Idea: Keep an index of the maps already parsed

[wismill]

When we resolve include statements, we may parse the same file multiple times, e.g.:

xkb_symbols "base" { … };
xkb_symbols "map1" { include "file(base)" };
xkb_symbols "map2" { include "file(map1)" };

I we want "file(map2)", we end up parsing "base" 3 times and "map1" 2 times, but also all the maps in between…

Caching all parsed maps could be costly, but what if we simply keep an index file/map → map position in file? Then when looking up for a map, we can first check this index and if the map was already parsed, start parsing exactly where the map is or start from scratch if the file or map was not parsed yet.

This would be useful mostly for symbols.