Block kit generated view JSON fails on Client.OpenView with Block ID needs to be unique error despite not being set

[peterlanoie]

What happened

Opening a slack.ModalViewRequest created from unmarshalled JSON produced by Slack's block kit builder fails when no block_id JSON fields are present.

Slack documentation states that block_id is NOT required.

Comment for views.go/ValidateUniqueBlockID func states it "will verify ... if set" but doesn't appear to check that.

Expected behavior

View should open

Steps to reproduce

• Create a new modal view using Slack's block kit builder tool with 2 input blocks. (note: as generated, there are no block_ids set on the input blocks.)
• Save view JSON to file or in code literal
• Unmarshal view JSON to slack.ModalViewRequest
• Attempt to slack.Client.Open() the slack.ModalViewRequest
• Fails with error: Block ID needs to be unique

reproducible code

package main

import (
	"encoding/json"
	"fmt"

	"github.com/slack-go/slack"
)

// modal generated with 2 standard plain text inputs, no `block_id` fields present
var slackModal string = `
{
	"type": "modal",
	"title": {
		"type": "plain_text",
		"text": "My App",
		"emoji": true
	},
	"submit": {
		"type": "plain_text",
		"text": "Submit",
		"emoji": true
	},
	"close": {
		"type": "plain_text",
		"text": "Cancel",
		"emoji": true
	},
	"blocks": [
		{
			"type": "input",
			"element": {
				"type": "plain_text_input",
				"action_id": "plain_text_input-action"
			},
			"label": {
				"type": "plain_text",
				"text": "Label",
				"emoji": true
			}
		},
		{
			"type": "input",
			"element": {
				"type": "plain_text_input",
				"action_id": "plain_text_input-action"
			},
			"label": {
				"type": "plain_text",
				"text": "Label",
				"emoji": true
			}
		}
	]
}
`

func main() {
	var view slack.ModalViewRequest
	json.Unmarshal([]byte(slackModal), &view)
	client := slack.New("X", slack.OptionDebug(true))
	_, err := client.OpenView("X", view)
	if err != nil {
		fmt.Printf(err.Error())
	}
}

Versions

• Go: 1.20
• slack-go/slack: 0.12.1