Find PR base branch without GitHub API and enable test skipping

.gitlab-ci.yml

@@ -119,8 +119,7 @@ default:
 
 .gitlab_base_ref_params: &gitlab_base_ref_params
   - |
-    # FIXME: Disabled until we find a way to not hit GitHub API rate limit
-    if false && [[ ! $CI_COMMIT_BRANCH =~ ^(master|release/.*)$ ]]; then
+    if [[ ! $CI_COMMIT_BRANCH =~ ^(master|release/.*)$ ]]; then
       export GIT_BASE_REF=$(.gitlab/find-gh-base-ref.sh)
       if [[ -n "$GIT_BASE_REF" ]]; then
         export GRADLE_PARAMS="$GRADLE_PARAMS -PgitBaseRef=origin/$GIT_BASE_REF"

.gitlab/find-gh-base-ref.sh

@@ -40,74 +40,44 @@ if [[ $(git log --pretty=oneline origin/master..HEAD | wc -l) -eq 1 ]]; then
   exit 0
 fi
 
-# In GitLab: we have no reference to the base branch or even the PR number.
-# We have to find it from the current branch name, which is defined in
-# CI_COMMIT_REF_NAME.
-if [[ -z "${CI_COMMIT_REF_NAME}" ]]; then
-  echo "CI_COMMIT_REF_NAME is not set, not running in GitLab CI?" >&2
-  exit 1
-fi
-
-# In GitLab, CI_PROJECT_NAME is set, otherwise, set it for testing.
-export CI_PROJECT_NAME="${CI_PROJECT_NAME:-dd-trace-java}"
+get_distance_from_merge_base() {
+  local candidate_base="$1"
+  merge_base_sha=$(git merge-base "$candidate_base" HEAD)
+  distance=$(git log --pretty=oneline "$merge_base_sha".."$CURRENT_HEAD_SHA" | wc -l)
+  echo "Distance from $candidate_base is $distance" >&2
+  echo "$distance"
+}
 
-if [[ -z "${GITHUB_TOKEN:-}" ]]; then
-  echo "GITHUB_TOKEN is not set, fetching from AWS SSM" >&2
-  if ! command -v aws >/dev/null 2>&1; then
-    echo "aws is not installed, please install it" >&2
-    exit 1
+# Find the best base ref: the master/release branch whose merge base is closest to HEAD.
+# If there are multiple candidates (e.g. immediately after a release branch is created), we cannot
+# disambiguate and return an error.
+# NOTE: GitHub API is more robust for this task, but we hit rate limits.
+BEST_CANDIDATES=(origin/master)
+BEST_DISTANCE=$(get_distance_from_merge_base origin/master)
+mapfile -t CANDIDATE_BASES < <(git branch -a --sort=committerdate --format='%(refname:short)' --list 'origin/release/v*' | tac)
+for candidate_base in "${CANDIDATE_BASES[@]}"; do
+  distance=$(get_distance_from_merge_base "$candidate_base")
+  if [[ $distance -lt $BEST_DISTANCE ]]; then
+    BEST_DISTANCE=$distance
+    BEST_CANDIDATES=("$candidate_base")
+  elif [[ $distance -eq $BEST_DISTANCE ]]; then
+    BEST_CANDIDATES+=("$candidate_base")
   fi
-  set +e
-  GITHUB_TOKEN=$(aws ssm get-parameter --name "ci.$CI_PROJECT_NAME.gh_release_token" --with-decryption --query "Parameter.Value" --output text)
-  set -e
-  if [[ -z "${GITHUB_TOKEN:-}" ]]; then
-    echo "Failed to fetch GITHUB_TOKEN from AWS SSM" >&2
-    exit 1
-  fi
-  export GITHUB_TOKEN
-fi
-
-if ! command -v curl >/dev/null 2>&1; then
-  echo "curl is not installed, please install it" >&2
-  exit 1
-fi
+done
 
-if ! command -v jq >/dev/null 2>&1; then
-  echo "jq is not installed, please install it" >&2
-  exit 1
+if [[ ${#BEST_CANDIDATES[@]} -eq 1 ]]; then
+  # Remote the origin/ prefix
+  base_ref="${BEST_CANDIDATES[0]#origin/}"
+  echo "Base ref is ${base_ref}" >&2
+  save_cache "${base_ref}" "$CURRENT_HEAD_SHA"
+  echo "${base_ref}"
+  exit 0
 fi
 
-while true; do
-  set +e
-  PR_DATA=$(curl \
-    -XGET \
-    --silent \
-    --include \
-    --fail-with-body \
-    -H 'Accept: application/vnd.github+json' \
-    -H "Authorization: Bearer ${GITHUB_TOKEN}" \
-    -H "X-GitHub-Api-Version: 2022-11-28" \
-    "https://api.github.com/repos/datadog/dd-trace-java/pulls?head=DataDog:${CI_COMMIT_REF_NAME}&sort=updated&direction=desc")
-  exit_code=$?
-  set -e
-  if [[ ${exit_code} -eq 0 ]]; then
-    PR_NUMBER=$(echo "$PR_DATA" | sed '1,/^[[:space:]]*$/d' | jq -r '.[].number')
-    PR_BASE_REF=$(echo "$PR_DATA" | sed '1,/^[[:space:]]*$/d' | jq -r '.[].base.ref')
-    if [[ -n "${PR_BASE_REF:-}" ]]; then
-      echo "PR is https://github.com/datadog/dd-trace-java/pull/${PR_NUMBER} and base ref is ${PR_BASE_REF}">&2
-      save_cache "${PR_BASE_REF}" "$CURRENT_HEAD_SHA"
-      echo "${PR_BASE_REF}"
-      exit 0
-    fi
-  fi
-  if echo "$PR_DATA" | grep -q "^x-ratelimit-reset:"; then
-    reset_timestamp=$(echo -n "$PR_DATA" | grep "^x-ratelimit-reset:" | sed -e 's/^x-ratelimit-reset: //' -e 's/\r//')
-    now=$(date +%s)
-    sleep_time=$((reset_timestamp - now + 1))
-    echo "GitHub rate limit exceeded, sleeping for ${sleep_time} seconds" >&2
-    sleep "${sleep_time}"
-    continue
-  fi
-  echo -e "GitHub request failed for an unknown reason:\n$(echo "$PR_DATA" | sed '/^$/q')" >&2
-  exit 1
-done
+# If base ref is ambiguous, we cannot determine the correct one.
+# Example: a release branch is created, and a PR is opened starting from the
+# commit where the release branch was created. The distance to the merge base
+# for both master and the release branch is the same. In this case, we bail
+# out, and make no assumption on which is the correct base ref.
+echo "Base ref is ambiguous, candidates are: ${BEST_CANDIDATES[*]}" >&2
+exit 1