PANIC=Format method: runtime error: invalid memory address or nil pointer dereference with go 1.17

[wallrj]

When I run the following short script with Go 1.17 it prints a PANIC=Format method message

package main

import (
	"github.com/kr/pretty"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

func main() {
	o := corev1.Secret{
		ObjectMeta: metav1.ObjectMeta{
			Name: "foo",
		},
	}
	pretty.Println(o)
}

$ go1.16.1 run ./
v1.Secret{
    TypeMeta:   v1.TypeMeta{},
    ObjectMeta: v1.ObjectMeta{
        Name:                       "foo",
        GenerateName:               "",
        Namespace:                  "",
        SelfLink:                   "",
        UID:                        "",
        ResourceVersion:            "",
        Generation:                 0,
        CreationTimestamp:          v1.Time{},
        DeletionTimestamp:          (*v1.Time)(nil),
        DeletionGracePeriodSeconds: (*int64)(nil),
        Labels:                     {},
        Annotations:                {},
        OwnerReferences:            nil,
        Finalizers:                 nil,
        ClusterName:                "",
        ManagedFields:              nil,
    },
    Immutable:  (*bool)(nil),
    Data:       {},
    StringData: {},
    Type:       "",
}

$ go1.17 run ./
v1.Secret{
%!v(PANIC=Format method: runtime error: invalid memory address or nil pointer dereference)

[christophcemper]

Yes,

also getting a panic for time pointers

%!v(PANIC=Format method: value method time.Time.GoString called using nil *Time pointer)

with a *time.Time in a struct that = nil

Go 1.17.6
Prettty v0.3.0

[kr]

Some relevant info in https://go.dev/issue/20995.

[drinktee]

Same issue. How to fix ?

[barrettj12]

Still observing this on Go 1.18.5.

[jameinel]

So the go dev issue 20995 says that the workaround (while a bit ugly) is to essentially check to see if you have a pointer, and whether the Elem of the pointer has the method:

if fieldType.Kind() == reflect.Ptr && field.IsNil() {
	// Method defined on a value receiver.
	if _, ok := fieldType.Elem().MethodByName("Check"); ok {
		continue // Ignore since value can't be retrieved from nil pointer
	}
}

Essentially you are saying "oh, I have a nil pointer, let me check if the method is defined on the Value (non-pointer) of this type".
I'm not sure if that means all of the kr/pretty code that says "you have a custom formatter" then needs to do this check (but the custom formatter is defined on a value type but I have a nil pointer)
It doesn't seem bad to just say "ignore custom formatters if you have a nil pointer"

[benhoyt]

We fixed this in our canonical fork at canonical@771f4dc (see discussion at canonical#1). It's fixed in a similar way to how fmt does when calling GoString and other user-defined methods. I've also created a pull request here with the same fix: #87

[PrMinisterGR]

Shouldn't there be a new proper release with this fix integrated?

[kr]

Shouldn't there be a new proper release with this fix integrated?

Yes indeed. Just tagged v0.3.1. Thank you.