Python-slack-sdk: chat_update fails to update block messages to text messages

[bentheye]

Description

The chat_update method fails to update messages that use blocks when text is used for the update. This happens despite the request response having "ok": True.

What type of issue is this? (place an x in one of the [ ])

• [x] bug
• [ ] enhancement (feature request)
• [ ] question
• [ ] documentation related
• [ ] testing related
• [ ] discussion

Requirements (place an x in each of the [ ])

• [x] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've searched for any related issues and avoided creating a duplicate issue.

---

Bug Report

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Reproducible in:

slackclient version: 2.2.0

python version: 3.7

OS version(s): macOS 10.14.6

Steps to reproduce:

1. Use chat_postMessage to post a message with blocks instead of text
2. Try to update it with chat_update using text instead of blocks

Expected result:

The message should update

Actual result:

Nothing happens (but ok is received in response)

[seratch]

The ok: true response means the text attribute is successfully updated (but it's not visible for humans). It's possible to remove the blocks by giving an empty array as below:

import slack

client = slack.WebClient(token='xoxb-xxx-xxx-xxx')
post_resp = client.chat_postMessage(
    channel='C12345678',
    user='U12345678',
    text='initial',
    blocks=[
        {
            "type": "section",
            "text": {
                "type": "mrkdwn",
                "text": "This is a mrkdwn section block :ghost: *this is bold*, and ~this is crossed out~, and <https://google.com|this is a link>"
            }
        }
    ]
)
print(post_resp)

ts = post_resp['message']['ts']
update_resp = client.chat_update(
    channel='C12345678',
    user='U12345678',
    ts=ts,
    text='modified',
    blocks=[]
)
print(update_resp)

[seratch]

I've answered this question then. Allow me to close this issue now. If you have something to ask/discuss further, please feel free to reopen it.