ci: Add job for testing interface stability across builds

The idea is that both the bindists should product libraries with the
same ABI and interface hash.
So the job checks with ghc-pkg to make sure the computed ABI
is the same.

In future this job can be extended to check for the other facets of
interface determinism.

Fixes #22180

1 files changed, 17 insertions, 0 deletions

diff --git a/.gitlab/ci.sh b/.gitlab/ci.sh
index 5a9097aaab..bce606f679 100755
--- a/.gitlab/ci.sh
+++ b/.gitlab/ci.sh
@@ -801,6 +801,22 @@ function lint_author(){
   done
 }
 
+function abi_of(){
+  DIR=$(realpath $1)
+  mkdir -p "$OUT"
+  pushd $DIR
+  summarise_hi_files
+  popd
+}
+
+# Checks that the interfaces in folder $1 match the interfaces in folder $2
+function compare_interfaces_of(){
+  OUT=$PWD/out/run1 abi_of $1
+  OUT=$PWD/out/run2 abi_of $2
+  check_interfaces out/run1 out/run2 abis "Mismatched ABI hash"
+  check_interfaces out/run1 out/run2 interfaces "Mismatched interface hashes"
+}
+
 
 setup_locale
 
@@ -899,6 +915,7 @@ case $1 in
   abi_test) abi_test ;;
   cabal_test) cabal_test ;;
   lint_author) shift; lint_author "$@" ;;
+  compare_interfaces_of) shift; compare_interfaces_of "$@" ;;
   clean) clean ;;
   save_cache) save_cache ;;
   shell) shift; shell "$@" ;;