Allow specifying individual border dimensions in `border`

[ShadelessFox]

I'm implementing a dynamic LaF change, and this means that no UI resources should be hard-coded or held on when retrieved from UIManager.

I currently have a lot of code that looks like this throughout my codebase:

panel.setBorder(BorderFactory.createMatteBorder(1, 0, 0, 0, UIManager.getColor("Component.borderColor")));

The code above creates a border that only has one segment on top.

I want to make use of FlatLaf's style client property border, but setting individual insets to 0 has no effect; all four segments are painted anyway.

A more extreme example follows:

field.setBorder(BorderFactory.createCompoundBorder(
    BorderFactory.createMatteBorder(0, 0, 1, 0, UIManager.getColor("Component.borderColor")),
    BorderFactory.createEmptyBorder(6, 8, 6, 8)));

So as a workaround I have to override component's updateUI and set a new border there:

var panel = new JPanel() {
    @Override
    public void updateUI() {
        super.updateUI();
        setBorder(BorderFactory.createMatteBorder(1, 0, 0, 0, UIManager.getColor("Component.borderColor")))
    }
};

Am I missing something? Thanks!

[ShadelessFox]

After some testing, I noticed that some controls (e.g., JScrollPane) get insets applied correctly, and some (e.g., JPanel) don't:

var child1 = new JPanel();
child1.putClientProperty(FlatClientProperties.STYLE, "border: 1,0,0,0, #ff0000");
child1.setPreferredSize(new Dimension(100, 100));

var child2 = new JScrollPane();
child2.putClientProperty(FlatClientProperties.STYLE, "border: 1,0,0,0, #ff0000");
child2.setPreferredSize(new Dimension(100, 100));

var frame = new JFrame("Demo");
frame.setLayout(new BorderLayout());
frame.add(child1, BorderLayout.WEST);
frame.add(child2, BorderLayout.EAST);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);