ComputeError / panic on projection pushdown using .count()

[nameexhaustion]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl

(
    pl.LazyFrame(dict(x=1))
    .select(records=pl.count())
    .select(pl.lit(1).alias("x"), pl.all())
    .collect()
)

Log output

polars.exceptions.ComputeError: column 'records' not available in schema Schema:
name: x, data type: Int64

Issue description

Originally came across this when running a long lazy query that led to a panic pyo3_runtime.PanicException: called Result::unwrap()on anErr value: ColumnNotFound(ErrString("records")). When reducing to the provided MRE, the error instead becomes a ComputeError.

This is the panic backtrace of the original query, but it's likely the issue happens much earlier from where the panic happens. The records column is created via .select(records=pl.count()) (in a similar fashion to the one in the MRE):

Panic backtrace

thread '<unnamed>' panicked at /home/runner/work/polars/polars/crates/polars-plan/src/utils.rs:384:68:
called `Result::unwrap()` on an `Err` value: ColumnNotFound(ErrString("records"))
stack backtrace:
   0: rust_begin_unwind
             at /rustc/475c71da0710fd1d40c046f9cee04b733b5b2b51/library/std/src/panicking.rs:597:5
   1: core::panicking::panic_fmt
             at /rustc/475c71da0710fd1d40c046f9cee04b733b5b2b51/library/core/src/panicking.rs:72:14
   2: core::result::unwrap_failed
             at /rustc/475c71da0710fd1d40c046f9cee04b733b5b2b51/library/core/src/result.rs:1653:5
   3: polars_plan::utils::aexprs_to_schema
   4: polars_plan::logical_plan::builder_alp::ALogicalPlanBuilder::project
   5: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
   6: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
   7: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
   8: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
   9: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  10: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  11: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  12: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  13: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  14: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  15: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  16: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  17: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  18: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  19: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  20: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  21: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  22: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  23: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  24: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  25: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  26: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  27: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  28: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  29: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  30: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  31: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  32: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  33: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  34: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  35: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  36: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  37: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  38: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::pushdown_and_assign
  39: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  40: core::iter::adapters::map::map_try_fold::{{closure}}
  41: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::no_pushdown_restart_opt
  42: polars_plan::logical_plan::optimizer::projection_pushdown::functions::melt::process_melt
  43: polars_plan::logical_plan::optimizer::projection_pushdown::ProjectionPushDown::push_down
  44: polars_plan::logical_plan::optimizer::optimize
  45: polars_lazy::frame::LazyFrame::optimize_with_scratch
  46: polars_lazy::frame::LazyFrame::prepare_collect
  47: polars_lazy::frame::LazyFrame::collect
  48: polars::lazyframe::_::<impl polars::lazyframe::PyLazyFrame>::__pymethod_collect__
  49: pyo3::impl_::trampoline::trampoline
  50: _PyEval_EvalFrameDefault
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/ceval.c:5284:29
  51: _PyEval_EvalFrame
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/./Include/internal/pycore_ceval.h:73:16
  52: _PyEval_Vector
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/ceval.c:6425:24
  53: _PyVectorcall_Call
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Objects/call.c:245:16
  54: _PyObject_Call
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Objects/call.c:328:16
  55: do_call_core
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/ceval.c:7343:12
  56: _PyEval_EvalFrameDefault
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/ceval.c:5367:22
  57: _PyEval_EvalFrame
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/./Include/internal/pycore_ceval.h:73:16
  58: _PyEval_Vector
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/ceval.c:6425:24
  59: PyEval_EvalCode
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/ceval.c:1140:21
  60: run_eval_code_obj
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/pythonrun.c:1710:9
  61: run_mod
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/pythonrun.c:1731:19
  62: pyrun_file
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/pythonrun.c:1626:15
  63: _PyRun_SimpleFileObject
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/pythonrun.c:440:13
  64: _PyRun_AnyFileObject
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Python/pythonrun.c:79:15
  65: pymain_run_file_obj
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Modules/main.c:360:15
  66: pymain_run_file
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Modules/main.c:379:15
  67: pymain_run_python
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Modules/main.c:601:21
  68: Py_RunMain
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Modules/main.c:680:5
  69: pymain_main
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Modules/main.c:710:12
  70: Py_BytesMain
             at /tmp/python-build.20231011043018.472516/Python-3.11.6/Modules/main.c:734:12
  71: __libc_start_main
  72: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
...
pyo3_runtime.PanicException: called `Result::unwrap()` on an `Err` value: ColumnNotFound(ErrString("records"))

Expected behavior

The MRE should provide the following output instead of erroring (it works if projection_pushdown is set to False):

shape: (1, 2)
┌─────┬─────────┐
│ x   ┆ records │
│ --- ┆ ---     │
│ i32 ┆ u32     │
╞═════╪═════════╡
│ 1   ┆ 1       │
└─────┴─────────┘

Installed versions

--------Version info---------
Polars:              0.19.9
Index type:          UInt32
Platform:            Linux-5.15.90.1-microsoft-standard-WSL2-x86_64-with-glibc2.31
Python:              3.11.6 (main, Oct  4 2023, 13:44:03) [GCC 9.4.0]

----Optional dependencies----
adbc_driver_sqlite:  <not installed>
cloudpickle:         <not installed>
connectorx:          <not installed>
deltalake:           <not installed>
fsspec:              2023.9.2
gevent:              <not installed>
matplotlib:          3.8.0
numpy:               1.26.0
openpyxl:            <not installed>
pandas:              2.1.1
pyarrow:             13.0.0
pydantic:            2.4.2
pyiceberg:           <not installed>
pyxlsb:              <not installed>
sqlalchemy:          <not installed>
xlsx2csv:            <not installed>
xlsxwriter:          3.1.6