feat: allow module in ident

[aljazerzen]

No description provided.

[snth]

Interesting. First thought I had when reading through the example is one could possibly also use "this" for this purpose. Not arguing for it at this point, just putting it out there as an idea to explore.

"module" is possibly more explicit and using "this" would be overloading the use of "this".

Counterargument to that is that this is overloading the use of "module". Furthermore in a pipeline "this" references the current namespace and makes the component objects (columns) available with "this.column_name". The usage here would be analogous with "this" referencing the current (module) namespace and making its objects available through "this.object".

WDYT?

[aljazerzen]

The added test is just a parser test, so nothing is implemented yet.

You are right that module is very similar to this, but this refers to the "current" relation in the pipeline.

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Background for this change:

I'm experimenting with a rewrite of name resolution and my new strategy is to not to implement it all at once. Instead, I'll simplify the language (and make it much more inconvenient to use), so I get basics working. Then I can try to simplify it back into what we have now, or something very similar. I don't plan on merging the "inconvenient" version of the language into main, because that would require a lot of campaigning to get the language design accepted by all.

This PR is needed because I need a way of distinguishing between column references and declaration references.

First I tried to do that with #1619 (i.e. .my_column for columns), but such changes require rewriting all of our tests manually, which would mean adding dots in front of all column names we have in sql.rs, which is a lot.

My next idea is to instead require explicit module or project or super for all declaration references. This is similar to what we just did with adding db. prefix to all table references. It would look something like this:

let x = (from project.db.my_table | select {a, b})

from module.x
select {a, b}