mounts: prohibit relative paths in YAML

[AkihiroSuda]

YAMLs with relative paths like mounts: [{location: .}] are not longer allowed.

Relative paths are still allowed in CLI: limactl create --mount=DIR

Fix #3948

[jandubois]

I've not looked in detail, but returning an error from FillDefaults seems wrong. This is a validation error that should be caught in Validate. Otherwise there is no reason to have 2 separate functions.

I also think the --mount-only option should be a separate PR and not mixed in with a bug fix.

EDIT: I see it is already a separate PR, and just stacked with this one.

[AkihiroSuda]

Updated to avoid returning err from FillDefault

[jandubois]

This is still not the right fix. The regression was introduced by #3339. It unconditionally expands all local filenames to absolute names. We should only call Expand() when the location actually is a tilde-path:

--- pkg/limayaml/defaults.go
+++ pkg/limayaml/defaults.go
@@ -713,10 +713,12 @@ func FillDefault(ctx context.Context, y, d, o *limatype.LimaYAML, filePath strin
 				mounts[i].NineP.Cache = ptr.Of(Default9pCacheForRO)
 			}
 		}
-		if location, err := localpathutil.Expand(mount.Location); err == nil {
-			mounts[i].Location = location
-		} else {
-			logrus.WithError(err).Warnf("Couldn't expand location %q", mount.Location)
+		if localpathutil.IsTildePath(mount.Location) {
+			if location, err := localpathutil.Expand(mount.Location); err == nil {
+				mounts[i].Location = location
+			} else {
+				logrus.WithError(err).Warnf("Couldn't expand location %q", mount.Location)
+			}
 		}
 		if mount.MountPoint == nil {
 			mountLocation := mounts[i].Location

This fixes the existing validation:

❯ cat mount.yaml
images: [{location: /foo}]
mounts: [{location: foo}]

❯ l tmpl validate mount.yaml
FATA[0000] failed to validate YAML file "mount.yaml": field `mounts[0].location` must be an absolute path, got "foo"

[jandubois]

Thanks, LGTM