• closesBUG: pd.wide_to_long can't handle stubname equal to suffix #46939(Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• Allcode checks passed.
• Addedtype annotations to new arguments/methods/functions.
• Added an entry in the latestdoc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature. (Will add after review)

Aspandas allows an index in a multiindex and a column to have the same name, I think it's reasonable to allow stubname equal suffix.

However, I think the root cause is in themelt function. It's stated in the docstring that

    value_name : scalar, default 'value'        Name to use for the 'value' column, can't be an existing column label.

But ifvalue_name == var_name, illogical result is returned. Example:

df = pd.DataFrame(    {        "A": {0: "a", 1: "b", 2: "c"},        "B": {0: 1, 1: 3, 2: 5},        "C": {0: 2, 1: 4, 2: 6},    })pd.melt(    df,    id_vars=["A"],    value_vars=["B"],    var_name="myVarname",    value_name="myVarname",)

Result:

I think it's more reasonable to also raise an error ifvalue_name == var_name inmelt