The poster credited Mapbox for tiles OpenFreeMap had served
The footer's attribution is a licence statement, so it has to be true rather than
merely present. posterDefaults ships "(c) Mapbox (c) OpenStreetMap" and any caller
that did not override it printed exactly that -- including country-posters, whose
maps run on the fleet's MapLibre default, where Mapbox serves nothing at all and
OpenFreeMap, OpenMapTiles and OpenStreetMap are the three parties whose licences
actually apply. research-map had a hand-written pair for the two providers, which
was right for research-map and helped nobody else.
The obvious approach is to read the style's sources. Checked against the live
style rather than assumed, and it does not work: tiles.openfreemap.org/styles/
liberty declares two sources and NEITHER carries an attribution field. The credit
lives in the TileJSON the vector source points at, which the engine fetches and
merges into the SOURCE OBJECT once it loads. The style is the request and the
source is what came back, and only the second one knows. map-attribution.js reads
the live source first and falls back to any style-declared value.
The TileJSON value is HTML with anchors and a © entity, and a poster footer
is text, so it is flattened rather than printed raw. Repeated credits collapse.
When nothing can be read -- no map, a style that throws before it has loaded -- it
returns empty and the caller keeps its own string, because a blank licence line is
the one outcome that is never acceptable.
The check uses the real TileJSON string as its fixture. A tidy invented style
would have passed while the real map printed the wrong credit, and its first
negative test is exactly that: reading the style alone returns nothing for
OpenFreeMap.
Cut directly on main rather than on the branch this began life in, so it does not
wait behind a poster-layout change it has nothing to do with. A wrong tile credit
is a licence problem; the layout question it was sitting behind is not.
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