Added support for yarn berry (#4)

* Added support for yarn berry

* Added check for .yarnrc.yaml also

Author: abhishekt98

build.go

@@ -1,18 +1,21 @@
 package yarn
 
 import (
-	"fmt"
-	"os"
-	"path/filepath"
-	"strconv"
-	"time"
-
-	"github.com/paketo-buildpacks/packit/v2"
-	"github.com/paketo-buildpacks/packit/v2/chronos"
-	"github.com/paketo-buildpacks/packit/v2/draft"
-	"github.com/paketo-buildpacks/packit/v2/postal"
-	"github.com/paketo-buildpacks/packit/v2/sbom"
-	"github.com/paketo-buildpacks/packit/v2/scribe"
+    "fmt"
+    "os"
+    "os/exec"
+    "path/filepath"
+    "strconv"
+    "strings"
+    "time"
+    "encoding/json"
+
+    "github.com/paketo-buildpacks/packit/v2"
+    "github.com/paketo-buildpacks/packit/v2/chronos"
+    "github.com/paketo-buildpacks/packit/v2/draft"
+    "github.com/paketo-buildpacks/packit/v2/postal"
+    "github.com/paketo-buildpacks/packit/v2/sbom"
+    "github.com/paketo-buildpacks/packit/v2/scribe"
 )
 
 //go:generate faux --interface DependencyManager --output fakes/dependency_manager.go
@@ -41,13 +44,38 @@ func Build(
 			return packit.BuildResult{}, err
 		}
 
-		planner := draft.NewPlanner()
-		entry, _ := planner.Resolve("yarn", context.Plan.Entries, nil)
-		version, ok := entry.Metadata["version"].(string)
-		if !ok {
-			version = "default"
-		}
-
+        planner := draft.NewPlanner()
+        entry, _ := planner.Resolve("yarn", context.Plan.Entries, nil)
+        version, ok := entry.Metadata["version"].(string)
+        if !ok {
+            version = "default"
+        }
+
+        // Detect Yarn Berry (modern) by presence of .yarnrc.yml/.yarnrc.yaml
+        isBerryYarn := false
+        if _, statErr := os.Stat(filepath.Join(context.WorkingDir, ".yarnrc.yml")); statErr == nil {
+            isBerryYarn = true
+        } else if _, statErr := os.Stat(filepath.Join(context.WorkingDir, ".yarnrc.yaml")); statErr == nil {
+            isBerryYarn = true
+        }
+
+        // If package.json declares packageManager: "yarn@<ver>", prefer that ONLY for Berry projects
+        var pmYarnVersion string
+        if data, readErr := os.ReadFile(filepath.Join(context.WorkingDir, "package.json")); readErr == nil {
+            var pkg struct {
+                PackageManager string `json:"packageManager"`
+            }
+            if jsonErr := json.Unmarshal(data, &pkg); jsonErr == nil {
+                pm := strings.TrimSpace(pkg.PackageManager)
+                if strings.HasPrefix(pm, "yarn@") {
+                    v := strings.TrimPrefix(pm, "yarn@")
+                    if idx := strings.IndexAny(v, " +#"); idx != -1 {
+                        v = v[:idx]
+                    }
+                    pmYarnVersion = v
+                }
+            }
+        }
 		dependency, err := dependencyManager.Resolve(
 			filepath.Join(context.CNBPath, "buildpack.toml"),
 			entry.Name,
@@ -71,8 +99,15 @@ func Build(
 			launchMetadata = packit.LaunchMetadata{BOM: bom}
 		}
 
-		cachedSHA, ok := yarnLayer.Metadata[DependencyCacheKey].(string)
-		if ok && postal.Checksum(dependency.Checksum).MatchString(cachedSHA) {
+        // Use resolved dependency version as the install version (override with packageManager only for Berry)
+		
+        resolvedInstallVersion := dependency.Version
+        if isBerryYarn && pmYarnVersion != "" {
+            resolvedInstallVersion = pmYarnVersion
+        }
+
+        cachedSHA, ok := yarnLayer.Metadata[DependencyCacheKey].(string)
+        if ok && !isBerryYarn && postal.Checksum(dependency.Checksum).MatchString(cachedSHA) {
 			logger.Process("Reusing cached layer %s", yarnLayer.Path)
 			logger.Break()
 
@@ -85,25 +120,63 @@ func Build(
 			}, nil
 		}
 
-		logger.Process("Executing build process")
+        logger.Process("Executing build process")
 
 		yarnLayer, err = yarnLayer.Reset()
 		if err != nil {
 			return packit.BuildResult{}, err
 		}
 
-		yarnLayer.Launch, yarnLayer.Build, yarnLayer.Cache = launch, build, build
-
-		logger.Subprocess("Installing Yarn")
-
-		duration, err := clock.Measure(func() error {
-			return dependencyManager.Deliver(dependency, context.CNBPath, yarnLayer.Path, context.Platform.Path)
-		})
-		if err != nil {
-			return packit.BuildResult{}, err
-		}
-		logger.Action("Completed in %s", duration.Round(time.Millisecond))
-		logger.Break()
+        yarnLayer.Launch, yarnLayer.Build, yarnLayer.Cache = launch, build, build
+
+        logger.Subprocess("Installing Yarn %s", resolvedInstallVersion)
+
+        var duration time.Duration
+        if isBerryYarn {
+            // Persist Corepack cache under the yarn layer so the runtime doesn't re-download Yarn
+            corepackDir := filepath.Join(yarnLayer.Path, "corepack")
+            if mkErr := os.MkdirAll(corepackDir, 0o755); mkErr != nil {
+                return packit.BuildResult{}, mkErr
+            }
+			
+
+            duration, err = clock.Measure(func() error {
+                steps := [][]string{
+                    {"corepack", "enable"},
+                    {"corepack", "prepare", fmt.Sprintf("yarn@%s", resolvedInstallVersion), "--activate"},
+                }
+                for _, args := range steps {
+
+                    cmd := exec.Command(args[0], args[1:]...)
+                    cmd.Env = append(os.Environ(), "COREPACK_HOME="+corepackDir)
+                    cmd.Stdout = os.Stdout
+                    cmd.Stderr = os.Stderr
+                    if err := cmd.Run(); err != nil {
+                        return err
+                    }
+                }
+                return nil
+            })
+            if err != nil {
+                return packit.BuildResult{}, err
+            }
+            logger.Action("Completed in %s", duration.Round(time.Millisecond))
+            logger.Break()
+            // Ensure COREPACK_HOME is present in build and launch images
+            yarnLayer.Build = true
+            yarnLayer.Launch = true
+            yarnLayer.BuildEnv.Default("COREPACK_HOME", filepath.Join(yarnLayer.Path, "corepack"))
+            yarnLayer.LaunchEnv.Default("COREPACK_HOME", filepath.Join(yarnLayer.Path, "corepack"))
+        } else {
+            duration, err = clock.Measure(func() error {
+                return dependencyManager.Deliver(dependency, context.CNBPath, yarnLayer.Path, context.Platform.Path)
+            })
+            if err != nil {
+                return packit.BuildResult{}, err
+            }
+            logger.Action("Completed in %s", duration.Round(time.Millisecond))
+            logger.Break()
+        }
 
 		sbomDisabled, err := checkSbomDisabled()
 		if err != nil {
@@ -134,9 +207,13 @@ func Build(
 			}
 		}
 
-		yarnLayer.Metadata = map[string]interface{}{
-			DependencyCacheKey: dependency.Checksum,
-		}
+        cacheValue := dependency.Checksum
+        if isBerryYarn || cacheValue == "" {
+            cacheValue = dependency.Version
+        }
+        yarnLayer.Metadata = map[string]interface{}{
+            DependencyCacheKey: cacheValue,
+        }
 
 		return packit.BuildResult{
 			Layers: []packit.Layer{yarnLayer},

buildpack.toml

@@ -29,6 +29,20 @@ api = "0.7"
     uri = "https://paketo-artifacts.s3.us-east-1.amazonaws.com/yarn/yarn_1.22.19_linux_noarch_bionic_3235ba55.tgz"
     version = "1.22.19"
 
+  [[metadata.dependencies]]
+    checksum = "sha256:c8d3eae160a892e32837db3dcae515e843e5383fef52b8141940c8bcf8b6d59f"
+    cpe = "cpe:2.3:a:yarnpkg:yarn:4.9.2:*:*:*:*:*:*:*"
+    id = "yarn"
+    licenses = ["BSD-2-Clause"]
+    name = "Yarn"
+    purl = "pkg:generic/yarn@4.9.2"
+    source = "https://registry.npmjs.org/yarn/-/yarn-4.9.2.tgz"
+    source-checksum = "sha256:c8d3eae160a892e32837db3dcae515e843e5383fef52b8141940c8bcf8b6d59f"
+    stacks = ["io.buildpacks.stacks.bionic", "io.buildpacks.stacks.jammy", "io.buildpacks.stacks.noble", "*"]
+    strip-components = 1
+    uri = "https://registry.npmjs.org/yarn/-/yarn-4.9.2.tgz"
+    version = "4.9.2"
+    
   [[metadata.dependencies]]
     checksum = "sha256:88268464199d1611fcf73ce9c0a6c4d44c7d5363682720d8506f6508addf36a0"
     cpe = "cpe:2.3:a:yarnpkg:yarn:1.22.22:*:*:*:*:*:*:*"