add "rm -f rc.cpp"

Thanks

You are linking against the "o2" target, but it's not being located anywhere. You have to add find_package(o2 OPTIONAL) to the root CMakeLists.txt. And since the o2 project does not seem to install any CMake or pkgconfig files, you'll have to write your own Findo2.cmake and add it to cmake/modules. You can look on some of the files there to get an idea how to write the Findo2.cmake file.

No spaces inside "( )"

Space after if

Move { on the same line as the if

Missed one string :)

I have tried it now ;)

Normally you would append WebEngineWidgets to the list above, but since it's only needed to build your resource, it should be moved below your find_package(o2) and made conditional:

if (o2_FOUND)
   find_package(Qt5 OPTIONAL_COMPONENTS WebEngineWidgets)
endif ()

Please add

set_package_properties(o2 PROPERTIES
    DESCRIPTION "OAuth1 and OAuth2 library for Qt. Needed to build the Tomboy resource."
    URL "https://github.com/pipacs/o2"
    TYPE OPTIONAL)

To make it easier for packagers to figure out what they need to package.

Are you sure this works? The library does not install any pkgconfig files (does not install anything for that matter), so I doubt this finds anything...

QLatin1String

} else {

Move to the same line as the if

This will unfortunately affect your resource code too, even though it's only needed because of o2 :-(

You could add a CMakeLists.txt to the o2 subdirectory, where you remove these definitions and build the o2 library as a static library. Then you just put add_subdirectory(o2) here and you are done.

If you go for the approach described above, remove those files from here.

If you don't go for the approach described above (i.e. you stick to what you have now), then remove this, because in that case there won't be any "o2" library to link against.

o2 infects the resource code, so the option are also needed for my code

please no unrelated added/deleted newlines, they make it quite harder to use git blame f.ex.

This license is not Debian compatible ( https://www.debian.org/social_contract.html#guidelines), because:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

This means you need to write the copyright, if you use the software: "Copyright (c) 2011, Andre Somers"

and the part:

• Neither the name of the Rathenau Instituut, Andre Somers nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

So you need to ask Andre Somers before redistrubution, becuase his name is paort of the copyright and this is against the DFSG #1, because you have a "royality" how can deside if you can redistrubute or not. And do not hold in the "Desert Island" test (https://people.debian.org/~bap/dfsg-faq.html)

typo? forgotten ) ? or is this only a error in the view?

Add a note that you have a copy of the o2 lib inside the sudir o2 and the lisnce of that lib + the git checkout.
+ document every change to the libriary as a set of patches ( if you made any changes that are not upstream)

Btw distributions are mostly not happy with copies of libraries, so they wanna strip this out again. If the library ( I know that Dan suggested you to ship a copy).

So if we can delete the copy with the nexit iteration, it would be great.

wrongy copied file? This should only exist in the o2 sudir? Is there is any file thatis under this lisence in that folder?

If not: delete
otherwise you need to specifiy which files are under what licsense, because files without a lisence headers exist like the .rc and the CMakeLists.txt file.

nippicking: missing lisence header - this is something that upstream should fix and not you with the copy, but please inform upstream about this.