:mccr8 did a ton of modernization of the syntax supported by the rust IPDL parser we use for searchfox at https://github.com/amccreight/ipdl_parser back in March which should make us able to understand maybe all of the IPDL stuff in the tree, so it would be nice to update to using this. I've been trying to push hard on making sure we have test coverage for things like this because it's so easy to break these things and not notice it, but it's also frequently a bit of an initial effort to bootstrap, so this has languished as my graphing work has gone slower than desired. However, graphing is finally here enough that it really wants the IPDL enhancements; bug 1773165 in particular could benefit.
So I'm going to mainly add the test coverage in this bug which hopefully should make it trivial for us to take updates in the future.
Note that I did file bug 1661067 on switching to using the in-tree parser for consistency, but that involves significantly more work. (And why would we do that if we've got an equivalent rust parser? Woo rust!)