users should be able to call config multiple times within the same model

[jthandy]

Issue

dbt's clobber configuration fields (eg. materialized', bind', etc) can be currently be specified in multiple config() blocks. This looks like:

{{ config(materialized='view') }}
{{ config(materialized='table') }}

Here, the model is correctly built as a table. A more realistic use case might involve a macro that itself calls config() with some default arguments. Subsequent calls to config() may override some of this behavior. Eg:

-- macros/config.sql
{% macro base_config() %}
  {{ config(materialized='table', sort='timestamp', dist='id') }}
{% endmacro %}

-- models/some_model.sql

{{ base_config() }}
{{ config(dist='all') }}

While the paradigm works for dbt's clobber configs, it does not currently work for the append- and extend- configs (like post-hooks and vars, for instance).

Append configs

Given:

{{ config({"post-hook": 'select 1 as id'}) }}
{{ config({"post-hook": 'select 2 as id'}) }}

Expected:

post-hooks == ["select 1 as id", "select 2 as id"]

Extend configs

Given:

{{ config({"vars": {"abc": 123}) }}
{{ config({"vars": {"def": 456}) }}

Expected:

vars == {"abc": 123, "def": 456}

Todo:

• Support the specification of append configs multiple times
• Support the specification of extend configs multiple times
• add test for multiple specifications of clobber, append, and extend configs