internal/mod/modpkgload: symbolic links do not count as package files

[rogpeppe]

What version of CUE are you using (cue version)?

$ cue version
v0.9.4

Does this issue reproduce with the latest stable release?

Yes (v0.9.4)

What did you do?

[!unix] skip
exec cp x/x.cue_actual x/x.cue
exec cue export
cmp stdout want-stdout

rm x/x.cue
exec ln -s x.cue_actual ./x/x.cue
exec cue export .

-- want-stdout --
{
    "message": "Hallo, Welt!"
}
-- cue.mod/module.cue --
module: "example.com"

language: version: "v0.9.0"
-- main.cue --
package main

import "example.com/x"
x
-- x/x.cue_actual --
package x

message: "Hallo, Welt!"

What did you expect to see?

A passing test

What did you see instead?

> [!unix] skip
> exec cp x/x.cue_actual x/x.cue
> exec cue export
[stdout]
{
    "message": "Hallo, Welt!"
}
> cmp stdout want-stdout
> rm x/x.cue
> exec ln -s x.cue_actual ./x/x.cue
> exec cue export .
[stderr]
example.com@v0: import failed: cannot find package "example.com/x": cannot find module providing package example.com/x:
    ./main.cue:3:8
[exit status 1]
FAIL: /tmp/z.txtar:8: unexpected command failure