Allow custom version of npm

Co-authored-by: Ralf Pannemans <[email protected]>

README.md

@@ -38,6 +38,12 @@ file that looks like the following:
     launch = true
 ```
 
+## 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.                                                                       |
+
 ## Usage
 
 To package this buildpack for consumption:

build.go

@@ -1,11 +1,14 @@
 package npminstall
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/paketo-buildpacks/libnodejs"
+	"github.com/paketo-buildpacks/packit/v2/pexec"
 	"github.com/paketo-buildpacks/packit/v2/sbom"
 
 	"github.com/paketo-buildpacks/packit/v2"
@@ -71,6 +74,22 @@ func Build(entryResolver EntryResolver,
 		if err != nil {
 			return packit.BuildResult{}, err
 		}
+		logger.Process("Checking custom npm version")
+		npmVersion, found := environment.Lookup("BP_NPM_VERSION")
+		if found {
+			args := []string{"install", "-g", fmt.Sprintf("npm@%s", npmVersion)}
+			logger.Subprocess("Running 'npm %s'", strings.Join(args, " "))
+
+			executable := pexec.NewExecutable("npm")
+			err = executable.Execute(pexec.Execution{
+				Args:   args,
+				Stdout: logger.ActionWriter,
+				Stderr: logger.ActionWriter,
+			})
+			if err != nil {
+				return packit.BuildResult{}, fmt.Errorf("npm update failed: %w", err)
+			}
+		}
 
 		logger.Process("Resolving installation process")
 

buildpack.toml

@@ -2,6 +2,7 @@ api = "0.7"
 
 [buildpack]
   homepage = "https://github.com/paketo-buildpacks/npm-install"
+  version = "1.1.1"
   id = "paketo-buildpacks/npm-install"
   name = "Paketo Buildpack for NPM Install"
   sbom-formats = ["application/vnd.cyclonedx+json", "application/spdx+json", "application/vnd.syft+json"]
@@ -28,6 +29,10 @@ api = "0.7"
 	  name = "BP_NODE_PROJECT_PATH"
     description = "path to the root of the Node.js project"
 
+	[[metadata.configurations]]
+    name = "BP_NPM_VERSION"
+    description = "configures a custom npm version"
+
   [[metadata.configurations]]
 	  name = "NODE_HOME"
     description = "path the Node.js installation"