Fix build cache miss in runtimeHintsTest task

Prior to this change, a build cache miss would occur in
runtimeHintsTest tasks when executing the build from two different
locations, causing the tasks to re-execute. This was due to an
absolute path to the agent jar being included in the -javaagent
argument supplied to the test JVM process.

This change introduces a RuntimeHintsAgentArgumentProvider allowing
finer grained control over the way Gradle computes the build cache
key. With this change, the contents of the agent jar file are
considered, rather than the absolute file location.

See gh-30838

buildSrc/src/main/java/org/springframework/build/hint/RuntimeHintsAgentPlugin.java

@@ -18,9 +18,16 @@ package org.springframework.build.hint;
 
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
+import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.plugins.JavaPlugin;
+import org.gradle.api.provider.Property;
+import org.gradle.api.tasks.Classpath;
+import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.bundling.Jar;
 import org.gradle.api.tasks.testing.Test;
+import org.gradle.process.CommandLineArgumentProvider;
+
+import java.util.Collections;
 
 /**
  * {@link Plugin} that configures the {@code RuntimeHints} Java agent to test tasks.
@@ -49,10 +56,31 @@ public class RuntimeHintsAgentPlugin implements Plugin<Project> {
 				test.systemProperty("org.graalvm.nativeimage.imagecode", "runtime");
 			});
 			project.afterEvaluate(p -> {
-				Jar jar = project.getRootProject().project("spring-core-test").getTasks().withType(Jar.class).named("jar").get();
-				agentTest.jvmArgs("-javaagent:" + jar.getArchiveFile().get().getAsFile() + "=" + agentExtension.asJavaAgentArgument());
+				agentTest.getJvmArgumentProviders().add(createRuntimeHintsAgentArgumentProvider(project, agentExtension));
 			});
 			project.getTasks().getByName("check", task -> task.dependsOn(agentTest));
 		});
 	}
+
+	private static RuntimeHintsAgentArgumentProvider createRuntimeHintsAgentArgumentProvider(Project project, RuntimeHintsAgentExtension agentExtension) {
+		Jar jar = project.getRootProject().project("spring-core-test").getTasks().withType(Jar.class).named("jar").get();
+		RuntimeHintsAgentArgumentProvider agentArgumentProvider = project.getObjects().newInstance(RuntimeHintsAgentArgumentProvider.class);
+		agentArgumentProvider.getAgentJar().from(jar.getArchiveFile());
+		agentArgumentProvider.getJavaAgentArgument().set(agentExtension.asJavaAgentArgument());
+		return agentArgumentProvider;
+	}
+
+	interface RuntimeHintsAgentArgumentProvider extends CommandLineArgumentProvider {
+
+		@Classpath
+		ConfigurableFileCollection getAgentJar();
+
+		@Input
+		Property<String> getJavaAgentArgument();
+
+		@Override
+		default Iterable<String> asArguments() {
+			return Collections.singleton("-javaagent:" + getAgentJar().getSingleFile() + "=" + getJavaAgentArgument().get());
+		}
+	}
 }