text/template: panic: indirection through nil pointer to embedded struct #48215
Description
What version of Go are you using (go version)?
$ go version go version go1.17 darwin/amd64
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
go env Output
$ go env
What did you do?
This is similar to #30143 and #28242.
While working with a template, I was getting panics that were hard to debug because there is no contextual information available to pinpoint where is the problem in the template/data.
I was able to reduce template to reproduce the panic:
package main
import (
"io"
"testing"
"text/template"
)
func TestTemplateExecute(t *testing.T) {
type A struct {
S string
}
type B struct {
*A
}
tmpl := template.Must(template.New("").Parse(`{{ .S }}`))
// tmpl.Execute panics
if err := tmpl.Execute(io.Discard, B{}); err != nil {
t.Fatal(err)
}
}https://play.golang.org/p/0l9Ud0i7ZzH
What did you expect to see?
I expected an error with contextual information, similar to when the nil pointer is not an embedded field:
template: :1:5: executing "" at <.A.S>: nil pointer evaluating *main.A.S
Test Function
package main
import (
"io"
"testing"
"text/template"
)
func TestTemplateExecute(t *testing.T) {
type A struct {
S string
}
type B struct {
A *A
}
tmpl := template.Must(template.New("").Parse(`{{ .A.S }}`))
if err := tmpl.Execute(io.Discard, B{}); err != nil {
t.Fatal(err)
}
}What did you see instead?
panic: reflect: indirection through nil pointer to embedded struct