Mismatched variant nesting generates [object Object] in class

[Cael6]

Describe the bug
When using the extend capabilities, if a variation's value does not match the shape of the extended tv result, it will add [object Object] to the class list rather than calculate the value.

For example:

const styles = tv({
  slots: {
    base: "button",
    other: "other",
  },
  variants: {
    variation: {
      blue: {
        base: "blue",
        other: "other-blue",
      },
    },
  },
});

const extendedStyles = tv({
  extend: styles,
  variants: {
    variation: {
      blue: "extended-blue",
    },
  },
});

styles uses an object to apply variations to variation, but extendedStyles uses a string to apply to just the base.

To Reproduce
Steps to reproduce the behavior:

1. Go to codesandbox example
2. Inspect Button's class

Expected behavior
I expect that both blue and extended-blue are applied to Button's class.

Screenshots

Desktop (please complete the following information):

• OS: macOS
• Browser: Chrome
• Version: 121.0.6167.184 (Official Build) (arm64)

Additional context
I'm using TypeScript 5.3.3, but on previous versions of TypeScript I believe it would simply omit [object Object] instead of adding in the desired class.

[thefalked]

For me it would make sense to use like this:

const styles = tv({
  slots: {
    base: "button",
    other: "other",
  },
  variants: {
    variation: {
      blue: {
        base: "blue",
        other: "other-blue",
      },
    },
  },
});

const extendedStyles = tv({
  extend: styles,
  variants: {
    variation: {
      blue: {
        base: "extended-blue",
      },
    },
  },
});

or if you want to add the blue: "extended-blue" it would apply to all slots, not just the base one.

keep in mind that base is the name of the slot not the "base" for all slots.

[Cael6]

Yes, it would work if you matched the structure between styles and extendedStyles, but it should also work with my example as well.

Consider a case where styles is defined in a library and extendedStyles is defined in an application using that library. The types allow you to define extendedStyles as I did in the example, so it ends up not working as expected because the original blue class from styles does not get applied.

It is a very difficult bug to track down if you're not aware of the problem.