[Rock-dev] clang vs. typelib

[Sylvain Joyeux]

> We could also place references to TLB files in TLB files themself,
> and generate a TLB File per header file. In this case we could stop
> parsing anything, it there is already a TLB file for an included
> header. This could lead to big speedups, as we don't reparse all the
> headers over and over again.

Before going into modifications on the typelib side, I would rather
look into why it is so slow (and ask the clang mailing list how to
make it faster). Compiling a file that includes base/Pose.hpp and does
something with a base::Pose takes 1.61s on my machine, not 15s. Maybe
there would be a way to prune the traversal at the declaration level
since we really don't care about the inside of the methods.

If we come to that, I would really really not break the self-contained
nature of tlb files, because it won't be manageable (if you update a
linked tlb file because a struct change but NOT the other ones, you
are breaking the type definitions). What would definitely be doable is
to save a self-contained TLB per header file in a cache folder and
have the clang importer merge these tlbs into the current registry
whenever an include is found. Now, how do you detect the includes
without traversing the AST ? And -- more importantly -- how do you
make sure that the cache is properly invalidated when some
include-in-include-in-include file gets invalidated ? Or when the
import options (such as the opaque list) gets modified ? Big can of
worms.

Sylvain