Problem: libzmq 4.2.0 cmake build broken

It seems that there is a bug in libzmq 4.2.0 cmake configs that prevents
linking to it without installing.

Solution: disable libzmq 4.2.0 for cmake builds

.travis.yml

@@ -17,13 +17,13 @@ addons:
 
 env:
   matrix:
-#    - BUILD_TYPE=cmake DRAFT=enabled
-    - BUILD_TYPE=cmake ZMQ_VERSION=4.2.5
-    - BUILD_TYPE=cmake ZMQ_VERSION=4.2.0
+#    - ZMQ_BUILD_TYPE=cmake DRAFT=enabled
+    - ZMQ_BUILD_TYPE=cmake ZMQ_VERSION=4.2.5
+    - ZMQ_BUILD_TYPE=pkgconf ZMQ_VERSION=4.2.0
 
 matrix:
   include:
-  # - env: BUILD_TYPE=cmake DO_CLANG_FORMAT_CHECK=1 CLANG_FORMAT=/usr/local/clang-5.0.0/bin/clang-format
+  # - env: ZMQ_BUILD_TYPE=cmake DO_CLANG_FORMAT_CHECK=1 CLANG_FORMAT=/usr/local/clang-5.0.0/bin/clang-format
     # os: linux
     # addons:
     # apt:
@@ -39,14 +39,14 @@ matrix:
           packages:
             - g++-7
       env:
-        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7" BUILD_TYPE=cmake ZMQ_VERSION=4.2.5 DRAFT=1
+        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7" ZMQ_BUILD_TYPE=cmake ZMQ_VERSION=4.2.5 DRAFT=1
 
 sudo: required
 
 before_install:
   - pip install --user cpp-coveralls
 
-# Build and check this project according to the BUILD_TYPE
+# Build and check this project according to the ZMQ_BUILD_TYPE
 script:
   - eval "${MATRIX_EVAL}"
   - ./ci_build.sh

README.md

@@ -71,7 +71,6 @@ cpp zmq (which will also include libzmq for you).
 #find cppzmq wrapper, installed by make of cppzmq
 find_package(cppzmq)
 if(cppzmq_FOUND)
-    include_directories(${ZeroMQ_INCLUDE_DIR} ${cppzmq_INCLUDE_DIR})
     target_link_libraries(*Your Project Name* ${cppzmq_LIBRARY})
 endif()
 ```

ci_build.sh

@@ -16,11 +16,23 @@ install_zeromq() {
     curl -L https://github.com/zeromq/libzmq/archive/v${ZMQ_VERSION}.tar.gz \
       >zeromq.tar.gz
     tar -xvzf zeromq.tar.gz
+    if [ "${ZMQ_BUILD_TYPE}" = "cmake" ] ; then
         cmake -Hlibzmq-${ZMQ_VERSION} -B${LIBZMQ} -DWITH_PERF_TOOL=OFF \
                                                   -DZMQ_BUILD_TESTS=OFF \
                                                   -DCMAKE_BUILD_TYPE=Release \
                                                   ${ZEROMQ_CMAKE_FLAGS}
         cmake --build ${LIBZMQ}
+    elif [ "${ZMQ_BUILD_TYPE}" = "pkgconf" ] ; then
+        pushd .
+        cd libzmq-${ZMQ_VERSION}
+        ./autogen.sh
+        ./configure
+        sudo make VERBOSE=1 -j5 install
+        popd
+    else
+        echo "Unsupported build type ${ZMQ_BUILD_TYPE}."
+        exit 1
+    fi
 }
 
 # build zeromq first
@@ -28,6 +40,7 @@ install_zeromq() {
 if [ "${ZMQ_VERSION}" != "" ] ; then install_zeromq ; fi
 
 # build cppzmq
+# for pkgconf ZMQ_BUILD_TYPE ZeroMQ_DIR is invalid but it should still work
 pushd .
 ZeroMQ_DIR=${LIBZMQ} cmake -H. -B${CPPZMQ} ${ZEROMQ_CMAKE_FLAGS}
 cmake --build ${CPPZMQ}

demo/CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
 
 project(cppzmq-demo CXX)
 
-find_package(cppzmq REQUIRED)
+find_package(cppzmq)
 
 enable_testing()
 add_executable(
@@ -15,9 +15,6 @@ target_link_libraries(
     cppzmq
     )
 
-target_include_directories(demo PRIVATE ${cppzmq_INCLUDE_DIR}
-                                        ${ZeroMQ_INCLUDE_DIR})
-
 add_test(
   NAME
     demo

tests/CMakeLists.txt

@@ -36,9 +36,6 @@ target_link_libraries(
     cppzmq
     )
 
-target_include_directories(unit_tests PRIVATE ${cppzmq_INCLUDE_DIR}
-                                              ${ZeroMQ_INCLUDE_DIR})
-
 add_test(
   NAME
     unit