ComboBox and Spinner: no longer use preferred height for arrow button width, because preferred height may be zero, which would hide arrow button (see https://github.com/scijava/scijava-ui-swing/issues/77#issuecomment-1261452712)

- arrow button width depends on combobox/spinner height
- default/max button width is height of a raw combobox/spinner (without insets)
- min button width is 3/4 of default button width

CHANGELOG.md

@@ -1,6 +1,14 @@
 FlatLaf Change Log
 ==================
 
+## 3.0-SNAPSHOT
+
+#### Fixed bugs
+
+- ComboBox and Spinner: Fixed missing arrow buttons if preferred height is zero.
+  Minimum width of arrow buttons is 3/4 of default width.
+
+
 ## 2.5
 
 #### New features and improvements

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java

@@ -308,11 +308,14 @@ public class FlatComboBoxUI
 					// limit button width to height of a raw combobox (without insets)
 					FontMetrics fm = comboBox.getFontMetrics( comboBox.getFont() );
 					int maxButtonWidth = fm.getHeight() + scale( padding.top ) + scale( padding.bottom );
+					int minButtonWidth = (maxButtonWidth * 3) / 4;
 
+					// make button square (except if width is limited)
 					Insets insets = getInsets();
-					int buttonWidth = Math.min( parent.getPreferredSize().height - insets.top - insets.bottom, maxButtonWidth );
+					int buttonWidth = Math.min( Math.max( parent.getHeight() - insets.top - insets.bottom, minButtonWidth ), maxButtonWidth );
+
 					if( buttonWidth != arrowButton.getWidth() ) {
-						// set width of arrow button to preferred height of combobox
+						// set width of arrow button
 						int xOffset = comboBox.getComponentOrientation().isLeftToRight()
 							? arrowButton.getWidth() - buttonWidth
 							: 0;

flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatSpinnerUI.java

@@ -483,9 +483,10 @@ public class FlatSpinnerUI
 			// limit buttons width to height of a raw spinner (without insets)
 			FontMetrics fm = spinner.getFontMetrics( spinner.getFont() );
 			int maxButtonWidth = fm.getHeight() + scale( padding.top ) + scale( padding.bottom );
+			int minButtonWidth = (maxButtonWidth * 3) / 4;
 
-			// make button area square (if spinner has preferred height)
-			int buttonsWidth = Math.min( parent.getPreferredSize().height - insets.top - insets.bottom, maxButtonWidth );
+			// make button area square (except if width is limited)
+			int buttonsWidth = Math.min( Math.max( buttonsRect.height, minButtonWidth ), maxButtonWidth );
 			buttonsRect.width = buttonsWidth;
 
 			if( parent.getComponentOrientation().isLeftToRight() ) {