Multiple lockfiles error

These changes build on top of [existing pnpm support](#1224) and modify the failure message shown when multiple lockfiles are detected to now include pnpm.

lib/failure.sh

@@ -115,31 +115,53 @@ fail_iojs_unsupported() {
 }
 
 fail_multiple_lockfiles() {
+  local build_dir="${1:-}"
   local has_modern_lockfile=false
-  if [ -f "${1:-}/yarn.lock" ] || [ -f "${1:-}/package-lock.json" ]; then
-    has_modern_lockfile=true
-  fi
 
-  if [ -f "${1:-}/yarn.lock" ] && [ -f "${1:-}/package-lock.json" ]; then
-    mcount "failures.two-lock-files"
-    meta_set "failure" "two-lock-files"
+  declare -A lockfiles=(
+    ["npm"]="package-lock.json"
+    ["pnpm"]="pnpm-lock.yaml"
+    ["Yarn"]="yarn.lock"
+  )
+
+  local detected_package_managers=()
+  for package_manager in "${!lockfiles[@]}"; do
+    lockfile="${lockfiles["$package_manager"]}"
+    if [ -f "$build_dir/$lockfile" ]; then
+      has_modern_lockfile=true
+      detected_package_managers+=("$package_manager")
+    fi
+  done
+
+  if (( "${#detected_package_managers[*]}" > 1 )); then
+    readarray -td '' package_managers_sorted < <(printf '%s\0' "${detected_package_managers[@]}" | sort -z --ignore-case)
+    mcount "failures.multiple-lock-files"
+    meta_set "failure" "multiple-lock-files"
     header "Build failed"
-    warn "Two different lockfiles found: package-lock.json and yarn.lock
+    warn "Multiple lockfiles found
 
-       Both npm and yarn have created lockfiles for this application,
+       Multiple package managers ($(IFS=','; printf '%s' "${package_managers_sorted[*]}")) have created lockfiles 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.
+         the pnpm and/or Yarn file.
 
-         $ git rm yarn.lock
+         $ git rm ${lockfiles["pnpm"]}
+         $ git rm ${lockfiles["Yarn"]}
 
-       - To use yarn to install your application's dependencies please delete
-         the package-lock.json file.
+       - To use Yarn to install your application's dependencies please delete
+         the npm and/or pnpm lockfiles.
 
-         $ git rm package-lock.json
+         $ git rm ${lockfiles["npm"]}
+         $ git rm ${lockfiles["pnpm"]}
+
+       - To use pnpm to install your application's dependencies please delete
+         the npm and/or Yarn lockfiles.
+
+         $ git rm ${lockfiles["npm"]}
+         $ git rm ${lockfiles["Yarn"]}
     " https://help.heroku.com/0KU2EM53
     fail
   fi
@@ -148,20 +170,18 @@ fail_multiple_lockfiles() {
     mcount "failures.shrinkwrap-lock-file-conflict"
     meta_set "failure" "shrinkwrap-lock-file-conflict"
     header "Build failed"
-    warn "Two different lockfiles found
+    warn "Multiple lockfiles conflicting with npm-shrinkwrap.json
 
-       Your application has two lockfiles defined, but only one can be used
+       Your application has multiple lockfiles defined which conflicts with the
+       shrinkwrap file you've been using. Only one lockfile can be used
        to install dependencies. Installing dependencies using the wrong lockfile
        can result in missing packages or subtle bugs in production.
 
-       It's most likely that you recently installed yarn which has its own
-       lockfile by default, which conflicts with the shrinkwrap file you've been
-       using.
-
        Please make sure there is only one of the following files in your
        application directory:
 
        - yarn.lock
+       - pnpm-lock.yaml
        - package-lock.json
        - npm-shrinkwrap.json
     " https://help.heroku.com/0KU2EM53

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

@@ -0,0 +1,9 @@
+{
+  "name": "yarn",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT",
+  "dependencies": {
+    "lodash": "^4.16.4"
+  }
+}