Error: "Debug Failure. File ... has unknown extension"

[arggh]

Describe the bug

Suddenly, after working for a while, Svelte for VS Code stops working. It will still give me options for auto-importing files, but there is no path included in the options and selecting an option doesn't add any imports to the file being edited.

The error shown in the output tab says:

Error: Debug Failure. File ../components/LanguageSelectButton.svelte has unknown extension.

Not sure what the error actually means, but pretty sure the file has a known extension, .svelte.

The output tab content for Svelte

Using Svelte v3.43.0 from /Users/arggh/Develop/example/example-foo/node_modules/svelte/compiler
Error: Debug Failure. File ../../../../../packages/example-ui/src/LanguageSelect/LanguageSelect.svelte has unknown extension.
at Object.extensionFromPath (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:20405:51)
at getJSExtensionForFile (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:117454:136)
at removeExtensionAndIndexPostFix (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:117447:42)
at getLocalModuleSpecifier (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:117000:17)
at computeModuleSpecifiers (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:116967:33)
at Object.getModuleSpecifiersWithCacheInfo (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:116927:26)
at getModuleSpecifiers (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:146057:72)
at /Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:146060:26
at Object.flatMap (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:713:25)
at getNewImportFixes (/Users/arggh/.vscode-insiders/extensions/svelte.svelte-vscode-105.4.0/node_modules/typescript/lib/typescript.js:146059:28)
Using Svelte v3.43.0 from /Users/arggh/Develop/example/node_modules/svelte/compiler
SnapshotManager File Statistics:
Project files: 0
Svelte files: 204
From node_modules: 309
Total: 729
Using Svelte v3.43.0 from /Users/arggh/Develop/example/node_modules/svelte/compiler

Screenshots

System (please complete the following information):

• OS: Mac OS 11.6 M1
• IDE: VSCode
• Plugin/Package: Svelte for VSCode

[jasonlyu123]

We might need a reproducible for this one. The error is thrown by typescript as shown in the error stack. Typescript's codebase is very complex. Without a reproducible, it's really hard to track down the problem.

[jasonlyu123]

I guess I have found a reproducible. Can you check if you have the "typescript.preferences.importModuleSpecifierEnding": "js", or "javacript.preferences.importModuleSpecifierEnding": "js", config?

[jasonlyu123]

It's also possible that the "typescript.preferences.importModuleSpecifierEnding" config is set to auto but there's an existing import in the file that imported with a js file extension like import {} from 'path/to/module.js'. It is quite tricky to fix on our side. I can't find a workaround for all cases.

Guess it would be better we file an issue on the typescript repo to ask if they can remove this debug assertion or not. This might also happen in a lot of tooling for component frameworks with a custom file extension. I tried and it also appears in vetur (for vue). So it might be more beneficial to "fix" on the typescript side.

[dummdidumm]

If the module specified ending is the problem - this might get much more pressing soon, when TS 4.5 is released which brings a ESM mode where module specifier endings are mandatory.