Support yarn workspace focusing

lib/cache.sh

@@ -134,7 +134,7 @@ save_default_cache_directories() {
 
   if [[ "$YARN" == "true" ]]; then
     if [[ -d "$yarn_cache_dir" ]]; then
-      if [[ "$YARN_2" == "true" ]] && ! node_modules_enabled "$BUILD_DIR"; then
+      if [[ "$YARN_2" == "true" ]]; then
         cp -RTf "$yarn_cache_dir" "$cache_dir/node/cache/yarn"
       else
         mv "$yarn_cache_dir" "$cache_dir/node/cache/yarn"

lib/dependencies.sh

@@ -146,7 +146,12 @@ yarn_2_install() {
   echo "Running 'yarn install' with yarn.lock"
   cd "$build_dir" || return
 
-  monitor "yarn-2-install" yarn install --immutable 2>&1
+  if [ -n "$YARN2_FOCUS_WORKSPACE" ]; then
+    echo "Running focused install for workspace $YARN2_FOCUS_WORKSPACE"
+    monitor "yarn-2-install" yarn workspaces focus "$YARN2_FOCUS_WORKSPACE"
+  else
+    monitor "yarn-2-install" yarn install --immutable 2>&1
+  fi
 }
 
 yarn_prune_devdependencies() {
@@ -172,6 +177,11 @@ yarn_prune_devdependencies() {
       meta_set "skipped-prune" "true"
       return 0
     fi
+    if [ -n "$YARN2_FOCUS_WORKSPACE" ]; then
+      echo "Running focused install with --production flag"
+      monitor "yarn-prune" yarn workspaces focus --production $YARN2_FOCUS_WORKSPACE
+      return 0
+    fi
     cd "$build_dir" || return
     echo "Running 'yarn heroku prune'"
     export YARN_PLUGINS="${buildpack_dir}/yarn2-plugins/prune-dev-dependencies/bundles/@yarnpkg/plugin-prune-dev-dependencies.js"

test/fixtures/yarn-2-workspaces/.gitignore

@@ -0,0 +1,4 @@
+node_modules
+.yarn/*
+!.yarn/releases
+!.yarn/plugins

test/fixtures/yarn-2-workspaces/.yarnrc.yml

@@ -0,0 +1,7 @@
+nodeLinker: "node-modules"
+
+plugins:
+  - path: .yarn/plugins/@yarnpkg/plugin-workspace-tools.cjs
+    spec: "@yarnpkg/plugin-workspace-tools"
+
+yarnPath: ".yarn/releases/yarn-berry.js"

test/fixtures/yarn-2-workspaces/apps/server/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "@sample/server",
+  "version": "1.0.0",
+  "license": "MIT",
+  "dependencies": {
+    "express": "^4.18.2"
+  }
+}

test/fixtures/yarn-2-workspaces/apps/web/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "@sample/web",
+  "version": "1.0.0",
+  "license": "MIT",
+  "dependencies": {
+    "react": "^18.2.0"
+  }
+}

test/fixtures/yarn-2-workspaces/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "yarn-2-workspaces",
+  "version": "1.0.0",
+  "workspaces": [
+    "apps/*"
+  ],
+  "scripts": {
+    "start": "echo start"
+  },
+  "license": "MIT"
+}