fix(ir): make impure ibis.random() and ibis.uuid() functions return unique node instances

[kszucs]

Resolves #8921

[cpcloud]

There's also now and today and probably others.

[cpcloud]

I think this is a bug fix, since it has to do with output correctness.

[kszucs]

There's also now and today and probably others.

I am planning to address that in a follow-up.

[cpcloud]

Any reason why those can't be done in this PR?

[jcrist]

Are now and today impure in the same sense? Implemented using CURRENT_TIMESTAMP these will return the same value for every instance of the expression when the query executes (even though they may return a different value for two subsequent executions). In contrast random() and uuid() will generally return a new value for each call in an expression (some backends like clickhouse handle this a bit differently).

[cpcloud]

Ah, good point. I hadn't considered that select now() = now() whereas select random() <> random().

Do we know whether that's true for all of our backends?

[cpcloud]

Anyway, that's sufficiently different that I think it can be done in a follow up.

Comment is no longer relevant.

[jcrist]

Do we know whether that's true for all of our backends?

I wouldn't be surprised if it's broken for pandas/dask/polars, but semantically I think it should be true for all backends.

[cpcloud]

@kszucs Let me know when you want me to regen snapshots.

[kszucs]

We still have a problem which is definitely solvable but would expand the scope of this PR heavily:

# semantically this should produce two different columns
t.select(x=ibis.random(), y=ibis.random())

# semantically this should produce identical columns
rand = ibis.random()
t.select(x=rand, y=rand)

Currently we compile both as rand() AS x, rand() AS y which behaves differently on the backends. After this PR the two random values are equal from ibis' perspective, but ideally we should ensure that they produce the same columns on all backends.
The solution could be to inject an additional subselect:

SELECT *, randcol AS x, randcol AS y FROM (SELECT *, rand() as randcol FROM ...)  # where randcol name would be generated

For clickhoue and mysql all the random calls produce the same value in a select, but we could also overcome that with similar strategies.

[cpcloud]

Can that be done in a follow up?

[kszucs]

Can that be done in a follow up?

Definitely! That is slightly harder and we need to work around backend specifics.

Yes, please regenerate the snapshots for the failing backends!

[cpcloud]

Clouds are passing:

…/ibis on  impure is 📦 v8.0.0 via 🐍 v3.11.8 via ❄️   impure (ibis-3.11.8-env)
❯ pytest -m 'bigquery or snowflake' -n auto --dist loadgroup --snapshot-update
==================================================================================== test session starts ====================================================================================
platform linux -- Python 3.11.8, pytest-8.1.1, pluggy-1.4.0
benchmark: 4.0.0 (defaults: timer=time.perf_counter disable_gc=False min_rounds=5 min_time=0.000005 max_time=1.0 calibration_precision=10 warmup=False warmup_iterations=100000)
Using --randomly-seed=168840051
rootdir: /home/cloud/src/ibis
configfile: pyproject.toml
plugins: xdist-3.5.0, pytest_httpserver-1.0.10, cov-5.0.0, benchmark-4.0.0, randomly-3.15.0, hypothesis-6.100.1, repeat-0.9.3, snapshot-0.9.0, mock-3.14.0, clarity-1.0.1
16 workers [3509 items]
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================================================================= 2921 passed, 45 skipped, 543 xfailed in 356.95s (0:05:56) =================================================================