From d2ee77434e0a37576cd3013dcb54696eebe5b9f2 Mon Sep 17 00:00:00 2001
From: Ralf Pannemans <ralf.pannemans@sap.com>
Date: Fri, 27 Sep 2024 13:41:08 +0200
Subject: [PATCH] Introduce BP_KEEP_NODE_BUILD_CACHE to safeguard existing
 behaviour

---
 README.md      |  7 ++++---
 build.go       | 21 ++++++++++++---------
 buildpack.toml |  6 ++++++
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/README.md b/README.md
index 5af3b5d0b..827a2b132 100644
--- a/README.md
+++ b/README.md
@@ -40,9 +40,10 @@ file that looks like the following:
 
 ## Configuration
 
-| Environment Variable          | Description                                                                                                                                                               |
-|-------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| `$BP_NPM_VERSION`     | If set, this custom version of `npm` will be used instead of the one provided by the `nodejs` installation.                                                                       |
+| Environment Variable        | Description                                                                                                                                                               |
+|-----------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `$BP_NPM_VERSION`           | If set, this custom version of `npm` will be used instead of the one provided by the `nodejs` installation.                                                               |
+| `$BP_KEEP_NODE_BUILD_CACHE` | If set to `true` (default `false`), the folder `node_modules/.cache` will not be removed after the build, but will be readonly at runtime.                                |
 
 ## Usage
 
diff --git a/build.go b/build.go
index 760d11a74..e43e8f47a 100644
--- a/build.go
+++ b/build.go
@@ -284,16 +284,19 @@ func Build(entryResolver EntryResolver,
 					return packit.BuildResult{}, err
 				}
 
-				linkName := filepath.Join(layer.Path, "node_modules", ".cache")
-				err = os.RemoveAll(linkName)
-				if err != nil {
-					return packit.BuildResult{}, err
-				}
+				keepBuildCache, _ := environment.Lookup("BP_KEEP_NODE_BUILD_CACHE")
+				if keepBuildCache != "true" {
+					linkName := filepath.Join(layer.Path, "node_modules", ".cache")
+					err = os.RemoveAll(linkName)
+					if err != nil {
+						return packit.BuildResult{}, err
+					}
 
-				cacheFolder := filepath.Join(os.TempDir(), NODE_MODULES_CACHE)
-				err = os.Symlink(cacheFolder, linkName)
-				if err != nil {
-					return packit.BuildResult{}, err
+					cacheFolder := filepath.Join(os.TempDir(), NODE_MODULES_CACHE)
+					err = os.Symlink(cacheFolder, linkName)
+					if err != nil {
+						return packit.BuildResult{}, err
+					}
 				}
 
 				if build {
diff --git a/buildpack.toml b/buildpack.toml
index b18193c9b..9f9d8dcbf 100644
--- a/buildpack.toml
+++ b/buildpack.toml
@@ -32,6 +32,11 @@ api = "0.7"
     name = "BP_NPM_VERSION"
     description = "configures a custom npm version"
 
+	[[metadata.configurations]]
+    name = "BP_KEEP_NODE_BUILD_CACHE"
+    default = "false"
+    description = "keep the 'node_modules/.cache' folder after the build (will be readonly at runtime)'"
+
   [[metadata.configurations]]
 	  name = "NODE_HOME"
     description = "path the Node.js installation"
@@ -45,5 +50,6 @@ api = "0.7"
     default = "error"
     description = "configures npm output verbosity"
 
+
 [[stacks]]
   id = "*"