refactor: rewrite vendor chunk to handle redirect exports

[QiroNT]

Description

fix #3731

I decided to not open a discussion, but this implementation should be more tested. I have no idea if it actually solved that kind of issue, but tested it solved that particular issue.

Before:

After:

And yes, performance is not great on large size projects, but I only have a medium size project, and here is the result:

Additional context

The real problem is the current implementation of vendor doesn't handle redirect exports, dependencies like framer-motion provided a combined export kinds of like this:

// index.js
export { foo } from "./foo.js"
export { bar } from "./bar.js"

and the import looks like:

// main.js
import { foo } from "./index.js"

In the current implementation of vendor, the file index.js is considered to be a vendor file, so every import to index.js is put inside vendor chunk.

But rollup handles this situation just fine, when vendor chunk is disabled, rollup splits dynamic import to bar seperately.

This implementation scans all redirect exports. Instead of marking index.js as a vendor file, this pr detects foo import from main.js and only marks foo.js as a vendor file, fixes the issue.

#6318 probably should be based on this implementation.

Side note: this implementation still allows setting manualChunks to undefined to disable vendor chunk.

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[QiroNT]

@benmccann could you help me test this on that SvelteKit issue?

[Shinigami92]

Code looks okay
Is it possible to add a test?

[benmccann]

this could use an explanation as to what the algorithm is and why this is being used instead of Rollup's default behavior

[QiroNT]

added a simple explanation, Is it okay?

[benmccann]

I didn't test it, but to be very blunt, my first reaction is that this is insanity. Rollup has built-in code splitting, so why build some very complicated thing to replace it? At the very least there needs to be some explanation of what this is doing and what its benefits are. My initial reaction is that I would be much happier to just rip it all out and not deal with the added complexity and issues caused by this feature, but maybe I would feel differently given some explanation

[QiroNT]

added tests, but the tests are very barebone. I have no idea what edge cases to cover since I just ignored exports in traceImport in the last commit and it results in 305 -> 203 vendor files decrease with no change in vendor chunk. But it seems to be working for all projects I personally tested with no node_modules in source chunk and a decrease (or none for some) in vendor chunk.

[QiroNT]

My initial reaction is that I would be much happier to just rip it all out and not deal with the added complexity and issues caused by this feature, but maybe I would feel differently given some explanation.

Started a discussion about this, we should talk about it with more users to decide whether we implement it or just get rid of vendor chunk.