test: cover JSON_NO_IO, JSON_THROW/TRY/CATCH_USER, JSON_SKIP_LIBRARY_VERSION_CHECK, and JSON_DisableEnumSerialization in CI (#5423)

These four supported configuration macros were never actually compiled
anywhere in the test matrix:

- JSON_NO_IO and the JSON_THROW_USER/JSON_TRY_USER/JSON_CATCH_USER trio
  are exercised together in a new tests/src/unit-no_io_and_user_exceptions.cpp,
  which is automatically picked up by the existing unit-*.cpp test glob and
  thus built across the whole standard test matrix.
- JSON_SKIP_LIBRARY_VERSION_CHECK is exercised by a new, dedicated
  tests/src/skip_library_version_check.cpp, compiled directly by the new
  ci_test_skiplibraryversioncheck target in cmake/ci.cmake: the scenario it
  simulates (mixing two differently-versioned inclusions of the library)
  unavoidably triggers the compiler's own "macro redefined" warning, which
  would fail under the library's own -Weverything/-Werror unit test matrix
  for a reason unrelated to the macro under test.
- JSON_DisableEnumSerialization already had #if-guarded tests in several
  unit-*.cpp files (from #4384), but no CMake target ever actually set the
  JSON_DisableEnumSerialization CMake option, so that guarded code was never
  compiled. Add ci_test_disableenumserialization, mirroring the existing
  ci_test_noimplicitconversions/ci_test_noglobaludls targets. Building the
  full test suite with this option on surfaced one real, narrow gap: get<T>()
  on std::vector<std::byte> (used by unit-regression2.cpp's custom BinaryType
  tests) relies on std::byte being handled via enum serialization, so add the
  same #if-guard convention to the two affected SECTIONs there.

Both new CI targets are added to the ci_cmake_options matrix in
.github/workflows/ubuntu.yml, alongside the existing ci_test_* targets.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

cmake/ci.cmake

@@ -242,6 +242,40 @@ add_custom_target(ci_test_noglobaludls
     COMMENT "Compile and test with global UDLs disabled"
 )
 
+###############################################################################
+# Disable enum serialization.
+###############################################################################
+
+add_custom_target(ci_test_disableenumserialization
+    COMMAND ${CMAKE_COMMAND}
+    -DCMAKE_BUILD_TYPE=Debug -GNinja
+    -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_DisableEnumSerialization=ON
+    -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_disableenumserialization
+    COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_disableenumserialization
+    COMMAND cd ${PROJECT_BINARY_DIR}/build_disableenumserialization && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
+    COMMENT "Compile and test with enum serialization disabled"
+)
+
+###############################################################################
+# Skip the multiple-inclusion library version check.
+###############################################################################
+
+# tests/src/skip_library_version_check.cpp deliberately simulates a scenario
+# (mixing two differently-versioned inclusions of the library in one
+# translation unit) that unavoidably triggers the compiler's own "macro
+# redefined" warning, so -- unlike the ci_test_* targets above -- it is
+# compiled directly here, with a modest warning set, instead of being folded
+# into the library's own -Weverything/-Werror unit test matrix.
+add_custom_target(ci_test_skiplibraryversioncheck
+    COMMAND ${CMAKE_COMMAND} -E make_directory ${PROJECT_BINARY_DIR}/skip_library_version_check
+    COMMAND ${CMAKE_CXX_COMPILER} -std=c++11 -Wall -Wextra
+        -I${PROJECT_SOURCE_DIR}/include
+        ${PROJECT_SOURCE_DIR}/tests/src/skip_library_version_check.cpp
+        -o ${PROJECT_BINARY_DIR}/skip_library_version_check/skip_library_version_check
+    COMMAND ${PROJECT_BINARY_DIR}/skip_library_version_check/skip_library_version_check
+    COMMENT "Compile and run a translation unit simulating a mismatched library version, with JSON_SKIP_LIBRARY_VERSION_CHECK defined"
+)
+
 ###############################################################################
 # Coverage.
 ###############################################################################