Emit better error messages for jarhell (#76217) (#76299)

When checking for jarhell while loading plugins, exceptions other than jarhell can occur. The wrapped exception message in these cases refers to jarhell failing, but in actuality it was eg a filesystem error. This commit separates the two cases, jarhell failure and other failure.

Co-authored-by: E Bala <balasubramanyam.evani@gmail.com>

server/src/main/java/org/elasticsearch/plugins/PluginsService.java

@@ -607,8 +607,10 @@ static void checkBundleJarHell(Set<URL> classpath, Bundle bundle, Map<String, Se
             Set<URL> union = new HashSet<>(classpath);
             union.addAll(bundle.urls);
             JarHell.checkJarHell(union, logger::debug);
-        } catch (Exception e) {
-            throw new IllegalStateException("failed to load plugin " + bundle.plugin.getName() + " due to jar hell", e);
+        } catch (final IllegalStateException ise) {
+            throw new IllegalStateException("failed to load plugin " + bundle.plugin.getName() + " due to jar hell", ise);
+        } catch (final Exception e) {
+            throw new IllegalStateException("failed to load plugin " + bundle.plugin.getName() + " while checking for jar hell", e);
         }
     }
 

server/src/test/java/org/elasticsearch/plugins/PluginsServiceTests.java

@@ -530,6 +530,26 @@ public void testJarHellDuplicateClassWithCore() throws Exception {
         assertThat(e.getCause().getMessage(), containsString("Level"));
     }
 
+    public void testJarHellWhenExtendedPluginJarNotFound() throws Exception {
+        Path pluginDir = createTempDir();
+        Path pluginJar = pluginDir.resolve("dummy.jar");
+
+        Path otherDir = createTempDir();
+        Path extendedPlugin = otherDir.resolve("extendedDep-not-present.jar");
+
+        PluginInfo info = new PluginInfo("dummy", "desc", "1.0", Version.CURRENT, "1.8",
+            "Dummy", Arrays.asList("extendedPlugin"), false, PluginType.ISOLATED, "", false);
+
+        PluginsService.Bundle bundle = new PluginsService.Bundle(info, pluginDir);
+        Map<String, Set<URL>> transitiveUrls = new HashMap<>();
+        transitiveUrls.put("extendedPlugin", Collections.singleton(extendedPlugin.toUri().toURL()));
+
+        IllegalStateException e = expectThrows(IllegalStateException.class, () ->
+            PluginsService.checkBundleJarHell(JarHell.parseClassPath(), bundle, transitiveUrls));
+
+        assertEquals("failed to load plugin dummy while checking for jar hell", e.getMessage());
+    }
+
     public void testJarHellDuplicateClassWithDep() throws Exception {
         Path pluginDir = createTempDir();
         Path pluginJar = pluginDir.resolve("plugin.jar");