fix: jbang provider accepted invalid JDK folders

src/main/java/dev/jbang/devkitman/jdkproviders/JBangJdkProvider.java

@@ -88,7 +88,7 @@ protected boolean acceptFolder(@NonNull Path jdkFolder) {
 		// We additionally allow folders that are named with a number
 		// (e.g. "11", "17", etc.) for backwards compatibility with older
 		// JBang versions
-		return (super.acceptFolder(jdkFolder) && isValidId(jdkFolder.getFileName().toString())
+		return super.acceptFolder(jdkFolder) && (isValidId(jdkFolder.getFileName().toString())
 				|| JavaUtils.parseToInt(jdkFolder.getFileName().toString(), 0) > 0)
 				&& !FileUtils.isLink(jdkFolder);
 	}

src/test/java/dev/jbang/devkitman/jdkproviders/JBangJdkProviderTest.java

@@ -0,0 +1,77 @@
+package dev.jbang.devkitman.jdkproviders;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.notNullValue;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import org.hamcrest.Matchers;
+import org.junit.jupiter.api.Test;
+
+import dev.jbang.devkitman.BaseTest;
+import dev.jbang.devkitman.Jdk;
+import dev.jbang.devkitman.util.FileUtils;
+
+public class JBangJdkProviderTest extends BaseTest {
+
+	@Test
+	void testJBangProviderIgnoresNumericLinkWithoutJavac() throws IOException {
+		// Create a directory without javac
+		Path jreHome = config.cachePath().resolve("jre17");
+		initMockJdkDir(jreHome, "17.0.7", "JAVA_RUNTIME_VERSION", false, false, false, false);
+
+		// Create a symbolic link with numeric name pointing to the directory without
+		// javac
+		Path numericLink = config.installPath().resolve("17");
+		FileUtils.createLink(numericLink, jreHome);
+
+		// Verify the link exists and points to a directory without javac
+		assertThat("Link should exist", Files.exists(numericLink), Matchers.is(true));
+		assertThat("Target should not have javac", FileUtils.isLink(numericLink), Matchers.is(true));
+
+		// The JBang provider should not accept this folder since it has no javac
+		JBangJdkProvider provider = createJbangProvider();
+		Jdk.InstalledJdk jdk = provider.getInstalledByPath(numericLink);
+
+		// This should be null because the link points to a directory without javac
+		assertThat("Numeric link without javac should not be accepted", jdk, Matchers.nullValue());
+	}
+
+	@Test
+	void testJBangProviderAcceptsNumericFolderWithJavac() throws IOException {
+		// Create a directory with numeric name and javac (backwards compatibility
+		// scenario)
+		Path jreHome = config.installPath().resolve("17");
+		initMockJdkDir(jreHome, "17.0.7", "JAVA_VERSION", true, false, false, false);
+
+		// Verify it's not a link
+		assertThat("Should be a regular folder", FileUtils.isLink(jreHome), Matchers.is(false));
+
+		// The JBang provider should accept this folder since it has javac
+		JBangJdkProvider provider = createJbangProvider();
+		Jdk.InstalledJdk jdk = provider.getInstalledByPath(jreHome);
+
+		assertThat("Numeric folder with javac should be accepted", jdk, notNullValue());
+		assertThat(jdk.version(), Matchers.is("17.0.7"));
+	}
+
+	@Test
+	void testJBangProviderIgnoresNumericFolderWithoutJavac() throws IOException {
+		// Create a directory with numeric name but without javac
+		Path jreHome = config.installPath().resolve("17");
+		initMockJdkDir(jreHome, "17.0.7", "JAVA_RUNTIME_VERSION", false, false, false, false);
+
+		// Verify it's not a link and doesn't have javac
+		assertThat("Should be a regular folder", FileUtils.isLink(jreHome), Matchers.is(false));
+
+		// The JBang provider should not accept this folder since it has no javac
+		JBangJdkProvider provider = createJbangProvider();
+		Jdk.InstalledJdk jdk = provider.getInstalledByPath(jreHome);
+
+		// This should be null because the folder has no javac, despite having a numeric
+		// name
+		assertThat("Numeric folder without javac should not be accepted", jdk, Matchers.nullValue());
+	}
+}