Github user rdblue commented on a diff in the pull request:
https://github.com/apache/spark/pull/19136#discussion_r137587367
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/SchemaRequiredDataSourceV2.java
---
@@ -0,0 +1,42 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.sources.v2;
+
+import org.apache.spark.sql.sources.v2.reader.DataSourceV2Reader;
+import org.apache.spark.sql.types.StructType;
+
+/**
+ * A variant of `DataSourceV2` which requires users to provide a schema
when reading data. A data
+ * source can inherit both `DataSourceV2` and `SchemaRequiredDataSourceV2`
if it supports both schema
+ * inference and user-specified schemas.
+ */
+public interface SchemaRequiredDataSourceV2 {
+
+ /**
+ * Create a `DataSourceV2Reader` to scan the data for this data source.
+ *
+ * @param schema the full schema of this data source reader. Full schema
usually maps to the
+ * physical schema of the underlying storage of this data
source reader, e.g.
+ * parquet files, JDBC tables, etc, while this reader may
not read data with full
--- End diff --
Maybe update the doc here, since JDBC sources and Parquet files probably
shouldn't implement this. CSV and JSON are the examples that come to mind for
sources that require a schema.
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