Cms: Can't save new matrix block type in Craft 3.4.1

[ryanmwc]

Description

I had created a matrix field earlier in the week with several block types while in version 3.3.x and then updated to version 3.4.1 yesterday. Sometime after the update, I created a new block type, added a field, and saved it, then I got an error. From the logs:

2020-01-31 01:18:17 [-][1][op4ovmv6f9nluvrgh8poqhbdat [error][yii\base\ErrorException:1] yii\base\ErrorException: Unknown: Input variables exceeded 1000. To increase the limit change max_input_vars in php.ini. in /Users/me/Sites/MWC/vendor/yiisoft/yii2/base/ErrorException.php:43
Stack trace:
#0 /Users/me/Sites/MWC/vendor/craftcms/cms/bootstrap/web.php(51): ::unknown()
#1 /Users/me/Sites/MWC/web/index.php(20): ::unknown()
#2 {main}
2020-01-31 01:18:15 [-][1][op4ovmv6f9nluvrgh8poqhbdat][info][application] $_GET = [
    'p' => 'mwclogin/settings/fields/edit/37'
]

I had googled around searching for Input variables exceeded 1000. To increase the limit change max_input_vars in php.ini but a few SO responses said that increasing the limit was not the right thing to do, that it's a solution to the wrong problem.

Steps to reproduce

1. Create a matrix field in version 3.3.x
2. Update to 3.4.1
3. Add a new block type to existing matrix field
4. Add a text field
5. Save the field
6. See the error

Here's a gif:

Just to be clear what's going on in the gif, I'm scrolling down to create a new block type in my existing matrix field called "Test", I create a new plain text field called "Test", and I save the field and see the error.

Additional info

• Craft version: 3.4.1
• PHP version: 7.3.9
• Database driver & version: MySQL 5.6.21

[nettum]

This error is pretty common (regardless of craft 3.4) if your matrix is getting big (e.g. with supertables inside your matrix and lots of linkfield fields).
I'm pretty sure you will need to up the max_input_vars variable in your php settings. At least until craft finds a better way to save field-settings data. Any ETA on this @brandonkelly? Craft 4?

[brandonkelly]

That error was added in 21d13d4b053bd45e25082ac0e10baba4ea39c9a0, per #876. It actually gives you an opportunity to increase max_input_vars, and then reload the browser window, which will resubmit all of your changes exactly as they were initially submitted, this time hopefully without hitting the same server limitation.

We do plan to fix this in the long run by making the form post JSON data rather than serialized form data, so the max_input_vars will stop applying.

[JoppeDC]

Not sure if this issue should be closed. It's a pretty serious issue and needs a fix. I'm guessing it might get lost in the closed list.

[JayBox325]

Agreed, this should be left open. Having this issue today.