Allow additional JVM args when running tests via toolchain

See gh-27089

buildSrc/src/main/java/org/springframework/boot/build/toolchain/ToolchainExtension.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.build.toolchain;
 
 import org.gradle.api.Project;
+import org.gradle.api.provider.ListProperty;
 import org.gradle.api.provider.Property;
 import org.gradle.jvm.toolchain.JavaLanguageVersion;
 
@@ -29,10 +30,13 @@ public class ToolchainExtension {
 
 	private final Property<JavaLanguageVersion> maximumCompatibleJavaVersion;
 
+	private final ListProperty<String> testJvmArgs;
+
 	private final JavaLanguageVersion javaVersion;
 
 	public ToolchainExtension(Project project) {
 		this.maximumCompatibleJavaVersion = project.getObjects().property(JavaLanguageVersion.class);
+		this.testJvmArgs = project.getObjects().listProperty(String.class);
 		String toolchainVersion = (String) project.findProperty("toolchainVersion");
 		this.javaVersion = (toolchainVersion != null) ? JavaLanguageVersion.of(toolchainVersion) : null;
 	}
@@ -41,6 +45,10 @@ public class ToolchainExtension {
 		return this.maximumCompatibleJavaVersion;
 	}
 
+	public ListProperty<String> getTestJvmArgs() {
+		return this.testJvmArgs;
+	}
+
 	JavaLanguageVersion getJavaVersion() {
 		return this.javaVersion;
 	}

buildSrc/src/main/java/org/springframework/boot/build/toolchain/ToolchainPlugin.java

@@ -16,9 +16,6 @@
 
 package org.springframework.boot.build.toolchain;
 
-import java.util.Collections;
-import java.util.List;
-
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.plugins.JavaPluginExtension;
@@ -56,7 +53,7 @@ public class ToolchainPlugin implements Plugin<Project> {
 			JavaToolchainSpec toolchainSpec = project.getExtensions().getByType(JavaPluginExtension.class)
 					.getToolchain();
 			toolchainSpec.getLanguageVersion().set(toolchain.getJavaVersion());
-			configureTestToolchain(project);
+			configureTestToolchain(project, toolchain);
 		}
 	}
 
@@ -71,11 +68,11 @@ public class ToolchainPlugin implements Plugin<Project> {
 		project.getTasks().withType(Test.class, (task) -> task.setEnabled(false));
 	}
 
-	private void configureTestToolchain(Project project) {
-		project.getTasks().withType(Test.class, (test) -> {
-			List<String> arguments = Collections.singletonList("--illegal-access=warn");
-			test.jvmArgs(arguments);
-		});
+	private void configureTestToolchain(Project project, ToolchainExtension toolchain) {
+		if (!toolchain.getTestJvmArgs().isPresent()) {
+			return;
+		}
+		project.getTasks().withType(Test.class, (test) -> test.jvmArgs(toolchain.getTestJvmArgs().get()));
 	}
 
 }

spring-boot-project/spring-boot/build.gradle

@@ -9,6 +9,10 @@ plugins {
 
 description = "Spring Boot"
 
+toolchain {
+	testJvmArgs.add("--add-opens=java.base/java.net=ALL-UNNAMED")
+}
+
 def tomcatConfigProperties = "$buildDir/tomcat-config-properties"
 
 configurations {