[cfe-dev] Saving+loading the Clang AST

[Kevin Modzelewski via cfe-dev]

It's a long story, but I'd like to dump the ASTs for all of the C files in
a build and then run a post-processing program on all of the ASTs at once.
In the end it's sort of like a libTooling tool, except 1) it runs on
multiple files at once, and 2) ideally for performance and consistency with
the build process, it would delegate the parsing to the initial dumping
process and not do it every time we run the post-processing program.

My approach has been to instrument the build process with a custom clang
plugin that uses a Serialization/ASTWriter to dump the AST to a file.  This
process seems to be working well, but I've had a lot of issues trying to
read the AST back out.

Namely, that serialization code seems to be pretty geared towards the needs
of the PCH save+load process and is pretty hard to use.  I've done the work
of setting up a special CompilerInstance just for loading the AST, but I
keep getting "configuration mismatch" errors.  I assume I need to
separately persist the command line flags and be more careful to set up the
CompilerInstance the same way that the dumping program does it, but it's
already been a lot of source diving and I'm not sure this is even a
supported use of these classes.

My question is -- is this the right way to be saving+loading the clang
AST?  It's looking like it's going to be easier to define a new, pared-down
format than use ASTWriter and Reader (and will be nicer for consumers by
not having to pull in much of clang), but I've read that you're supposed to
be able to use the clang AST like this.

Alternatively, if I should use a different approach that would be good
information too.  All of the projects I've seen parse things on demand and
then I assume have issues making sure all the flags are correct.

Thanks,
Kevin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20180911/09b9623b/attachment.html>