Render templates from embed.FS (#89)

* Upgrade to go 1.16

* Add EmbedFileSystem to render templates from `embed.FS`

* Require go 1.16 in fs_embed.go and fs_embed_test.go

Author: dominik-lekse

README.md

@@ -171,7 +171,27 @@ admin/edit
 home
 ~~~
 
-You can also load templates from memory by providing the Asset and AssetNames options,
+Templates can be loaded from an `embed.FS`.
+
+~~~ go
+// ...
+
+//go:embed templates/*.html templates/*.tmpl
+var embeddedTemplates embed.FS
+
+// ...
+
+r := render.New(render.Options{
+    Directory: "templates",
+    FileSystem: &EmbedFileSystem{
+        FS: embeddedTemplates,
+    },
+    Extensions: []string{".html", ".tmpl"},
+})
+// ...
+~~~
+
+You can also load templates from memory by providing the `Asset` and `AssetNames` options,
 e.g. when generating an asset file using [go-bindata](https://github.com/jteeuwen/go-bindata).
 
 ### Layouts

fs_embed.go

@@ -0,0 +1,31 @@
+// +build go1.16
+
+package render
+
+import (
+	"embed"
+	"io/fs"
+	"path/filepath"
+)
+
+// EmbedFileSystem implements FileSystem on top of an embed.FS
+type EmbedFileSystem struct {
+	embed.FS
+}
+
+var _ FileSystem = &EmbedFileSystem{}
+
+func (e *EmbedFileSystem) Walk(root string, walkFn filepath.WalkFunc) error {
+	return fs.WalkDir(e.FS, root, func(path string, d fs.DirEntry, err error) error {
+		if d == nil {
+			return nil
+		}
+
+		info, err := d.Info()
+		if err != nil {
+			return err
+		}
+
+		return walkFn(path, info, err)
+	})
+}

fs_embed_test.go

@@ -0,0 +1,57 @@
+// +build go1.16
+
+package render
+
+import (
+	"embed"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+//go:embed fixtures/*/*.html fixtures/*/*.tmpl fixtures/*/*/*.tmpl fixtures/*/*.amber fixtures/*/*/*.amber
+var EmbedFixtures embed.FS
+
+func TestEmbedFileSystemTemplateLookup(t *testing.T) {
+	baseDir := "fixtures/template-dir-test"
+	fname0Rel := "0"
+	fname1Rel := "subdir/1"
+	fnameShouldParsedRel := "dedicated.tmpl/notbad"
+	dirShouldNotParsedRel := "dedicated"
+
+	r := New(Options{
+		Directory:  baseDir,
+		Extensions: []string{".tmpl", ".html"},
+		FileSystem: &EmbedFileSystem{
+			FS: EmbedFixtures,
+		},
+	})
+
+	expect(t, r.TemplateLookup(fname1Rel) != nil, true)
+	expect(t, r.TemplateLookup(fname0Rel) != nil, true)
+	expect(t, r.TemplateLookup(fnameShouldParsedRel) != nil, true)
+	expect(t, r.TemplateLookup(dirShouldNotParsedRel) == nil, true)
+}
+
+func TestEmbedFileSystemHTMLBasic(t *testing.T) {
+	render := New(Options{
+		Directory: "fixtures/basic",
+		FileSystem: &EmbedFileSystem{
+			FS: EmbedFixtures,
+		},
+	})
+
+	var err error
+	h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		err = render.HTML(w, http.StatusOK, "hello", "gophers")
+	})
+
+	res := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/foo", nil)
+	h.ServeHTTP(res, req)
+
+	expectNil(t, err)
+	expect(t, res.Code, 200)
+	expect(t, res.Header().Get(ContentType), ContentHTML+"; charset=UTF-8")
+	expect(t, res.Body.String(), "<h1>Hello gophers</h1>\n")
+}

go.mod

@@ -1,5 +1,5 @@
 module github.com/unrolled/render
 
-go 1.12
+go 1.16
 
 require github.com/eknkc/amber v0.0.0-20171010120322-cdade1c07385