- support key prefixes for Linux desktop environments (issue #974)

- support custom key prefixes (issue #649)
- support multi-prefixed keys
- changed handling of prefixed keys

flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java

@@ -37,6 +37,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -44,6 +45,7 @@ import java.util.MissingResourceException;
 import java.util.Properties;
 import java.util.ResourceBundle;
 import java.util.ServiceLoader;
+import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.IntUnaryOperator;
@@ -100,6 +102,8 @@ public abstract class FlatLaf
 	private static Map<String, String> globalExtraDefaults;
 	private Map<String, String> extraDefaults;
 	private static Function<String, Color> systemColorGetter;
+	private static Set<String> uiKeyPlatformPrefixes;
+	private static Set<String> uiKeySpecialPrefixes;
 
 	private String desktopPropertyName;
 	private String desktopPropertyName2;
@@ -1122,6 +1126,92 @@ public abstract class FlatLaf
 		FlatLaf.systemColorGetter = systemColorGetter;
 	}
 
+	/**
+	 * Returns UI key prefix, used in FlatLaf properties files, for light or dark themes.
+	 * Return value is either {@code [light]} or {@code [dark]}.
+	 *
+	 * @since 3.6
+	 */
+	public static String getUIKeyLightOrDarkPrefix( boolean dark ) {
+		return dark ? "[dark]" : "[light]";
+	}
+
+	/**
+	 * Returns set of UI key prefixes, used in FlatLaf properties files, for current platform.
+	 * If UI keys in properties files start with a prefix (e.g. {@code [someprefix]Button.background}),
+	 * then they are only used if that prefix is contained in this set
+	 * (or is one of {@code [light]} or {@code [dark]} depending on current theme).
+	 * <p>
+	 * By default, the set contains one or more of following prefixes:
+	 * <ul>
+	 *   <li>{@code [win]} on Windows
+	 *   <li>{@code [mac]} on macOS
+	 *   <li>{@code [linux]} on Linux
+	 *   <li>{@code [unknown]} on other platforms
+	 *   <li>{@code [gnome]} on Linux with GNOME desktop environment
+	 *   <li>{@code [kde]} on Linux with KDE desktop environment
+	 *   <li>on Linux, the value of the environment variable {@code XDG_CURRENT_DESKTOP},
+	 *       split at colons and converted to lower case (e.g. if value of  {@code XDG_CURRENT_DESKTOP}
+	 *       is {@code ubuntu:GNOME}, then {@code [ubuntu]} and {@code [gnome]})
+	 * </ul>
+	 * <p>
+	 * You can add own prefixes to the set.
+	 * The prefixes must start with '[' and end with ']' characters, otherwise they will be ignored.
+	 *
+	 * @since 3.6
+	 */
+	public static Set<String> getUIKeyPlatformPrefixes() {
+		if( uiKeyPlatformPrefixes == null ) {
+			uiKeyPlatformPrefixes = new HashSet<>();
+			uiKeyPlatformPrefixes.add(
+				SystemInfo.isWindows ? "[win]" :
+				SystemInfo.isMacOS ? "[mac]" :
+				SystemInfo.isLinux ? "[linux]" : "[unknown]" );
+
+			// Linux
+			if( SystemInfo.isLinux ) {
+				if( SystemInfo.isGNOME )
+					uiKeyPlatformPrefixes.add( "[gnome]" );
+				else if( SystemInfo.isKDE )
+					uiKeyPlatformPrefixes.add( "[kde]" );
+
+				// add values from XDG_CURRENT_DESKTOP for other desktops
+				String desktop = System.getenv( "XDG_CURRENT_DESKTOP" );
+				if( desktop != null ) {
+					// XDG_CURRENT_DESKTOP is a colon-separated list of strings
+					// https://specifications.freedesktop.org/desktop-entry-spec/latest/recognized-keys.html#key-onlyshowin
+					// e.g. "ubuntu:GNOME" on Ubuntu 24.10 or "GNOME-Classic:GNOME" on CentOS 7
+					for( String desk : StringUtils.split( desktop.toLowerCase( Locale.ENGLISH ), ':', true, true ) )
+						uiKeyPlatformPrefixes.add( '[' + desk + ']' );
+				}
+			}
+		}
+		return uiKeyPlatformPrefixes;
+	}
+
+	/**
+	 * Returns set of special UI key prefixes, used in FlatLaf properties files.
+	 * Unlike other prefixes, properties with special prefixes are preserved.
+	 * You can access them using `UIManager`. E.g. `UIManager.get( "[someSpecialPrefix]someKey" )`.
+	 * <p>
+	 * By default, the set contains following special prefixes:
+	 * <ul>
+	 *   <li>{@code [style]}
+	 * </ul>
+	 * <p>
+	 * You can add own prefixes to the set.
+	 * The prefixes must start with '[' and end with ']' characters, otherwise they will be ignored.
+	 *
+	 * @since 3.6
+	 */
+	public static Set<String> getUIKeySpecialPrefixes() {
+		if( uiKeySpecialPrefixes == null ) {
+			uiKeySpecialPrefixes = new HashSet<>();
+			uiKeySpecialPrefixes.add( "[style]" );
+		}
+		return uiKeySpecialPrefixes;
+	}
+
 	private static void reSetLookAndFeel() {
 		EventQueue.invokeLater( () -> {
 			LookAndFeel lookAndFeel = UIManager.getLookAndFeel();

flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java

@@ -41,6 +41,7 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Properties;
+import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import javax.swing.Icon;
@@ -62,7 +63,6 @@ import com.formdev.flatlaf.util.HSLColor;
 import com.formdev.flatlaf.util.LoggingFacade;
 import com.formdev.flatlaf.util.SoftCache;
 import com.formdev.flatlaf.util.StringUtils;
-import com.formdev.flatlaf.util.SystemInfo;
 import com.formdev.flatlaf.util.UIScale;
 
 /**
@@ -105,6 +105,39 @@ class UIDefaultsLoader
 		return lafClasses;
 	}
 
+	static Properties newUIProperties( boolean dark ) {
+		// UI key prefixes
+		String lightOrDarkPrefix = FlatLaf.getUIKeyLightOrDarkPrefix( dark );
+		Set<String> platformPrefixes = FlatLaf.getUIKeyPlatformPrefixes();
+		Set<String> specialPrefixes = FlatLaf.getUIKeySpecialPrefixes();
+
+		return new Properties() {
+			@Override
+			public synchronized Object put( Object k, Object value ) {
+				// process key prefixes (while loading properties files)
+				String key = (String) k;
+				while( key.startsWith( "[" ) ) {
+					int closeIndex = key.indexOf( ']' );
+					if( closeIndex < 0 )
+						return null; // ignore property with invalid prefix
+
+					String prefix = key.substring( 0, closeIndex + 1 );
+
+					if( specialPrefixes.contains( prefix ) )
+						break; // keep special prefix
+
+					if( !lightOrDarkPrefix.equals( prefix ) && !platformPrefixes.contains( prefix ) )
+						return null; // ignore property
+
+					// prefix is known and enabled --> remove prefix
+					key = key.substring( closeIndex + 1 );
+				}
+
+				return super.put( key, value );
+			}
+		};
+	}
+
 	static void loadDefaultsFromProperties( List<Class<?>> lafClasses, List<FlatDefaultsAddon> addons,
 		Consumer<Properties> intellijThemesHook, Properties additionalDefaults, boolean dark, UIDefaults defaults )
 	{
@@ -113,8 +146,10 @@ class UIDefaultsLoader
 			// which avoids that system color getter is invoked multiple times
 			systemColorCache = (FlatLaf.getSystemColorGetter() != null) ? new HashMap<>() : null;
 
+			// all properties files will be loaded into this map
+			Properties properties = newUIProperties( dark );
+
 			// load core properties files
-			Properties properties = new Properties();
 			for( Class<?> lafClass : lafClasses ) {
 				String propertiesName = '/' + lafClass.getName().replace( '.', '/' ) + ".properties";
 				try( InputStream in = lafClass.getResourceAsStream( propertiesName ) ) {
@@ -201,41 +236,6 @@ class UIDefaultsLoader
 			if( additionalDefaults != null )
 				properties.putAll( additionalDefaults );
 
-			// collect all platform specific keys (but do not modify properties)
-			ArrayList<String> platformSpecificKeys = new ArrayList<>();
-			for( Object okey : properties.keySet() ) {
-				String key = (String) okey;
-				if( key.startsWith( "[" ) &&
-					(key.startsWith( "[win]" ) ||
-					 key.startsWith( "[mac]" ) ||
-					 key.startsWith( "[linux]" ) ||
-					 key.startsWith( "[light]" ) ||
-					 key.startsWith( "[dark]" )) )
-				  platformSpecificKeys.add( key );
-			}
-
-			// remove platform specific properties and re-add only properties
-			// for current platform, but with platform prefix removed
-			if( !platformSpecificKeys.isEmpty() ) {
-				// handle light/dark specific properties
-				String lightOrDarkPrefix = dark ? "[dark]" : "[light]";
-				for( String key : platformSpecificKeys ) {
-					if( key.startsWith( lightOrDarkPrefix ) )
-						properties.put( key.substring( lightOrDarkPrefix.length() ), properties.remove( key ) );
-				}
-
-				// handle platform specific properties
-				String platformPrefix =
-					SystemInfo.isWindows ? "[win]" :
-					SystemInfo.isMacOS ? "[mac]" :
-					SystemInfo.isLinux ? "[linux]" : "[unknown]";
-				for( String key : platformSpecificKeys ) {
-					Object value = properties.remove( key );
-					if( key.startsWith( platformPrefix ) )
-						properties.put( key.substring( platformPrefix.length() ), value );
-				}
-			}
-
 			// get (and remove) wildcard replacements, which override all other defaults that end with same suffix
 			HashMap<String, String> wildcards = new HashMap<>();
 			Iterator<Entry<Object, Object>> it = properties.entrySet().iterator();

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

@@ -42,7 +42,6 @@ import com.formdev.flatlaf.FlatClientProperties;
 import com.formdev.flatlaf.FlatLaf;
 import com.formdev.flatlaf.util.HiDPIUtils;
 import com.formdev.flatlaf.util.StringUtils;
-import com.formdev.flatlaf.util.SystemInfo;
 
 /**
  * Support for styling components in CSS syntax.
@@ -325,22 +324,24 @@ public class FlatStylingSupport
 			return null;
 
 		Map<String, Object> oldValues = new HashMap<>();
+		outer:
 		for( Map.Entry<String, Object> e : style.entrySet() ) {
 			String key = e.getKey();
 			Object newValue = e.getValue();
 
 			// handle key prefix
-			if( key.startsWith( "[" ) ) {
-				if( (SystemInfo.isWindows && key.startsWith( "[win]" )) ||
-					(SystemInfo.isMacOS && key.startsWith( "[mac]" )) ||
-					(SystemInfo.isLinux && key.startsWith( "[linux]" )) ||
-					(key.startsWith( "[light]" ) && !FlatLaf.isLafDark()) ||
-					(key.startsWith( "[dark]" ) && FlatLaf.isLafDark()) )
-				{
-					// prefix is known and enabled --> remove prefix
-					key = key.substring( key.indexOf( ']' ) + 1 );
-				} else
-					continue;
+			while( key.startsWith( "[" ) ) {
+				int closeIndex = key.indexOf( ']' );
+				if( closeIndex < 0 )
+					continue outer;
+
+				String prefix = key.substring( 0, closeIndex + 1 );
+				String lightOrDarkPrefix = FlatLaf.getUIKeyLightOrDarkPrefix( FlatLaf.isLafDark() );
+				if( !lightOrDarkPrefix.equals( prefix ) && !FlatLaf.getUIKeyPlatformPrefixes().contains( prefix ) )
+					continue outer;
+
+				// prefix is known and enabled --> remove prefix
+				key = key.substring( closeIndex + 1 );
 			}
 
 			Object oldValue = applyProperty.apply( key, newValue );

flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java

@@ -31,6 +31,7 @@ public class SystemInfo
 	public static final boolean isWindows;
 	public static final boolean isMacOS;
 	public static final boolean isLinux;
+	/** @since 3.6 */ public static final boolean isUnknownOS;
 
 	// OS versions
 	public static final long osVersion;
@@ -59,6 +60,7 @@ public class SystemInfo
 	public static final boolean isJetBrainsJVM_11_orLater;
 
 	// UI toolkits
+	/** @since 3.6 */ public static final boolean isGNOME;
 	public static final boolean isKDE;
 
 	// other
@@ -75,6 +77,7 @@ public class SystemInfo
 		isWindows = osName.startsWith( "windows" );
 		isMacOS = osName.startsWith( "mac" );
 		isLinux = osName.startsWith( "linux" );
+		isUnknownOS = !isWindows && !isMacOS && !isLinux;
 
 		// OS versions
 		osVersion = scanVersion( System.getProperty( "os.version" ) );
@@ -104,7 +107,13 @@ public class SystemInfo
 		isJetBrainsJVM_11_orLater = isJetBrainsJVM && isJava_11_orLater;
 
 		// UI toolkits
-		isKDE = (isLinux && System.getenv( "KDE_FULL_SESSION" ) != null);
+		String desktop = isLinux ? System.getenv( "XDG_CURRENT_DESKTOP" ) : null;
+		isGNOME = (isLinux &&
+			(System.getenv( "GNOME_DESKTOP_SESSION_ID" ) != null ||
+			 (desktop != null && desktop.contains( "GNOME" ))));
+		isKDE = (isLinux &&
+			(System.getenv( "KDE_FULL_SESSION" ) != null ||
+			 (desktop != null && desktop.contains( "KDE" ))));
 
 		// other
 		isProjector = Boolean.getBoolean( "org.jetbrains.projector.server.enable" );

flatlaf-core/src/main/resources/com/formdev/flatlaf/FlatLaf.properties

@@ -50,6 +50,9 @@ mini.font = -3
 #defaultFont = ...
 
 # font weights
+#  fallback for unknown platform
+light.font = +0
+semibold.font = +0
 #  Windows
 [win]light.font = "Segoe UI Light"
 [win]semibold.font = "Segoe UI Semibold"
@@ -59,15 +62,12 @@ mini.font = -3
 #  Linux
 [linux]light.font = "Lato Light", "Ubuntu Light", "Cantarell Light"
 [linux]semibold.font = "Lato Semibold", "Ubuntu Medium", "Montserrat SemiBold"
-#  fallback for unknown platform
-light.font = +0
-semibold.font = +0
 
 # monospaced
+monospaced.font = Monospaced
 [win]monospaced.font = Monospaced
 [mac]monospaced.font = Menlo, Monospaced
 [linux]monospaced.font = "Liberation Mono", "Ubuntu Mono", Monospaced
-monospaced.font = Monospaced
 
 # styles
 [style].h00 = font: $h00.font

flatlaf-core/src/main/resources/com/formdev/flatlaf/IntelliJTheme$ThemeLaf.properties

@@ -95,8 +95,8 @@ Spinner.buttonDisabledArrowColor = $ComboBox.buttonDisabledArrowColor
 #---- TabbedPane ----
 
 # colors from JBUI.CurrentTheme.DefaultTabs.inactiveUnderlineColor()
-[light]TabbedPane.inactiveUnderlineColor = #9ca7b8
-[dark]TabbedPane.inactiveUnderlineColor = #747a80
+{*-light}TabbedPane.inactiveUnderlineColor = #9ca7b8
+{*-dark}TabbedPane.inactiveUnderlineColor = #747a80
 
 
 #---- ToggleButton ----