fix(compiler-sfc): analyze export default by AST

[sxzz]

closes #7038, closes #7041, closes #7078

vite plugin PR vitejs/vite#10888

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thanks to @btea

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[znck]

I think it's safer if we use as __VUE_DEFAULT__ in the else case (see highlighted line in the screenshot below).

[sxzz]

@znck Done.

[yyx990803]

A problem with this approach: rewriteDefault is used in @vitejs/plugin-vue here, on the script string already transformed by compileScript. This means the string no longer matches the Node positions in the AST exposed on the SFC descriptor.

I think we need to do something similar to reactivity transform's transformAST:

1. Accept both the AST and the corresponding MagicString instance in rewriteDefault
2. Also expose the MagicString instance on the script block returned by compileScript
3. In @vitejs/plugin-vue, feature detect by checking whether MagicString instance is available

• If yes, use AST-based rewrite by passing in AST + MagicString
• If no, fallback to old usage

[yyx990803]

@sxzz did you end up re-creating vitejs/vite#10888 for https://github.com/vitejs/vite-plugin-vue?

[sxzz]

@yyx990803 No, I haven't done it yet.

[sxzz]

@yyx990803 Done vitejs/vite-plugin-vue#136