If I change {{block "stylesheets" .}}{{end -}} to {{template "stylesheets" . -}} in my example, the problem goes away. Thanks to Владимир Мулько on golang-nuts for this suggestion!

/cc @rsc @robpike ... who owns templates these days?

This is almost certainly a bug, and a mysterious one at that. Since it's a bug in text/template (the example uses html/template but the problem exists in the lower-level library) I can look at it.

Reports on the mailing list say this one broke it:

commit 2b583a190eb14c69bffe5d488d2d6d3862fe76ea
Author: Jess Frazelle <me@jessfraz.com>
Date:   Wed Jun 22 21:57:52 2016 -0700

    text/template: fix Parse when called twice with empty text
    
    Fixes #16156
    
    Change-Id: I6989db4fd392583a2d490339cefc525b07c11b90
    Reviewed-on: https://go-review.googlesource.com/24380
    Reviewed-by: Andrew Gerrand <adg@golang.org>
    Run-TryBot: Andrew Gerrand <adg@golang.org>

I just run "git bisect" and it also came out with 2b583a1 as the first bad commit.

In the breaking CL, it looks to me like

if t.tmpl[new.name] != nil && parse.IsEmptyTree(tree.Root) && t.Tree != nil {

is checking the wrong thing tree. t.tmpl[new.name] is the interesting template, not t itself. Should probably be:

if old := t.tmpl[new.name]; old != nil && parse.IsEmptyTree(tree.Root) && old.Tree != nil {

The non-determinacy of the example is likely due to html/template walking a map and making calls a variety of orders (that should all behave the same).

Yes, I think that's the fix.

@rsc's change fixes the test here but breaks the TestEmptyTemplate test. Working on it.

CL https://golang.org/cl/38420 mentions this issue.

Reopening for backport.

CL https://golang.org/cl/39594 mentions this issue.

Cherry-pick submitted.

This has not been fixed in 1.8.1

master.gohtml
...
{{block "DocumentFile" .}}
{{.FileFolder}}
{{end}}
...

acount.gohtml
{{define "DocumentFile"}}{{end}}

template: master.gohtml:187:63: executing "DocumentFile" at <.FileFolder>: can't evaluate field FileFolder in type *auth.User masterTmpl account map[page:0xc042671150 account:0xc0424c38c0 accountGroups:0xc0427d4620]

@minervadata Please post a complete program that reproduces the problem you are seeing.

@robpike this is part of framework

tmpl.go
var masterTmpl = template.New("masterTmpl").Funcs(TmplFunc) func ParseSubTmpls(subTmplPath string) (t *template.Template) { t, err := template.Must(masterTmpl.Clone()).ParseGlob(filepath.Join(TmplPath, subTmplPath)) if err != nil { logger.Lgr.Println(err, subTmplPath, t) } return }

account.go
var accountTmpl = tmpl.ParseSubTmpls("account/templates/account/*")

master.gohtml
{{define "DocumentHeader"}} {{block "DocumentOption" .}} {{end}} {{block "DocumentFile" .}} {{.FileFolder}} {{end}} {{end}}
account.gohtml
{{define "DocumentFile"}}{{end}} {{define "account"}} {{with .account}}{{template "DocumentHeader" .}}{{end}} {{end}}

This is not a complete program, it's several incomplete snippets from several files. You should be able to create a single, complete file of Go source code that can be compiled in isolation and demonstrate the problem. The template text can be constants in the source.

Given your example I should be able to copy the text to file.go with no editing and run
go run file.go
and see the problem.

A playground link would be even better.

Please open a new issue (golang.org/issue/new) for other problems with html/template. The error message you are reporting is unrelated to the failure this issue was about.