Function mountPairToLayerStack

plugins/diff/windows/windows.go:358–400

mountPairToLayerStack ensures that the two sets of mount-lists are actually a correct parent-and-child, or orphan-and-empty-list, and return the full list of layers, starting with the upper-most (most childish?)

(lower, upper []mount.Mount)

// parent-and-child, or orphan-and-empty-list, and return the full list of layers, starting
// with the upper-most (most childish?)
func mountPairToLayerStack(lower, upper []mount.Mount) ([]string, error) {

	// May return an ErrNotImplemented, which will fall back to LCOW
	upperLayer, upperParentLayerPaths, err := mountsToLayerAndParents(upper)
	if err != nil {
		return nil, fmt.Errorf("upper mount invalid: %w", err)
	}

	lowerLayer, lowerParentLayerPaths, err := mountsToLayerAndParents(lower)
	if errdefs.IsNotImplemented(err) {
		// Upper was a windows-layer, lower is not. We can't handle that.
		return nil, fmt.Errorf("windowsDiff cannot diff a windows-layer against a non-windows-layer: %w", errdefs.ErrInvalidArgument)
	} else if err != nil {
		return nil, fmt.Errorf("lower mount invalid: %w", err)
	}

	// Trivial case, diff-against-nothing
	if lowerLayer == "" {
		if len(upperParentLayerPaths) != 0 {
			return nil, fmt.Errorf("windowsDiff cannot diff a layer with parents against a null layer: %w", errdefs.ErrInvalidArgument)
		}
		return []string{upperLayer}, nil
	}

	if len(upperParentLayerPaths) < 1 {
		return nil, fmt.Errorf("windowsDiff cannot diff a layer with no parents against another layer: %w", errdefs.ErrInvalidArgument)
	}

	if upperParentLayerPaths[0] != lowerLayer {
		return nil, fmt.Errorf("windowsDiff cannot diff a layer against a layer other than its own parent: %w", errdefs.ErrInvalidArgument)
	}

	if len(upperParentLayerPaths) != len(lowerParentLayerPaths)+1 {
		return nil, fmt.Errorf("windowsDiff cannot diff a layer against a layer with different parents: %w", errdefs.ErrInvalidArgument)
	}
	for i, upperParent := range upperParentLayerPaths[1:] {
		if upperParent != lowerParentLayerPaths[i] {
			return nil, fmt.Errorf("windowsDiff cannot diff a layer against a layer with different parents: %w", errdefs.ErrInvalidArgument)
		}
	}

	return append([]string{upperLayer}, upperParentLayerPaths...), nil
}

func uniqueRef() string {
	t := time.Now()