Generate dependencies of preprocessed modules to avoid importing #ifdef import

[Arthapz]

No description provided.

[waruqi]

        local clang, toolname = target:tool("cxx")
        assert(toolname == "clang")
        -- ...
        os.vrunv(clang, table.join(defines, {"-E", "-x", "c++", file,  "-o", ifile}))

[waruqi]

or we can use

    local compinst = compiler.load("cxx", {target = target})
    local compflags = table.join("-E", "-x", "c++", compinst:compflags({target = target}))
    os.vrunv(compinst:program(), table.join(compflags, "-o", ifile))

and remove it, because compflags contain them and more too.

local defines = {}
                for _, define in ipairs(target:get("defines")) do
                    table.insert(defines, "-D" .. define)
                end

[Arthapz]

yeah i did use compflags at first but when some flags that are in compflags (like -std=c++20 for clang or -fmodule-ts for gcc) prevent -E from working (the compiler try to search module imports, we don't want that)

[Arthapz]

Ah i need to take care of dependency include directories, or the preprocessing will fail

fatal error: 'xxx.h' file not found

[Arthapz]

it's seem we can't do anything more for clang without llvm/llvm-project#51792
llvm/llvm-project#59287 (comment)

[waruqi]

thanks!

[Arthapz]

Maybe soon i can add support of p1689 for clang llvm/llvm-project#57293 (comment)