[CI] Enforce lockfile is kept up to date

.circleci/config.yml

@@ -198,6 +198,7 @@ aliases:
     command: |
       ./scripts/circleci/check_license.sh
       ./scripts/circleci/check_cache.sh
+      ./scripts/circleci/validate_yarn_lockfile.sh
     when: always
 
   - &download-dependencies-gradle

scripts/circleci/validate_yarn_lockfile.sh

@@ -0,0 +1,39 @@
+#!/bin/bash
+
+# Abort the mission if any command fails
+set -e
+
+# Allow the script to be invoked from various environments
+if [[ -z "${OVERRIDE_YARN_BINARY}" ]]; then
+  YARN_BINARY=$(command -v yarn)
+else
+  YARN_BINARY="${OVERRIDE_YARN_BINARY}"
+fi
+
+REACT_NATIVE_TEMP_DIR=$(mktemp -d /tmp/react-native-XXXXXXXX)
+
+function cleanup {
+  set +e
+  rm -rf "$REACT_NATIVE_TEMP_DIR"
+  set -e
+}
+
+function msg {
+  echo -e " "
+  echo -e "\\x1B[36m${1}\\x1B[0m";
+  echo -e "\\x1B[36m${1//?/=}\\x1B[0m"
+}
+
+trap cleanup EXIT
+
+cp -R ./package.json "$REACT_NATIVE_TEMP_DIR"
+cp -R ./yarn.lock "$REACT_NATIVE_TEMP_DIR"
+pushd "$REACT_NATIVE_TEMP_DIR" >/dev/null
+
+if ! $YARN_BINARY --ignore-scripts --silent --non-interactive --mutex network --frozen-lockfile; then
+  msg "Yarn validation failed."
+  echo "This means the package.json and yarn.lock disagree in some way."
+  echo "Try fixing it by running \`yarn\` and committing the changes."
+fi
+
+popd >/dev/null