Accept a dqrobotics::dqrobotics target from a parent project

CMakeLists.txt

@@ -9,6 +9,10 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
 option(MARINHO_LAB_SAS_CORE_BUILD_EXAMPLES "Build the example executables" ON)
+# A parent project that links the library into its own binary (and provides
+# dqrobotics::dqrobotics from a non-installed target) can turn the install rules
+# and the exported CMake package off.
+option(MARINHO_LAB_SAS_CORE_INSTALL "Install the library, headers and CMake package" ON)
 
 # Shared library by default; build a static library with -DBUILD_SHARED_LIBS=OFF.
 # The option() establishes the default while still honouring a value that a
@@ -21,30 +25,35 @@ endif()
 
 find_package(Eigen3 REQUIRED)
 
-# dqrobotics does not ship a CMake package: locate its header and library manually.
-# The public header lives at <prefix>/include/dqrobotics/DQ.h, so we search for
-# the path-qualified name. We fail early and with a clear message if it is absent.
-find_path(DQROBOTICS_INCLUDE_DIR
-    NAMES dqrobotics/DQ.h
-    PATHS /usr /usr/local /opt/homebrew
-    HINTS ENV CMAKE_PREFIX_PATH)
-find_library(DQROBOTICS_LIBRARY
-    NAMES dqrobotics
-    PATHS /usr /usr/local /opt/homebrew
-    HINTS ENV CMAKE_PREFIX_PATH)
-if(NOT DQROBOTICS_INCLUDE_DIR OR NOT DQROBOTICS_LIBRARY)
-    message(FATAL_ERROR "dqrobotics not found (looked for dqrobotics/DQ.h and libdqrobotics). "
-                        "Install it from https://launchpad.net/~dqrobotics-dev/+archive/ubuntu/development "
-                        "or build it from https://github.com/dqrobotics/cpp")
+# A parent project may provide dqrobotics::dqrobotics itself, e.g. as an ALIAS
+# of a dqrobotics target it builds in-tree with add_subdirectory (as the
+# marinholab-sas-core Python package does). Otherwise, find an installed one.
+if(NOT TARGET dqrobotics::dqrobotics)
+    # dqrobotics does not ship a CMake package: locate its header and library manually.
+    # The public header lives at <prefix>/include/dqrobotics/DQ.h, so we search for
+    # the path-qualified name. We fail early and with a clear message if it is absent.
+    find_path(DQROBOTICS_INCLUDE_DIR
+        NAMES dqrobotics/DQ.h
+        PATHS /usr /usr/local /opt/homebrew
+        HINTS ENV CMAKE_PREFIX_PATH)
+    find_library(DQROBOTICS_LIBRARY
+        NAMES dqrobotics
+        PATHS /usr /usr/local /opt/homebrew
+        HINTS ENV CMAKE_PREFIX_PATH)
+    if(NOT DQROBOTICS_INCLUDE_DIR OR NOT DQROBOTICS_LIBRARY)
+        message(FATAL_ERROR "dqrobotics not found (looked for dqrobotics/DQ.h and libdqrobotics). "
+                            "Install it from https://launchpad.net/~dqrobotics-dev/+archive/ubuntu/development "
+                            "or build it from https://github.com/dqrobotics/cpp")
+    endif()
+
+    # Model dqrobotics as an imported target so its include dir and library location
+    # are carried through the build/install regardless of the install prefix.
+    add_library(dqrobotics::dqrobotics UNKNOWN IMPORTED GLOBAL)
+    set_target_properties(dqrobotics::dqrobotics PROPERTIES
+        IMPORTED_LOCATION "${DQROBOTICS_LIBRARY}"
+        INTERFACE_INCLUDE_DIRECTORIES "${DQROBOTICS_INCLUDE_DIR}")
 endif()
 
-# Model dqrobotics as an imported target so its include dir and library location
-# are carried through the build/install regardless of the install prefix.
-add_library(dqrobotics::dqrobotics UNKNOWN IMPORTED GLOBAL)
-set_target_properties(dqrobotics::dqrobotics PROPERTIES
-    IMPORTED_LOCATION "${DQROBOTICS_LIBRARY}"
-    INTERFACE_INCLUDE_DIRECTORIES "${DQROBOTICS_INCLUDE_DIR}")
-
 # ---- Library (shared by default; build static with -DBUILD_SHARED_LIBS=OFF) ----
 add_library(marinholab_sas_core
     src/sas_clock.cpp
@@ -89,37 +98,39 @@ if(MARINHO_LAB_SAS_CORE_BUILD_EXAMPLES)
 endif()
 
 # ---- Install ----
-include(GNUInstallDirs)
-install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
-install(TARGETS marinholab_sas_core
-        EXPORT marinholab_sas_core-targets
-        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-        RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
-
-if(MARINHO_LAB_SAS_CORE_BUILD_EXAMPLES)
-    install(TARGETS sas_core_example sas_clock_example sas_clock_sched_fifo_example
-                    thread_manager_example sas_robot_driver_example
+if(MARINHO_LAB_SAS_CORE_INSTALL)
+    include(GNUInstallDirs)
+    install(DIRECTORY include/ DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+    install(TARGETS marinholab_sas_core
+            EXPORT marinholab_sas_core-targets
+            ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+            LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
             RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
-endif()
 
-# ---- CMake package ----
-include(CMakePackageConfigHelpers)
-install(EXPORT marinholab_sas_core-targets
-        FILE marinholab_sas_core-targets.cmake
+    if(MARINHO_LAB_SAS_CORE_BUILD_EXAMPLES)
+        install(TARGETS sas_core_example sas_clock_example sas_clock_sched_fifo_example
+                        thread_manager_example sas_robot_driver_example
+                RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
+    endif()
+
+    # ---- CMake package ----
+    include(CMakePackageConfigHelpers)
+    install(EXPORT marinholab_sas_core-targets
+            FILE marinholab_sas_core-targets.cmake
+            DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/marinholab_sas_core)
+
+    configure_package_config_file(
+        ${CMAKE_CURRENT_SOURCE_DIR}/cmake/marinholab_sas_core-config.cmake.in
+        ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config.cmake
+        INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/marinholab_sas_core)
+
+    write_basic_package_version_file(
+        ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config-version.cmake
+        VERSION ${PROJECT_VERSION}
+        COMPATIBILITY SameMajorVersion)
+
+    install(FILES
+        ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config.cmake
+        ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config-version.cmake
         DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/marinholab_sas_core)
-
-configure_package_config_file(
-    ${CMAKE_CURRENT_SOURCE_DIR}/cmake/marinholab_sas_core-config.cmake.in
-    ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config.cmake
-    INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/marinholab_sas_core)
-
-write_basic_package_version_file(
-    ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config-version.cmake
-    VERSION ${PROJECT_VERSION}
-    COMPATIBILITY SameMajorVersion)
-
-install(FILES
-    ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config.cmake
-    ${CMAKE_CURRENT_BINARY_DIR}/marinholab_sas_core-config-version.cmake
-    DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/marinholab_sas_core)
+endif()