`--cycle` keeps setting the same profile if `update_mtime` fails

[m0ar]

I'm configuring autorandr with Nix, both with home-manager on arch linux and on NixOS. In both scenarios, the config files for autorandr are linked from a readonly filesystem with a 0 timestamp:

❯ tree /etc/xdg         
/etc/xdg
└── autorandr
    ├── default
    │   ├── config -> /etc/static/xdg/autorandr/default/config
    │   ├── postswitch.d
    │   │   └── kb -> /etc/static/xdg/autorandr/default/postswitch.d/kb
    │   └── setup -> /etc/static/xdg/autorandr/default/setup
    └── office
        ├── config -> /etc/static/xdg/autorandr/office/config
        ├── postswitch.d
        │   └── kb -> /etc/static/xdg/autorandr/office/postswitch.d/kb
        └── setup -> /etc/static/xdg/autorandr/office/setup

❯ ls -lAL /etc/xdg/autorandr/*          
/etc/xdg/autorandr/default:
total 12
-r--r--r-- 1 root root   55 Jan  1  1970 config
drwxr-xr-x 2 root root 4096 Mar 24 12:20 postswitch.d
-r--r--r-- 1 root root 1295 Jan  1  1970 setup

/etc/xdg/autorandr/office:
total 12
-r--r--r-- 1 root root   55 Jan  1  1970 config
drwxr-xr-x 2 root root 4096 Mar 24 12:20 postswitch.d
-r--r--r-- 1 root root 1295 Jan  1  1970 setup

Why it fails

`--cycle will always select the first profile, since:

• --cycle depends on sorting by mtime
• os.utime will fail if the file is readonly
• the return value indicating success from update_mtime is ignored, so the current (epoch 0) mtime stays

Here is the relevant code:

# toplevel, return value of update_mtime is ignored
            if "--dry-run" not in options:
                update_mtime(os.path.join(scripts_path, "config"))


def update_mtime(filename):
    "Update a file's mtime"
    try:
        os.utime(filename, None)
        return True
    except:
        # this will fail
        return False

Proposed fixes

Either:

1. call os.utime with follow_symlinks = false, and update and read mtime from the link instead of the destination
2. extend symlink profile detection to work with actual dirs for the autorandr and profiles dirs, but when the actual config is a symlink (not entirely sure how this part of the code works atm)