gleam build doesn't have permission to link priv on Windows

[PastMoments]

On Windows running gleam build on a project with a priv directory will error. This seems to be caused by a Windows-specific symlink behaviour.
https://blogs.windows.com/windowsdeveloper/2016/12/02/symlinks-windows-10/

You can enable "Developer Mode", which will grant the symlink permission.

If there's no easy way to fix this, then printing out a warning to enable this setting would probably be okay.

Using Gleam v1.1.0

Reproducing:

gleam new project_name
cd project_name
mkdir priv
gleam build

> gleam build
Downloading packages
 Downloaded 2 packages in 0.02s
  Compiling gleam_stdlib
  Compiling gleeunit
  Compiling project_name
error: File IO failure

An error occurred while trying to link this file:

    C:\Users\USERNAME\Desktop\project_name\build\dev\erlang\project_name\priv

The error message from the file IO library was:

    A required privilege is not held by the client. (os error 1314)

[lpil]

Ah sorry! This is very frustrating.

What would be the best thing to do here? Perhaps we can try and link first, but if the linking fails then we can fall back to scanning the priv directory and copying all the files across. It'll be a lot slower but should always work.

[PastMoments]

That seems like the only option with the way Windows/rust std works. With some change detection to the contents of the priv directory, the slowness shouldn't be too bad, at least when iterating on just the Gleam code itself.

We use this to symlink right now
https://doc.rust-lang.org/std/os/windows/fs/fn.symlink_dir.html

Windows treats symlink creation as a privileged action, therefore this function is likely to fail unless the user makes changes to their system to permit symlink creation. Users can try enabling Developer Mode, granting the SeCreateSymbolicLinkPrivilege privilege, or running the process as an administrator.

I think it would be a good idea to emit this warning when it does the copying anyways, so if the user cares about the slowness they know how to fix it.

If anyone is curious, here's the way the rust std implements symlinking.
https://github.com/rust-lang/rust/blob/1.77.2/library/std/src/os/windows/fs.rs#L620
https://github.com/rust-lang/rust/blob/1.77.2/library/std/src/sys/pal/windows/fs.rs#L1261
https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createsymboliclinkw

Looks like it's already doing all that it can do on Windows.

[johannesvollmer]

I have Rust experience and feel confident that copying the files sounds simple enough. Is someone already working on this?

[lpil]

Not that I'm aware of

[johannesvollmer]

Already started looking into the issue. Three biggest question would be, if we can write a useful test for this. I can test locally today, but it shouldn't fail in the future.

I'll have a look into it :)

[johannesvollmer]

Is GitHub issues the primary communication? The discord server seems to be about using Gleam, not about contributing.

[lpil]

It is, yes.