Test for package-lock.json

If the user has not specified a version for npm, but there is a package-lock.json we should automatically install npm 5

Fixes #422

bin/compile

@@ -55,6 +55,7 @@ trap 'handle_failure' ERR
 
 [ -e "$BUILD_DIR/node_modules" ] && PREBUILD=true || PREBUILD=false
 [ -f "$BUILD_DIR/yarn.lock" ] && YARN=true || YARN=false
+[ -f "$BUILD_DIR/package-lock.json" ] && NPM_LOCK=true || NPM_LOCK=false
 
 ### Failures that should be caught immediately
 
@@ -106,7 +107,7 @@ install_bins() {
   else
     warn_node_engine "$node_engine"
     install_nodejs "$node_engine" "$BUILD_DIR/.heroku/node"
-    install_npm "$npm_engine" "$BUILD_DIR/.heroku/node"
+    install_npm "$npm_engine" "$BUILD_DIR/.heroku/node" $NPM_LOCK
     mcount "version.node.$(node --version)"
   fi
 

lib/binaries.sh

@@ -74,6 +74,13 @@ install_iojs() {
 
 install_npm() {
   local version="$1"
+  local dir="$2"
+  local npm_lock="$3"
+
+  if $npm_lock && [ "$version" == "" ]; then
+    echo "Detected package-lock.json: defaulting npm to version 5.x.x"
+    version="5.x.x"
+  fi
 
   if [ "$version" == "" ]; then
     echo "Using default npm version: `npm --version`"

test/fixtures/npm-lockfile-no-version/package-lock.json

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

test/fixtures/npm-lockfile-no-version/package.json

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

test/run

@@ -119,6 +119,13 @@ testErrorYarnAndNpmLockfiles() {
   assertCapturedError
 }
 
+testDefaultToNpm5() {
+  compile "npm-lockfile-no-version"
+  assertCaptured "Detected package-lock.json"
+  assertCaptured "Downloading and installing npm 5."
+  assertCapturedSuccess
+}
+
 testWarnUnmetDepNpm() {
   compile "unmet-dep"
   assertCaptured "fail npm install"