Add a test for the module

test/CMakeLists.txt

@@ -2,7 +2,9 @@ add_subdirectory(gtest)
 
 set(TEST_MAIN_SRC test-main.cc gtest-extra.cc gtest-extra.h util.cc)
 add_library(test-main STATIC ${TEST_MAIN_SRC})
-target_link_libraries(test-main gtest fmt)
+target_include_directories(test-main PUBLIC
+  $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>)
+target_link_libraries(test-main gtest)
 
 include(CheckCXXCompilerFlag)
 
@@ -29,16 +31,20 @@ endfunction()
 # Adds a test.
 # Usage: add_fmt_test(name srcs...)
 function(add_fmt_test name)
-  cmake_parse_arguments(ADD_FMT_TEST "HEADER_ONLY" "" "" ${ARGN})
+  cmake_parse_arguments(ADD_FMT_TEST "HEADER_ONLY;MODULE" "" "" ${ARGN})
 
   set(sources ${name}.cc ${ADD_FMT_TEST_UNPARSED_ARGUMENTS})
-  set(libs test-main)
   if (ADD_FMT_TEST_HEADER_ONLY)
     set(sources ${sources} ${TEST_MAIN_SRC} ../src/os.cc)
     set(libs gtest fmt-header-only)
     if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
       set(PEDANTIC_COMPILE_FLAGS ${PEDANTIC_COMPILE_FLAGS} -Wno-weak-vtables)
     endif ()
+  elseif (ADD_FMT_TEST_MODULE)
+    set(libs test-main test-module)
+    set_source_files_properties(${name}.cc PROPERTIES OBJECT_DEPENDS test-module)
+  else ()
+    set(libs test-main fmt)
   endif ()
   add_fmt_executable(${name} ${sources})
   target_link_libraries(${name} ${libs})
@@ -74,6 +80,20 @@ add_fmt_test(ranges-test)
 add_fmt_test(scan-test)
 add_fmt_test(wchar-test)
 
+if (FMT_CAN_MODULE)
+  # The tests need {fmt} to be compiled as traditional library
+  # because of visibility of implementation details.
+  # If module support is present the module tests require a
+  # test-only module to be built from {fmt}
+  add_library(test-module OBJECT ${CMAKE_SOURCE_DIR}/src/fmt.cc)
+  target_compile_features(test-module PUBLIC ${FMT_REQUIRED_FEATURES})
+  target_include_directories(test-module PUBLIC
+    $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>)
+  enable_module(test-module)
+
+  add_fmt_test(module-test MODULE)
+endif ()
+
 if (NOT MSVC)
   # FMT_ENFORCE_COMPILE_STRING is not supported under MSVC due to compiler bugs.
   add_fmt_test(enforce-checks-test)