plugin-vue doesn't respect configured loaders since 1.8

[jods4]

Describe the bug

plugin-vue merges inline TS scripts in SFC, and compiles them itself with ESBuild.
Doing so bypasses any loader configuration for TS, which is unexpected and creates problems (see below).

This is a regression that was introduced in 1.8 by this commit 93d9a2d#diff-50999b66ad3fff48fd315417d4f8c98741da9f85a0fa6bb4ba212cc8f8bac967L271-R267

Specifically, the new behavior is to always merge inline ts scripts (previously it was done only for devServer):

vite/packages/plugin-vue/src/main.ts

Lines 267 to 268 in 93d9a2d

	if ((!script.lang || script.lang === 'ts') && !script.src) {
	scriptCode = rewriteDefault(script.content, '_sfc_main')

Once merged, the inlined ts scripts are converted to JS by esbuild directly, without regard for any specific loader / config:

vite/packages/plugin-vue/src/main.ts

Lines 190 to 205 in 93d9a2d

	// handle TS transpilation
	let resolvedCode = output.join('\n')
	if (
	(descriptor.script?.lang === 'ts' ||
	descriptor.scriptSetup?.lang === 'ts') &&
	!descriptor.script?.src // only normal script can have src
	) {
	const { code, map } = await transformWithEsbuild(
	resolvedCode,
	filename,
	{ loader: 'ts', sourcemap: options.sourceMap },
	resolvedMap
	)
	resolvedCode = code
	resolvedMap = resolvedMap ? (map as any) : resolvedMap
	}

This breaks builds that have non-default configuration. Solving this will close the following issues:

• [@vitejs/plugin-vue] Type definition generation in library mode is broken #5044 (type generation with rollup-plugin-typescript2)
• Regression in plugin-vue 1.8 can't import const enum #5795 (const enums with rollup-plugin-typescript2)

The easiest fix is to go back to not inlining TS outside devServer.
A more complex fix is to apply loaders from config when building TS inside SFC. This is IMHO less preferred because it has a high impact on the performance of devServer.

Reproduction

See #5044 or #5795

System Info

System:
    OS: Windows 10 10.0.19042
    CPU: (12) x64 Intel(R) Core(TM) i7-9850H CPU @ 2.60GHz
    Memory: 7.69 GB / 15.79 GB
  Binaries:
    Node: 16.6.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.10 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 7.19.1 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.19041.1266.0), Chromium (100.0.1185.50), ChromiumDev (102.0.1227.0)
    Internet Explorer: 11.0.19041.1566

Used Package Manager

npm

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[jods4]

I made a PR for the simple fix (revert, don't inline during build): #7909