Getting error 'Area is already set' while changing theme for Magento 2.2.4

Question

I have copied magento-frontend-luma theme and change vendor\theme name and paste in design folder magento2\app\design\frontend\Webmyne\pruthvi

In registration.php

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::THEME,
    'frontend/Webmyne/pruthvi',
    __DIR__
);

In theme.xml

<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
    <title>Webmyne Pruthvi</title>
    <parent>Magento/blank</parent>
    <media>
        <preview_image>media/preview.jpg</preview_image>
    </media>
</theme>

In composer.json

{
    "name": "webmyne/pruthvi",
    "description": "N/A",
    "require": {
        "php": "7.0.2|7.0.4|~7.0.6|~7.1.0",
        "magento/theme-frontend-blank": "100.2.*",
        "magento/framework": "101.0.*"
    },
    "type": "magento2-theme",
    "version": "100.2.3",
    "license": [
        "OSL-3.0",
        "AFL-3.0"
    ],
    "autoload": {
        "files": [
            "registration.php"
        ]
    }
}

But when I try to change theme from CONTENT > Design > Configuration

I am getting the error 'Area is already set'

Answer 1

I think the problem is in your registration.php file

try changing it this way

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::THEME,
    'Webmyne_pruthvi',
    __DIR__
);

so deleting the frontend part in the declaration. There is no need to specify the area if you're inheriting from a theme that has already declared is for the frontend area.

Answer 2

This is a re-owned issue of Magento 2.2.4 C.E.

Magento has been fixed by Daniel Ruf at https://github.com/magento/magento2/commit/7019a0a1392095185505ff3ca7b97dd3e9cb4ef2 at PR #15137 and already merge at 2.2-develop branch

You need to modify the code of setForcedArea method and Replace that method code using below one.

public function setForcedArea($templateId)
{
    if (!isset($this->area)) {
        $this->area = $this->emailConfig->getTemplateArea($templateId);
    }
    return $this;
}

Reference: