feat: add support for Add-Reads and SplashScreen-Image manifest attributes

Extends manifest attribute support for jars beyond PR jbangdev#2439 to handle
Add-Reads module dependencies and SplashScreen-Image extraction.

Changes:
- Add Project.ATTR_ADD_READS and Project.ATTR_SPLASH_SCREEN_IMAGE constants
- Import Add-Reads and SplashScreen-Image attributes from jar manifests
- Process Add-Reads: converts to --add-reads JVM flags (Java 9+)
- Process SplashScreen-Image: extracts image and passes -splash flag
- Fix KeyValue.of() to support values containing '=' signs

Add-Reads implementation:
- Parses space-separated module dependencies (e.g., "mod1=mod2 mod3=mod4")
- Generates --add-reads flags for each dependency pair
- Version-gated for Java 9+ with runAsModule check

SplashScreen-Image implementation:
- Extracts splash image from jar to <jarPath>.splash.<ext> in cache
- Smart caching: only re-extracts if jar is newer than cached image
- Fails gracefully with warnings (never breaks the build)
- Adds -splash:<path> flag before other JVM options

KeyValue parser fix:
- Changed split("=") to split("=", 2) to handle values with '='
- Enables manifest directives like //MANIFEST Add-Reads=mod1=mod2

This builds on PR jbangdev#2439's copyManifestAttribute() and
addAllUnnamedManifestOptions() patterns.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: maxandersen

src/main/java/dev/jbang/source/Project.java

@@ -57,6 +57,8 @@ public class Project {
 	public static final String ATTR_ADD_EXPORTS = "Add-Exports";
 	public static final String ATTR_ADD_OPENS = "Add-Opens";
 	public static final String ATTR_ENABLE_NATIVE_ACCESS = "Enable-Native-Access";
+	public static final String ATTR_ADD_READS = "Add-Reads";
+	public static final String ATTR_SPLASH_SCREEN_IMAGE = "SplashScreen-Image";
 
 	public enum BuildFile {
 		jbang("build.jbang");

src/main/java/dev/jbang/source/ProjectBuilder.java

@@ -447,6 +447,8 @@ private Project importJarMetadata(Project prj, boolean importModuleName) {
 					copyManifestAttribute(attrs, prj, Project.ATTR_ADD_EXPORTS);
 					copyManifestAttribute(attrs, prj, Project.ATTR_ADD_OPENS);
 					copyManifestAttribute(attrs, prj, Project.ATTR_ENABLE_NATIVE_ACCESS);
+					copyManifestAttribute(attrs, prj, Project.ATTR_ADD_READS);
+					copyManifestAttribute(attrs, prj, Project.ATTR_SPLASH_SCREEN_IMAGE);
 
 				}
 

src/main/java/dev/jbang/source/generators/JarCmdGenerator.java

@@ -5,6 +5,7 @@
 import java.net.ServerSocket;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -98,11 +99,32 @@ protected List<String> generateCommandLineList() throws IOException {
 		Jdk jdk = project.projectJdk();
 		String javacmd = JavaUtil.resolveInJavaHome("java", jdk);
 
+		// Handle splash screen - extract image from jar and pass -splash:path
+		String splashImage = project.getManifestAttributes().get(Project.ATTR_SPLASH_SCREEN_IMAGE);
+		if (splashImage != null) {
+			Path jarPath = ctx.getJarFile();
+			if (jarPath != null && Files.exists(jarPath)) {
+				Path splashPath = extractSplashImage(jarPath, splashImage);
+				if (splashPath != null) {
+					optionalArgs.add("-splash:" + splashPath.toAbsolutePath());
+				}
+			}
+		}
+
 		if (!runAsModule && jdk.majorVersion() >= 9) {
 			addAllUnnamedManifestOptions(optionalArgs, project.getManifestAttributes().get(Project.ATTR_ADD_OPENS),
 					"--add-opens=");
 			addAllUnnamedManifestOptions(optionalArgs, project.getManifestAttributes().get(Project.ATTR_ADD_EXPORTS),
 					"--add-exports=");
+
+			// Add-Reads: module1=module2 module3=module4 → --add-reads=module1=module2
+			// --add-reads=module3=module4
+			String addReads = project.getManifestAttributes().get(Project.ATTR_ADD_READS);
+			if (addReads != null) {
+				Arrays.stream(addReads.trim().split("\\s+"))
+					.filter(val -> !val.isEmpty())
+					.forEach(val -> optionalArgs.add("--add-reads=" + val));
+			}
 		}
 
 		if (!runAsModule && jdk.majorVersion() >= 22) {
@@ -330,4 +352,43 @@ private static void addPropertyFlags(Map<String, String> properties, String def,
 		properties.forEach((k, e) -> result.add(def + k + "=" + e));
 	}
 
+	/**
+	 * Extract splash screen image from jar to cache directory for use with -splash
+	 * flag.
+	 *
+	 * @param jarPath   Path to the jar file
+	 * @param imagePath Path to image inside jar (from manifest SplashScreen-Image
+	 *                  attribute)
+	 * @return Path to extracted image, or null if extraction failed
+	 */
+	private static Path extractSplashImage(Path jarPath, String imagePath) {
+		try (java.util.jar.JarFile jar = new java.util.jar.JarFile(jarPath.toFile())) {
+			java.util.jar.JarEntry entry = jar.getJarEntry(imagePath);
+			if (entry == null) {
+				Util.warnMsg("Splash screen image not found in jar: " + imagePath);
+				return null;
+			}
+
+			// Extract to jar's directory with unique name
+			String jarName = jarPath.getFileName().toString();
+			int extIndex = imagePath.lastIndexOf('.');
+			String imageExt = (extIndex > 0) ? imagePath.substring(extIndex) : "";
+			Path targetPath = jarPath.getParent().resolve(jarName + ".splash" + imageExt);
+
+			// Extract if not cached or jar is newer
+			if (!Files.exists(targetPath) ||
+					Files.getLastModifiedTime(jarPath).compareTo(Files.getLastModifiedTime(targetPath)) > 0) {
+				try (InputStream is = jar.getInputStream(entry)) {
+					Files.copy(is, targetPath, StandardCopyOption.REPLACE_EXISTING);
+				}
+				Util.verboseMsg("Extracted splash screen to: " + targetPath);
+			}
+
+			return targetPath;
+		} catch (IOException e) {
+			Util.warnMsg("Failed to extract splash screen: " + e.getMessage());
+			return null;
+		}
+	}
+
 }

src/main/java/dev/jbang/source/parser/KeyValue.java

@@ -18,7 +18,7 @@ public String getValue() {
 	}
 
 	public static KeyValue of(String line) {
-		String[] split = line.split("=");
+		String[] split = line.split("=", 2);
 		String key;
 		String value = null;