IntelliJ Themes: support customizing through properties files (issue #824)

re-written how .theme.json values are applied:
- old: .theme.json values were applied as last step to a UIDefaults object (after processing all FlatLaf properties files)
- new: .theme.json values are applied to the properties map while loading all FlatLaf properties files

flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/DemoPrefs.java

@@ -52,6 +52,8 @@ public class DemoPrefs
 	}
 
 	public static void setupLaf( String[] args ) {
+//		com.formdev.flatlaf.demo.intellijthemes.IJThemesDump.install();
+
 		// set look and feel
 		try {
 			if( args.length > 0 )

flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/intellijthemes/IJThemesDump.java

@@ -0,0 +1,118 @@
+/*
+ * Copyright 2025 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.formdev.flatlaf.demo.intellijthemes;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.io.Writer;
+import java.nio.charset.StandardCharsets;
+import java.util.Properties;
+import java.util.concurrent.atomic.AtomicReference;
+import javax.swing.LookAndFeel;
+import javax.swing.UIDefaults;
+import javax.swing.UIManager;
+import com.formdev.flatlaf.FlatLaf;
+import com.formdev.flatlaf.IntelliJTheme;
+import com.formdev.flatlaf.util.LoggingFacade;
+
+/**
+ * @author Karl Tauber
+ */
+public class IJThemesDump
+{
+	// same as UIDefaultsLoader.KEY_PROPERTIES
+	private static final String KEY_PROPERTIES = "FlatLaf.internal.properties";
+
+	public static void enablePropertiesRecording() {
+		System.setProperty( KEY_PROPERTIES, "true" );
+	}
+
+	public static void install() {
+		enablePropertiesRecording();
+
+		UIManager.addPropertyChangeListener( e -> {
+			if( "lookAndFeel".equals( e.getPropertyName() ) ) {
+				LookAndFeel lookAndFeel = UIManager.getLookAndFeel();
+				if( lookAndFeel instanceof IntelliJTheme.ThemeLaf ) {
+					IntelliJTheme theme = (lookAndFeel.getClass() == IntelliJTheme.ThemeLaf.class)
+						? ((IntelliJTheme.ThemeLaf)lookAndFeel).getTheme()
+						: null;
+					String name = (theme != null) ? theme.name : lookAndFeel.getClass().getSimpleName();
+					File dir = new File( "dumps/properties" );
+					dumpProperties( dir, name, UIManager.getLookAndFeelDefaults() );
+				}
+			}
+		} );
+	}
+
+	public static void dumpProperties( File dir, String name, UIDefaults defaults ) {
+		String content = dumpPropertiesToString( defaults );
+		if( content == null )
+			return;
+
+		// write to file
+		File file = new File( dir, name + ".properties" );
+		file.getParentFile().mkdirs();
+		try( Writer fileWriter = new OutputStreamWriter(
+			new FileOutputStream( file ), StandardCharsets.UTF_8 ) )
+		{
+			fileWriter.write( content );
+		} catch( IOException ex ) {
+			LoggingFacade.INSTANCE.logSevere( null, ex );
+		}
+	}
+
+	public static String dumpPropertiesToString( UIDefaults defaults ) {
+		Properties properties = (Properties) defaults.get( KEY_PROPERTIES );
+		if( properties == null )
+			return null;
+
+		// dump to string
+		StringWriter stringWriter = new StringWriter( 100000 );
+		PrintWriter out = new PrintWriter( stringWriter );
+		out.printf( "@baseTheme = %s%n", FlatLaf.isLafDark() ? "dark" : "light" );
+		AtomicReference<String> lastPrefix = new AtomicReference<>();
+		properties.entrySet().stream()
+			.sorted( (e1, e2) -> ((String)e1.getKey()).compareTo( (String) e2.getKey() ) )
+			.forEach( e -> {
+				String key = (String) e.getKey();
+				String value = (String) e.getValue();
+				String prefix = keyPrefix( key );
+				if( !prefix.equals( lastPrefix.get() ) ) {
+					lastPrefix.set( prefix );
+					out.printf( "%n%n#---- %s ----%n%n", prefix );
+				}
+
+				out.printf( "%-50s = %s%n", key, value.replace( ";", "; \\\n\t" ) );
+			} );
+
+		return stringWriter.toString().replace( "\r", "" );
+	}
+
+	private static String keyPrefix( String key ) {
+		int dotIndex = key.indexOf( '.' );
+		return (dotIndex > 0)
+			? key.substring( 0, dotIndex )
+			: key.endsWith( "UI" )
+				? key.substring( 0, key.length() - 2 )
+				: "";
+	}
+}

flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/intellijthemes/IJThemesPanel.java

@@ -276,20 +276,21 @@ public class IJThemesPanel
 			return;
 
 		EventQueue.invokeLater( () -> {
-			setTheme( themeInfo );
+			setTheme( themeInfo, false );
 		} );
 	}
 
-	private void setTheme( IJThemeInfo themeInfo ) {
+	private void setTheme( IJThemeInfo themeInfo, boolean reload ) {
 		if( themeInfo == null )
 			return;
 
 		// change look and feel
 		if( themeInfo.lafClassName != null ) {
-			if( themeInfo.lafClassName.equals( UIManager.getLookAndFeel().getClass().getName() ) )
+			if( !reload && themeInfo.lafClassName.equals( UIManager.getLookAndFeel().getClass().getName() ) )
 				return;
 
-			FlatAnimatedLafChange.showSnapshot();
+			if( !reload )
+				FlatAnimatedLafChange.showSnapshot();
 
 			try {
 				UIManager.setLookAndFeel( themeInfo.lafClassName );
@@ -298,7 +299,8 @@ public class IJThemesPanel
 				showInformationDialog( "Failed to create '" + themeInfo.lafClassName + "'.", ex );
 			}
 		} else if( themeInfo.themeFile != null ) {
-			FlatAnimatedLafChange.showSnapshot();
+			if( !reload )
+				FlatAnimatedLafChange.showSnapshot();
 
 			try {
 				if( themeInfo.themeFile.getName().endsWith( ".properties" ) )
@@ -320,7 +322,9 @@ public class IJThemesPanel
 
 		// update all components
 		FlatLaf.updateUI();
-		FlatAnimatedLafChange.hideSnapshotWithAnimation();
+
+		if( !reload )
+			FlatAnimatedLafChange.hideSnapshotWithAnimation();
 	}
 
 	private void browsePlugin() {
@@ -386,8 +390,8 @@ public class IJThemesPanel
 			// use invokeLater() because KEY_LAF_THEME_FILE is updated after this event
 			EventQueue.invokeLater( () -> {
 				selectedCurrentLookAndFeel();
+				lastLafChangeTime = System.currentTimeMillis();
 			} );
-			lastLafChangeTime = System.currentTimeMillis();
 		}
 	}
 
@@ -435,7 +439,7 @@ public class IJThemesPanel
 				}
 
 				if( reload )
-					setTheme( themesList.getSelectedValue() );
+					setTheme( themesList.getSelectedValue(), true );
 			}
 		}
 	}