[Vekhir]

data-default 0.8.0.0 incorporates data-default-class and moves the Default (def) constructor into a different namespace.
data-default-class 0.2.0.0 re-exports the module for compatibility.

Introduce the new flag "data-default", with which yesod uses data-default directly. To keep the CI passing, it is off by default; at some point in the future, it may be enabled by default.

Before submitting your PR, check that you've:

• Bumped the version number

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

[Vekhir]

Better to use data-default-class 0.2.0.0 which isn't restricted by the bounds.