File all-std.cxx is an include-all-standard-headers file intended to be built with

g++-10 all-std.cxx -std=c++2a -E > gcc-10-libstdc++-e.cpp2

clang++-12 all-std.cxx -std=c++2a -E > clang-12-libstdc++-e.cpp2

cl all-std.cxx -std:c++latest /E > msvc-msstl-e.cpp2

each of which generates a single .cpp2 test file representing the contents of a stdlib implementation.

Note: Not all implementations actually support all standard headers. So for each compiler invocation above just manually edit all-std.cxx to comment out the headers that implementation doesn't understand.

Each such .cpp2 file is then compiled with cppfront and the output .cpp file tested to be diff-identical ith the .cpp2 input, to ensure that cppfront correctly passes Cpp1 code through unchanged.

Here's a test script:

cppfront gcc-10-libstdc++-e.cpp2
diff -s -Z gcc-10-libstdc++-e.cpp2 gcc-10-libstdc++-e.cpp

cppfront clang-12-libstdc++-e.cpp2
diff -s -Z clang-12-libstdc++-e.cpp2 clang-12-libstdc++-e.cpp

cppfront msvc-msstl-e.cpp2
diff -s -Z msvc-msstl-e.cpp2 msvc-msstl-e.cpp

Each diff should report "files ... are identical".