[CT-1924] Support 'contract' config outside model yaml file

[MichelleArk]

In the first cut of dbt constraints, constraints_enabled (= “this model is contracted and should be treated as such”, to be renamed to contract) can only be set in model yaml files, alongside the columns attribute to enable parse-time validation.

We should either:

1. Resolve some tech debt around parsing ([CT-1747] Enable flagging nodes/configs for deferred validation #6511) to enable setting this config elsewhere ((dbt_project.yml, yaml file, within .sql file) or,
2. Remove the at parse-time validation, failure will happen at runtime

Relevant discussions:

• dbt Constraints / model contracts #6271 (comment)
• [CT-1747] Enable flagging nodes/configs for deferred validation #6511 (comment)

[jtcohen6]

Let's take #6511 off the critical path, and take the "lazy" approach for now, by raising the error at runtime instead of parse time.

#6986 is going to give us a neat place to raise this error at runtime:

dbt-core/core/dbt/include/global_project/macros/adapters/columns.sql

Lines 41 to 47 in 5858095

	{% macro default__get_empty_schema_sql(columns) %}
	select
	{% for i in columns %}
	{%- set col = columns[i] -%}
	cast(null as {{ col['data_type'] }}) as {{ col['name'] }}{{ ", " if not loop.last }}
	{%- endfor -%}
	{% endmacro %}

If col['data_type'] == "", let's raise a clear exception — rather than having it crop up as a harder-to-debug syntax error when we submit this query to the data platform:

cast(col_name as ),

Then, we should remove these validation checks:

dbt-core/core/dbt/parser/base.py

Lines 313 to 324 in 5858095

	# If we have "contract" in the config, copy to node level, for backwards
	# compatibility with earlier node-only config.
	if config_dict.get("contract", False):
	parsed_node.contract = True
	parser_name = type(self).__name__
	if parser_name == "ModelParser":
	original_file_path = parsed_node.original_file_path
	error_message = "\n `contract=true` can only be configured within `schema.yml` files\n NOT within a model file(ex: .sql, .py) or `dbt_project.yml`."
	raise ParsingError(
	f"Original File Path: ({original_file_path})\nConstraints must be defined in a `yml` schema configuration file like `schema.yml`.\nOnly the SQL table materialization is supported for constraints. \n`data_type` values must be defined for all columns and NOT be null or blank.{error_message}"
	)

dbt-core/core/dbt/parser/schemas.py

Lines 1015 to 1025 in 5858095

	def constraints_data_type_validator(self, patched_node):
	data_type_errors = set()
	for column, column_info in patched_node.columns.items():
	if column_info.data_type is None:
	data_type_error = {column}
	data_type_errors.update(data_type_error)
	data_type_errors_msg = (
	f"\n Columns with `data_type` Blank/Null Errors: {data_type_errors}"
	)
	data_type_errors_msg_payload = f"{data_type_errors_msg if data_type_errors else None}"
	return data_type_errors_msg_payload