0' encoding='UTF-8' standalone='no'?>
<doxygen xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="compound.xsd" version="1.9.5" xml:lang="en-US">
  <compounddef id="test_8cmake" kind="file" language="C++">
    <compoundname>test.cmake</compoundname>
      <sectiondef kind="func">
      <memberdef kind="function" id="test_8cmake_1a44019289305eb00ccec292780743b509" prot="public" static="no" const="no" explicit="no" inline="no" virt="non-virtual">
        <type></type>
        <definition>function</definition>
        <argsstring>(my_function _inp1) cmake_parse_arguments(ARGS &quot;&quot; &quot;VAR2&quot; &quot;&quot; $</argsstring>
        <name>function</name>
        <param>
          <type>my_function</type>
          <declname>_inp1</declname>
        </param>
        <briefdescription>
        </briefdescription>
        <detaileddescription>
<para>This is a description of <computeroutput>my_function</computeroutput></para>
<para><parameterlist kind="param"><parameteritem>
<parameternamelist>
<parametername>_inp1</parametername>
</parameternamelist>
<parameterdescription>
<para>A positional argument </para>
</parameterdescription>
</parameteritem>
<parameteritem>
<parameternamelist>
<parametername>VAR2</parametername>
</parameternamelist>
<parameterdescription>
<para>A named argument </para>
</parameterdescription>
</parameteritem>
</parameterlist>
</para>
        </detaileddescription>
        <inbodydescription>
        </inbodydescription>
        <location file="cmake/test.cmake" line="9" column="1" bodyfile="cmake/test.cmake" bodystart="9" bodyend="10"/>
      </memberdef>
      </sectiondef>
    <briefdescription>
    </briefdescription>
    <detaileddescription>
    </detaileddescription>
    <programlisting>
<codeline lineno="1"><highlight class="preprocessor">###<sp/>This<sp/>is<sp/>a<sp/>description<sp/>of<sp/>`my_function`</highlight><highlight class="normal"></highlight></codeline>
<codeline lineno="2"><highlight class="normal"></highlight><highlight class="preprocessor">###</highlight><highlight class="normal"></highlight></codeline>
<codeline lineno="3"><highlight class="normal"></highlight><highlight class="preprocessor">###<sp/>@param<sp/>_inp1<sp/>A<sp/>positional<sp/>argument</highlight><highlight class="normal"></highlight></codeline>
<codeline lineno="4"><highlight class="normal"></highlight><highlight class="preprocessor">###<sp/>@param<sp/>VAR2<sp/>A<sp/>named<sp/>argument</highlight></codeline>
<codeline lineno="9"><highlight class="normal">function(my_function<sp/>_inp1)</highlight></codeline>
<codeline lineno="10"><highlight class="normal"><sp/><sp/><sp/><sp/>cmake_parse_arguments(ARGS<sp/></highlight><highlight class="stringliteral">&quot;&quot;</highlight><highlight class="normal"><sp/></highlight><highlight class="stringliteral">&quot;VAR2&quot;</highlight><highlight class="normal"><sp/></highlight><highlight class="stringliteral">&quot;&quot;</highlight><highlight class="normal"><sp/>${ARGN})</highlight></codeline>
<codeline lineno="11"><highlight class="normal">endfunction()</highlight></codeline>
    </programlisting>
    <location file="cmake/test.cmake"/>
  </compounddef>
</doxygen>

So there are a few things to fix:

• Use the cmake comment token: #
• Change the parsing to extract the type/definition from the function caller, i.e. add_custom_target() -> target. There is no type prefix like def my_function: in python
• Parse bodystart, bodyend accordingly (look for endfunction(), endmacro() or closing parenthesis ) )
• Change language in compounddef to cmake
• Disable argstring or compute it including cmake_parse_argument or cmake-file-api (currently not possible there either)
• Disable or fix the code highlighter

[albert-github]

In the #9906 (comment) mentioned:

There is no default support for these kind of files in doxygen, you probably can get some good results using a filter and translate the cmake files to something doxygen understands (like C++ code), with settings like INPUT_FILTER etc. this might be possible.

but in the presented "Doxyfile (Relevant parts)" (better to use the outcome of doxygen -x Doxyfile as this shows the differences with the default settings), there is nothing about a filter so doxygen sees the cmake file as C++ code and the cmake file is no C++ code. You will probably have had some warnings as well.

[LecrisUT]

There is EXTENSION_MAPPING to map it to c++ code, and that is why it picks up at /// "comments". But C++ parser is ill-suited for building on top of this because:

• It has different comment tokens
• It requires a type prefix: i.e. void in void my_function(), class in class my_class, etc.

You will probably have had some warnings as well.

Of course there were warnings like that, and surprisingly only for VAR2, even though _inp1 should also be ill defined there.

[albert-github]

When having cmake code like:

### This is a description of `my_function`
### 
### @param _inp1 A positional argument
### @param VAR2 A named argument
function(my_function _inp1)
  cmake_parse_arguments(ARGS "" "VAR2" "" ${ARGN})
  ...
endfunction()

this would be in C++ terms something like:

/// This is a description of `my_function`
///
/// @param _inp1 A positional argument
/// @param VAR2 A named argument
void my_function(char* _inp1)
  cmake_parse_arguments(ARGS "" "VAR2" "" ${ARGN});
  ...
}

and this should be done by the filter (probably the filter should even do more).

[LecrisUT]

Doxygen does not have any parser for cmake, so it does not know how to handle any of this. If I use the first version, no xml output is produced at all. There is no cmake related filter:

• Not in FILE_PATTERNS because it is not built-in
• INPUT_FILTER requires a custom parser

But even if we change it to be c++ like function, that doesn't solve the main issues that a new language format needs to be defined in order to address all of the other checkboxed issues. For example, how do we convert option() or set(CACHE). How about add_library() and find_package()?

[albert-github]

You have to write the filter yourself, doxygen doesn't provide the filter just the possibility to use it.

[LecrisUT]

Again, INPUT_FILTER is not appropriate due to how different these are. The xml output format is fine and useful to output to breathe to generate documentations, but the parser itself needs to be reformulated. There are no return type, you should distinguish between option(), set(CACHE), set(PARENT_SCOPE), etc.