Repository: gatsbyjs/gatsby
File: packages/gatsby/src/utils/webpack-utils.ts (TypeScript)

Code before:
      } = options

      return {
        loader: require.resolve(`postcss-loader`),
        options: {
          ident: `postcss-${++ident}`,
          sourceMap: !PRODUCTION,
          plugins: (loader: Loader): postcss.Plugin<any>[] => {
            const autoprefixerOptions = {
              overrideBrowserslist,
              flexbox: `no-2009`,
            }
            plugins =
              (typeof plugins === `function` ? plugins(loader) : plugins) || []

            if (plugins && plugins.length) {
              const autoprefixerOverride: autoprefixer.Autoprefixer = plugins.find(
                plugin => plugin.postcssPlugin === `autoprefixer`
              )
              Object.assign(
                autoprefixerOptions,
                autoprefixerOverride.options || {}
              )
            }

            return [flexbugs, autoprefixer(autoprefixerOptions), ...plugins]
          },
          ...postcssOpts,
        },
      }
    },

    file: (options = {}) => {
      return {
        loader: require.resolve(`file-loader`),
        options: {
          name: `${assetRelativeRoot}[name]-[hash].[ext]`,
          ...options,
        },
      }
    },

    url: (options = {}) => {
      return {
        loader: require.resolve(`url-loader`),
        options: {
          limit: 10000,
          name: `${assetRelativeRoot}[name]-[hash].[ext]`,
          fallback: require.resolve(`file-loader`),
          ...options,
        },

Review comment (bug):
I had to look at it a while but I think this can be simplified a bit. For example, something like this:

```suggestion
            const autoPrefixPlugin = autoprefixer({
              overrideBrowserslist,
              flexbox: `no-2009`,
              ...(plugins.find(({postcssPlugin}) => postcssPlugin === `autoprefixer`)?.options ?? {}),
            })

            return [flexbugs, autoPrefixPlugin, ...plugins]
```

(Github doesn't allow me to suggest across the two diff sections but you'd obviously remove the `const autoprefixerOptions` part in favor of this)

You could put the ``(plugins.find(({postcssPlugin}) => postcssPlugin === `autoprefixer`)?.options ?? {})`` part in a static function and abstract that out of the inner part, like this:
```js
function getPrefixerOptions(plugins){
  const plugin = plugins.find(({postcssPlugin}) => postcssPlugin === `autoprefixer`);
  return plugin?.options ?? {}
}
```

Code after:
      } = options

      return {
        loader: require.resolve(`postcss-loader`),
        options: {
          ident: `postcss-${++ident}`,
          sourceMap: !PRODUCTION,
          plugins: (loader: Loader): postcss.Plugin<any>[] => {
            plugins =
              (typeof plugins === `function` ? plugins(loader) : plugins) || []

            const autoprefixerPlugin = autoprefixer({
              overrideBrowserslist,
              flexbox: `no-2009`,
              ...((plugins.find(
                plugin => plugin.postcssPlugin === `autoprefixer`
              ) as autoprefixer.Autoprefixer)?.options ?? {}),
            })

            return [flexbugs, autoprefixerPlugin, ...plugins]
          },
          ...postcssOpts,
        },
      }
    },

    file: (options = {}) => {
      return {
        loader: require.resolve(`file-loader`),
        options: {
          name: `${assetRelativeRoot}[name]-[hash].[ext]`,
          ...options,
        },
      }
    },

    url: (options = {}) => {
      return {
        loader: require.resolve(`url-loader`),
        options: {
          limit: 10000,
          name: `${assetRelativeRoot}[name]-[hash].[ext]`,
          fallback: require.resolve(`file-loader`),
          ...options,
        },
      }
    },

    js: options => {
      return {
        options: {