feat!: define default index name and return IndexMetadata after building index

java/lance-jni/src/blocking_dataset.rs

@@ -730,20 +730,20 @@ fn inner_release_native_dataset(env: &mut JNIEnv, obj: JObject) -> Result<()> {
 }
 
 #[no_mangle]
-pub extern "system" fn Java_org_lance_Dataset_nativeCreateIndex(
-    mut env: JNIEnv,
-    java_dataset: JObject,
-    columns_jobj: JObject, // List<String>
+pub extern "system" fn Java_org_lance_Dataset_nativeCreateIndex<'local>(
+    mut env: JNIEnv<'local>,
+    java_dataset: JObject<'local>,
+    columns_jobj: JObject<'local>, // List<String>
     index_type_code_jobj: jint,
-    name_jobj: JObject,              // Optional<String>
-    params_jobj: JObject,            // IndexParams
-    replace_jobj: jboolean,          // replace
-    train_jobj: jboolean,            // train
-    fragments_jobj: JObject,         // List<Integer>
-    index_uuid_jobj: JObject,        // String
-    arrow_stream_addr_jobj: JObject, // Optional<Long>
-) {
-    ok_or_throw_without_return!(
+    name_jobj: JObject<'local>,              // Optional<String>
+    params_jobj: JObject<'local>,            // IndexParams
+    replace_jobj: jboolean,                  // replace
+    train_jobj: jboolean,                    // train
+    fragments_jobj: JObject<'local>,         // List<Integer>
+    index_uuid_jobj: JObject<'local>,        // String
+    arrow_stream_addr_jobj: JObject<'local>, // Optional<Long>
+) -> JObject<'local> {
+    ok_or_throw!(
         env,
         inner_create_index(
             &mut env,
@@ -758,23 +758,23 @@ pub extern "system" fn Java_org_lance_Dataset_nativeCreateIndex(
             index_uuid_jobj,
             arrow_stream_addr_jobj,
         )
-    );
+    )
 }
 
 #[allow(clippy::too_many_arguments)]
-fn inner_create_index(
-    env: &mut JNIEnv,
-    java_dataset: JObject,
-    columns_jobj: JObject, // List<String>
+fn inner_create_index<'local>(
+    env: &mut JNIEnv<'local>,
+    java_dataset: JObject<'local>,
+    columns_jobj: JObject<'local>, // List<String>
     index_type_code_jobj: jint,
-    name_jobj: JObject,              // Optional<String>
-    params_jobj: JObject,            // IndexParams
-    replace_jobj: jboolean,          // replace
-    train_jobj: jboolean,            // train
-    fragments_jobj: JObject,         // Optional<List<String>>
-    index_uuid_jobj: JObject,        // Optional<String>
-    arrow_stream_addr_jobj: JObject, // Optional<Long>
-) -> Result<()> {
+    name_jobj: JObject<'local>,              // Optional<String>
+    params_jobj: JObject<'local>,            // IndexParams
+    replace_jobj: jboolean,                  // replace
+    train_jobj: jboolean,                    // train
+    fragments_jobj: JObject<'local>,         // Optional<List<String>>
+    index_uuid_jobj: JObject<'local>,        // Optional<String>
+    arrow_stream_addr_jobj: JObject<'local>, // Optional<Long>
+) -> Result<JObject<'local>> {
     let columns = env.get_strings(&columns_jobj)?;
     let index_type = IndexType::try_from(index_type_code_jobj)?;
     let name = env.get_string_opt(&name_jobj)?;
@@ -837,38 +837,43 @@ fn inner_create_index(
     };
 
     let params = params_result?;
-    let mut dataset_guard =
-        unsafe { env.get_rust_field::<_, _, BlockingDataset>(java_dataset, NATIVE_DATASET) }?;
 
-    let mut index_builder = dataset_guard
-        .inner
-        .create_index_builder(&columns_slice, index_type, params.as_ref())
-        .replace(replace)
-        .train(train);
+    // Execute index creation in a block to ensure dataset_guard is dropped
+    // before we call into_java (which needs to borrow env again)
+    let index_metadata = {
+        let mut dataset_guard =
+            unsafe { env.get_rust_field::<_, _, BlockingDataset>(java_dataset, NATIVE_DATASET) }?;
+
+        let mut index_builder = dataset_guard
+            .inner
+            .create_index_builder(&columns_slice, index_type, params.as_ref())
+            .replace(replace)
+            .train(train);
 
-    if let Some(name) = name {
-        index_builder = index_builder.name(name);
-    }
+        if let Some(name) = name {
+            index_builder = index_builder.name(name);
+        }
 
-    if let Some(fragment_ids) = fragment_ids {
-        index_builder = index_builder.fragments(fragment_ids);
-    }
+        if let Some(fragment_ids) = fragment_ids {
+            index_builder = index_builder.fragments(fragment_ids);
+        }
 
-    if let Some(index_uuid) = index_uuid {
-        index_builder = index_builder.index_uuid(index_uuid);
-    }
+        if let Some(index_uuid) = index_uuid {
+            index_builder = index_builder.index_uuid(index_uuid);
+        }
 
-    if let Some(reader) = batch_reader {
-        index_builder = index_builder.preprocessed_data(Box::new(reader));
-    }
+        if let Some(reader) = batch_reader {
+            index_builder = index_builder.preprocessed_data(Box::new(reader));
+        }
 
-    if skip_commit {
-        RT.block_on(index_builder.execute_uncommitted())?;
-    } else {
-        RT.block_on(index_builder.into_future())?
-    }
+        if skip_commit {
+            RT.block_on(index_builder.execute_uncommitted())?
+        } else {
+            RT.block_on(index_builder.into_future())?
+        }
+    };
 
-    Ok(())
+    (&index_metadata).into_java(env)
 }
 
 fn should_skip_commit(index_type: IndexType, params_opt: &Option<String>) -> Result<bool> {

java/src/main/java/org/lance/Dataset.java

@@ -765,16 +765,17 @@ public void restore() {
    * @param name the name of the created index
    * @param params index params
    * @param replace whether to replace the existing index
+   * @return the metadata of the created index
    * @deprecated please use {@link Dataset#createIndex(IndexOptions)} instead.
    */
   @Deprecated
-  public void createIndex(
+  public Index createIndex(
       List<String> columns,
       IndexType indexType,
       Optional<String> name,
       IndexParams params,
       boolean replace) {
-    createIndex(
+    return createIndex(
         IndexOptions.builder(columns, indexType, params)
             .replace(replace)
             .withIndexName(name.orElse(null))
@@ -785,11 +786,12 @@ public void createIndex(
    * Creates a new index on the dataset.
    *
    * @param options options for building index
+   * @return the metadata of the created index
    */
-  public void createIndex(IndexOptions options) {
+  public Index createIndex(IndexOptions options) {
     try (LockManager.ReadLock readLock = lockManager.acquireReadLock()) {
       Preconditions.checkArgument(nativeDatasetHandle != 0, "Dataset is closed");
-      nativeCreateIndex(
+      return nativeCreateIndex(
           options.getColumns(),
           options.getIndexType().ordinal(),
           options.getIndexName(),
@@ -802,7 +804,7 @@ public void createIndex(IndexOptions options) {
     }
   }
 
-  private native void nativeCreateIndex(
+  private native Index nativeCreateIndex(
       List<String> columns,
       int indexTypeCode,
       Optional<String> name,

java/src/test/java/org/lance/ScalarIndexTest.java

@@ -53,6 +53,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class ScalarIndexTest {
@@ -79,12 +80,18 @@ public void testCreateBTreeIndex() throws Exception {
         IndexParams indexParams = IndexParams.builder().setScalarIndexParams(scalarParams).build();
 
         // Create BTree index on 'id' column
-        dataset.createIndex(
-            Collections.singletonList("id"),
-            IndexType.BTREE,
-            Optional.of("btree_id_index"),
-            indexParams,
-            true);
+        Index index =
+            dataset.createIndex(
+                Collections.singletonList("id"),
+                IndexType.BTREE,
+                Optional.of("btree_id_index"),
+                indexParams,
+                true);
+
+        // Verify the returned Index object
+        assertEquals("btree_id_index", index.name());
+        assertNotNull(index.uuid());
+        assertFalse(index.fields().isEmpty());
 
         // Verify index was created and is in the list
         assertTrue(
@@ -343,12 +350,17 @@ public void testCreateZonemapIndex() throws Exception {
         IndexParams indexParams = IndexParams.builder().setScalarIndexParams(scalarParams).build();
 
         // Create Zonemap index on 'value' column
-        dataset.createIndex(
-            Collections.singletonList("value"),
-            IndexType.ZONEMAP,
-            Optional.of("zonemap_value_index"),
-            indexParams,
-            true);
+        Index index =
+            dataset.createIndex(
+                Collections.singletonList("value"),
+                IndexType.ZONEMAP,
+                Optional.of("zonemap_value_index"),
+                indexParams,
+                true);
+
+        // Verify the returned Index object
+        assertEquals("zonemap_value_index", index.name());
+        assertNotNull(index.uuid());
 
         // Verify index was created
         assertTrue(

python/python/tests/test_column_names.py

@@ -87,6 +87,7 @@ def test_scalar_index_with_mixed_case(self, mixed_case_dataset):
         indices = mixed_case_dataset.list_indices()
         assert len(indices) == 1
         assert indices[0]["fields"] == ["userId"]
+        assert indices[0]["name"] == "userId_idx"
 
         # Query using the indexed column
         result = mixed_case_dataset.to_table(filter="userId = 50")
@@ -96,6 +97,9 @@ def test_scalar_index_with_mixed_case(self, mixed_case_dataset):
         plan = mixed_case_dataset.scanner(filter="userId = 50").explain_plan()
         assert "ScalarIndexQuery" in plan
 
+        stats = mixed_case_dataset.stats.index_stats("userId_idx")
+        assert stats["index_type"] == "BTree"
+
     def test_alter_column_with_mixed_case(self, mixed_case_dataset):
         """Altering columns works with mixed-case column names."""
         # alter_columns uses direct schema lookup, not SQL parsing
@@ -347,6 +351,7 @@ def test_scalar_index_with_special_chars(self, special_char_dataset):
         assert len(indices) == 1
         # Field with special chars is returned in quoted format for SQL compatibility
         assert indices[0]["fields"] == ["`user-id`"]
+        assert indices[0]["name"] == "user-id_idx"
 
         # Query using the indexed column (requires backticks in filter)
         result = special_char_dataset.to_table(filter="`user-id` = 50")
@@ -356,6 +361,9 @@ def test_scalar_index_with_special_chars(self, special_char_dataset):
         plan = special_char_dataset.scanner(filter="`user-id` = 50").explain_plan()
         assert "ScalarIndexQuery" in plan
 
+        stats = special_char_dataset.stats.index_stats("user-id_idx")
+        assert stats["index_type"] == "BTree"
+
     def test_alter_column_with_special_chars(self, special_char_dataset):
         """Altering columns works with special character column names."""
         # alter_columns uses direct schema lookup
@@ -455,6 +463,7 @@ def test_scalar_index_with_nested_mixed_case(self, nested_mixed_case_dataset):
         indices = nested_mixed_case_dataset.list_indices()
         assert len(indices) == 1
         assert indices[0]["fields"] == ["MetaData.userId"]
+        assert indices[0]["name"] == "MetaData.userId_idx"
 
         # Query using the indexed column
         result = nested_mixed_case_dataset.to_table(filter="MetaData.userId = 50")
@@ -466,20 +475,27 @@ def test_scalar_index_with_nested_mixed_case(self, nested_mixed_case_dataset):
         ).explain_plan()
         assert "ScalarIndexQuery" in plan
 
+        stats = nested_mixed_case_dataset.stats.index_stats("MetaData.userId_idx")
+        assert stats["index_type"] == "BTree"
+
     def test_scalar_index_on_top_level_mixed_case(self, nested_mixed_case_dataset):
         """Scalar index on top-level mixed-case column works."""
         nested_mixed_case_dataset.create_scalar_index("rowId", index_type="BTREE")
 
         indices = nested_mixed_case_dataset.list_indices()
         assert len(indices) == 1
         assert indices[0]["fields"] == ["rowId"]
+        assert indices[0]["name"] == "rowId_idx"
 
         result = nested_mixed_case_dataset.to_table(filter="rowId = 50")
         assert result.num_rows == 1
 
         plan = nested_mixed_case_dataset.scanner(filter="rowId = 50").explain_plan()
         assert "ScalarIndexQuery" in plan
 
+        stats = nested_mixed_case_dataset.stats.index_stats("rowId_idx")
+        assert stats["index_type"] == "BTree"
+
     def test_scalar_index_with_lowercased_nested_path(self, nested_mixed_case_dataset):
         """Scalar index creation should work even when path is lowercased.
 
@@ -562,6 +578,7 @@ def test_scalar_index_with_nested_special_chars(self, nested_special_char_datase
         assert len(indices) == 1
         # Fields with special chars are returned in quoted format for SQL compatibility
         assert indices[0]["fields"] == ["`meta-data`.`user-id`"]
+        assert indices[0]["name"] == "meta-data.user-id_idx"
 
         # Query using the indexed column (backticks required in filter)
         result = nested_special_char_dataset.to_table(
@@ -575,6 +592,9 @@ def test_scalar_index_with_nested_special_chars(self, nested_special_char_datase
         ).explain_plan()
         assert "ScalarIndexQuery" in plan
 
+        stats = nested_special_char_dataset.stats.index_stats("meta-data.user-id_idx")
+        assert stats["index_type"] == "BTree"
+
     def test_scalar_index_on_top_level_special_chars(self, nested_special_char_dataset):
         """Scalar index on top-level special char column works."""
         nested_special_char_dataset.create_scalar_index("`row-id`", index_type="BTREE")

python/src/dataset.rs

@@ -81,7 +81,7 @@ use lance_index::{
 };
 use lance_io::object_store::ObjectStoreParams;
 use lance_linalg::distance::MetricType;
-use lance_table::format::{BasePath, Fragment};
+use lance_table::format::{BasePath, Fragment, IndexMetadata};
 use lance_table::io::commit::CommitHandler;
 
 use crate::error::PythonErrorExt;
@@ -1809,7 +1809,7 @@ impl Dataset {
         train: Option<bool>,
         storage_options: Option<HashMap<String, String>>,
         kwargs: Option<&Bound<PyDict>>,
-    ) -> PyResult<()> {
+    ) -> PyResult<PyLance<IndexMetadata>> {
         let columns: Vec<&str> = columns.iter().map(|s| &**s).collect();
         let index_type = index_type.to_uppercase();
         let idx_type = match index_type.as_str() {
@@ -1979,19 +1979,21 @@ impl Dataset {
         use std::future::IntoFuture;
 
         // Use execute_uncommitted if fragment_ids is provided, otherwise use execute
-        if has_fragment_ids {
+        let index_metadata = if has_fragment_ids {
             // For fragment-level indexing, use execute_uncommitted
-            let _index_metadata = rt()
+            let index_metadata = rt()
                 .block_on(None, builder.execute_uncommitted())?
                 .infer_error()?;
             // Note: We don't update self.ds here as the index is not committed
+            index_metadata
         } else {
             // For regular indexing, use the standard execute path
-            rt().block_on(None, builder.into_future())?.infer_error()?;
+            let index_metadata = rt().block_on(None, builder.into_future())?.infer_error()?;
             self.ds = Arc::new(new_self);
-        }
+            index_metadata
+        };
 
-        Ok(())
+        Ok(PyLance(index_metadata))
     }
 
     fn drop_index(&mut self, name: &str) -> PyResult<()> {

rust/lance-index/src/traits.rs

@@ -153,14 +153,16 @@ pub trait DatasetIndexExt {
     ///            if not provided, it will auto-generate one.
     ///  - `params`: index parameters.
     ///  - `replace`: replace the existing index if it exists.
+    ///
+    /// Returns the metadata of the created index.
     async fn create_index(
         &mut self,
         columns: &[&str],
         index_type: IndexType,
         name: Option<String>,
         params: &dyn IndexParams,
         replace: bool,
-    ) -> Result<()>;
+    ) -> Result<IndexMetadata>;
 
     /// Drop indices by name.
     ///