[lwip-users] Can't build "Working example" from BUILDING

[Grant Edwards]

I'm trying to get started porting lwIP to an RTOS. Having never worked
with lwip before, I thought I would first just build 2_1_3_RC1 for
Linux. I'm following the directions in BUILDING:

    Working example
    ===============
    Working build examples can be found in the
    contrib/ports/{win32, unix}/example_app
    subdirectory.
    To use them, create a build directory and call cmake with
    the lwIP root dir:

     - mkdir build
     - cd build
     - cmake ..
     - cmake --build .

    The CMakeLists.txt will autoselect the correct port
    for your system (supported: Linux, Windows, Darwin).

The first problem is that I don't have doxygen installed (and don't
really have any desire to install it):

    $ mkdir build
    $ cd build
    $ cmake ..
    -- The C compiler identification is GNU 10.3.0
    -- The CXX compiler identification is GNU 10.3.0
    -- Detecting C compiler ABI info
    -- Detecting C compiler ABI info - done
    -- Check for working C compiler: /usr/bin/cc - skipped
    -- Detecting C compile features
    -- Detecting C compile features - done
    -- Detecting CXX compiler ABI info
    -- Detecting CXX compiler ABI info - done
    -- Check for working CXX compiler: /usr/bin/c++ - skipped
    -- Detecting CXX compile features
    -- Detecting CXX compile features - done
    -- Could NOT find Doxygen (missing: DOXYGEN_EXECUTABLE)
    Doxygen needs to be installed to generate the doxygen documentation
    -- Configuring done
    CMake Error at CMakeLists.txt:20 (add_dependencies):
      The dependency target "lwipdocs" of target "dist" does not exist.
    
    -- Generating done
    CMake Generate step failed.  Build files cannot be regenerated correctly.

I tried commenting out the lwipdocs target in CMakeLists.txt, and that
allowed the 'cmake ..' command to finish, but the subsequent 'cmake --build .'
command then does nothing:

    $ rm -rf build
    $ mkdir build
    $ cd build
    $ cmake ..
    -- The C compiler identification is GNU 10.3.0
    -- The CXX compiler identification is GNU 10.3.0
    -- Detecting C compiler ABI info
    -- Detecting C compiler ABI info - done
    -- Check for working C compiler: /usr/bin/cc - skipped
    -- Detecting C compile features
    -- Detecting C compile features - done
    -- Detecting CXX compiler ABI info
    -- Detecting CXX compiler ABI info - done
    -- Check for working CXX compiler: /usr/bin/c++ - skipped
    -- Detecting CXX compile features
    -- Detecting CXX compile features - done
    -- Could NOT find Doxygen (missing: DOXYGEN_EXECUTABLE)
    Doxygen needs to be installed to generate the doxygen documentation
    -- Configuring done
    -- Generating done
    -- Build files have been written to: 
/home/grante/lwip/lwip-STABLE-2_1_3_RC1/build
    $ tree . > /tmp/before.tree
    $ cmake --build .
    $ tree . > /tmp/after.tree
    $ diff /tmp/{before,after}.tree

I'm obviously missing something, but what?

--
Grant