Fix: treat all instances of macro variables as case-insensitive

[georgesittas]

What the title says. We now treat all macro references in SQL as case-insensitive. The rationale is that we already normalize variables and blueprint_variables, so doing it for all variables feels like a natural extension of that. The motivating problem was the following:

MODEL (
    name foo.bar_@{X},
    blueprints ((X := 'bla')),
);

SELECT
  1 AS c

The @{X} variable is not rendered, because we don't do case-insensitive lookups for @{...}-type variables:

>>> from sqlmesh import Context
>>> ctx = Context()
>>> ctx.models
mappingproxy({'"db"."foo"."bar_@{x}"': SqlModel<foo.bar_@{X}: test.sql>})

[georgesittas]

This is more nuanced than I initially thought. I'm planning to revert part of this PR so that we don't lowercase everything in locals. The reason is that Python objects can also be included in it AFAICT and since symbols in Python are case-sensitive, we want to treat them as such.

[georgesittas]

This change has a subtle side-effect: today, despite being counter-intuitive, one can actually reference a variable defined in Python within a model:

# model.sql
MODEL (name test, kind full);
SELECT @x_plus_one() AS xp1, @X AS x

# macros.py
from sqlmesh import macro

X = 1

@macro()
def x_plus_one(evaluator):
    return X + 1

The above configuration is correct and the model renders into:

SELECT
  2 AS "xp1",
  1 AS "x"

After this PR, the reference @X will be invalid because we'll look up the lowercase "x" in locals, which won't match the Python uppercase key "X", resulting in:

Macro variable 'X' is undefined.

I think this is fine. I doubt anyone's relying on Python variables being exposed to SQL models today. I don't think we've even documented this anywhere, it's just a weird side-effect of populating locals with python_env items.

[georgesittas]

The idea here is to make variable lookups in SQL case-insensitive; the template method is only used for substituting variables in SQL, as far as I can tell.

[georgesittas]

Again, this should just affect SQL models that have @DEF– now the defined variables are automatically stored as lowercase.

[izeigerman]

Do we need to update docs anywhere?

[georgesittas]

Do we need to update docs anywhere?

Maybe, I'll take a look and update if needed. 👍