[PATCH] Stop whitelisting footway=*, and add footway=separate to blacklist candidates for sidewalk=*

[JeroenHoek]

To resolve #10851, #10976, #15439, and #19389 the validator checks if ways have footway=* set with one of the values typically used for sidewalk=*. This seems to be a fairly common mistake, so it's good to have a warning here.

Issues

There are three minor issues with the current validation approach I would like to resolve.

footway=separate is missing

The validator checks for left, right, both, none, and no. separate is missing from this list.

Doesn't treat no and none equally

The validator treats none in a different manner as the rest; giving users the suggestion to use sidewalk=no instead. Currently the documentation on the wiki and TagInfo (​https://taginfo.openstreetmap.org/keys/sidewalk#values) show that these are now treated as synonyms, with no preference for one or the other. It doesn't seem necessary for JOSM to have a preference one way or another, especially if mappers are simply using what other local mappers do.

Whitelists all other possible footway values

While the above values are clear examples of misstagging, footway is not an invalid key, and is used to provide a refining of highway=footway. The validator acknowledges this for access_aisle, crossing, and sidewalk, but excludes everything else. This seems too strict compared to the other rules — we don't whitelist values for highway=* for example. Mappers can (and do) create new values, and some are gaining broader acceptance. This check seems superfluous with the checks for values that probably mean sidewalk=* in place.

Patch

In the attached patch:

• A check for footway=separate is added.
• Special treatment for none is removed, none is added to the general footway=* check.
• The whitelist for footway=* is removed.

Are there any issues I am overlooking or reintroducing with this patch?