Add checks for Yarn 2

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Add warning for Yarn 2 usage, warn user of ignoring engine from package.json ([#761](https://github.com/heroku/heroku-buildpack-nodejs/pull/761))
 - Add warning for if .yarnrc file exists when using Yarn 2 ([#768](https://github.com/heroku/heroku-buildpack-nodejs/pull/768))
 - Add warning for if .npmrc file exists when using Yarn 2 ([#764](https://github.com/heroku/heroku-buildpack-nodejs/pull/764))
+- Add checks for Yarn 2 ([#759](https://github.com/heroku/heroku-buildpack-nodejs/pull/759))
 
 ## master
 - Update Travis badge to `master` and other changes in README ([#753](https://github.com/heroku/heroku-buildpack-nodejs/pull/753))

bin/compile

@@ -140,18 +140,36 @@ create_build_env
 [ ! "$NPM_CONFIG_CACHE" ] && NPM_CONFIG_CACHE=$(mktemp -d -t npmcache.XXXXX)
 export YARN_CACHE_FOLDER NPM_CONFIG_CACHE
 
+### Configure vendored package manager
+export YARN2_PATH
+
 if [[ "$YARN2" == "true" ]]; then
   if [[ "$NODE_MODULES_CACHE" == "true" ]]; then
     warn "
       WARNING- You are using Yarn2. The buildpack won't cache, because Yarn 2 does not provide node modules.
       "
   fi
+
   if [[ -f "$BUILD_DIR/.npmrc" ]]; then
     warn "There is an existing .npmrc file that will not be used. All configurations are read from the .yarnrc.yml file."
   fi
+
   if [[ -f "$BUILD_DIR/.yarnrc" ]]; then
     warn "There is an existing .yarnrc file that will not be used. All configurations are read from the .yarnrc.yml file."
   fi
+
+  ### Configure Yarn 2
+  # fail for no yarnrc.yml
+  fail_missing_yarnrc_yml "$BUILD_DIR"
+
+  # get yarn_path
+  YARN2_PATH=$(get_yarn_path "$BUILD_DIR")
+
+  # fail for no yarnPath in rc
+  fail_missing_yarn_path "$BUILD_DIR" "$YARN2_PATH"
+
+  # fail for missing yarn in .yarn/releases
+  fail_missing_yarn_vendor "$BUILD_DIR" "$YARN2_PATH"
 fi
 
 install_bins() {
@@ -162,7 +180,7 @@ install_bins() {
   yarn_engine=$(read_json "$BUILD_DIR/package.json" ".engines.yarn")
 
   if [[ "$YARN2" == "true" && -n "$yarn_engine" ]]; then
-    warn " You should be using a vendored version of Yarn. Heroku will ignore the engine from the package.json. "
+    warn "You should be using a vendored version of Yarn. Heroku will ignore the engine from the package.json."
   fi
 
   meta_set "node-version-request" "$node_engine"

lib/failure.sh

@@ -361,6 +361,77 @@ fail_invalid_semver() {
   fi
 }
 
+# Yarn 2 failures
+
+fail_missing_yarnrc_yml() {
+  local build_dir="$1"
+
+  if [[ ! -f "$build_dir/.yarnrc.yml" ]]; then
+    mcount "failures.missing-yarnrc-yml"
+    meta_set "failure" "missing-yarnrc-yml"
+    header "Build failed"
+    warn "The yarnrc.yml file could not found
+
+      It looks like the yarnrc.yml file is missing from this project. Please
+      make sure this file is checked into version control and made available to
+      Heroku.
+
+      To generate yarnrc.yml, make sure Yarn 2 is installed on your local
+      machine and set the version in your project directory with:
+
+       $ yarn set version berry
+      "
+    fail
+  fi
+}
+
+fail_missing_yarn_path() {
+  local build_dir="$1"
+  local yarn_path="$2"
+
+  if [[ "$yarn_path" == "" ]]; then
+    mcount "failures.missing-yarn-path"
+    meta_set "failure" "missing-yarn-path"
+    header "Build failed"
+    warn "The 'yarnPath' could not be read from the yarnrc.yml file
+
+      It looks like yarnrc.yml is missing the 'yarnPath' value, which is needed
+      to identify the location of yarn for this build.
+
+      To generate properly set 'yarnPath', make sure Yarn 2 is installed on your
+      local machine and set the version in your project directory with:
+
+       $ yarn set version berry
+      "
+    fail
+  fi
+}
+
+fail_missing_yarn_vendor() {
+  local build_dir="$1"
+  local yarn_path="$2"
+
+  if [[ ! -f "$build_dir/$yarn_path" ]]; then
+    mcount "failures.missing-yarn-vendor"
+    meta_set "failure" "missing-yarn-vendor"
+    header "Build failed"
+    warn "Yarn was not found
+
+      It looks like yarn is missing from $yarn_path, which is needed to continue
+      this build on Heroku. Yarn 2 recommends vendoring Yarn under the '.yarn'
+      directory, so remember to check the '.yarn' directory into version control
+      to use during builds.
+
+      To generate the vendor correctly, make sure Yarn 2 is installed on your
+      local machine and run the following in your project directory:
+
+       $ yarn install
+       $ yarn set version berry
+      "
+    fail
+  fi
+}
+
 log_other_failures() {
   local log_file="$1"
   if grep -qi "sh: 1: .*: not found" "$log_file"; then

lib/yarn2.sh

@@ -19,3 +19,8 @@ detect_yarn2() {
     echo "false"
   fi
 }
+
+get_yarn_path() {
+  local build_dir="$1"
+  $YQ r "$build_dir/.yarnrc.yml" yarnPath 2>&1
+}

test/fixtures/yarn-2-with-engine/.yarnrc.yml

@@ -0,0 +1 @@
+yarnPath: .yarn/releases/yarn-rc.js

test/fixtures/yarn-2-without-cache/.yarnrc.yml

@@ -0,0 +1 @@
+yarnPath: .yarn/releases/yarn-rc.js