Code `Quill.import('mod');` makes TS think it needs to `import('mod')`

[joscha]

The quill library has a static method called import on it's exported symbol, which is used like this:

Quill.import('dependency');

These dependencies are not actually imports, they are strings in a map. Unfortunately ts.preProcessFile thinks they are valid imports.
I tried fixing the issue, but there is some logic missing and I am unsure how to debug the test I added properly with me being able to look at the scanner state. Maybe someone can give me a hint on how to complete my fix in #23358, please?

TypeScript Version: master (edcf087)

Search Terms: Quill, .import, static import, preprocessFiles

Code

Quill.import('delta');

see https://github.com/Microsoft/TypeScript/pull/23358/files#diff-fa5d406e8b31aa069cd80d9698ca0590R63

Expected behavior:
Quill.import('delta'); is treated like any other code (a function call of the function import on a symbol Quill)

Actual behavior:
TS thinks this is a proper import a la import('delta'), ignoring the fact that there is a preceding Quill..

Playground Link: See #23358

Related Issues:
#23358

[mhegazy]

You are seeing an error on VS 2015? or this is an API issue? we have stopped using preprocessFile for a while now..

[joscha]

@mhegazy we are using the API for a typescript webpack loader, so we are seeing it when using that, but the root cause is the function itself. Apart from that I am unaware of any other product is affected.

[mhegazy]

thanks for the context. but why not just use the sourceFile?

[joscha]

thanks for the context. but why not just use the sourceFile?

Sorry, I am not following? We need to transform the dependency information in something that webpack can understand, e.g. we have a snippet of code that looks like this:

const preProcessedFileInfo = ts.preProcessFile(content, true, true);
return preProcessedFileInfo.importedFiles.map(({ fileName }) => `require("${fileName}");`).join('\n');

[mhegazy]

but you do parse the file at some point don't you?

This API has a mini-parser that tries to speculatively find imports. there is historical reasons why this API exists. We used it when we had VS running its own language service (not using tsserver) and it had do some speculative calculation of the project shape before the compiler tells it for sure about the files.. it is a long story, but my guess is that is most users of the compiler API do not need to use this function.

If you do parse (i.e. call createSourceFile or createProgram) then you have an AST, you can walk the AST to get the info you need.

[joscha]

If you do parse (i.e. call createSourceFile or createProgram) then you have an AST, you can walk the AST to get the info you need.

I am sure we can, that's also what https://github.com/pahen/detective-typescript does for example, even without using the ts-provided AST. There are a lot of ways doing this, including a terrible regex or changing the code to Quill['import']('mod') (what we did in the meantime), but the way we have written the code is using the API ts.preProcessFile, because it did what we needed at the time. This API has a fault as outlined in the issue description. I would like to fix this fault, if possible and avoid rewriting a large chunk of some other component. I am happy to spend the time finding a fix, however the way this discussion is going right now, it feels as if you are suggesting to leave the API as-is and I should look elsewhere to fix my problem?

[mhegazy]

Fix for this issue is welcome. We have no intention to remove or deprecate this API. I was just pointing out what it does in detail.