Skip dev dependency pruning on tests with PNPM (#1259)

* Skip dev dependency pruning on tests with PNPM

Matches functionality already present for Yarn and
NPM. Didn't include an additional flag to skip
pruning in contexts where it's needed at runtime,
as it's not necessary for my specific use-case and
I wasn't sure of naming conventions here.

* Added tests, opt-out flag, and changelog entry

---------

Co-authored-by: Colin Casey <casey.colin@gmail.com>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Skip pnpm pruning if `NODE_ENV` is not set to `production` or if `PNPM_SKIP_PRUNING` is set to `true` ([#1259](https://github.com/heroku/heroku-buildpack-nodejs/pull/1259))
 
 ## [v248] - 2024-05-10
 

lib/dependencies.sh

@@ -340,6 +340,20 @@ pnpm_prune_devdependencies() {
 
   cd "$build_dir" || return
 
+  if [ "$NODE_ENV" == "test" ]; then
+    echo "Skipping because NODE_ENV is 'test'"
+    meta_set "skipped-prune" "true"
+    return 0
+  elif [ "$NODE_ENV" != "production" ]; then
+    echo "Skipping because NODE_ENV is not 'production'"
+    meta_set "skipped-prune" "true"
+    return 0
+  elif [ "$PNPM_SKIP_PRUNING" == "true" ]; then
+    echo "Skipping because PNPM_SKIP_PRUNING is '$PNPM_SKIP_PRUNING'"
+    meta_set "skipped-prune" "true"
+    return 0
+  fi
+
   pnpm_version=$(pnpm --version)
   pnpm_major_version=$(echo "$pnpm_version" | cut -d "." -f 1)
   pnpm_minor_version=$(echo "$pnpm_version" | cut -d "." -f 2)

test/run

@@ -1952,6 +1952,43 @@ testPnpmSafePruningSupport() {
   assertCapturedSuccess
 }
 
+testPnpmSkipPruning() {
+  cache_dir=$(mktmpdir)
+
+  # skip pruning in test environment
+  env_dir=$(mktmpdir)
+  echo "test" > "$env_dir/NODE_ENV"
+  compile "pnpm-8.15.5" "$cache_dir" "$env_dir"
+  assertCaptured "Pruning devDependencies"
+  assertCaptured "Skipping because NODE_ENV is 'test'"
+  assertCapturedSuccess
+
+  # skip pruning in non-production environment
+  env_dir=$(mktmpdir)
+  echo "development" > "$env_dir/NODE_ENV"
+  compile "pnpm-8.15.5" "$cache_dir" "$env_dir"
+  assertCaptured "Pruning devDependencies"
+  assertCaptured "Skipping because NODE_ENV is not 'production'"
+  assertCapturedSuccess
+
+  # skip pruning if explicitly configured to do so
+  env_dir=$(mktmpdir)
+  echo "true" > "$env_dir/PNPM_SKIP_PRUNING"
+  compile "pnpm-8.15.5" "$cache_dir" "$env_dir"
+  assertCaptured "Pruning devDependencies"
+  assertCaptured "Skipping because PNPM_SKIP_PRUNING is 'true'"
+  assertCapturedSuccess
+
+  # otherwise, prune away
+  env_dir=$(mktmpdir)
+  echo "production" > "$env_dir/NODE_ENV"
+  echo "false" > "$env_dir/PNPM_SKIP_PRUNING"
+  compile "pnpm-8.15.5" "$cache_dir" "$env_dir"
+  assertCaptured "Pruning devDependencies"
+  assertCaptured "- dotenv 16.4.5"
+  assertCapturedSuccess
+}
+
 # Utils
 
 pushd "$(dirname 0)" >/dev/null