AMT_CG_rt is pinned to CG_rt

[hdoupe]

I am creating a separate issue for the bug found in #606.

_AMT_CG_rt{1,2,3} -- If _CG_rt{i} is altered, then the corresponding rate _AMT_CG_rt{i} is pinned to the former rate, i = 1, 2, and 3. But _AMT_CG_rt4 is not affected. If _CG_rt{1,2,3} are not altered then _AMT_CG_rt{1,2,3} are correctly set to the specified values. See http://ospc-taxes7.herokuapp.com/taxbrain/edit/1406/?start_year=2017 and http://ospc-taxes7.herokuapp.com/taxbrain/edit/1407/?start_year=2017

This is probably a bug and not a feature. @martinholmer found the relevant issues and PRs:

First, look at item 4 in Tax-Calculator issue 1074 and item 4 in Tax-Calculator pull request 1109, which was merged on December 22, 2016.

Then look at TaxBrain pull request #448 (merged on January 12, 2017), which was supposed to be the fix on the TaxBrain side. However, the #448 TaxBrain changes did not eliminate the AMT_fixup logic in views.py, which had been added earlier on September 26, 2016, in pull request #342.

So, maybe I'm reading too fast, but it seems as if the behavior you've found was once considered a "feature", then became to be viewed as a "bug", but was never removed from TaxBrain. You're doing a great job on this TaxBrain debugging, so I'll leave it to you to read these issues and pull requests more carefully than I have to see what the intention was. Only then will you be able to determine if this behavior is a "feature" or a "bug".

I will open a PR with a test exposing this bug shortly.

@brittainhard @PeterDSteinberg

[talumbau]

@hdoupe can you look at this issue and see if it sheds light on the problem:

#340

I'm wondering if your POST contains a parameter that is no longer in the TaxBrain GUI interface. It should still be fixed if there is a problem, but the discussion in #340 seems relevant

[hdoupe]

@talumbau I'm pretty sure that it is still in the TaxBrain GUI interface.

https://www.ospc.org/taxbrain/

And the corresponding entry in taxcalc/current_law_policy.json

    "_AMT_CG_rt1": {
        "long_name": "Long term capital gain and qualified dividends (AMT) rate 1",
        "description": "Capital gain and qualified dividends (stacked on top of regular income) below threshold 1 are taxed at this rate. ",
        "section_1": "Capital Gains And Dividends",
        "section_2": "AMT - Long Term Capital Gains And Qualified Dividends",
        "irs_ref": "Form 6251, line 47, in-line. ",
        "notes": "",
        "row_var": "FLPDYR",
        "row_label": ["2013"],
        "start_year": 2013,
        "cpi_inflated": false,
        "col_var": "",
        "col_label": "",
        "value": [0.0]
    },

I see that you removed AMT capital gains in #342 but I'm having trouble figuring out where it was added back in or why it is still in the TaxBrain GUI

I can maybe see the value in pinning AMT_CG_rt to CG_rt when AMT_CG_rt is not modified but CG_rt is. But, if AMT_CG_rt is modified, then I don't think that it should be changed. Perhaps, amt_fixup should be:

def amt_fixup(request, reform, model):
    """
    Take the regular tax captial gains parameters from the user reform
    and set them as the equivalent Alternative Minimum Tax capital
    gains parameters
    """
    cap_gains_params = ["CG_rt1", "CG_thd1_0", "CG_thd1_1",
                        "CG_thd1_2", "CG_thd1_3", "CG_thd1_cpi",
                        "CG_rt2", "CG_thd2_0", "CG_thd2_1",
                        "CG_thd2_2", "CG_thd2_3", "CG_thd2_cpi",
                        "CG_rt3"]

    for cgparam in cap_gains_params:
        if cgparam in reform and 'AMT_' + cgparam not in reform:
            reform['AMT_' + cgparam] = reform[cgparam]
            if cgparam.endswith("_cpi"):
                setattr(model, 'AMT_' + cgparam, reform[cgparam])
            else:
                setattr(model, 'AMT_' + cgparam, reform[cgparam][0])

@martinholmer