Reject shrinking disk during YAML validation

cmd/limactl/edit.go

@@ -118,13 +118,13 @@ func editAction(cmd *cobra.Command, args []string) error {
 		return err
 	}
 	if err := limayaml.Validate(y, true); err != nil {
-		rejectedYAML := "lima.REJECTED.yaml"
-		if writeErr := os.WriteFile(rejectedYAML, yBytes, 0o644); writeErr != nil {
-			return fmt.Errorf("the YAML is invalid, attempted to save the buffer as %q but failed: %w: %w", rejectedYAML, writeErr, err)
-		}
-		// TODO: may need to support editing the rejected YAML
-		return fmt.Errorf("the YAML is invalid, saved the buffer as %q: %w", rejectedYAML, err)
+		return saveRejectedYAML(yBytes, err)
+	}
+
+	if err := limayaml.ValidateYAMLAgainstLatestConfig(yBytes, yContent); err != nil {
+		return saveRejectedYAML(yBytes, err)
 	}
+
 	if err := os.WriteFile(filePath, yBytes, 0o644); err != nil {
 		return err
 	}
@@ -171,3 +171,13 @@ func askWhetherToStart() (bool, error) {
 func editBashComplete(cmd *cobra.Command, _ []string, _ string) ([]string, cobra.ShellCompDirective) {
 	return bashCompleteInstanceNames(cmd)
 }
+
+// saveRejectedYAML writes the rejected config and returns an error.
+func saveRejectedYAML(y []byte, origErr error) error {
+	rejectedYAML := "lima.REJECTED.yaml"
+	if writeErr := os.WriteFile(rejectedYAML, y, 0o644); writeErr != nil {
+		return fmt.Errorf("the YAML is invalid, attempted to save the buffer as %q but failed: %w: %w", rejectedYAML, writeErr, origErr)
+	}
+	// TODO: may need to support editing the rejected YAML
+	return fmt.Errorf("the YAML is invalid, saved the buffer as %q: %w", rejectedYAML, origErr)
+}

pkg/limayaml/validate.go

@@ -595,3 +595,37 @@ func warnExperimental(y *LimaYAML) {
 		logrus.Warn("`mountInotify` is experimental")
 	}
 }
+
+// ValidateYAMLAgainstLatestConfig validates the values between the latest YAML and the updated(New) YAML.
+func ValidateYAMLAgainstLatestConfig(yNew, yLatest []byte) error {
+	var l, n LimaYAML
+	var err error
+	if err = Unmarshal(yLatest, &l, "Unmarshal latest YAML bytes"); err != nil {
+		return err
+	}
+	if err = Unmarshal(yNew, &n, "Unmarshal new YAML byte"); err != nil {
+		return err
+	}
+
+	// Handle editing the template without a disk value
+	if n.Disk == nil && l.Disk == nil {
+		return nil
+	}
+
+	// Disk value must be provided, as it is required when creating an instance.
+	nDisk, err := units.RAMInBytes(*n.Disk)
+	if err != nil {
+		return err
+	}
+	lDisk, err := units.RAMInBytes(*l.Disk)
+	if err != nil {
+		return err
+	}
+
+	// Reject shrinking disk
+	if nDisk < lDisk {
+		return fmt.Errorf("field `disk`: shrinking the disk (%v --> %v) is not supported", *l.Disk, *n.Disk)
+	}
+
+	return nil
+}