Smarter warning (#390)

Warnings that mention npm installs can be confusing if you're using yarn to install your dependencies.

lib/failure.sh

 warnings=$(mktemp -t heroku-buildpack-nodejs-XXXX)
 
+detect_package_manager() {
+  case $YARN in
+    true) echo "yarn";;
+    *) echo "npm";;
+  esac
+}
+
 failure_message() {
   local warn="$(cat $warnings)"
   echo ""
@@ -136,7 +143,8 @@ warn_econnreset() {
 
 warn_unmet_dep() {
   local log_file="$1"
+  local package_manager=$(detect_package_manager)
   if grep -qi 'unmet dependency' "$log_file" || grep -qi 'unmet peer dependency' "$log_file"; then
-    warn "Unmet dependencies don't fail npm install but may cause runtime issues" "https://github.com/npm/npm/issues/7494"
+    warn "Unmet dependencies don't fail $package_manager install but may cause runtime issues" "https://github.com/npm/npm/issues/7494"
   fi
 }

test/fixtures/unmet-dep-yarn/package.json

+{
+  "name": "unmet-dep",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "start": "node server.js"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "grunt-steroids": "0.2.3"
+  }
+}

test/fixtures/unmet-dep-yarn/yarn.lock

+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+ansi-styles@~0.2.0:
+  version "0.2.0"
+  resolved "https://registry.yarnpkg.com/ansi-styles/-/ansi-styles-0.2.0.tgz#359ab4b15dcd64ba6d74734b72c36360a9af2c19"
+
+chalk@0.3.0:
+  version "0.3.0"
+  resolved "https://registry.yarnpkg.com/chalk/-/chalk-0.3.0.tgz#1c98437737f1199ebcc1d4c48fd41b9f9c8e8f23"
+  dependencies:
+    ansi-styles "~0.2.0"
+    has-color "~0.1.0"
+
+grunt-steroids@0.2.3:
+  version "0.2.3"
+  resolved "https://registry.yarnpkg.com/grunt-steroids/-/grunt-steroids-0.2.3.tgz#ac24d8597bbeae40cab972ead0a4a4ec5e6aa0a9"
+  dependencies:
+    chalk "0.3.0"
+    lodash "2.4.1"
+    wrench "1.5.4"
+    xml2js "0.4.1"
+
+has-color@~0.1.0:
+  version "0.1.7"
+  resolved "https://registry.yarnpkg.com/has-color/-/has-color-0.1.7.tgz#67144a5260c34fc3cca677d041daf52fe7b78b2f"
+
+lodash@2.4.1:
+  version "2.4.1"
+  resolved "https://registry.yarnpkg.com/lodash/-/lodash-2.4.1.tgz#5b7723034dda4d262e5a46fb2c58d7cc22f71420"
+
+sax@0.5.x:
+  version "0.5.8"
+  resolved "https://registry.yarnpkg.com/sax/-/sax-0.5.8.tgz#d472db228eb331c2506b0e8c15524adb939d12c1"
+
+wrench@1.5.4:
+  version "1.5.4"
+  resolved "https://registry.yarnpkg.com/wrench/-/wrench-1.5.4.tgz#2e8d9d3db3568cc1c001a4c8dceca772e5d21643"
+
+xml2js@0.4.1:
+  version "0.4.1"
+  resolved "https://registry.yarnpkg.com/xml2js/-/xml2js-0.4.1.tgz#dee0630173a5c6ea62797f848615fd55c6bc6992"
+  dependencies:
+    sax "0.5.x"
+    xmlbuilder ">=0.4.2"
+
+xmlbuilder@>=0.4.2:
+  version "8.2.2"
+  resolved "https://registry.yarnpkg.com/xmlbuilder/-/xmlbuilder-8.2.2.tgz#69248673410b4ba42e1a6136551d2922335aa773"

test/run

@@ -88,8 +88,19 @@ testYarnEngine() {
   assertCapturedSuccess
 }
 
-testWarnUnmetDep() {
+testWarnUnmetDepNpm() {
   compile "unmet-dep"
+  assertCaptured "fail npm install"
+  assertCaptured "may cause runtime issues"
+  assertCapturedSuccess
+  compile "no-version"
+  assertNotCaptured "may cause runtime issues"
+  assertCapturedSuccess
+}
+
+testWarnUnmetDepYarn() {
+  compile "unmet-dep-yarn"
+  assertCaptured "fail yarn install"
   assertCaptured "may cause runtime issues"
   assertCapturedSuccess
   compile "no-version"