Fix regression: restore binary javaLauncher convention for toolchain detection

The previous change removed the per-binary javaLauncher convention wiring (nativeImages.configureEach(options -> options.getJavaLauncher().convention(defaultJavaLauncher))), breaking graalvmNative.binaries.main.javaLauncher resolution and NativeImageOptionsTest ('toolchain defaults to the current Java version').

Restore the convention and resolve defaultJavaLauncher directly to the toolchain launcher when toolchain detection is enabled. Whether the toolchain actually contains native-image is decided at build time by NativeImageExecutableLocator, which falls back to GRAALVM_HOME — so the convention stays queryable while the explicit-vs-convention launcher feature is preserved.

Author: vpelikh

native-gradle-plugin/src/main/java/org/graalvm/buildtools/gradle/internal/DefaultGraalVmExtension.java

@@ -63,8 +63,6 @@
 
 import java.io.File;
 
-import static org.graalvm.buildtools.utils.SharedConstants.NATIVE_IMAGE_EXE;
-
 public abstract class DefaultGraalVmExtension implements GraalVMExtension {
     private final transient NamedDomainObjectContainer<NativeImageOptions> nativeImages;
     private final transient NativeImagePlugin plugin;
@@ -80,6 +78,9 @@ public DefaultGraalVmExtension(NamedDomainObjectContainer<NativeImageOptions> na
         this.project = project;
         this.defaultJavaLauncher = project.getObjects().property(JavaLauncher.class);
         getToolchainDetection().convention(false);
+        // Every binary exposes a javaLauncher convention so graalvmNative.binaries.main.javaLauncher
+        // is always resolvable (e.g. its metadata.languageVersion) when toolchain detection is on. §FS-native-invocation.1.5
+        nativeImages.configureEach(options -> options.getJavaLauncher().convention(defaultJavaLauncher));
         getTestSupport().convention(true);
         AgentOptions agentOpts = getAgent();
         agentOpts.getDefaultMode().convention("standard");
@@ -108,26 +109,14 @@ private void configureToolchain() {
                     if (toolchainService == null) {
                         return null;
                     }
-                    // Probe the resolved toolchain for native-image before using it.
-                    // If native-image is absent, return null so the native-image locator
-                    // falls back to the Gradle JVM (java.home) per §FS-native-invocation.1.5.
+                    // Resolve the toolchain launcher for the configured Java toolchain.
+                    // This keeps graalvmNative.binaries.main.javaLauncher queryable (e.g. its
+                    // metadata.languageVersion) whenever toolchain detection is enabled.
+                    // Whether the toolchain actually contains native-image is decided at build
+                    // time by NativeImageExecutableLocator, which falls back to GRAALVM_HOME
+                    // when the launcher's installation lacks it. §FS-native-invocation.1.5
                     JavaPluginExtension javaConvention = project.getExtensions().getByType(JavaPluginExtension.class);
-                    Provider<JavaLauncher> javaToolchainLauncher = toolchainService.launcherFor(javaConvention.getToolchain());
-                    // Verify toolchain contains native-image by probing it
-                    Provider<JavaLauncher> probeResult = javaToolchainLauncher.map(l -> {
-                        try {
-                            File nativeImage = l.getMetadata().getInstallationPath().file("bin/" + NATIVE_IMAGE_EXE).getAsFile();
-                            if (nativeImage.exists()) {
-                                return l;
-                            }
-                            // native-image not found; return null so the locator falls back to the Gradle JVM (java.home)
-                            return null;
-                        } catch (Exception e) {
-                            // Probe failed; return null so the locator falls back to the Gradle JVM (java.home)
-                            return null;
-                        }
-                    });
-                    return probeResult;
+                    return toolchainService.launcherFor(javaConvention.getToolchain());
                 })
         );
     }