Github user hvanhovell commented on the pull request:
https://github.com/apache/spark/pull/12134#issuecomment-204958652
@gatorsmile good catch!
Let me try to explain why this happens. All `visit*` functions in the
ANTLR4 generated visitor use the `AbstractParseTreeVisitor.visitChildren(...)`
function for the default implementation. See:
https://github.com/antlr/antlr4/blob/master/runtime/Java/src/org/antlr/v4/runtime/tree/AbstractParseTreeVisitor.java#L61-L75
This has both advantages and disadvantages. The disadvantage is that this
will select the result of the last defined context child. In the create table
example you give, the last child is `TBLPROPERTIES('prop1Key '= "prop1Val", '
`prop2Key` '= "prop2Val")`, this makes the visitor return a `Map[String,
String]` instead of a `LogicalPlan`. The advantage is that this provides a very
nice default implementation for rules with exclusive ORs (the `statement` rule
for instance).
The current approach of excluding every illegal option is error prone and
is quite code intense. I think it is easier to improve the visitors default
behavior by limiting the 'visitChildren' to one and only one child.
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