[gdal-dev] Adding ignored fields to layers

[Even Rouault]

Hi Ari,

> When fields are added to a layer, the field definition that is stored in
> the layer definition is created as a clone of the provided field definition.
> 
> Neither field definitions nor geometry field definitions set the ignored
> flag of the clone.
> 
> Is this a feature and not a bug?

Mostly a feature I'd say. Why would you want to do this ? The ignored flag is 
only taken into account on reading, where you don't create a field definition 
but get the one of the source layer and may call SetIgnored() on it.
You create field definition objects when writing a new layer, and the ignored 
flag doesn't make sense in that context.

> 
> I was already making a PR but I see in the field definition clone code
> the comment "TODO(schwehr): Can we use IsIgnored()?"

IsSame() also ignores the bIgnore flag, for similar reasons. This is more a 
transient state of the object rather than something that really qualifies it. 
Probably comments should be added in both places to mention this is done on 
purpose.

Even

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