Error out when two different lockfiles are present in the repo (#411)

Error out when two different lockfiles are present in the repo

Fixes #410

bin/compile

@@ -61,6 +61,7 @@ trap 'handle_failure' ERR
 fail_dot_heroku "$BUILD_DIR"
 fail_dot_heroku_node "$BUILD_DIR"
 fail_invalid_package_json "$BUILD_DIR"
+fail_yarn_and_npm_lockfiles "$BUILD_DIR"
 warn_prebuilt_modules "$BUILD_DIR"
 warn_missing_package_json "$BUILD_DIR"
 

lib/failure.sh

@@ -63,6 +63,31 @@ fail_dot_heroku_node() {
   fi
 }
 
+fail_yarn_and_npm_lockfiles() {
+  if [ -f "${1:-}/yarn.lock" ] && [ -f "${1:-}/package-lock.json" ]; then
+    mcount "failures.two-lock-files"
+    header "Build failed"
+    warn "Two different lock files found: package-lock.json and yarn.lock
+
+       Both npm and yarn have created lock files for this application,
+       but only one can be used to install dependencies. Installing
+       dependencies using the wrong package manager can result in missing
+       packages or subtle bugs in production.
+
+       - To use npm to install your application's dependencies please delete
+         the yarn.lock file.
+
+         $ git rm yarn.lock
+
+       - To use yarn to install your application's dependences please delete
+         the package-lock.json file.
+
+         $ git rm package-lock.json
+    " https://kb.heroku.com/why-is-my-node-js-build-failing-because-of-conflicting-lock-files
+    exit 1
+  fi
+}
+
 warning() {
   local tip=${1:-}
   local url=${2:-https://devcenter.heroku.com/articles/nodejs-support}

test/fixtures/yarn-and-npm-lockfiles/package-lock.json

+{
+  "name": "yarn",
+  "version": "1.0.0",
+  "lockfileVersion": 1,
+  "packageIntegrity": "sha512-4+lHSm8TaNvPyMeXgKHJuEJTZ7e9GkTnM2diAM0bJGwaayn7IfeF0M/COETD9Np6vuSjqraOuBlw+i5B2EYTKA==",
+  "dependencies": {
+    "lodash": {
+      "version": "4.17.4",
+      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.4.tgz",
+      "integrity": "sha1-eCA6TRwyiuHYbcpkYONptX9AVa4="
+    }
+  }
+}

test/fixtures/yarn-and-npm-lockfiles/package.json

+{
+  "name": "yarn",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT",
+  "dependencies": {
+    "lodash": "^4.16.4"
+  }
+}

test/fixtures/yarn-and-npm-lockfiles/yarn.lock

+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+lodash:
+  version "4.16.4"
+  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.16.4.tgz#01ce306b9bad1319f2a5528674f88297aeb70127"
+

test/run

@@ -110,6 +110,15 @@ testYarnOnlyEngine() {
   assertCapturedSuccess
 }
 
+testErrorYarnAndNpmLockfiles() {
+  compile "yarn-and-npm-lockfiles"
+  assertNotCaptured "Creating runtime environment"
+  assertCaptured "Two different lock files found: package-lock.json and yarn.lock"
+  assertCaptured "Both npm and yarn have created lock files"
+  assertCaptured "https://kb.heroku.com/why-is-my-node-js-build-failing-because-of-conflicting-lock-files"
+  assertCapturedError
+}
+
 testWarnUnmetDepNpm() {
   compile "unmet-dep"
   assertCaptured "fail npm install"