server: Refresh the error template

We cannot cache it forever, as that will not allow the end user to edit and preview it.

diff --git a/commands/server.go b/commands/server.go
index a339a176013926606bbdb834d7fa08c0c57d5645..a1605e97cf10f9cedc1d25d120fbeffd49584361 100644 (file)
--- a/commands/server.go
+++ b/commands/server.go
@@ -35,6 +35,8 @@ import (
 
        "github.com/gohugoio/hugo/common/htime"
        "github.com/gohugoio/hugo/common/paths"
+       "github.com/gohugoio/hugo/hugolib"
+       "github.com/gohugoio/hugo/tpl"
        "golang.org/x/sync/errgroup"
 
        "github.com/gohugoio/hugo/livereload"
@@ -522,11 +524,25 @@ func (c *commandeer) serve(s *serverCmd) error {
                roots = []string{""}
        }
 
-       templHandler := c.hugo().Tmpl()
-       errTempl, found := templHandler.Lookup("_server/error.html")
-       if !found {
-               panic("template server/error.html not found")
+       // Cache it here. The HugoSites object may be unavaialble later on due to intermitent configuration errors.
+       // To allow the en user to change the error template while the server is running, we use
+       // the freshest template we can provide.
+       var (
+               errTempl     tpl.Template
+               templHandler tpl.TemplateHandler
+       )
+       getErrorTemplateAndHandler := func(h *hugolib.HugoSites) (tpl.Template, tpl.TemplateHandler) {
+               if h == nil {
+                       return errTempl, templHandler
+               }
+               templHandler := h.Tmpl()
+               errTempl, found := templHandler.Lookup("_server/error.html")
+               if !found {
+                       panic("template server/error.html not found")
+               }
+               return errTempl, templHandler
        }
+       errTempl, templHandler = getErrorTemplateAndHandler(c.hugo())
 
        srv := &fileServer{
                baseURLs: baseURLs,
@@ -534,8 +550,11 @@ func (c *commandeer) serve(s *serverCmd) error {
                c:        c,
                s:        s,
                errorTemplate: func(ctx any) (io.Reader, error) {
+                       // hugoTry does not block, getErrorTemplateAndHandler will fall back
+                       // to cached values if nil.
+                       templ, handler := getErrorTemplateAndHandler(c.hugoTry())
                        b := &bytes.Buffer{}
-                       err := templHandler.Execute(errTempl, b, ctx)
+                       err := handler.Execute(templ, b, ctx)
                        return b, err
                },
        }