ci: Add job to test interface file determinism guarantees

In this job we can run on every commit we add a test which builds the
Cabal library twice and checks that the ABI hash and interface hash is
stable across the two builds.

* We run the test 20 times to try to weed out any race conditions due to
  `-j`
* We run the builds in different temporary directories to try to weed
  out anything related to build directory affecting ABI or interface
  file hash.

Fixes #22180

2 files changed, 100 insertions, 0 deletions

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f19c78c561..f6ef3e2c3f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -753,6 +753,46 @@ perf:
   rules:
     - if: '$CI_MERGE_REQUEST_LABELS !~ /.*fast-ci.*/'
 
+############################################################
+# ABI testing
+############################################################
+
+abi-test:
+  stage: testing
+  needs:
+    - job: x86_64-linux-fedora33-release
+      optional: true
+    - job: nightly-x86_64-linux-fedora33-release
+      optional: true
+    - job: release-x86_64-linux-fedora33-release
+      optional: true
+  dependencies: null
+  image: "registry.gitlab.haskell.org/ghc/ci-images/x86_64-linux-fedora33:$DOCKER_REV"
+  rules:
+    - if: $CI_MERGE_REQUEST_ID
+    - if: '$CI_COMMIT_BRANCH == "master"'
+    - if: '$CI_COMMIT_BRANCH =~ /ghc-[0.9]+\.[0-9]+/'
+  tags:
+    - x86_64-linux
+  script:
+    - root=$(pwd)/ghc
+    - |
+      mkdir tmp
+      tar -xf ghc-x86_64-linux-fedora33-release.tar.xz -C tmp
+      pushd tmp/ghc-*/
+      ./configure --prefix=$root
+      make install
+      popd
+      rm -Rf tmp
+    - export BOOT_HC=$(which ghc)
+    - export HC=$root/bin/ghc
+    - .gitlab/ci.sh abi_test
+  artifacts:
+    paths:
+      - out
+  rules:
+    - if: '$CI_MERGE_REQUEST_LABELS !~ /.*fast-ci.*/'
+
 
 ############################################################
 # Documentation deployment via GitLab Pages
diff --git a/.gitlab/ci.sh b/.gitlab/ci.sh
index b840500aa4..5a9097aaab 100755
--- a/.gitlab/ci.sh
+++ b/.gitlab/ci.sh
@@ -663,6 +663,36 @@ function test_hadrian() {
 
 }
 
+function summarise_hi_files() {
+  for iface in $(find . -type f -name "*.hi" | sort); do echo "$iface  $($HC --show-iface $iface | grep "  ABI hash:")"; done | tee $OUT/abis
+  for iface in $(find . -type f -name "*.hi" | sort); do echo "$iface  $($HC --show-iface $iface | grep "  interface hash:")"; done | tee $OUT/interfaces
+  for iface in $(find . -type f -name "*.hi" | sort); do
+      fname="$OUT/$(dirname $iface)"
+      mkdir -p $fname
+      $HC --show-iface $iface > "$OUT/$iface"
+  done
+}
+
+function cabal_abi_test() {
+  if [ -z "$OUT" ]; then
+    fail "OUT not set"
+  fi
+
+  cp -r libraries/Cabal $DIR
+  pushd $DIR
+  echo $PWD
+
+  start_section "Cabal test: $OUT"
+  mkdir -p "$OUT"
+  run "$HC" \
+    -hidir tmp -odir tmp -fforce-recomp -haddock \
+    -iCabal/Cabal/src -XNoPolyKinds Distribution.Simple -j"$cores" \
+    "$@" 2>&1 | tee $OUT/log
+  summarise_hi_files
+  popd
+  end_section "Cabal test: $OUT"
+}
+
 function cabal_test() {
   if [ -z "$OUT" ]; then
     fail "OUT not set"
@@ -693,6 +723,35 @@ function run_perf_test() {
   OUT=out/Cabal-O2 cabal_test -O2
 }
 
+function check_interfaces(){
+  difference=$(diff "$1/$3" "$2/$3") || warn "diff failed"
+  if [ -z "$difference" ]
+   then
+      info "$1 and $2 $3 match"
+   else
+     echo $difference
+     for line in $(echo "$difference" | tr ' ' '\n' | grep ".hi" | sort | uniq); do
+       diff "$1/$line" "$2/$line"
+     done
+     fail "$3"
+  fi
+}
+
+function abi_test() {
+  for i in {1..20}; do info "iteration $i"; run_abi_test; done
+}
+
+function run_abi_test() {
+  if [ -z "$HC" ]; then
+    fail "HC not set"
+  fi
+  mkdir -p out
+  OUT="$PWD/out/run1" DIR=$(mktemp -d XXXX-looooooooong) cabal_abi_test -O0
+  OUT="$PWD/out/run2" DIR=$(mktemp -d XXXX-short) cabal_abi_test -O0
+  check_interfaces out/run1 out/run2 abis "Mismatched ABI hash"
+  check_interfaces out/run1 out/run2 interfaces "Mismatched interface hashes"
+}
+
 function save_cache () {
   info "Storing cabal cache from $CABAL_DIR to $CABAL_CACHE..."
   rm -Rf "$CABAL_CACHE"
@@ -837,6 +896,7 @@ case $1 in
     exit $res ;;
   run_hadrian) shift; run_hadrian "$@" ;;
   perf_test) run_perf_test ;;
+  abi_test) abi_test ;;
   cabal_test) cabal_test ;;
   lint_author) shift; lint_author "$@" ;;
   clean) clean ;;