Less strict dictionary merging in core

[yanMHG]

In

https://github.com/fsspec/filesystem_spec/blob/7b774c26e30e5ae60b5b63bf4e345a1b32028a4e/fsspec/core.py#L337C9-L337C41

the dictionaries extra_kwargs and kws are merged with kw = dict(**extra_kwargs, **kws). This may be an issue when there is redundant information in the two dictionaries, resulting in a TypeError: dict() got multiple values for keyword argument (indeed I have just faced this exact situation in a project). I understand it is correct to raise this error when the same key is mapped to different values, but it is not necessary when the values are the same.

An alternative way to approach this merge is with kw = extra_kwargs | kws and raising the error only when there are overlapping keys with different values, something along the lines of

if any(k_1 == k_2 and v_1 != v_2 for k_1, v_1 in extra_kwargs.items() for k_2, v_2 in kws.items()):
    raise ValueError("Tried to merge dictionaries with same key and different values.")
else:
    kw = extra_kwargs | kws

[martindurant]

The simpler alternative would be

kw = extra_kwargs | kws

alone (you have this some lines below) without the check.

which does something different, but maybe the right thing?