$ find * -type f |xargs perl contrib/scripts/spdx.pl
  $ git rm contrib/scripts/spdx.pl

  git ls-files -z -- ':(exclude)src/settings/plugins/keyfile/tests/keyfiles' | xargs -0 -n1 sed -i '1 { /^$/d }'

We no longer add these. If you use Emacs, configure it yourself.

Also, due to our "smart-tab" usage the editor anyway does a subpar
job handling our tabs. However, on the upside every user can choose
whatever tab-width he/she prefers. If "smart-tabs" are used properly
(like we do), every tab-width will work.

No manual changes, just ran commands:

    F=($(git grep -l -e '-\*-'))
    sed '1 { /\/\* *-\*-  *[mM]ode.*\*\/$/d }'     -i "${F[@]}"
    sed '1,4 { /^\(#\|--\|dnl\) *-\*- [mM]ode/d }' -i "${F[@]}"

Check remaining lines with:

    git grep -e '-\*-'

The ultimate purpose of this is to cleanup our files and eventually use
SPDX license identifiers. For that, first get rid of the boilerplate lines.

We have certain artificial properties that not only depend on one
property alone or that depend on a property in another(!) setting.

For that, we have synth_func.

Other than that, synth_func and get_func are really fundamentally
similar and should be merged. That is because the distinction whether a
property value is "synthetized" or just based on a plain property is
minor. It's better to have the general concept of "convert property to
GVariant" in one form only.

Note that compare_property() is by default implemented based
on get_func. Hence, if get_func and synth_func get merged,
compare_property() will also require access to the NMConnection.

Also it makes some sense: some properties are artificial and actually
stored in "another" setting of the connection. But still, the property
descriptor for the property is in this setting. The example is the
"bond.interface-name" which only exists on D-Bus. It's stored as
"connection.interface-name".
I don't really like to say "exists on D-Bus only". It's still a valid
property, despite in NMSetting it's stored somehow differently (or not
at all). So, this is also just a regular property for which we have a
property-info vtable.
Does it make sense to compare such properties? Maybe. But the point is that
compare_property() function needs sometimes access to the entire
connection. So add the argument.

Order the code in our common way. No other changes.

- ensure to include the main header first (directly after
  "nm-default.h").

- reorder function definitions: get_property(), set_property(),
  *_init(), *_new(), finalize(), *_class_init().

NMSetting's compare_property() has and had two callers:
nm_setting_compare() and nm_setting_diff().

compare_property() accepts a NMSettingCompareFlags argument, but
at the same time, both callers have another complex (and
inconsistent!) set of pre-checks for shortcuting the call of
compare_property(): should_compare_prop().

Merge should_compare_prop() into compare_property(). This way,
nm_setting_compare() and nm_setting_diff() has less additional
code, and are simpler to follow. Especially nm_setting_compare()
is now trivial. And nm_setting_diff() is still complicated, but
not related to the question how the property compares or whether
it should be compared at all.

If you want to know whether it should be compared, all you need to do
now is follow NMSettingClass.compare_property().

This changes function pointer NMSettingClass.compare_property(),
which is public API. However, no user can actually use this (and shall
not!), because _nm_setting_class_commit_full() etc. is private API. A
user outside of libnm-core cannot create his/her own subclasses of
NMSetting, and never could in the past. So, this API/ABI change doesn't
matter.

NMSetting internally already tracked a list of all proper GObject properties
and D-Bus-only properties.

Rework the tracking of the list, so that:

- instead of attaching the data to the GType of the setting via
  g_type_set_qdata(), it is tracked in a static array indexed by
  NMMetaSettingType. This allows to find the setting-data by simple
  pointer arithmetic, instead of taking a look and iterating (like
  g_type_set_qdata() does).

  Note, that this is still thread safe, because the static table entry is
  initialized in the class-init function with _nm_setting_class_commit().
  And it only accessed by following a NMSettingClass instance, thus
  the class constructor already ran (maybe not for all setting classes,
  but for the particular one that we look up).

  I think this makes initialization of the metadata simpler to
  understand.
  Previously, in a first phase each class would attach the metadata
  to the GType as setting_property_overrides_quark(). Then during
  nm_setting_class_ensure_properties() it would merge them and
  set as setting_properties_quark(). Now, during the first phase,
  we only incrementally build a properties_override GArray, which
  we finally hand over during nm_setting_class_commit().

- sort the property infos by name and do binary search.

Also expose this meta data types as internal API in nm-setting-private.h.
While not accessed yet, it can prove beneficial, to have direct (internal)
access to these structures.

Also, rename NMSettingProperty to NMSettInfoProperty to use a distinct
naming scheme. We already have 40+ subclasses of NMSetting that are called
NMSetting*. Likewise, NMMetaSetting* is heavily used already. So, choose a
new, distinct name.

Previously, each (non abstract) NMSetting class had to register
its name and priority via _nm_register_setting().

Note, that libnm-core.la already links against "nm-meta-setting.c",
which also redundantly keeps track of the settings name and gtype
as well.

Re-use NMMetaSettingInfo also in libnm-core.la, to track this meta
data.

The goal is to get rid of private data structures that track
meta data about NMSetting classes. In this case, "registered_settings"
hash. Instead, we should have one place where all this meta data
is tracked. This was, it is also accessible as internal API,
which can be useful (for keyfile).

Note that NMSettingClass has some overlap with NMMetaSettingInfo.
One difference is, that NMMetaSettingInfo is const, while NMSettingClass
is only initialized during the class_init() method. Appart from that,
it's mostly a matter of taste, whether we attach meta data to
NMSettingClass, to NMMetaSettingInfo, or to a static-array indexed
by NMMetaSettingType.

Note, that previously, _nm_register_setting() was private API. That
means, no user could subclass a functioning NMSetting instance. The same
is still true: NMMetaSettingInfo is internal API and users cannot access
it to create their own NMSetting subclasses. But that is almost desired.
libnm is not designed, to be extensible via subclassing, nor is it
clear why that would be a useful thing to do. One day, we should remove
the NMSetting and NMSettingClass definitions from public headers. Their
only use is subclassing the types, which however does not work.

While libnm-core was linking already against nm-meta-setting.c,
nm_meta_setting_infos was unreferenced. So, this change increases
the binary size of libnm and NetworkManager (1032 bytes). Note however
that roughly the same information was previously allocated at runtime.

- Don't use @parent_class name. This local variable (and @object_class) is
  the class instance up-cast to the pointer types of the parents. The point
  here is not that it is the direct parent. The point is, that it's the
  NMSettingClass type.
  Also, it can only be used inconsistently, in face of NMSettingIP4Config,
  who's parent type is NMSettingIPConfig. Clearly, inside
  nm-setting-ip4-config.c we wouldn't want to use the "parent_class"
  name. Consistently rename @parent_class to @setting_class.

- Also rename the pointer to the own class to @klass. "setting_class" is also the
  wrong name for that, because the right name would be something like
  "setting_6lowpan_class".
  However, "klass" is preferred over the latter, because we commonly create new
  GObject implementations by copying an existing one. Generic names like "klass"
  and "self" inside a type implementation make that simpler.

- drop useless comments like

     /* virtual functions */
     /* Properties */

  It's better to logically and visually structure the code, and avoid trival
  remarks about that. They only end up being used inconsistently. If you
  even need a stronger visual separator, then an 80 char /****/ line
  should be preferred.