When generating output data, nmcli iterates over a list of
property-descriptors (nmc_fields_ip4_config), creates an intermediate
array (output_data) and finally prints it.
However, previously both the meta data (nmc_fields_ip4_config) and
the intermediate format use the same type NmcOutputField. This means,
certain fields are relevant to describe a property, and other fields
are output/formatting fields.
Split this up. Now, the meta data is tracked in form of an NMMetaAbstractInfo
lists. This separates the information about properties from intermediate steps
during creation of the output.
Note that currently functions like print_ip4_config() still have all the
knowledge about how to generate the output. That is wrong, instead, the
meta data (NMMetaAbstractInfo) should describe how to create the output
and then all those functions could be replaced. This means, later we want
to add more knowledge to the NMMetaAbstractInfo, so it is important to
keep them separate from NmcOutputField.
Embed a @meta_type structure in NMMetaSettingInfoEditor and
NMMetaPropertyInfo. This allows to make the NMMeta*Info instances
themself to become generic and they can be passed around as generic
NMMetaAbstractInfo types.
For one, the embedded NMMetaType pointer can be used to determine
of which type a NMMetaAbstractInfo instance is. On the other hand,
the NMMetaType struct can be extended to be a VTable to provide
generic access to the type.
In the end, both NMMetaSettingInfoEditor and NMMetaPropertyInfo are
conceptionally very similar: the describe a certain type and provide
accessors.
In nmcli we have yet another NMMetaAbstractInfo type: NmcOutputField
will be modified to become another implementation of meta data (it
already is, it just cannot be used interchangable with the other
types).
Also, embed the NMMetaSettingInfoEditor in the NMMetaPropertyInfo
instance. This allows from a given NMMetaPropertyInfo to retrieve it's
parent NMMetaSettingInfoEditor.
"nm-meta-setting-desc.h" contains static type description, vtable and (internal)
accessor functions. Add accessor functions that operate on top of the type description
to "nm-meta-setting-access.h".
