Parse and modify top-level declarations in a module

[Lms24]

Describe the feature

I'd like to be able to modify top-level declarations within a module to, for example, modify objects that are exported in a separate statement. Something like:

// currently, there's no magicast-native way of accessing this declaration
const myConfig = defineConfig({/*...*/})
export default myConfig;

I'm using magicast in a script that's supposed to modify a user's vite.config.js and this quite common way of specifying a vite config unfortunately causes problems.

API proposal:

I'm thinking about something along these lines:

const originalCode = `
  const myConfig = defineConfig({/*...*/})
  export default myConfig;
`

const mod = parseModule(originalCode);

// example modification
mod.$declarations.myConfig = builders.raw(...)

Once we have a way of accessing/modifying declarations, we could for example adjust theaddVitePlugin helper to use the $declarations field to adjust the config object if it is not directly default-exported.

I'm happy to give this a try to implement but I'd like to hear your thoughts around this first.

This is somewhat related to #45 but I believe modifying/parsing existing declarations isn't discussed in this issue.

Limitations

I think we need to accept that we couldn't possibly handle all kinds of declarations or complex syntax within them but for starters, I believe handling object declarations or function calls (like defineConfig) might be enough.

Additional information

• Would you be willing to help implement this feature?

[Lms24]

An alternative would be to directly link to the actual declaration in the mod.exports.default property. While more convenient, I'd argue it's quite a diversion from representing an AST data structure. Also not sure which of the two options would be easier to implement