fix(mangler): keep exported symbols for top_level: true

[sapphi-red]

I'm not going to work on a fix for a while so feel free to fix it if anyone wants to work on it.

Exported symbols are now not mangled.

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[codspeed-hq]

CodSpeed Performance Report

Merging #7927 will not alter performance

_{Comparing sapphi-red:test/mangle-top-level-vars (fe885dc) with main (547c102)}

Summary

✅ 29 untouched benchmarks

[camc314]

@ Boshen, what's the right way to fix this one?

we probably need access to ModuleRecord in this mangler to check what's exported/not right?

[sapphi-red]

I made the exported symbols to be not mangled. I made a function that iterates over the top-level statements to collect the exported symbols.

[Boshen]

Terser's toplevel option seems different to our top_level, is there an existing option in another minifier? Or perhaps we should never mangle top level symbols, as it doesn't make sense.

[Boshen]

@ Boshen, what's the right way to fix this one?

we probably need access to ModuleRecord in this mangler to check what's exported/not right?

Code may have been changed a lot after minfication, I think it's best to recollect them. Probably need something better to get some code reuse.

[Boshen]

The best approach is to have a symbol flag for the exports 🤔 but there aren't any...

[sapphi-red]

Terser's toplevel option seems different to our top_level

Is it different?
For input:

export const foo = ''
const bar = ''
export { bar }

terser outputs

/*
option:
{
  module: false,
  mangle: { toplevel: true }
}
*/
export const foo="";const o="";export{o as bar};

/*
option:
{
  module: false,
  mangle: { toplevel: false }
}
*/
export const foo="";const bar="";export{bar};

on https://try.terser.org/.

Or perhaps we should never mangle top level symbols, as it doesn't make sense.

Both:

• changing the behavior on whether the input contains ESM syntaxes like esbuild does
• having an option to specify the input/output format like SWC does

works for me.