For the past several months I've been working on developing a set of 
tests for the Fortran/C interoperability features added to Fortran via 
TS 29113, "Further Interoperability of Fortran with C":

https://wg5-fortran.org/N1901-N1950/N1942.pdf

The goal here is to exercise gfortran's implementation in a more 
systematic and complete way, including conformance with error detection 
requirements and the like as well as making sure correct programs run 
correctly.

I'm posting this as work-in-progress at this time because, well, there 
are a lot of bugs in the implementation causing lots of the tests to 
fail.  :-(  I know maintainers don't like patches that deliberately add 
FAILs to the test results and the normal practice seems to be to XFAIL 
known bugs with references to a PR.  Some of the bugs already have PRs 
open, but others don't.  What I plan to work on next is filing or 
updating the PRs with reference to the testcases that demonstrate the 
bugs, add the XFAILs, and then resubmit the patch for approval.  A few 
of these tests also still have some excessively verbose debugging output 
enabled which I'll also try to clean up before resubmitting.

I have a trivial patch for one set of failures (incorrect initialization 
of version fields) that I'll be posting shortly.  A couple of José's 
recent not-yet-committed patches also fix some of the bugs I've run 
into; I will note those in the corresponding PRs as I work through the list.

-Sandra