enable fmt_module tests by updating module-test.cc

- Update g++ module testing to use g++ version 15 instead of 14.
  The module support in version 14 isn't very stable and the module
  testing was not working due to unresolved locale symbols.
- Refactor test/CMakeLists.txt to enable testing for modules
- The tests in `module-test.cc` seem to not have been updated in some
  time despite changes in the main library.
- Wide String versions of several tests appear to be deprecated so have
  been commented out.
- Refactored tests related to `fmt::format_args` that now requires lvalue
  references as opposed to direct values.
- MSVC has some bugs that are still present since the module-test.cc
  file was initially written. We update the version detection to current
  versions.
- MSVC and the other compilers take different paths in determining the
  fmt::detail namespace. Used #ifdef macros to enforce this. This
  enables module testing to work on all compilers
- clang-format base.h due to lint failure on CI

Author: MathewBensonCode

.github/workflows/linux.yml

@@ -37,10 +37,10 @@ jobs:
             std: 23
             install: sudo apt install g++-13
             shared: -DBUILD_SHARED_LIBS=ON
-          - cxx: g++-14
+          - cxx: g++-15
             build_type: Release
             std: 23
-            install: sudo apt install g++-14
+            install: sudo apt install g++-15
             gen: Ninja
           - cxx: clang++-3.6
           - cxx: clang++-11
@@ -147,7 +147,7 @@ jobs:
     - name: Add repositories for newer GCC
       run: |
         sudo apt-add-repository ppa:ubuntu-toolchain-r/test
-      if: ${{ matrix.cxx == 'g++-13' || matrix.cxx == 'g++-14' }}
+      if: ${{ matrix.cxx == 'g++-13' || matrix.cxx == 'g++-15' }}
 
     - name: Install LLVM-20
       run: |

include/fmt/base.h

@@ -1872,10 +1872,10 @@ template <typename OutputIt, typename T, typename = void>
 struct has_insert : std::false_type {};
 
 template <typename OutputIt, typename T>
-struct has_insert<OutputIt, T,
-                  void_t<decltype(get_container(std::declval<OutputIt>())
-                                      .insert({}, std::declval<T>(),
-                                              std::declval<T>()))>>
+struct has_insert<
+    OutputIt, T,
+    void_t<decltype(get_container(std::declval<OutputIt>())
+                        .insert({}, std::declval<T>(), std::declval<T>()))>>
     : std::true_type {};
 
 // An optimized version of std::copy with the output value type (T).

test/CMakeLists.txt

@@ -19,7 +19,7 @@ function (add_fmt_test name)
       set(PEDANTIC_COMPILE_FLAGS ${PEDANTIC_COMPILE_FLAGS} -Wno-weak-vtables)
     endif ()
   elseif (ADD_FMT_TEST_MODULE)
-    set(libs test-main)
+    set(libs test-main fmt-module)
   else ()
     set(libs test-main fmt)
   endif ()
@@ -81,9 +81,7 @@ add_executable(perf-sanity perf-sanity.cc)
 target_link_libraries(perf-sanity fmt::fmt)
 
 if (FMT_MODULE)
-  # Module tests are currently disabled.
-  # add_fmt_test(module-test MODULE test-main.cc)
-  # target_link_libraries(module-test fmt-module)
+  add_fmt_test(module-test MODULE)
 endif ()
 
 if (NOT DEFINED MSVC_STATIC_RUNTIME AND MSVC)