Missing `mounts:` no longer defaults to mounting home directory

The issue points to a specific condition in the code (likely around line 376 in the linked diff) that determines default home directory mounting. Start by locating the config loading and mount handling logic in the codebase, likely in a file like config/config.go or vm/lima.go. Reproduce the bug by creating a colima.yaml without a mounts key, then trace through the code to see how the nil slice is handled. The fix involves adjusting the condition to treat a missing mounts key as triggering the default mount. Run the existing tests related to mounts to verify the fix.

Description

When starting up a colima.yaml without a mounts: key, it does not default to mounting the user's home directory as documented in the config file.

The config is also updated to mounts: null instead of the documented default of mounts: [].

Version

colima version 0.10.1
git commit: ed905203afdbc6fd4eae6cc301918099ff31e86e

runtime: docker
arch: aarch64
client: v29.2.1
server: v29.2.1
limactl version 2.0.3
zsh: command not found: qemu-img

Operating System

• macOS Intel <= 13 (Ventura)
• macOS Intel >= 14 (Sonoma)
• Apple Silicon <= 13 (Ventura)
• Apple Silicon >= 14 (Sonoma)
• Linux

Output of colima status

INFO[0000] colima is running using macOS Virtualization.Framework
INFO[0000] arch: aarch64
INFO[0000] runtime: docker
INFO[0000] mountType: virtiofs
INFO[0000] docker socket: unix:///Users/cflee/.colima/default/docker.sock
INFO[0000] containerd socket: unix:///Users/cflee/.colima/default/containerd.sock

Reproduction Steps

1. Write or modify the default instance's colima.yaml to have no mounts: line
2. Run colima start
3. Run colima ssh and ls to observe that the home directory is not mounted
4. Read the colima.yaml and observe that it reflects mounts: null
5. Run colima restart
6. Run colima ssh and ls to observe that the home directory is still not mounted

Expected behaviour

Upon colima start, when mounts: is not stated, the home directory should be mounted matching the behaviour stated in the config file, and the config file should be updated to mounts: [] (and that should have this behaviour).

# Colima default behaviour: $HOME is mounted as writable.
# Default: []

Additional context

I suspect this is a regression in v0.10.0 from #1485 as the condition for mounting the user's home directory was updated from len(conf.Mounts) == 0 (would be true where the mounts key is missing as it's unmarshaled into a nil slice that has len 0) to conf.Mounts != nil && len(conf.Mounts) == 0 (would be false as it's a nil slice)