On 30 November 2016 at 11:08, Bruno Cardoso Lopes via Phabricator via cfe-commits <cfe-commits@lists.llvm.org> wrote:
> > I suspect the problem is instead that #import just doesn't work properly > with modules > > (specifically, either with local submodule visibility or with modules > that do not export *), > > because it doesn't care whether the previous inclusion is visible or > not, and as a result it assumes > > "I've heard about someone #including this ever" means the same thing as > "the contents of this file > > are visible right now". I know that #pragma once has this issue, so I'd > expect #import to also suffer from it. > > Taking a look at this, any ideas on what's the right approach with the > #import's here? So instead of entering the header, is there a way to make > the contents for the module matching the built-in header to become > available/visible at that point? The right thing to do would be to track the set of headers whose #import / #include-with-#pragma-once is visible, and only skip inclusions if there is a *visible* #import / #include-with-#pragma-once of that header. (Much like we only skip an include due to an include guard if there is a visible definition of the include guard macro.) For instance, instead of a single `isImport` bit on `HeaderFileInfo`, we could store a list of IDs of submodules that have imported the header, and check whether any of those are visible when deciding whether to skip an inclusion, but there's probably a cheaper way (in common cases) to get the same effect.
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