lsp: diagnostic on module with no imports or exports

[kitsonk]

Something like "warning, this file doesn't contain any imports/exports and is therefore falsely considered global"

Originally posted by @KotlinIsland in denoland/vscode_deno#405 (comment)

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TypeScript has a design limitation where scripts are considered global scripts when they lack any import or export statements. While this does not cause any issues with the CLI, it does mean these symbols "leak" into the global context when using the LSP. We could provide a diagnostic that indicates this, with a quick fix which would be to append export {} to the file.

[DetachHead]

the isolatedModules compiler option should cover this, but it doesn't seem to be supported anymore? #12599

[KotlinIsland]

Does Deno support scripts at all? If not you could just secretly inject export {} so the LSP thinks it's a module

[kitsonk]

We should avoid "magically" augmenting the source code.

As stated, we should provide a quick fix that allows the author to fix it themselves.

[DetachHead]

imo it's also bad to "magically" half-enable a compiler flag. if there's a reason that isolatedModules works differently in deno can the documentation be updated to explain it?

[KotlinIsland]

Wouldn't adding a diagnostic like this just be the exact same as not disabling the error message in the first place?

"'input.ts' cannot be compiled under '--isolatedModules' because it is considered a global script file. Add an import, export, or an empty 'export {}' statement to make it a module."

[kitsonk]

We disable error messages equally at the moment across the language server and when checking on the CLI. The diagnostic is meaningless on the CLI, the reason why it is disabled, and misleading from the language server as it would complain about the file being a script which doesn't work with isolated modules, something the user has no control over.

So to implement the feature we would have to determine which context we are in, suppress it in one and rewrite it in another as well as inject a code action.

[KotlinIsland]

Get typescript to add a "scripts-are-modules" mode that all it does is injects a export {} during analysis. Then use that.

[kitsonk]

The whole TypeScript issue is covered at microsoft/TypeScript#18232, including your suggestion, so it isn't like it hasn't been discussed before. We also have #9593 that covers the topic as well.

[kitsonk]

This should no longer be an issue, as we force module consideration on TypeScript.

[KotlinIsland]

@kitsonk Awesome news! I'm interested in this, could you link to some more info please?