Interface stability testing

The tests in this directory verify that the interfaces of exposed by GHC's core libraries do not inadvertently change. They use the utils/dump-decls utility to dump all exported declarations of all exposed modules for the following packages:

• base

These are compared against the expected exports in the test's corresponding .stdout file.

Updating expected output

The base-exports test in particular has rather platform-dependent output. Consequently, updating its output can be a bit tricky. There are two ways by which one can do this:

• Extrapolation: The various platforms' base-exports.stdout files are similar enough that one can often apply the same patch of one file to the others. For instance:

  for f in testsuite/tests/interface-stability/base-exports.stdout-*; do
    git show | sed -e "s/base-exports.stdout/$(basename $f)/" | patch -p1
  done

  In the case of conflicts, increasing the fuzz factor (using -F) can be quite effective.

• Using CI: Each CI job produces a tarball, unexpected-test-output.tar.gz, which contains the output produced by the job's failing tests. Simply download this tarball and extracting the appropriate base-exports.stdout-* files into this directory.