Show an error when a dependency of the current file has an error

[llakala]

If you're currently editing a file, and a module you're importing has an error, the current file won't show any errors - it'll look like the file is totally fine, even if it's obviously not. This is because the file can't compile, as a dependency couldn't compile.

In my imagined fix, the current file would show an error on the import (or on every line of the file -- implementation detail), saying "This file can't compile and show errors, as the dependency dependency_name has errors. Fix those errors first so this file can compile!" Maybe even a code action to open that other file - but that's just a bonus.

[lpil]

This is a fantastic idea! Love it.

I think we should only show it for files that are currently open, to avoid lots of noise. If possible only in currently visible files, but I don't know if LSP can do that.

Where would we put the diagnostic? I wanted to say we could put it on the module that starts the import chain to the one that has the error, but there may not always be one.

[llakala]

When would there not be a module starting the import chain?

I would put it on the "lowest" level of the dependency chain, for clarity. For example, let's say foo.gleam has a error. That file is imported by bar.gleam, which is then imported by baz.gleam. The chain would be: current.gleam -> baz.gleam -> bar.gleam -> foo.gleam. If we import both baz and bar in the file, I would want to show it on the bar import, not the baz import.

[lpil]

When there's multiple branches in the import chain and we don't get to the second branch yet.

[kwando]

Lovely idea, this thing catches me quite frequently :)