[GitHub] [spark] HyukjinKwon commented on a change in pull request #27774: [SPARK-31023][SQL] Support foldable schemas by `from_json`

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HyukjinKwon commented on a change in pull request #27774: [SPARK-31023][SQL] Support foldable schemas by `from_json`
URL: https://github.com/apache/spark/pull/27774#discussion_r387358620
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/ExprUtils.scala
 ##########
 @@ -47,14 +47,18 @@ object ExprUtils {
     dataType.asInstanceOf[StructType]
   }
 
-  def evalTypeExpr(exp: Expression): DataType = exp match {
-    case Literal(s, StringType) => DataType.fromDDL(s.toString)
-    case e @ SchemaOfJson(_: Literal, _) =>
-      val ddlSchema = e.eval(EmptyRow).asInstanceOf[UTF8String]
-      DataType.fromDDL(ddlSchema.toString)
-    case e => throw new AnalysisException(
-      "Schema should be specified in DDL format as a string literal or output of " +
-        s"the schema_of_json function instead of ${e.sql}")
+  def evalTypeExpr(exp: Expression): DataType = {
+    if (exp.foldable) {
+      exp.eval() match {
+        case s: UTF8String if s != null => DataType.fromDDL(s.toString)
+        case _ => throw new AnalysisException(
+          s"The expression '${exp.sql}' must be evaluated to a valid string.")
+      }
+    } else {
+      throw new AnalysisException(
+        "Schema should be specified in DDL format as a string literal or output of " +
 
 Review comment:
   literal -> foldable expression such as a literal.
   

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