UIDefaultsLoader: added if() function (inspired by Less CSS)

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

@@ -312,6 +312,24 @@ class UIDefaultsLoader
 			case "true":	resultValueType[0] = ValueType.BOOLEAN; return true;
 		}
 
+		// check for function "if"
+		//     Syntax: if(condition,trueValue,falseValue)
+		//       - condition: evaluates to true if:
+		//           - is not "null"
+		//           - is not "false"
+		//           - is not an integer with zero value
+		//       - trueValue: used if condition is true
+		//       - falseValue: used if condition is false
+		if( value.startsWith( "if(" ) && value.endsWith( ")" ) ) {
+			List<String> params = splitFunctionParams( value.substring( 3, value.length() - 1 ), ',' );
+			if( params.size() != 3 )
+				throwMissingParametersException( value );
+
+			boolean ifCondition = parseCondition( params.get( 0 ), resolver, addonClassLoaders );
+			String ifValue = params.get( ifCondition ? 1 : 2 );
+			return parseValue( key, resolver.apply( ifValue ), resultValueType, resolver, addonClassLoaders );
+		}
+
 		// check for function "lazy"
 		//     Syntax: lazy(uiKey)
 		if( value.startsWith( "lazy(" ) && value.endsWith( ")" ) ) {
@@ -420,6 +438,20 @@ class UIDefaultsLoader
 		}
 	}
 
+	private static boolean parseCondition( String condition,
+		Function<String, String> resolver, List<ClassLoader> addonClassLoaders )
+	{
+		try {
+			Object conditionValue = parseValue( "", resolver.apply( condition ), null, resolver, addonClassLoaders );
+			return (conditionValue != null &&
+				!conditionValue.equals( false ) &&
+				!conditionValue.equals( 0 ) );
+		} catch( IllegalArgumentException ex ) {
+			// ignore errors (e.g. variable or property not found) and evaluate to false
+			return false;
+		}
+	}
+
 	private static Object parseBorder( String value, Function<String, String> resolver, List<ClassLoader> addonClassLoaders ) {
 		if( value.indexOf( ',' ) >= 0 ) {
 			// top,left,bottom,right[,lineColor[,lineThickness]]
@@ -584,7 +616,7 @@ class UIDefaultsLoader
 		String function = value.substring( 0, paramsStart ).trim();
 		List<String> params = splitFunctionParams( value.substring( paramsStart + 1, value.length() - 1 ), ',' );
 		if( params.isEmpty() )
-			throw new IllegalArgumentException( "missing parameters in function '" + value + "'" );
+			throwMissingParametersException( value );
 
 		if( parseColorDepth > 100 )
 			throw new IllegalArgumentException( "endless recursion in color function '" + value + "'" );
@@ -592,6 +624,7 @@ class UIDefaultsLoader
 		parseColorDepth++;
 		try {
 			switch( function ) {
+				case "if":			return parseColorIf( value, params, resolver, reportError );
 				case "rgb":			return parseColorRgbOrRgba( false, params, resolver, reportError );
 				case "rgba":		return parseColorRgbOrRgba( true, params, resolver, reportError );
 				case "hsl":			return parseColorHslOrHsla( false, params );
@@ -620,6 +653,21 @@ class UIDefaultsLoader
 		throw new IllegalArgumentException( "unknown color function '" + value + "'" );
 	}
 
+	/**
+	 * Syntax: if(condition,trueValue,falseValue)
+	 * <p>
+	 * This "if" function is only used if the "if" is passed as parameter to another
+	 * color function. Otherwise the general "if" function is used.
+	 */
+	private static Object parseColorIf( String value, List<String> params, Function<String, String> resolver, boolean reportError ) {
+		if( params.size() != 3 )
+			throwMissingParametersException( value );
+
+		boolean ifCondition = parseCondition( params.get( 0 ), resolver, Collections.emptyList() );
+		String ifValue = params.get( ifCondition ? 1 : 2 );
+		return parseColorOrFunction( resolver.apply( ifValue ), resolver, reportError );
+	}
+
 	/**
 	 * Syntax: rgb(red,green,blue) or rgba(red,green,blue,alpha)
 	 *   - red:   an integer 0-255 or a percentage 0-100%
@@ -1029,4 +1077,8 @@ class UIDefaultsLoader
 			LoggingFacade.INSTANCE.logSevere( "FlatLaf: '" + uiKey + "' not found in UI defaults.", null );
 		return value;
 	}
+
+	private static void throwMissingParametersException( String value ) {
+		throw new IllegalArgumentException( "missing parameters in function '" + value + "'" );
+	}
 }

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatCompletionProvider.java

@@ -405,6 +405,13 @@ class FlatCompletionProvider
 			setParameterizedCompletionParams( '(', ",", ')' );
 			setParameterChoicesProvider( this );
 
+			addFunction( "if",
+				"condition", "evaluates to true if: is not \"null\" and is not \"false\" and is not an integer with zero value",
+				"trueValue", "used if condition is true",
+				"falseValue", "used if condition is false" );
+			addFunction( "lazy",
+				"uiKey", "UI key (without leading '$')" );
+
 			addFunction( "rgb",
 				"red", "0-255 or 0-100%",
 				"green", "0-255 or 0-100%",

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemeTokenMaker.java

@@ -51,7 +51,11 @@ public class FlatThemeTokenMaker
 		tokenMap.put( "false", Token.LITERAL_BOOLEAN );
 		tokenMap.put( "true", Token.LITERAL_BOOLEAN );
 
-		// functions
+		// general functions
+		tokenMap.put( "if", TOKEN_FUNCTION );
+		tokenMap.put( "lazy", TOKEN_FUNCTION );
+
+		// color functions
 		tokenMap.put( "rgb", TOKEN_FUNCTION );
 		tokenMap.put( "rgba", TOKEN_FUNCTION );
 		tokenMap.put( "hsl", TOKEN_FUNCTION );
@@ -72,7 +76,6 @@ public class FlatThemeTokenMaker
 		tokenMap.put( "tint", TOKEN_FUNCTION );
 		tokenMap.put( "shade", TOKEN_FUNCTION );
 		tokenMap.put( "contrast", TOKEN_FUNCTION );
-		tokenMap.put( "lazy", TOKEN_FUNCTION );
 
 		// function options
 		tokenMap.put( "relative", Token.RESERVED_WORD );

flatlaf-theme-editor/theme-editor-test.properties

@@ -29,6 +29,24 @@ Prop.true = true
 Prop.var = @var1
 Prop.ref = $Prop.string
 
+Prop.ifNotNull = if(#000,#0f0,#dfd)
+Prop.ifNull = if(null,#0f0,#dfd)
+Prop.ifTrue = if(true,#0f0,#dfd)
+Prop.ifFalse = if(false,#0f0,#dfd)
+Prop.ifOne = if(1,#0f0,#dfd)
+Prop.ifZero = if(0,#0f0,#dfd)
+@varTrue = true
+@varFalse = false
+@varTrueValue = #0f0
+@varFalseValue = #dfd
+Prop.ifVarTrue = if(@varTrue,@varTrueValue,@varFalseValue)
+Prop.ifVarFalse = if(@varFalse,@varTrueValue,@varFalseValue)
+Prop.ifTrueColorFunc = if(true,lighten(#f00,20%),darken(#f00,20%))
+Prop.ifFalseColorFunc = if(false,lighten(#f00,20%),darken(#f00,20%))
+Prop.ifUndefinedVar = if(@undefinedVar,#0f0,#dfd)
+Prop.ifUndefinedProp = if($undefinedProp,#0f0,#dfd)
+Prop.ifColor = lighten(if(#000,#0f0,#dfd), 10%)
+Prop.ifColorVar = lighten(if(@varTrue,@varTrueValue,@varFalseValue), 10%)
 Prop.lazy = lazy(Prop.string)
 
 Prop.colorFunc1 = rgb(12,34,56)