[Feature] Extend partial parsing behavior for env vars to {{ target }} also

[dbeatty10]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Avoid full parses and use partial parsing when {{ target }} values have not changed.

The implementation would more granularly track where those inputs are being used — that is, extending what we've done for env vars to {{ target }}. I believe the relevant partial parsing code related to environment variables is here.

Describe alternatives you've considered

No response

Who will this benefit?

This will allow dbt to complete the parsing phase faster by using partial parsing to only parse the changed files (or files related to those changes).

Are you interested in contributing this feature?

No response

Anything else?

From dbt-labs/docs.getdbt.com#1066 (comment) and #9844 (comment)

[jaysobel]

I think this is the parent for an issue I just experienced.

Basically when you run the following commands:

1. dbt build -s some_model
2. dbt build -s some_model
3. dbt build -s some_model --target default_target

You only get partial parsing on (2). Even though the passed target to (3) is the default target that was used for (1) and (2), you still get a Unable to do partial parsing warning, and the slower startup time.

And when you add:

4. dbt build -s some_model

You again get Unable to do partial parsing.

This is a problem for 3rd party tools that populate the defaults proactively (read: dbt Power User run buttons) because any interspersing of manual commands gives you this thrashing back and forth.