fix(jdbc): fall back to unscoped schema listing for HANA

Closes #11209

agents/common/src/main/java/com/dbx/agent/StandardJdbcMetadata.java

@@ -65,6 +65,15 @@ public final class StandardJdbcMetadata {
                 } catch (Exception | AbstractMethodError ignored) {
                 }
             }
+            // HANA's databaseName (for example HXE) is not a JDBC catalog.
+            // Its driver returns no rows, rather than throwing, for that catalog.
+            // Retry without it before falling back to only the current schema.
+            if (names.isEmpty() && catalog != null && profile.getCatalogFallbackEnabled()) {
+                try {
+                    appendSchemas(names, meta.getSchemas(null, null));
+                } catch (Exception | AbstractMethodError ignored) {
+                }
+            }
             try {
                 addNonBlank(names, conn.getSchema());
             } catch (Exception | AbstractMethodError ignored) {

agents/common/src/test/java/com/dbx/agent/StandardJdbcMetadataTest.java

@@ -10,12 +10,14 @@ import java.lang.reflect.Proxy;
 import java.sql.Connection;
 import java.sql.DatabaseMetaData;
 import java.sql.ResultSet;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -48,10 +50,12 @@ class StandardJdbcMetadataTest {
     @Test
     void scopesSchemasToTheConnectionCatalog() {
         AtomicReference<Object[]> capturedArgs = new AtomicReference<>();
+        AtomicInteger schemaCalls = new AtomicInteger();
         DatabaseMetaData meta = proxy(DatabaseMetaData.class, new MethodHandler() {
             @Override
             public Object handle(Method method, Object[] args) {
                 if ("getSchemas".equals(method.getName())) {
+                    schemaCalls.incrementAndGet();
                     capturedArgs.set(args);
                     return rows(row("TABLE_SCHEM", "APP"));
                 }
@@ -74,6 +78,57 @@ class StandardJdbcMetadataTest {
         assertEquals(List.of("APP"), StandardJdbcMetadata.INSTANCE.listSchemas(conn, profile, "initial_catalog"));
         assertEquals("regular_catalog", capturedArgs.get()[0]);
         assertEquals(null, capturedArgs.get()[1]);
+        assertEquals(1, schemaCalls.get());
+    }
+
+    @ParameterizedTest
+    @CsvSource({"false, false, true", "true, false, true", "false, true, true", "false, false, false"})
+    void retriesEmptyCatalogSchemasBeforeAddingCurrentSchema(boolean fallbackFails, boolean currentCatalog, boolean fallbackEnabled) {
+        List<String> catalogs = new ArrayList<>();
+        DatabaseMetaData meta = proxy(DatabaseMetaData.class, new MethodHandler() {
+            @Override
+            public Object handle(Method method, Object[] args) {
+                if ("getSchemas".equals(method.getName())) {
+                    String catalog = (String) args[0];
+                    catalogs.add(catalog);
+                    if (catalog != null) {
+                        return rows();
+                    }
+                    if (fallbackFails) {
+                        throw new UnsupportedOperationException("Unscoped schemas unavailable");
+                    }
+                    return rows(row("TABLE_SCHEM", "DBX_USER"), row("TABLE_SCHEM", "DBX_DEMO"), row("TABLE_SCHEM", "SYS"));
+                }
+                return defaultValue(method.getReturnType());
+            }
+        });
+        Connection conn = proxy(Connection.class, new MethodHandler() {
+            @Override
+            public Object handle(Method method, Object[] args) {
+                if ("getMetaData".equals(method.getName())) {
+                    return meta;
+                }
+                if ("getCatalog".equals(method.getName())) {
+                    return currentCatalog ? "HXE" : null;
+                }
+                if ("getSchema".equals(method.getName())) {
+                    return "DBX_USER";
+                }
+                return defaultValue(method.getReturnType());
+            }
+        });
+
+        JdbcAgentProfile effectiveProfile = fallbackEnabled ? profile : new JdbcAgentProfile("example.Driver", "jdbc:example:") {
+            @Override
+            public boolean getCatalogFallbackEnabled() {
+                return false;
+            }
+        };
+        assertEquals(
+            fallbackFails || !fallbackEnabled ? List.of("DBX_USER") : List.of("DBX_DEMO", "DBX_USER"),
+            StandardJdbcMetadata.INSTANCE.listSchemas(conn, effectiveProfile, currentCatalog ? "initial_catalog" : "HXE")
+        );
+        assertEquals(fallbackEnabled ? Arrays.asList("HXE", null) : List.of("HXE"), catalogs);
     }
 
     @Test