Add support for sql.j2

[Gregory108]

Developing in DBT means writing in a combination of database-specific SQL dialect and jinja2. At least, VSCode with Better Jinja plugin is able to help with prompts and check syntaxis of both languages simultaneously - iff model file extension is .sql.j2. However, dbt does not recognise such files as model.

Suggestion:

• make dbt run [-m] work agnostic of anything after .sql extension suffix

[jtcohen6]

@Gregory108 Thanks for the issue! We've got a very similar one open: #3484, which is in progress in #3498.

The Jinja folks have thrown their weight behind the .jinja file extension, though I understand that .j2 is also a popular choice (docs, stackoverflow conversation).

Personally, I don't have strong feelings about preferring .jinja vs. .j2. I suppose we could support any arbitrary suffix after .sql. dbt does name models based on their file names, and it support dots in model file names today, so I think a model file named models/my.sql.model.sql.j2 would do some surprising things. I think we'd need to consider that an unreasonable edge case, and one we can't hope to support.

In the meantime, I'm going to close this as a duplicate of #3484, which will be doing the heavy lifting. I'd encourage you to leave a comment there if you feel strongly about supporting .sql.j2 in particular (or other extensions in general), in addition to .sql.jinja.