SSM Package fileinput does not accept 'mixed' keyword MF6

[laat0003]

Howdy,
Unsure if this is a bug or intended so apologies upfront for being annoying.

Describe the bug
SSM package throws an error if you try and use the keyword 'mixed' in the fileinput

To Reproduce
try something like this:

ssm = flopy.mf6.ModflowGwtssm(gwt, fileinput=[('rch',"trans_1spc.spca"), ("evt", "trans_2spc.spca", "MIXED")])

and you will get this:

(1) An error occurred when storing data "fileinput" in a recarray. fileinput data is a one or two dimensional list containing the variables " <spc6_filename>" (some variables may be optional, see MF6 documentation), but data "[('rch', 'trans_1spc.spca'), ('evt', 'trans_2spc.spca', 'MIXED')]" was supplied.

Expected behavior
This works and is what I thought was supposed to be happening with the original constructor.
ssm = flopy.mf6.ModflowGwtssm(gwt, fileinput=[('rch',"trans_1spc.spca")])
ssm.fileinput.append_list_as_record(["evt", "trans_2spc.spca", "MIXED"])

Desktop (please complete the following information):

• OS: Windows 11
  -Flopy version 3.4.1

Great work as always.
Cheers,
Tariq

[langevin-usgs]

I've verified that flopy is having trouble with the MIXED keyword. @spaulins-usgs, can you take a look? You can easily reproduce this issue with a MODFLOW 6 autotest here. Try adding the keyword "MIXED" to any of these lines in the FILEINPUT block (as shown below), and flopy will give the error reported by @laat0003.

    # ssm package
    sourcerecarray = [()]
    fileinput = [
        ("RCH-1", f"{gwtname}.rch1.spc"),
        ("RCH-2", f"{gwtname}.rch2.spc"),
        ("RCH-3", f"{gwtname}.rch3.spc", "MIXED"),
        ("RCH-4", f"{gwtname}.rch4.spc"),
    ]
    ssm = flopy.mf6.ModflowGwtssm(
        gwt, print_flows=True, sources=sourcerecarray, fileinput=fileinput
    )

[spaulins-usgs]

@laat0003 please try the latest flopy code from the develop branch. It has a fix that should solve this problem.

[wpbonelli]

removing from 3.4.3 milestone as this was closed by #1920 which was included in 3.4.2