Automigrations: GFM fails with complex addon object

[shilman]

Describe the bug

The GFM automigration fails on a main.js that contains a complex addons config, such as the following:

const postcssConfig = require('../postcss.config');

module.exports = {
    addons: [
        {
            name: '@storybook/addon-postcss',
            options: {
                postcssLoaderOptions: {
                    ...postcssConfig,
                    implementation: require('postcss')
                }
            }
        },

It tries to parse the addons field into an array, append an addon string to the array, and then set it again in the ConfigFile object.

• it should not parse addons and should append the string to the addons array in the AST to work around this issue.
• if the automigration fails anyway, it should produce a better error message stating the failure and the manual workaround

To Reproduce

https://github.com/inkline/inkline/blob/85c694daebf4eb18462988876d89ab95e4a0ab78/.storybook/main.js#L10-L18

System

No response

Additional context

No response

[tmeasday]

I'll also note it claimed to work:

[shilman]

Shiver me timbers!! I just released https://github.com/storybookjs/storybook/releases/tag/v7.0.0-rc.6 containing PR #21731 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb@next upgrade --prerelease