get_relation returns none in hook context

Describe the bug

The adapter.get_relation(...) method seems to return None within the post-hook context.

Why does this matter? Well, {{ this }} always has its type defined as None, and it’s fairly common that a user would want to use get_relation (perform a cache lookup) to get its relational type for the purposes of templating a post hook:

alter {{ relation.type }} {{ relation }} ... do something ...

Steps To Reproduce

macros/say_hi.sql

{% macro say_hi(relation) %}

    {% set rel = adapter.get_relation(this.database, this.schema, this.name) %}
    
   select 'say hi to my two best friends: the {{ relation.type }} {{ relation }} and the {{ rel.type }} {{ rel }}'

{% endmacro %}

models/my_model.sql

{{ config(
    post_hook = say_hi(this)
) }}

{{ say_hi(this) }}

dbt.log

create view "jerco"."dbt_jcohen"."my_model__dbt_tmp" as (
    select 'say hi to my two best friends: the None "jerco"."dbt_jcohen"."my_model" and the view "jerco"."dbt_jcohen"."my_model"'
  );
...
        select 'say hi to my two best friends: the None "jerco"."dbt_jcohen"."my_model" and the  None'
...

Expected behavior

I expected the result of get_relation to be defined for both the model and post-hook contexts.

The output of dbt --version:

$ dbt --version
installed version: 0.18.1
   latest version: 0.18.1

Additional context

In the meantime, it’s mostly possible to work around this by inferring the relational object type from the configuration of the model we’re post-hooking:

{% set relation_type='view' if model.config.materialized == 'view' else 'table' %}

[aaronsteers]

That is super helpful context and I think it gives me my path forward. Thanks so much!

[jtcohen6]

Coming back to this, and having revisited https://github.com/dbt-labs/dbt/issues/2370, I’m afraid to report that this does work if the hook is re-parsed at execute time, instead of set at parse time. Namely:

{{ config(
    post_hook = "{{ say_hi(this) }}"
) }}

{{ say_hi(this) }}

This is so not my favorite thing, but I’m going to close the issue. The real question is bigger than get_relation, and it’s whether hooks should always be re-parsed at execute time, without the need to nest a macro in an extra set of curlies.