fix(discovery): fix bugs and clean up in discovery package

- Add missing trailing space in nodeExecPrefix() for yarn, which caused
  "yarn execnext build" instead of "yarn exec next build".
- Add missing Rails detection via config.ru, which was dropped during
  the refactor from question/stack.go to discovery/stack.go.
- Add Rails case to discoverType() to return "ruby".
- Change pipenv build step from "pipenv install" to "pipenv sync" to
  match the original behavior (installs from lock file only).
- Remove redundant zero-value map initialization in discoverType().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: pjcdawkins

discovery/build_steps.go

@@ -68,7 +68,7 @@ func (d *Discoverer) discoverBuildSteps() ([]string, error) {
 				"# Install Pipenv as a global tool",
 				"python -m venv /app/.global",
 				"pip install pipenv==$PIPENV_TOOL_VERSION",
-				"pipenv install",
+				"pipenv sync",
 			)
 		case "pip":
 			buildSteps = append(

discovery/dependency_managers.go

@@ -94,7 +94,7 @@ func (d *Discoverer) nodeExecPrefix() string {
 	}
 
 	if slices.Contains(dependencyManagers, "yarn") {
-		return "yarn exec"
+		return "yarn exec "
 	}
 
 	if slices.Contains(dependencyManagers, "npm") {

discovery/discovery.go

@@ -10,6 +10,7 @@ const (
 	composerJSONFile = "composer.json"
 	packageJSONFile  = "package.json"
 	symfonyLockFile  = "symfony.lock"
+	rackFile         = "config.ru"
 )
 
 // Discoverer detects project characteristics from the filesystem.

discovery/runtime.go

@@ -51,6 +51,8 @@ func (d *Discoverer) discoverType() (string, error) {
 		return "php", nil
 	case platformifier.Django, platformifier.Flask:
 		return "python", nil
+	case platformifier.Rails:
+		return "ruby", nil
 	case platformifier.Express, platformifier.NextJS, platformifier.Strapi:
 		return "nodejs", nil
 	}
@@ -63,9 +65,6 @@ func (d *Discoverer) discoverType() (string, error) {
 	langCount := make(map[string]int)
 	for ext, count := range extCount {
 		if lang, ok := languageMap[ext]; ok {
-			if _, _ok := langCount[lang]; !_ok {
-				langCount[lang] = 0
-			}
 			langCount[lang] += count
 		}
 	}

discovery/stack.go

@@ -30,6 +30,17 @@ func (d *Discoverer) discoverStack() (platformifier.Stack, error) {
 		return platformifier.Django, nil
 	}
 
+	rackPath := utils.FindFile(d.fileSystem, "", rackFile)
+	if rackPath != "" {
+		f, err := d.fileSystem.Open(rackPath)
+		if err == nil {
+			defer f.Close()
+			if ok, _ := utils.ContainsStringInFile(f, "Rails.application.load_server", true); ok {
+				return platformifier.Rails, nil
+			}
+		}
+	}
+
 	requirementsPath := utils.FindFile(d.fileSystem, "", "requirements.txt")
 	if requirementsPath != "" {
 		f, err := d.fileSystem.Open(requirementsPath)