Error in custom sql order by only when where clause present

[brsanthu]

We have a custom sql dsl that supports subset of sql as outlined in playground.

As you can see, the order by name errors when there is a where clause otherwise it parses fine.

One peculiar thing with this dsl is we could have table name conflicts with keywords. For ex., order so we have specified KeywordOrId Rule which allows specified keyword variables like this. Error also goes away if we remove 'order' | from the Name rule.

Name returns string:
    'order' | ID
;

Any idea what I'm doing wrong?

[msujew]

Hey @brsanthu,

you're basically hitting an issue in our parser implementation. Mainly, a WhereExpr can be followed by any other amount of WhereExpr. Since order is handled as a Name, it will think that there's a new WhereExpr starting. While there's a fix that includes rewriting the grammar to lift different rules to the same level, note that this isn't valid SQL syntax, as multiple WhereExpr should be separated by AND or OR. You should adjust your grammar. See also langium-sql for a mostly complete implementation of DQL. That should fix the issue by itself.

Also note that SQL forbids keywords as identifiers, you should use string escaping instead (also implemented in langium-sql).

[brsanthu]

Thank you, now I see the issue with how WhereExpr is structured. Will fix it and retry.

Did you identify the root cause by looking at the grammar or by going through some intermediate generated json or js file? Just trying to udnerstand the flow of troubleshooting for such errors.

[msujew]

Did you identify the root cause by looking at the grammar or by going through some intermediate generated json or js file? Just trying to udnerstand the flow of troubleshooting for such errors.

It's mostly based on experience by looking at the grammar. I've seen that issue at least a dozen times in the past few years. The generated code from Langium is mostly useless to understand parser issues, as the parser is contructed from the grammar directly without an intermediate representation.