[generator] When using interface-constants, remove or obsolete interface alternatives. #600
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Context: #509 When using `generator --lang-features=interface-constants`, remove or obsolete interface alternatives. Due to our legacy workarounds for the C# shortcoming of not being able to place constants or members on interfaces, every interface with those members creates two additional "alternative" classes to provide users access to the members originally on the interface. For example, consider the Java interface [`android.os.Parcelable`][0]: // Java package android.os; public interface Parcelable { public static final int CONTENTS_FILE_DESCRIPTOR = 1; public static final int PARCELABLE_WRITE_RETURN_VALUE = 1; int describeContents(); void writeToParcel(Parcel dest, int flags); // ... } The binding in a C#7 world is: // C# Binding namespace Android.OS { public partial interface IParcelable { int DescribeContents(); void WriteToParcel(Parcel dest, [GeneratedEnum] ParcelableWriteFlags flags); } public abstract partial class Parcelable { internal Parcelable () {} public const int ContentsFileDescriptor = (int) 1; public const ParcelableWriteFlags ParcelableWriteReturnValue = (ParcelableWriteFlags) 1; } [Obsolete ("…", error: true)] public abstract partial class ParcelableConsts : Parcelable { private ParcelableConsts () {} public const int ContentsFileDescriptor = (int) 1; public const ParcelableWriteFlags ParcelableWriteReturnValue = (ParcelableWriteFlags) 1; } } `Parcelable` contains the interface constants which couldn't exist on `IParcelable`, and `ParcelableConsts` exists for backward compatibility (as we used `*Consts` types before we introduced the non-`*Consts` types), and is `[Obsolete(error:true)]`. In a C#8 world with `generator --lang-features=interface-constants` we no longer need to preserve these alternative types. The `*Consts` types have been `[Obsolete]` for over 5 years, but have only been `[Obsolete(error:true)]` since d16-4, released 2019-Dec-03. We feel it hasn't been an error long enough to remove it for *all* API levels, so we will stop emitting it for API-R. The `Parcelable` and similar alternative types are now redundant when `--lang-features=interface-constants,default-interface-methods` is used, as all members of the Java interface can now exist in the C# binding of that interface. Here, we will `[Obsolete]` the class and all members of the class, with a message referring to the new types and members to use. This results in an API-R binding of: // C# Binding, API-R namespace Android.OS { public partial interface IParcelable { int DescribeContents(); void WriteToParcel(Parcel dest, [GeneratedEnum] ParcelableWriteFlags flags); public const int ContentsFileDescriptor = (int) 1; public const ParcelableWriteFlags ParcelableWriteReturnValue = (ParcelableWriteFlags) 1; } [Obsolete ("Use 'Android.OS.IParcelable'. This class will be removed in a future release.")] public abstract partial class Parcelable { internal Parcelable () {} [Obsolete ("Use 'Android.OS.IParcelable.ContentsFileDescriptor'. This class will be removed in a future release.")] public const int ContentsFileDescriptor = (int) 1; [Obsolete ("Use 'Android.OS.IParcelable.ParcelableWriteReturnValue'. This class will be removed in a future release.")] public const ParcelableWriteFlags ParcelableWriteReturnValue = (ParcelableWriteFlags) 1; } } Additionally, fix a bug where fields that are marked `[Obsolete]` that are being changed into property getters were not having the obsolete attribute applied. [0]: https://developer.android.com/reference/android/os/Parcelable
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Context: #509.
Due to our legacy workarounds for the C# shortcoming of not being able to place constants or members on interfaces, every interface with those members creates two additional "alternative" classes to provide users access to the members originally on the interface.
For example, the Java interface
android.os.Parcelablecreates:interface IParcelablecontaining the interface declarationclass ParcelableConstscontaining the constants that are onParcelableclass Parcelablecontains the constants and static members that are onParcelableNow that we can support members on interfaces, we would like to start the process of removing these interface alternatives.
ParcelableConsts class
The XXXXConsts classes have been
[Obsolete]for over 5 years, and have been[Obsolete (iserror: true)]since 16.4. They haven't beeniserror: truefor long enough to completely remove, but we can remove them when--lang-features:interface-constantsis specified.In terms of
Mono.Android.dll, this means these classes will be removed for theAPI-Rbinding, but will still exist in previous bindings.Parcelable class
The XXXX class is now redundant when
interface-constantsanddefault-interface-methodsis specified, as all members of the interface can be generated on the interface.In this case, we
[Obsolete]all members in the alternativeParcelableclass with a message pointing to the original interface. Note that if the member already had[Obsolete]for another reason (like being deprecated in Java) we preserve that message instead.In terms of
Mono.Android.dll, this means these classes and their members will be[Obsolete]in theAPI-Rbinding, but not be obsoleted in previous bindings.Also fixed a bug where fields that are marked
[Obsolete]that are being changed into property getters where not having the obsolete attribute applied.Here's the diff on
Mono.Android.dll: https://gist.github.com/jpobst/717e67d6d21638c0600511ee34469c1d. Note thatmono-api-htmlapparently doesn't show removed classes, so I had to run it backwards. Thus everything reported as "additions" are actually "removals".