Implement basic messaging system

[machow]

• generic pattern for AST libraries to report human friendly name of AstNode instances
• sqlwhat only uses most recent message for now, relies on highlighting for context. (e.g. rather than "Check the 1st Select statement. Check the WHERE clause. Did you _?", Use highlighting + "Did you ?".
• sqlwhat uses human friendly names when can't find node or field (e.g. "Did you define a {ordinal} {node_name}" -> "Did you define a 2nd SELECT statement?")

[machow]

Note, there is a working implementation on

https://github.com/datacamp/sqlwhat/tree/feature-speaker

[machow]

The current messaging works by reporting a name for whatever node you're looking at. E.g.

"Check your SELECT statement"

This means that when you get the WHERE field of a SELECT statement, it will report whatever node is in that field. For example in

SELECT id FROM b WHERE id < 10, it will say something like...

"Check the binary expression <".

Let me know if this isn't ideal, since an alternative is that it would say the field you are checking, rather than the node it contains.

"Check the WHERE clause of your SELECT statement."

[filipsch]

cc @colinricardo cc @ncarchedi

[colinricardo]

@machow I think saying the field rather than the node is a bit easier for students. Can they be combined? e.g. "Check the binary expression < in the WHERE clause of your SELECT statement?"

[machow]

Can they be combined?

Yes! That's a great suggestion--I was trying to keep it as simple as possible, but that seems like the most useful default.