[MM-34798] Respect MM_SERVER_PATH when looking for templates (#17410)

shared/templates/templates.go

@@ -7,10 +7,12 @@ import (
 	"bytes"
 	"html/template"
 	"io"
+	"os"
 	"path/filepath"
 	"sync"
 
 	"github.com/fsnotify/fsnotify"
+	"github.com/mattermost/mattermost-server/v5/utils/fileutils"
 )
 
 // Container represents a set of templates that can be render
@@ -29,6 +31,15 @@ type Data struct {
 	HTML  map[string]template.HTML
 }
 
+func GetTemplateDirectory() (string, bool) {
+	templatesDir := "templates"
+	if mattermostPath := os.Getenv("MM_SERVER_PATH"); mattermostPath != "" {
+		templatesDir = filepath.Join(mattermostPath, templatesDir)
+	}
+
+	return fileutils.FindDir(templatesDir)
+}
+
 // NewFromTemplates creates a new templates container using a
 // `template.Template` object
 func NewFromTemplate(templates *template.Template) *Container {