Generated CMake C libraries do not correctly specify dependent generated source code filenames

[Gregory-Meyer]

Given the following CMakeLists.txt:

cmake_minimum_required(VERSION 3.8)

project(lcm-toy)

find_package(lcm REQUIRED)
include(${LCM_USE_FILE})

lcm_wrap_types(C_SOURCES c_sources C_HEADERS c_headers vector_t.lcm)

lcm_add_library(lcm-toy C STATIC ${c_sources} ${c_headers})
target_include_directories(lcm-toy PUBLIC
    $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>
)

and the LCM message definition file vector_t.lcm:

struct vector_t
{
    double x;
    double y;
    double z;
}

I get this failure when attempting to build the CMake project:

$ mkdir build
$ cd build
$ cmake ..
-- The C compiler identification is GNU 9.2.0
-- The CXX compiler identification is GNU 9.2.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done-- Build files have been written to: /home/gregjm/c/lcm-toy/build
$ cmake --build .
Scanning dependencies of target lcm-toy.sources
[ 25%] Generating _vector_t.h, _vector_t.c
[ 25%] Built target lcm-toy.sources
[ 50%] Generating _vector_t.h, _vector_t.c
Scanning dependencies of target lcm-toy
[ 50%] Generating _vector_t.h, _vector_t.c
[ 75%] Building C object CMakeFiles/lcm-toy.dir/_vector_t.c.o
cc: error: /home/gregjm/c/lcm-toy/build/_vector_t.c: No such file or directory
cc: fatal error: no input files
compilation terminated.
gmake[2]: *** [CMakeFiles/lcm-toy.dir/build.make:70: CMakeFiles/lcm-toy.dir/_vector_t.c.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:104: CMakeFiles/lcm-toy.dir/all] Error 2
gmake: *** [Makefile:84: all] Error 2
$ ls
CMakeCache.txt  CMakeFiles/  cmake_install.cmake  Makefile  vector_t.c  vector_t.h

Note that the files vector_t.h and vector_t.c are being generated, but the target lcm-types is attempting to compile using the file _vector_t.c.

I have created a pull request, #284, to address this issue.