directly support embed.FS and fs.FS on view engines

context/context_fs.go

@@ -0,0 +1,46 @@
+package context
+
+import (
+	"embed"
+	"fmt"
+	"io/fs"
+	"net/http"
+)
+
+// ResolveFS accepts a single input argument of any type
+// and tries to cast it to http.FileSystem.
+//
+// It affects the view engine filesystem resolver
+// and the Application's API Builder's `HandleDir` method.
+//
+// This package-level variable can be modified on initialization.
+var ResolveFS = func(fsOrDir interface{}) http.FileSystem {
+	var fileSystem http.FileSystem
+	switch v := fsOrDir.(type) {
+	case string:
+		fileSystem = http.Dir(v)
+	case http.FileSystem:
+		fileSystem = v
+	case embed.FS:
+		direEtries, err := v.ReadDir(".")
+		if err != nil {
+			panic(err)
+		}
+
+		if len(direEtries) == 0 {
+			panic("HandleDir: no directories found under the embedded file system")
+		}
+
+		subfs, err := fs.Sub(v, direEtries[0].Name())
+		if err != nil {
+			panic(err)
+		}
+		fileSystem = http.FS(subfs)
+	case fs.FS:
+		fileSystem = http.FS(v)
+	default:
+		panic(fmt.Sprintf(`unexpected "fsOrDir" argument type of %T (string or http.FileSystem or embed.FS or fs.FS)`, v))
+	}
+
+	return fileSystem
+}