Fix module build

CMakeLists.txt

@@ -33,7 +33,7 @@ list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake/modules)
 
 include(GNUInstallDirs)
 include(CTest)
-include(Sqlpp23TargetHelper)
+include(sqlpp23_target_helper)
 
 option(BUILD_MYSQL_CONNECTOR "Build MySQL Connector" OFF)
 option(BUILD_MARIADB_CONNECTOR "Build MariaDB Connector" OFF)

cmake/Sqlpp23TargetHelper.cmake → cmake/sqlpp23_target_helper.cmake

@@ -130,11 +130,15 @@ function(add_common)
     # Initialize helper variables based on target type (regular or module)
     if(ARG_MODULE_INTERFACE)
         set(TARGET_SUFFIX "_module")
-        # FILE_SETs of type CXX_MODULES cannot have the INTERFACE scope (exept
-        # on IMPORTED targets) and INTERFACE libraries only allow INTERFACE
-        # scope on their properties. That's why we cannot use the INTERFACE
-        # library type. For details see the discussion at
-        # https://discourse.cmake.org/t/header-only-libraries-and-c-20-modules/10680/11
+        # CMake has the following two limitations:
+        # - FILE_SETs of type CXX_MODULES cannot have the INTERFACE scope (except on IMPORTED targets).
+        # - INTERFACE libraries only allow INTERFACE scope on their properties.
+        # From these two limitations it follows that INTERFACE libraries cannot have FILE_SETs of type
+        # CXX_MODULES. That's why, as a workaround, we use an OBJECT library.
+        #
+        # For details see the discussion at
+        # https://discourse.cmake.org/t/header-only-libraries-and-c-20-modules/10680
+        # where the CMake devs explain that this limitation exists to prevent possible ODR violations.
         set(LIB_TYPE OBJECT)
         set(LIB_PROP_SCOPE PUBLIC)
     else()

cmake/sqlpp23_testing_helper.cmake

@@ -0,0 +1,60 @@
+# Copyright (c) 2026, Vesselin Atanasov
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification,
+# are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice, this
+#    list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice, this
+#    list of conditions and the following disclaimer in the documentation and/or
+#    other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+function(add_testing_target)
+    set(options)
+    set(oneValueArgs NAME)
+    set(multiValueArgs DEFINES MOD_DEPS)
+    cmake_parse_arguments(ARG "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
+
+    if(BUILD_WITH_MODULES)
+        # We are building with modules, so the _testing target created by this function MUST be a regular
+        # (non-INTERFACE) library. Otherwise, the object files owned by the OBJECT library dependencies
+        # in MOD_DEPS won't be linked, and we are going to get missing symbols during the linking (namely
+        # the static module initializer function won't be found).
+        #
+        # For details on how OBJECT libraries are linked see
+        # https://cmake.org/cmake/help/latest/manual/cmake-buildsystem.7.html#object-libraries
+        # https://cmake.org/cmake/help/latest/command/target_link_libraries.html#linking-object-libraries
+        set(LIB_TYPE)
+        set(LIB_PROP_SCOPE PUBLIC)
+    else()
+        # We are building without modules and the _testing target created by this function won't have any
+        # compiled files, and CMake will not let us build a empty regular (non-INTERFACE) library. So in
+        # this case we have to use an INTERFACE library.
+        set(LIB_TYPE INTERFACE)
+        set(LIB_PROP_SCOPE INTERFACE)
+    endif()
+    set(TARGET_NAME "sqlpp23_${ARG_NAME}_testing")
+    add_library(${TARGET_NAME} ${LIB_TYPE})
+    if(ARG_DEFINES)
+        target_compile_definitions(${TARGET_NAME} ${LIB_PROP_SCOPE} ${ARG_DEFINES})
+    endif()
+    target_link_libraries(${TARGET_NAME} ${LIB_PROP_SCOPE} sqlpp23_testing)
+    if(BUILD_WITH_MODULES)
+        set(MOD_FILE "${PROJECT_SOURCE_DIR}/tests/${ARG_NAME}/modules/sqlpp23.test.${ARG_NAME}.tables.cppm")
+        target_sources(${TARGET_NAME} PUBLIC FILE_SET CXX_MODULES FILES "${MOD_FILE}")
+        target_link_libraries(${TARGET_NAME} PUBLIC sqlpp23::core_module ${ARG_MOD_DEPS})
+    endif()
+endfunction()

tests/core/CMakeLists.txt

@@ -22,30 +22,9 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-if(BUILD_WITH_MODULES)
-    add_library(sqlpp23.test.core.tables.module)
-    target_sources(sqlpp23.test.core.tables.module
-      PUBLIC
-        FILE_SET all_my_modules TYPE CXX_MODULES FILES
-        modules/sqlpp23.test.core.tables.cppm
-    )
-    target_link_libraries(sqlpp23.test.core.tables.module PUBLIC sqlpp23::core_module)
-endif()
+include(sqlpp23_testing_helper)
 
-add_library(sqlpp23_core_testing INTERFACE)
-target_include_directories(sqlpp23_core_testing INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
-
-if(BUILD_WITH_MODULES)
-    target_link_libraries(sqlpp23_core_testing INTERFACE
-      sqlpp23_testing
-      sqlpp23::mock_db_module
-      sqlpp23.test.core.tables.module
-    )
-else()
-    target_link_libraries(sqlpp23_core_testing INTERFACE
-      sqlpp23_testing
-    )
-endif()
+add_testing_target(NAME core MOD_DEPS sqlpp23::mock_db_module)
 
 add_subdirectory(asserts)
 add_subdirectory(constraints)

tests/mysql/CMakeLists.txt

@@ -22,34 +22,15 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-if(BUILD_WITH_MODULES)
-    add_library(sqlpp23.test.mysql.tables.module)
-    target_sources(sqlpp23.test.mysql.tables.module
-      PUBLIC
-        FILE_SET all_my_modules TYPE CXX_MODULES FILES
-        modules/sqlpp23.test.mysql.tables.cppm
-    )
-    target_link_libraries(sqlpp23.test.mysql.tables.module PUBLIC sqlpp23::core_module)
-endif()
+include(sqlpp23_testing_helper)
 
 find_package(Threads REQUIRED)
-add_library(sqlpp23_mysql_testing INTERFACE)
-target_include_directories(sqlpp23_mysql_testing INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
 
-if(BUILD_WITH_MODULES)
-    target_link_libraries(sqlpp23_mysql_testing INTERFACE
-      sqlpp23_testing
-      sqlpp23::mysql_module
-      sqlpp23.test.mysql.tables.module
-    )
-else()
-    target_link_libraries(sqlpp23_mysql_testing INTERFACE
-      sqlpp23_testing
-    )
-endif()
+set(DEFINES)
 if (MSVC)
-    target_compile_options(sqlpp23_mysql_testing INTERFACE -DNOMINMAX)
+    list(APPEND DEFINES -DNOMINMAX)
 endif ()
+add_testing_target(NAME mysql DEFINES ${DEFINES} MOD_DEPS sqlpp23::mysql_module)
 
 add_subdirectory(asserts)
 add_subdirectory(constraints)

tests/postgresql/CMakeLists.txt

@@ -22,30 +22,9 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-if(BUILD_WITH_MODULES)
-  add_library(sqlpp23.test.postgresql.tables.module)
-  target_sources(sqlpp23.test.postgresql.tables.module
-    PUBLIC
-      FILE_SET all_my_modules TYPE CXX_MODULES FILES
-      modules/sqlpp23.test.postgresql.tables.cppm
-  )
-  target_link_libraries(sqlpp23.test.postgresql.tables.module PUBLIC sqlpp23::core_module)
-endif()
+include(sqlpp23_testing_helper)
 
-add_library(sqlpp23_postgresql_testing INTERFACE)
-target_include_directories(sqlpp23_postgresql_testing INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
-
-if(BUILD_WITH_MODULES)
-    target_link_libraries(sqlpp23_postgresql_testing INTERFACE
-      sqlpp23_testing
-      sqlpp23::postgresql_module
-      sqlpp23.test.postgresql.tables.module
-    )
-else()
-    target_link_libraries(sqlpp23_postgresql_testing INTERFACE
-      sqlpp23_testing
-    )
-endif()
+add_testing_target(NAME postgresql MOD_DEPS sqlpp23::postgresql_module)
 
 add_subdirectory(asserts)
 add_subdirectory(constraints)

tests/sqlite3/CMakeLists.txt

@@ -22,38 +22,17 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-if(BUILD_WITH_MODULES)
-    add_library(sqlpp23.test.sqlite3.tables.module)
-    target_sources(sqlpp23.test.sqlite3.tables.module
-      PUBLIC
-        FILE_SET all_my_modules TYPE CXX_MODULES FILES
-        modules/sqlpp23.test.sqlite3.tables.cppm
-    )
-    target_link_libraries(sqlpp23.test.sqlite3.tables.module PUBLIC sqlpp23::core_module)
-endif()
+include(sqlpp23_testing_helper)
 
-add_library(sqlpp23_sqlite3_testing INTERFACE)
-target_include_directories(sqlpp23_sqlite3_testing INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
-
-if(BUILD_WITH_MODULES)
-    target_link_libraries(sqlpp23_sqlite3_testing INTERFACE
-      sqlpp23_testing
-      sqlpp23::sqlite3_module
-      sqlpp23.test.sqlite3.tables.module
-    )
-else()
-    target_link_libraries(sqlpp23_sqlite3_testing INTERFACE
-      sqlpp23_testing
-    )
-endif()
+add_testing_target(NAME sqlite3 MOD_DEPS sqlpp23::sqlite3_module)
 
 function(sqlpp_slite3_test_add_target_link_libraries name)
-target_link_libraries(${name} PRIVATE sqlpp23_testing sqlpp23_sqlite3_testing)
-if (BUILD_SQLCIPHER_CONNECTOR)
-    target_link_libraries(${name} PRIVATE sqlpp23::sqlcipher)
-else()
-    target_link_libraries(${name} PRIVATE sqlpp23::sqlite3)
-endif()
+    target_link_libraries(${name} PRIVATE sqlpp23_testing sqlpp23_sqlite3_testing)
+    if (BUILD_SQLCIPHER_CONNECTOR)
+        target_link_libraries(${name} PRIVATE sqlpp23::sqlcipher)
+    else()
+        target_link_libraries(${name} PRIVATE sqlpp23::sqlite3)
+    endif()
 endfunction()
 
 add_subdirectory(asserts)