Register schema_of_csv and adding SQL tests

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala

@@ -532,7 +532,8 @@ object FunctionRegistry {
     castAlias("string", StringType),
 
     // csv
-    expression[CsvToStructs]("from_csv")
+    expression[CsvToStructs]("from_csv"),
+    expression[SchemaOfCsv]("schema_of_csv")
   )
 
   val builtin: SimpleFunctionRegistry = {

sql/core/src/test/resources/sql-tests/inputs/csv-functions.sql

@@ -10,3 +10,7 @@ select from_csv('1', 'a InvalidType');
 select from_csv('1', 'a INT', named_struct('mode', 'PERMISSIVE'));
 select from_csv('1', 'a INT', map('mode', 1));
 select from_csv();
+
+-- infer schema of json literal
+select schema_of_csv('1,abc');
+select schema_of_csv('1|abc', map('delimiter', '|'));

sql/core/src/test/resources/sql-tests/results/csv-functions.sql.out

@@ -1,5 +1,5 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 10
+-- Number of queries: 12
 
 
 -- !query 0
@@ -102,3 +102,19 @@ struct<>
 -- !query 9 output
 org.apache.spark.sql.AnalysisException
 Invalid number of arguments for function from_csv. Expected: one of 2 and 3; Found: 0; line 1 pos 7
+
+
+-- !query 10
+select schema_of_csv('1,abc')
+-- !query 10 schema
+struct<schemaofcsv(1,abc):string>
+-- !query 10 output
+struct<_c0:int,_c1:string>
+
+
+-- !query 11
+select schema_of_csv('1|abc', map('delimiter', '|'))
+-- !query 11 schema
+struct<schemaofcsv(1|abc):string>
+-- !query 11 output
+struct<_c0:int,_c1:string>