syntax error in svelte component causes entire webpack watch process to die

[elirov]

if you have an error in your .svelte part (only in the HTML part of it), such as:
{if <div/>
Then the entire webpack watch process will die instead of just showing a compile error and staying up.
It looks like svelte-loader doesn't produce any files, but webpack expects at least some type of output.

We get this in watchpack:
TypeError: The "path" argument must be of type string. Received undefined

Due to this, the yarn watch command needs to be restarted constantly.

--- FULL STACK TRACE ---

ERROR in ./tmpls/patient-intake/components/sections/Insurance.svelte
Module build failed (from ./node_modules/svelte-loader/index.js):
ParseError: Unexpected token
at error (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/utils/error.ts:25:16)
at Parser$1.error (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/parse/index.ts:101:3)
at Parser$1.acorn_error (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/parse/index.ts:94:8)
at read_expression (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/parse/read/expression.ts:34:10)
at mustache (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/parse/state/mustache.ts:379:22)
at new Parser$1 (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/parse/index.ts:53:12)
at parse (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/parse/index.ts:218:17)
at compile (/Users/elirov/workspace/xdocs/node_modules/svelte/src/compiler/compile/index.ts:94:14)
at injectVarsToCode (/Users/elirov/workspace/xdocs/node_modules/svelte-preprocess/dist/transformers/typescript.js:71:45)
at mixedImportsTranspiler (/Users/elirov/workspace/xdocs/node_modules/svelte-preprocess/dist/transformers/typescript.js:225:26)
@ ./tmpls/patient-intake/components/NewPatientView.svelte 23:0-52 60:17-26 215:2-11
@ ./tmpls/patient-intake/components/MainLayout.svelte 25:0-53 164:22-36 661:2-16
@ ./tmpls/patient-intake/init.js 16:0-69 29:35-45
@ ./src/client/dev/main.js 10:0-61 17:2-16

webpack 5.64.4 compiled with 1 error in 8726 ms
node:internal/validators:120
throw new ERR_INVALID_ARG_TYPE(name, 'string', value);
^

TypeError: The "path" argument must be of type string. Received undefined
at new NodeError (node:internal/errors:371:5)
at validateString (node:internal/validators:120:11)
at Object.dirname (node:path:1276:5)
at WatcherManager.watchFile (/Users/elirov/workspace/xdocs/node_modules/watchpack/lib/getWatcherManager.js:30:26)
at /Users/elirov/workspace/xdocs/node_modules/watchpack/lib/watchpack.js:280:41
at Object.exports.batch (/Users/elirov/workspace/xdocs/node_modules/watchpack/lib/watchEventSource.js:326:3)
at Watchpack.watch (/Users/elirov/workspace/xdocs/node_modules/watchpack/lib/watchpack.js:278:20)
at NodeWatchFileSystem.watch (/Users/elirov/workspace/xdocs/node_modules/webpack/lib/node/NodeWatchFileSystem.js:107:16)
at Watching.watch (/Users/elirov/workspace/xdocs/node_modules/webpack/lib/Watching.js:325:48)
at /Users/elirov/workspace/xdocs/node_modules/webpack/lib/Watching.js:303:13 {
code: 'ERR_INVALID_ARG_TYPE'
}

Node.js v17.1.0
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

[jasonlyu123]

From the description of sveltejs/svelte-preprocess#438. I can reproduce this problem. The steps to reproduce: Just clone the webpack template, run setupTypescript and add anything that would cause a markup error to App.svelte

It seems like it has something to do with this line.
https://github.com/sveltejs/svelte-loader/blame/5e7853f233d7be5592b0b5fc22da9b4d1a5b0c12/index.js#L81

If there's a preprocessed error. svelte-loader would add the file to webpack's file watcher list. The problem is not all preprocess-error has this property.