[cfe-dev] Question about ASTReader::resolvePendingMacro, namely SkipDirectiveHistory

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Hi folks!
I'm just checking a ASTReader::resolvePendingMacro, and looking at lines:

  // Don't read the directive history for a module; we don't have anywhere
  // to put it.
  if (M.isModule())
    return;

So there is a question, first why it is called DirectiveHistory? Why just not a directive?
Another thing is why we should skip it? I mean, we can store it in ASTReader::PP, and later if we're compiling another module we skip it, for it doesn't belong to current file right?

Or from another side, can't we just define something in one module and take it into account in another (dependent) one?

Thanks!
-Stepan