TAJO-2064: Supporting auto-completion in Tsql

[eminency]

Use tab key in Tsql

[blrunner]

Sorry for late review. I'll finish to review this PR in a few days.

[eminency]

Never mind.
It is not a critical patch.

[blrunner]

@eminency

If you implement Completer to DescFunctionCommand that shows built-in function description, this patch will be more useful.

[eminency]

@blrunner

Good, I've done.

[blrunner]

It looks like a ambiguous name. How about rename it to keywords or keywordList?

[blrunner]

Currently, many tajo inner-classes have been declared inside their top-class. How about put ConfCompleter inside TajoGetConfCommand?

[eminency]

I think it is a good suggestion.

[eminency]

@blrunner
Ok, please check what you commented.

[blrunner]

@eminency

Thanks for your reflection.

Well, I have one more suggestion. Currently, Tajo provides a SQL grammar file as following:

https://github.com/apache/tajo/blob/master/tajo-sql-parser/src/main/antlr4/org/apache/tajo/parser/sql/SQLLexer.g4

But if we have existing grammar file and SQLKeywords, when other contributors add new grammar, they must add it to above two files. I think that it is a little inefficient for maintaing codes. Even though it may be trouble, if you use SQLLexer.g4, this patch will be better. For reference, there are some unnecessary keywords to SQLLexter.g4 on tsql. So you need to filter theme at TajoCli::getKeywords.

[eminency]

@blrunner
SQL keywords are fetched from SQLLexer now.

[blrunner]

+1

Sorry for late review.
I found that the auto-completion ran as expected and your reflection about my opinion.