Support --empty flag for schema-only dry runs from dbt-core PR #8971

[FishtownBuildBot]

This change includes a variety of changes to improve the functionality and usability of the codebase. The most important changes include adding new test cases for running dbt run with and without the --empty flag, adding a new optional limit parameter to the create_ephemeral_from_node method and the BaseRelation class, and adding a new command line option --empty to limit the input refs and sources to zero rows.

Solution

• BaseRelation changes
  • Adds an optional limit to BaseRelation
  • Implements BaseRelation.render_limited: depending on the value of self.limit, this method templates sql to wrap a rendered relation in an 'empty' select statement. Further reasoning in the spike report
  • Updates BaseRelation.__str__ to use self.render_limited if self.limit is set
• Adds --empty flag to run and build commands.
  • This flag configuration is used to determine the value for resolve_limit on the BaseResolver
  • BaseResolver plumbs its resolve_limit to the Relation instance it is creating, which is responsible for rendering itself given an optional limit parameter.

[MichelleArk]

Originating issue: dbt-labs/dbt-core#8980

[runleonarun]

@matthewshaver I think we should aim to have all issues addressed by Friday 2/23 to give reviewers and authors enough time. Let me know if you need support!