compare preprocessor features to gcc cpp

Assuming that all registered issues are going to be resolved shortly, comparison to the preprocessor for gcc 8.0.0 pre-release shows that beluga

has no traditional mode;
follows the newline convention of its host system;
warns about space-separated backslash-newlines but does not perform line splicing for them;
allows backslashes to survive by appending spaces between them and newlines;
does not recognizes $ as a identifier letter;
warns appearance of NUL in all contexts and always replaces them with a space;
does not have -iquote option;
removes all spaces when combining <>-headers;
does not support precompiled headers;
has partial support for predefined macros intended for type properties;
allows no directives to appear in function-like macro arguments;
has no #pragmas for dependency, poisoning, system header and diagnostics;
preserves spaces in the middle of lines except when token separation is required;
removes unknown #pragmas with warnings;
does not encode a character constant with multiple characters;
does not accept -include and -imacros options;
does not allow to set target names when generating make dependencies;
has no way to ignore non-existing headers when generating make dependencies;
makes -o have the same meaning as -MF when -M or -MM is activated;
does not recognize DEPENDENCIES_OUTPUT;
has no -fpreprocessed and -fdirective-only options;
has no way to retain comments (-C and -CC);
does not support most of debug modes by -d;
does not accept include separators by -I-;
has no idea about sysroot and its replacement;
diagnoses and converts trigraphs in comments;
has -Wendif-label control warnings for all extra tokens that follow directives;
has no full support for environment variables;
does not allow to represent the current directory with empty paths in CPATH and C_INCLUDE_PATH;
ignores newlines within macro definitions from -D;
behaves differently when handling redundant include paths;
applies -fno-canonical-system-headers to all headers;
does not show on linemarkers if text comes from a system header; and
has -H not perform normal preprocessing, deliver #include hierarchy to stdout and provide no candidates for include guard;
differently optimize include guards (thus, -H shows a different sequence);
has preprocessing tool options (-H, -dM and -M) be mutually exclusive; and
outputs a different (but correct) sequence of make dependencies.

mycoboco / beluga

compare preprocessor features to gcc cpp #129