fix(compiler-sfc): allow export default substring

[btea]

fix #7038

[sxzz]

Consider this example:
export const foo = default_

Let's check if the brackets ({}) exist.
export { foo as default }

[sxzz]

Questions:

• (?:expr) is really necessary? It's just used to test here namedDefaultExportRE.test()
• (?:as)? why as optional? Is that really a valid syntax without as?
  • I think there are only two types of named default export: export { foo as default } and plus from 'xxx'
  • default is a keyword of JavaScript, so it can't be like export { default }. It's an invalid syntax.
  • Answer: export { default } from 'xxx'

FYI I wrote a regexp: /(^|\n|;)\s*export\s*{\s*([\w_$]+)\s*as\s*default/s

UPDATED regex /(^|\n|;)\s*export\s*{.*(\s*[\w_$]+\s+as\s+)?default/

[btea]

For the case without as, maybe can refer #5937

[sxzz]

@btea Oh, thanks! I just remembered.

[sxzz]

I just updated the regexp, maybe you can try it.

[btea]

It looks great, but the s flag doesn't seem to be needed.

[btea]

I tried it but it fails in these cases

core/packages/compiler-sfc/__tests__/rewriteDefault.spec.ts

Lines 18 to 33 in 7663a79

	expect(
	rewriteDefault(
	`const a = 1 \n export { a as b, a as default, a as c}`,
	'script'
	)
	).toMatchInlineSnapshot(`
	"const a = 1
	export { a as b, a as c}
	const script = a"
	`)
	expect(
	rewriteDefault(
	`const a = 1 \n export { a as b, a as default , a as c}`,
	'script'
	)

[sxzz]

@btea I think it's very hard to check it by regex, I think we could do it by AST. I trying to implement it.

[klyuevtech]

Hi gays! This new regexp ((^|\n|;)\sexport\s{.(\s[\w_$]+\s+as\s+)?default) could give false positive on a line like this one:
export { foo as bar }; const baz = "default";
Probably we should close the braces?
(^|\n|;)\s*export\s*{.*(\s*[\w_$]+\s+as\s+)?default\s*}

[sxzz]

@klyuevtech
Missing the case: export { a, a as default, c }
Matched the case but shouldn't export { somedefault }.

[klyuevtech]

@sxzz This one seems works well:
(^|\n|;)\s*export((\s*{[\w\s_$,]*([\w_$]+\s+as\s+)+)?|(\s*{\s*)+)default((\s|,)+[\w_$\s]*)?}

[btea]

@klyuevtech
It doesn't seem to match the following

core/packages/compiler-sfc/__tests__/rewriteDefault.spec.ts

Lines 112 to 115 in 7663a79

	expect(
	rewriteDefault(`export { foo, default } from './index.js'`, 'script')
	).toMatchInlineSnapshot(`
	"import { default as __VUE_DEFAULT__ } from './index.js'

[sxzz]

😮‍💨 I think it's too complex, even if we have a perfect regex.
We have the AST (PR #7068) already, so I think checking it through AST is better than a very complex regex

[znck]

AST based approach handles default in comments and strings, I think works better in all cases. Closing in favour of #7068.