feat: Add from_json Spark function

velox/docs/functions/spark/json.rst

@@ -11,3 +11,18 @@ JSON Functions
         SELECT json_object_keys(''); -- NULL
         SELECT json_object_keys(1); -- NULL
         SELECT json_object_keys('"hello"'); -- NULL
+
+.. spark:function:: from_json(jsonString) -> [json object]
+
+    Casting a JSON text to a supported type returns the value represented by this
+    JSON text. The JSON text must represent a valid value of the type it is casted
+    to, or null will be returned. Casting to ARRAY and MAP is supported when the
+    element type of the array is one of the supported types, or when the key type of
+    the map is VARCHAR and value type of the map is one of the supported types. When
+    casting from JSON to ROW, only JSON object are supported. Cast from JSON object
+    to ROW uses case sensitive match for the JSON keys.
+    Behaviors of the casts are shown with the examples below:::
+
+        SELECT from_json('{"a": 1}', 'ROW(a INT)'); -- {a=1}
+        SELECT from_json('["name", "age", "id"]', 'array<string>'); -- ['name', 'age', 'id']
+        SELECT from_json('{"a": 1, "b": 2}', 'map<string,int>'); -- {a=1, b=2}

velox/functions/sparksql/Register.cpp

@@ -55,6 +55,7 @@
 #include "velox/functions/sparksql/Uuid.h"
 #include "velox/functions/sparksql/specialforms/AtLeastNNonNulls.h"
 #include "velox/functions/sparksql/specialforms/DecimalRound.h"
+#include "velox/functions/sparksql/specialforms/FromJson.h"
 #include "velox/functions/sparksql/specialforms/MakeDecimal.h"
 #include "velox/functions/sparksql/specialforms/SparkCastExpr.h"
 
@@ -152,6 +153,9 @@ void registerAllSpecialFormGeneralFunctions() {
   exec::registerFunctionCallToSpecialForm(
       AtLeastNNonNullsCallToSpecialForm::kAtLeastNNonNulls,
       std::make_unique<AtLeastNNonNullsCallToSpecialForm>());
+  exec::registerFunctionCallToSpecialForm(
+      FromJsonCallToSpecialForm::kFromJson,
+      std::make_unique<FromJsonCallToSpecialForm>());
 }
 
 namespace {

velox/functions/sparksql/specialforms/CMakeLists.txt

@@ -15,10 +15,11 @@
 velox_add_library(
   velox_functions_spark_specialforms
   AtLeastNNonNulls.cpp
+  FromJson.cpp
   DecimalRound.cpp
   MakeDecimal.cpp
   SparkCastExpr.cpp
   SparkCastHooks.cpp)
 
 velox_link_libraries(velox_functions_spark_specialforms fmt::fmt
-                     velox_expression)
+                     velox_functions_json velox_expression)