Do not fail if gr-zeromq is not present. Make CI jobs happy.

CMakeLists.txt

@@ -613,8 +613,17 @@ if(ENABLE_UHD)
     endif()
 endif()
 
+find_package(ZEROMQ)
+set_package_properties(ZEROMQ PROPERTIES
+    PURPOSE "Used by the ZMQ_Signal_Source."
+    TYPE OPTIONAL
+)
 if(ENABLE_ZMQ)
-    list(APPEND GR_REQUIRED_COMPONENTS ZEROMQ)
+    if(NOT ZEROMQ_FOUND)
+        set(ENABLE_ZMQ OFF)
+    else()
+        list(APPEND GR_REQUIRED_COMPONENTS ZEROMQ)
+    endif()
 endif()
 
 find_package(GNURADIO)

cmake/Modules/FindZEROMQ.cmake

@@ -0,0 +1,82 @@
+# GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
+# This file is part of GNSS-SDR.
+#
+# SPDX-FileCopyrightText: 2023 C. Fernandez-Prades cfernandez(at)cttc.es
+# SPDX-License-Identifier: BSD-3-Clause
+
+#
+# Provides the following imported target:
+# ZeroMQ::ZeroMQ
+#
+
+if(NOT COMMAND feature_summary)
+    include(FeatureSummary)
+endif()
+
+if(NOT PKG_CONFIG_FOUND)
+    include(FindPkgConfig)
+endif()
+
+find_package(PkgConfig)
+pkg_check_modules(PC_ZEROMQ "libzmq")
+
+find_path(ZEROMQ_INCLUDE_DIRS
+    NAMES zmq.hpp
+    HINTS ${PC_ZEROMQ_INCLUDE_DIR} ${CMAKE_INSTALL_PREFIX}/include
+    PATHS /usr/local/include /usr/include /opt/local/include
+)
+
+find_library(ZEROMQ_LIBRARIES
+    NAMES zmq libzmq.so.5 ${ZEROMQ_LIBRARY_NAME}
+    HINTS ${PC_ZEROMQ_LIBDIR} ${CMAKE_INSTALL_PREFIX}/lib ${CMAKE_INSTALL_PREFIX}/lib64
+    PATHS /usr/lib
+        /usr/lib64
+        /usr/lib/alpha-linux-gnu
+        /usr/lib/x86_64-linux-gnu
+        /usr/lib/aarch64-linux-gnu
+        /usr/lib/arm-linux-gnueabi
+        /usr/lib/arm-linux-gnueabihf
+        /usr/lib/hppa-linux-gnu
+        /usr/lib/i386-linux-gnu
+        /usr/lib/m68k-linux-gnu
+        /usr/lib/mips-linux-gnu
+        /usr/lib/mips64el-linux-gnuabi64
+        /usr/lib/mipsel-linux-gnu
+        /usr/lib/powerpc-linux-gnuspe
+        /usr/lib/powerpc64-linux-gnu
+        /usr/lib/powerpc64le-linux-gnu
+        /usr/lib/riscv64-linux-gnu
+        /usr/lib/s390x-linux-gnu
+        /usr/lib/sh4-linux-gnu
+        /usr/lib/sparc64-linux-gnu
+        /usr/lib/x86_64-linux-gnux32
+        /usr/lib/x86_64-kfreebsd-gnu
+        /usr/lib/i386-kfreebsd-gnu
+        /usr/local/lib
+        /usr/local/lib64
+        /opt/local/lib
+)
+
+include(FindPackageHandleStandardArgs)
+# This is just to detect presence, include files not required
+find_package_handle_standard_args(ZEROMQ DEFAULT_MSG ZEROMQ_LIBRARIES)
+mark_as_advanced(ZEROMQ_LIBRARIES ZEROMQ_INCLUDE_DIRS)
+
+set_package_properties(ZEROMQ PROPERTIES URL "https://zeromq.org/")
+if(PC_ZEROMQ_VERSION)
+    set_package_properties(ZEROMQ PROPERTIES
+        DESCRIPTION "An open-source universal messaging library (found: v${PC_ZEROMQ_VERSION})"
+    )
+else()
+    set_package_properties(ZEROMQ PROPERTIES
+        DESCRIPTION "An open-source universal messaging library"
+    )
+endif()
+
+if(ZEROMQ_FOUND AND ZEROMQ_INCLUDE_DIRS AND NOT TARGET ZeroMQ::ZeroMQ)
+    add_library(ZeroMQ::ZeroMQ INTERFACE IMPORTED)
+    set_target_properties(ZeroMQ::ZeroMQ PROPERTIES
+        INTERFACE_INCLUDE_DIRECTORIES "${ZEROMQ_INCLUDE_DIRS}"
+        INTERFACE_LINK_LIBRARIES "${ZEROMQ_LIBRARIES}"
+    )
+endif()

src/algorithms/signal_source/adapters/zmq_signal_source.cc

@@ -95,9 +95,13 @@ auto ZmqSignalSource::get_right_block() -> gr::basic_block_sptr
     auto result = gr::basic_block_sptr();
 
     if (d_vec_block)
-        result = d_vec_block;  // NOLINT
+        {
+            result = d_vec_block;
+        }
     else
-        result = d_source_block;  // NOLINT
+        {
+            result = d_source_block;
+        }
 
     return result;
 }