In this PR, we add a generic views.ValuePointer type that can be used as a view for pointers
to basic types and struct types that do not require deep cloning and do not have corresponding
view types. Its Get/GetOk methods return stack-allocated shallow copies of the underlying value.
We then update the cmd/viewer codegen to produce getters that return either concrete views
when available or ValuePointer views when not, for pointer fields in generated view types.
This allows us to avoid unnecessary allocations compared to returning pointers to newly
allocated shallow copies.
Updates #14570
Signed-off-by: Nick Khyl <nickk@tailscale.com>
This adds a new package containing generic types to be used for defining preference hierarchies.
These include prefs.Item, prefs.List, prefs.StructList, and prefs.StructMap. Each of these types
represents a configurable preference, holding the preference's state, value, and metadata.
The metadata includes the default value (if it differs from the zero value of the Go type)
and flags indicating whether a preference is managed via syspolicy or is hidden/read-only for
another reason. This information can be marshaled and sent to the GUI, CLI and web clients
as a source of truth regarding preference configuration, management, and visibility/mutability states.
We plan to use these types to define device preferences, such as the updater preferences,
the permission mode to be used on Windows with #tailscale/corp#18342, and certain global options
that are currently exposed as tailscaled flags. We also aim to eventually use these types for
profile-local preferences in ipn.Prefs and and as a replacement for ipn.MaskedPrefs.
The generic preference types are compatible with the tailscale.com/cmd/viewer and
tailscale.com/cmd/cloner utilities.
Updates #12736
Signed-off-by: Nick Khyl <nickk@tailscale.com>
