PS-10100 [8.0]: Improve the way the base branch info is fetched in circleCI check

https://perconadev.atlassian.net/browse/PS-10100

The base branch information is crucial for performing clang-tidy checks
because the clang-tidy checks are configured run on only the changes
made in the source code files within a prticular pull request(even with
multiple commits) and the base branch is necessary to do the comparison
with the source branch to fetch the changes made in a PR.

So, Github API is used to dynamically fetch the pull request data which
is in turn used to filter out the base branch info. It has also been
made sure to handle cases where the circleCI checks are run in the
context of the fork(if enabled).
Curl is being used to fetch the JSON data from the API and all the
possible errors are handled and in such cases the base branch will be
set to 8.0 as a fallback.

Author: VarunNagaraju

.circleci/config.yml

@@ -16,6 +16,8 @@ jobs:
           command: |
             set -o xtrace
             UBUNTU_CODE_NAME="noble"
+            BASE_OWNER="percona"
+            BASE_REPO="percona-server"
             BASE_BRANCH="8.0"
             COMPILER_VERSION="19"
             BOOST_VERSION="1_77_0"
@@ -32,7 +34,63 @@ jobs:
             cd ~/project
             cmake -B /home/circleci/debug-build -DCMAKE_BUILD_TYPE=Debug -DWITH_BOOST=${BOOST_DIR} -DWITH_SSL=system -DWITH_AUTHENTICATION_LDAP=ON -DWITH_ROCKSDB=ON -DCMAKE_C_COMPILER=clang-${COMPILER_VERSION} -DCMAKE_CXX_COMPILER=clang++-${COMPILER_VERSION} -DCMAKE_CXX_FLAGS="-stdlib=libc++" -DCMAKE_EXE_LINKER_FLAGS="-stdlib=libc++" -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DWITH_SYSTEM_LIBS=ON -DWITH_FIDO=bundled -DWITH_ZSTD=bundled -DWITH_LZ4=bundled -DWITH_PROTOBUF=bundled ~/project
 
-            git remote add target "https://github.com/${CIRCLE_PROJECT_USERNAME}/${CIRCLE_PROJECT_REPONAME}"
+            # Method to fetch JSON from a Github API URL with error handling
+            fetch_json() {
+              local url="$1" tmp http_code curl_exit body
+              tmp=$(mktemp) || return 1
+              # write body to tmp, capture HTTP code on stdout
+              http_code=$(curl -sS --location --connect-timeout 10 --max-time 30 -w "%{http_code}" -o "$tmp" "$url" 2>/dev/null) || true
+              curl_exit=$?
+              body="$(cat "$tmp")"
+              rm -f "$tmp"
+
+              if [ $curl_exit -ne 0 ]; then
+                echo "curl exit $curl_exit for $url" >&2
+                return 2
+              fi
+              if [ -z "$http_code" ] || [ "$http_code" -ge 400 ]; then
+                echo "HTTP $http_code from $url" >&2
+                return 3
+              fi
+              if [ -z "${body:-}" ]; then
+                echo "empty response from $url" >&2
+                return 4
+              fi
+              if ! printf '%s' "$body" | jq -e . >/dev/null 2>&1; then
+                echo "response from $url is not valid JSON" >&2
+                return 5
+              fi
+
+              printf '%s' "$body"
+            }
+
+            PR_DATA=""
+            if [[ "$CIRCLE_BRANCH" =~ ^pull/[0-9]+$ ]]; then
+              # If the circleCI check is run in the context of the official percona repo.
+              PR_API_URL="https://api.github.com/repos/${BASE_OWNER}/${BASE_REPO}/pulls/${CIRCLE_PR_NUMBER}"
+              PR_DATA="$(fetch_json "$PR_API_URL")" || PR_DATA=""
+            else
+              # GitHub API URL to get open PRs matching this fork + branch
+              API_URL="https://api.github.com/repos/${BASE_OWNER}/${BASE_REPO}/pulls?head=${CIRCLE_PROJECT_USERNAME}:${CIRCLE_BRANCH}"
+              echo "Fetching PRs from: $API_URL" >&2
+
+              # Fetch PRs
+              PRS_JSON="$(fetch_json "$API_URL")" || PRS_JSON="[]"
+
+              # Filter PR whose head.sha matches CIRCLE_SHA1
+              PR_DATA="$(printf '%s' "$PRS_JSON" | jq --arg sha "$CIRCLE_SHA1" '.[] | select(.head.sha == $sha)')"
+            fi
+
+            if [[ -z "$PR_DATA" ]]; then
+              echo "Failed to find PR data for commit $CIRCLE_SHA1. $BASE_BRANCH will be used as the base branch."
+            else
+              BASE_BRANCH=$(echo "$PR_DATA" | jq -r '.base.ref')
+              PR_NUMBER=$(echo "$PR_DATA" | jq -r '.number')
+              echo "Found PR: $PR_NUMBER with base branch: $BASE_BRANCH"
+            fi
+
+            echo "$BASE_BRANCH"
+            git remote add target "https://github.com/${BASE_OWNER}/${BASE_REPO}"
             git fetch --no-tags --no-recurse-submodules target $BASE_BRANCH
 
             echo "Checking clang-format results"