Detect Bun runtime from package.json when no lockfile is present

pkg/stackbuild/bun.go

@@ -2,6 +2,8 @@ package stackbuild
 
 import (
 	"encoding/json"
+	"regexp"
+	"strings"
 
 	"github.com/moby/buildkit/client/llb"
 	"miren.dev/runtime/pkg/imagerefs"
@@ -34,13 +36,51 @@ func (s *BunStack) Detect() bool {
 		s.Event("file", "bun.lockb", "Found bun.lockb (Bun runtime, legacy)")
 		return true
 	}
+	if s.hasFile("bunfig.toml") {
+		s.Event("file", "bunfig.toml", "Found bunfig.toml (Bun runtime)")
+		return true
+	}
+	if s.detectPackageManagerBun() {
+		s.Event("config", "packageManager", "package.json packageManager field specifies bun")
+		return true
+	}
+	if s.detectBunInScripts() {
+		s.Event("config", "scripts", "package.json scripts reference bun")
+		return true
+	}
 	if s.detectInFile("Procfile", `web:\s+bun`) {
 		s.Event("file", "Procfile", "Procfile references bun")
 		return true
 	}
 	return false
 }
 
+func (s *BunStack) detectPackageManagerBun() bool {
+	data, err := s.readFile("package.json")
+	if err != nil {
+		return false
+	}
+	var pkg struct {
+		PackageManager string `json:"packageManager"`
+	}
+	if err := json.Unmarshal(data, &pkg); err != nil {
+		return false
+	}
+	return strings.HasPrefix(pkg.PackageManager, "bun@")
+}
+
+var bunCommandRe = regexp.MustCompile(`(?:^|\s)bunx?(?:\s|$)`)
+
+func (s *BunStack) detectBunInScripts() bool {
+	scripts := s.getPackageScripts()
+	for _, cmd := range scripts {
+		if bunCommandRe.MatchString(cmd) {
+			return true
+		}
+	}
+	return false
+}
+
 func (s *BunStack) Init(opts BuildOptions) {
 	s.SetCwd("/app")
 

pkg/stackbuild/stackbuild.go

@@ -76,8 +76,8 @@ func DetectStack(dir string, opts BuildOptions) (Stack, error) {
 	stacks := []Stack{
 		&RubyStack{MetaStack: ms},
 		&PythonStack{MetaStack: ms},
-		&NodeStack{MetaStack: ms},
 		&BunStack{MetaStack: ms},
+		&NodeStack{MetaStack: ms},
 		&GoStack{MetaStack: ms},
 		&RustStack{MetaStack: ms},
 	}

pkg/stackbuild/stackbuild_test.go

@@ -438,6 +438,127 @@ func TestBun(t *testing.T) {
 	buildLLB(t, dir, state)
 }
 
+func TestBunDetect(t *testing.T) {
+	testCases := []struct {
+		name     string
+		files    map[string]string
+		expected bool
+	}{
+		{
+			name: "bun.lock",
+			files: map[string]string{
+				"package.json": `{"name": "app"}`,
+				"bun.lock":     "",
+			},
+			expected: true,
+		},
+		{
+			name: "bun.lockb legacy",
+			files: map[string]string{
+				"package.json": `{"name": "app"}`,
+				"bun.lockb":    "",
+			},
+			expected: true,
+		},
+		{
+			name: "bunfig.toml",
+			files: map[string]string{
+				"package.json": `{"name": "app"}`,
+				"bunfig.toml":  "[install]\noptional = true\n",
+			},
+			expected: true,
+		},
+		{
+			name: "packageManager field",
+			files: map[string]string{
+				"package.json": `{"name": "app", "packageManager": "bun@1.1.0"}`,
+			},
+			expected: true,
+		},
+		{
+			name: "bun in scripts",
+			files: map[string]string{
+				"package.json": `{"name": "app", "scripts": {"start": "bun run index.ts"}}`,
+			},
+			expected: true,
+		},
+		{
+			name: "bun as standalone command in scripts",
+			files: map[string]string{
+				"package.json": `{"name": "app", "scripts": {"dev": "bun --watch index.ts"}}`,
+			},
+			expected: true,
+		},
+		{
+			name: "Procfile with bun",
+			files: map[string]string{
+				"package.json": `{"name": "app"}`,
+				"Procfile":     "web: bun run start",
+			},
+			expected: true,
+		},
+		{
+			name: "plain package.json no bun signals",
+			files: map[string]string{
+				"package.json": `{"name": "app", "scripts": {"start": "node index.js"}}`,
+			},
+			expected: false,
+		},
+		{
+			name: "no package.json",
+			files: map[string]string{
+				"index.ts": "console.log('hi')",
+			},
+			expected: false,
+		},
+		{
+			name: "bunx in scripts",
+			files: map[string]string{
+				"package.json": `{"name": "app", "scripts": {"test": "bunx vitest"}}`,
+			},
+			expected: true,
+		},
+		{
+			name: "bun at end of script command",
+			files: map[string]string{
+				"package.json": `{"name": "app", "scripts": {"start": "npx something && bun"}}`,
+			},
+			expected: true,
+		},
+		{
+			name: "bundle in scripts is not bun",
+			files: map[string]string{
+				"package.json": `{"name": "app", "scripts": {"start": "bundle exec rails server"}}`,
+			},
+			expected: false,
+		},
+		{
+			name: "packageManager field for npm not bun",
+			files: map[string]string{
+				"package.json": `{"name": "app", "packageManager": "npm@10.0.0"}`,
+			},
+			expected: false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+
+			for name, content := range tc.files {
+				require.NoError(t, os.WriteFile(filepath.Join(dir, name), []byte(content), 0644))
+			}
+
+			stack := &BunStack{
+				MetaStack: MetaStack{
+					dir: dir,
+				},
+			}
+			require.Equal(t, tc.expected, stack.Detect())
+		})
+	}
+}
+
 func TestGo(t *testing.T) {
 	if !checkDocker() {
 		t.Skip("Docker not available")