[SPARK-16975][SQL] Column-partition path starting '_' should be handled correctly

## What changes were proposed in this pull request?

Currently, Spark ignores path names starting with underscore `_` and `.`. This causes read-failures for the column-partitioned file data sources whose partition column names starts from '_', e.g. `_col`.

**Before**
```scala
scala> spark.range(10).withColumn("_locality_code", $"id").write.partitionBy("_locality_code").save("/tmp/parquet")
scala> spark.read.parquet("/tmp/parquet")
org.apache.spark.sql.AnalysisException: Unable to infer schema for ParquetFormat at /tmp/parquet20. It must be specified manually;
```

**After**
```scala
scala> spark.range(10).withColumn("_locality_code", $"id").write.partitionBy("_locality_code").save("/tmp/parquet")
scala> spark.read.parquet("/tmp/parquet")
res2: org.apache.spark.sql.DataFrame = [id: bigint, _locality_code: int]
```

## How was this patch tested?

Pass the Jenkins with a new test case.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #14585 from dongjoon-hyun/SPARK-16975-PARQUET.

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
index eac588fff2..4fcde58833 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
@@ -17,6 +17,7 @@
 
 package org.apache.spark.sql
 
+import java.io.File
 import java.math.MathContext
 import java.sql.{Date, Timestamp}
 
@@ -2637,6 +2638,14 @@ class SQLQuerySuite extends QueryTest with SharedSQLContext {
     }
   }
 
+  test("SPARK-16975: Column-partition path starting '_' should be handled correctly") {
+    withTempDir { dir =>
+      val parquetDir = new File(dir, "parquet").getCanonicalPath
+      spark.range(10).withColumn("_col", $"id").write.partitionBy("_col").save(parquetDir)
+      spark.read.parquet(parquetDir)
+    }
+  }
+
   test("SPARK-16644: Aggregate should not put aggregate expressions to constraints") {
     withTable("tbl") {
       sql("CREATE TABLE tbl(a INT, b INT) USING parquet")