runtime/local: add support for idiomatic folder structures (#1963)

* runtime/local: add support for idiomatic folder structures

* runtime/local: add test coverage

* runtime/local: increase test coverage

* runtime/local: add test for empty local source

* runtime/local: make entrypoint public

runtime/local/local.go

@@ -286,8 +286,13 @@ func (r *localRuntime) Create(s *runtime.Service, opts ...runtime.CreateOption)
 		options.Namespace = defaultNamespace
 	}
 	if len(options.Command) == 0 {
+		ep, err := Entrypoint(s.Source)
+		if err != nil {
+			return err
+		}
+
 		options.Command = []string{"go"}
-		options.Args = []string{"run", "."}
+		options.Args = []string{"run", ep}
 	}
 
 	// pass secrets as env vars
@@ -633,3 +638,42 @@ func (r *localRuntime) Stop() error {
 func (r *localRuntime) String() string {
 	return "local"
 }
+
+// Entrypoint determines the entrypoint for the service, since main.go doesn't always exist at
+// the top level
+func Entrypoint(dir string) (string, error) {
+	var entrypoints []string
+
+	filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// get the relative path to the directory
+		rel, err := filepath.Rel(dir, path)
+		if err != nil {
+			return err
+		}
+
+		// only look for files in the top level or the cmd folder
+		if dir := filepath.Dir(rel); !filepath.HasPrefix(dir, "cmd") && dir != "." {
+			return nil
+		}
+
+		// only look for main.go files
+		if filepath.Base(rel) == "main.go" {
+			entrypoints = append(entrypoints, rel)
+		}
+
+		return nil
+	})
+
+	switch len(entrypoints) {
+	case 0:
+		return "", errors.New("No entrypoint found")
+	case 1:
+		return entrypoints[0], nil
+	default:
+		return "", errors.New("More than one entrypoint found")
+	}
+}