Auto-derive MIGRATE_PIPELINE_ROOT in new_docker_build.sh

Resolution order (highest precedence first):
  1. exported MIGRATE_PIPELINE_ROOT (e.g. from a Jenkinsfile)
  2. MIGRATE_PIPELINE_ROOT set by .envrc in this directory
  3. derived from the script location (three levels up)

The script always lives at <root>/qt-migration-legatus/qt6-after/
qt6-migrated-legatus, so the pipeline root is three levels up. This
makes the script work in a fresh Jenkins checkout with no environment
setup at all, and .envrc is no longer required.

qt6-after/qt6-migrated-legatus/new_docker_build.sh

@@ -8,8 +8,8 @@ set -euo pipefail
 # Lts/Proxies/TrainingAreaBase) inside the prebuilt Docker image and
 # optionally runs the Jenkins builder to produce the release DEB packages.
 #
-# - Loads environment from .envrc
-# - Validates MIGRATE_PIPELINE_ROOT and rti_license.dat
+# - Resolves MIGRATE_PIPELINE_ROOT (exported variable, .envrc, or derived
+#   from the script location) and validates rti_license.dat
 # - Uses a prebuilt Docker image with all build dependencies installed
 #   (build it from ./Dockerfile via --build-prebuilt-image)
 # - Optional deletion of the prebuilt Docker image via --delete-prebuilt-image
@@ -55,8 +55,10 @@ Environment variable overrides:
   BUILD_NUMBER=<num>
   BUILD_TAG=<tag>
 
-Required .envrc variable:
-  MIGRATE_PIPELINE_ROOT=<absolute-path>
+MIGRATE_PIPELINE_ROOT resolution (highest precedence first):
+  1. exported MIGRATE_PIPELINE_ROOT (e.g. from a Jenkinsfile)
+  2. MIGRATE_PIPELINE_ROOT set by .envrc in this directory
+  3. derived from the script location (three levels up)
 
 Expected file:
   ${MIGRATE_PIPELINE_ROOT}/rti_license.dat
@@ -259,14 +261,30 @@ build_prebuilt_image() {
 
 require_command docker
 
-if [[ ! -f ".envrc" ]]; then
-  die ".envrc not found in current directory. Please create .envrc with required environment variables (e.g., MIGRATE_PIPELINE_ROOT)"
+# MIGRATE_PIPELINE_ROOT resolution (highest precedence first):
+#   1. exported environment variable (e.g. from a Jenkinsfile)
+#   2. .envrc in this directory (if present)
+#   3. derived from this script's location - the script always lives at
+#      <root>/qt-migration-legatus/qt6-after/qt6-migrated-legatus, so the
+#      pipeline root is three levels up. This makes the script work in a
+#      fresh Jenkins checkout with no environment setup at all.
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+MIGRATE_PIPELINE_ROOT_DEFAULT="$(cd "${SCRIPT_DIR}/../../.." && pwd)"
+PIPELINE_ROOT_EXPORTED="${MIGRATE_PIPELINE_ROOT:-}"
+
+if [[ -f ".envrc" ]]; then
+  set -a
+  # shellcheck disable=SC1091
+  source ".envrc"
+  set +a
 fi
 
-set -a
-# shellcheck disable=SC1091
-source ".envrc"
-set +a
+# An explicitly exported MIGRATE_PIPELINE_ROOT (Jenkinsfile) wins over .envrc
+if [[ -n "${PIPELINE_ROOT_EXPORTED}" ]]; then
+  MIGRATE_PIPELINE_ROOT="${PIPELINE_ROOT_EXPORTED}"
+else
+  MIGRATE_PIPELINE_ROOT="${MIGRATE_PIPELINE_ROOT:-${MIGRATE_PIPELINE_ROOT_DEFAULT}}"
+fi
 
 # Fixed configuration for the release validation-scope branch
 RELEASE_BUILD=ON