unable to parse fvExpressionField in controlDict

[HenningScheufler]

Thanks for sharing this execellent library

foamlib is unable to parse fvExpressionField functionObject in the controlDict :

test
{
    type    exprField;
    libs    (fieldFunctionObjects);
    field   pTotal;

    expression  "p + 0.5*(rho*magSqr(U))";
    dimensions  [ Pa ]; // this is the line that causes the error
}

It prints the following error message:

pyparsing.exceptions.ParseException: Expected end of text, found '{' (at char 1241), (line:58, col:1)

details:
https://www.openfoam.com/documentation/guides/latest/api/classFoam_1_1functionObjects_1_1fvExpressionField.html

[gerlero]

@HenningScheufler Thanks for reporting!

dimensions [ Pa ];

From the docs you linked, I understand this should be parsed as a dimensionSet; correct?

Are there any docs for this syntax and valid units? Searching for "Pa" in the OpenFOAM source code yielded no seemingly relevant results.

[HenningScheufler]

Im not sure how it works in details but this test could help:

applications/test/dimensionedType/Test-dimensionedType.C

i think it reads the controlDict in dimensionSet

etc/controlDict

[gerlero]

@HenningScheufler there's an extra example there ([Pa mm^2 s^-2]), but I still can't find a list of all units that are supported anywhere in the code.

[HenningScheufler]

I think they are read from a dictionary (etc/controlDict line 1125):

https://develop.openfoam.com/Development/openfoam/-/blob/master/etc/controlDict?ref_type=heads#L1125

[gerlero]

Oh! Interesting, thanks. I guess we could hardcode the units defined in that file (so as not to need OpenFOAM present) so that the parser understands them.

TBH not sure yet what should happen with scaled units (e.g. mm) since there’s no straightforward way to convert those to a dimension set (though I’m sure reading the code of dimensionSet should clear up how that works).

[gerlero]

@HenningScheufler just wondering... as a user, do you expect these units to be parsed by foamlib and returned as a FoamFile.DimensionSet? Or would you rather have direct access to the "raw" string (e.g. "Pa" in this case)?

[HenningScheufler]

Return the string is probably what would be expected, so Pa in this case

[gerlero]

@HenningScheufler Not sure if you still need this; but if so, what do you think of Copilot's idea at #435 (which is pretty much what I had in mind initially)?

[gerlero]

Or, I could allow [ and ] in regular entries and let that be parsed as "[ Pa ]"...