Missing externals feedback

[FlorianDeconinck]

When a variable is unknown, gt4py.cartesian expects it to be defined via the __externals__ mechanism. This in itself could be the subject of a ticket, but here we will assume it's the right behavior.

When the undefined variable is from a stencil the error is mildly helpful

gt4py.cartesian.frontend.exceptions.GTScriptSymbolError: Unknown symbol 'UNDEF_VAR' symbol in '<source>' (line: 3, col: 32)

The <source> field should at least give a stencil name. Running with build_info["debug"]=True doesn't help.

When the undefined variable is from a gtscript.function the error is even less readable:

gt4py.cartesian.frontend.exceptions.GTScriptSymbolError: Unknown symbol ValueError symbol in '<source>' (line: 5, col: 20)

Example code:

import gt4py.cartesian.gtscript as gtscript
from gt4py.cartesian.gtscript import (
    computation,
    interval,
    PARALLEL
)
from ndsl.boilerplate import get_factories_single_tile_numpy
from ndsl.constants import X_DIM, Y_DIM, Z_DIM
from ndsl.dsl.typing import FloatField 

stcil_fctry, qty_fctry = get_factories_single_tile_numpy(5, 5, 1, 1)

out_q = qty_fctry.zeros([X_DIM, Y_DIM, Z_DIM], "n/a")
in_q = qty_fctry.ones([X_DIM, Y_DIM, Z_DIM], "n/a")

@gtscript.function
def add_one(field: FloatField) -> FloatField:
    # from __externals__ import UNDEF_CST

    return field + UNDEF_CST

def copy(in_field: FloatField, out_field: FloatField):
    with computation(PARALLEL), interval(...):
        out_field = in_field + add_one(in_field)

copy_stcil = stcil_fctry.from_dims_halo(
    func=copy,
    compute_dims=[X_DIM, Y_DIM, Z_DIM],
    # externals={
    #     "UNDEF_CST": 5
    # }
)

copy_stcil(in_q, out_q)

Parent: #49

---

• Missing external in stencil reports name of the stencil
• Missing external in gtscript.function reports name of the function or at least calling stencil