Obsolete PreserveAttribute #5664
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jonpryor
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Jul 26, 2021
Fixes: dotnet#5664 The .NET 5+ replacement for [`Android.Runtime.PreserveAttribute`][0] is [`System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute`][1]. One "discrepancy" is that the relationship is "backwards": `[Preserve]` is an *assertion* that the member is required, and that the member should be preserved by the linker. `DynamicDependencyAttribute` is an indicator: *if* the member with `[DynamicDependency]` is preserved, then the members referenced by `[DynamicDependency]` will be preserved. Consider commit 15269f6: in a `[Preserve]` world, we had: // `Mono.Android.dll` [Preserve(AllMembers=true)] partial class JavaCollection { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } [Preserve(AllMembers=true)] partial class JavaDictionary { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } // … // `Mono.Android.Export.dll` partial class DynamicInvokeTypeInfo { public CodeExpression ToNative (CodeExpression arg) { switch (GetKind (type)) { case SymbolKind.Collection: return new CodeMethodCall (type.GetMethod ("ToLocalJniHandle"), arg); } } } This setup meant that even when `Mono.Android.Export.dll` *wasn't* used, all members of `JavaCollection` and `JavaDictionary` were preserved by the linker, increasing `.apk` size. With a `[DynamicDependency]` world in commit 15269f6, we now have: // `Mono.Android.dll` partial class JavaCollection { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } partial class JavaDictionary { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } // … // `Mono.Android.Export.dll` partial class DynamicInvokeTypeInfo { [DynamicDependency ("ToLocalJniHandle", "Android.Runtime.JavaCollection", "Mono.Android")] [DynamicDependency ("ToLocalJniHandle", "Android.Runtime.JavaDictionary", "Mono.Android")] public CodeExpression ToNative (CodeExpression arg) { switch (GetKind (type)) { case SymbolKind.Collection: return new CodeMethodCall (type.GetMethod ("ToLocalJniHandle"), arg); } } } Now, if `Mono.Android.Export.dll` *isn't* used, then `JavaCollection` and `JavaDictionary` can be removed, enabling smaller apps: > apkdiff -f -e dll$ before.apk after.apk Size difference in bytes ([*1] apk1 only, [*2] apk2 only): - 477 assemblies/Java.Interop.dll - 603 assemblies/System.Collections.Concurrent.dll - 1,388 assemblies/System.Private.CoreLib.dll - 30,291 assemblies/Mono.Android.dll Summary: - 32,759 Assemblies -4.19% (of 781,837) - 32,768 Package size difference -0.43% (of 7,645,409) [0]: https://docs.microsoft.com/en-us/dotnet/api/foundation.preserveattribute?view=xamarin-ios-sdk-12 [1]: https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.codeanalysis.dynamicdependencyattribute?view=net-5.0
jonpryor
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Jul 27, 2021
Fixes: #5664 The .NET 5+ replacement for [`Android.Runtime.PreserveAttribute`][0] is [`System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute`][1]. One "discrepancy" is that the relationship is "backwards": `[Preserve]` is an *assertion* that the member is required, and that the member should be preserved by the linker. `DynamicDependencyAttribute` is an indicator: *if* the member with `[DynamicDependency]` is preserved, then the members referenced by `[DynamicDependency]` will be preserved. Consider commit 15269f6: in a `[Preserve]` world, we had: // `Mono.Android.dll` [Preserve(AllMembers=true)] partial class JavaCollection { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } [Preserve(AllMembers=true)] partial class JavaDictionary { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } // … // `Mono.Android.Export.dll` partial class DynamicInvokeTypeInfo { public CodeExpression ToNative (CodeExpression arg) { switch (GetKind (type)) { case SymbolKind.Collection: return new CodeMethodCall (type.GetMethod ("ToLocalJniHandle"), arg); } } } This setup meant that even when `Mono.Android.Export.dll` *wasn't* used, all members of `JavaCollection` and `JavaDictionary` were preserved by the linker, increasing `.apk` size. With a `[DynamicDependency]` world in commit 15269f6, we now have: // `Mono.Android.dll` partial class JavaCollection { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } partial class JavaDictionary { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } // … // `Mono.Android.Export.dll` partial class DynamicInvokeTypeInfo { [DynamicDependency ("ToLocalJniHandle", "Android.Runtime.JavaCollection", "Mono.Android")] [DynamicDependency ("ToLocalJniHandle", "Android.Runtime.JavaDictionary", "Mono.Android")] public CodeExpression ToNative (CodeExpression arg) { switch (GetKind (type)) { case SymbolKind.Collection: return new CodeMethodCall (type.GetMethod ("ToLocalJniHandle"), arg); } } } Now, if `Mono.Android.Export.dll` *isn't* used, then `JavaCollection` and `JavaDictionary` can be removed, enabling smaller apps: > apkdiff -f -e dll$ before.apk after.apk Size difference in bytes ([*1] apk1 only, [*2] apk2 only): - 477 assemblies/Java.Interop.dll - 603 assemblies/System.Collections.Concurrent.dll - 1,388 assemblies/System.Private.CoreLib.dll - 30,291 assemblies/Mono.Android.dll Summary: - 32,759 Assemblies -4.19% (of 781,837) - 32,768 Package size difference -0.43% (of 7,645,409) [0]: https://docs.microsoft.com/en-us/dotnet/api/foundation.preserveattribute?view=xamarin-ios-sdk-12 [1]: https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.codeanalysis.dynamicdependencyattribute?view=net-5.0
jonpryor
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Jul 27, 2021
Fixes: #5664 The .NET 5+ replacement for [`Android.Runtime.PreserveAttribute`][0] is [`System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute`][1]. One "discrepancy" is that the relationship is "backwards": `[Preserve]` is an *assertion* that the member is required, and that the member should be preserved by the linker. `DynamicDependencyAttribute` is an indicator: *if* the member with `[DynamicDependency]` is preserved, then the members referenced by `[DynamicDependency]` will be preserved. Consider commit 15269f6: in a `[Preserve]` world, we had: // `Mono.Android.dll` [Preserve(AllMembers=true)] partial class JavaCollection { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } [Preserve(AllMembers=true)] partial class JavaDictionary { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } // … // `Mono.Android.Export.dll` partial class DynamicInvokeTypeInfo { public CodeExpression ToNative (CodeExpression arg) { switch (GetKind (type)) { case SymbolKind.Collection: return new CodeMethodCall (type.GetMethod ("ToLocalJniHandle"), arg); } } } This setup meant that even when `Mono.Android.Export.dll` *wasn't* used, all members of `JavaCollection` and `JavaDictionary` were preserved by the linker, increasing `.apk` size. With a `[DynamicDependency]` world in commit 15269f6, we now have: // `Mono.Android.dll` partial class JavaCollection { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } partial class JavaDictionary { public static IntPtr ToLocalJniHandle (ICollection? items) {…} } // … // `Mono.Android.Export.dll` partial class DynamicInvokeTypeInfo { [DynamicDependency ("ToLocalJniHandle", "Android.Runtime.JavaCollection", "Mono.Android")] [DynamicDependency ("ToLocalJniHandle", "Android.Runtime.JavaDictionary", "Mono.Android")] public CodeExpression ToNative (CodeExpression arg) { switch (GetKind (type)) { case SymbolKind.Collection: return new CodeMethodCall (type.GetMethod ("ToLocalJniHandle"), arg); } } } Now, if `Mono.Android.Export.dll` *isn't* used, then `JavaCollection` and `JavaDictionary` can be removed, enabling smaller apps: > apkdiff -f -e dll$ before.apk after.apk Size difference in bytes ([*1] apk1 only, [*2] apk2 only): - 477 assemblies/Java.Interop.dll - 603 assemblies/System.Collections.Concurrent.dll - 1,388 assemblies/System.Private.CoreLib.dll - 30,291 assemblies/Mono.Android.dll Summary: - 32,759 Assemblies -4.19% (of 781,837) - 32,768 Package size difference -0.43% (of 7,645,409) [0]: https://docs.microsoft.com/en-us/dotnet/api/foundation.preserveattribute?view=xamarin-ios-sdk-12 [1]: https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.codeanalysis.dynamicdependencyattribute?view=net-5.0
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The attribute is not needed in .NET6 and can interfere with supported .NET linker attributes. The linker is able to recognize and mark reflection patterns automatically and for custom scenarios better attribute is supported https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.codeanalysis.dynamicdependencyattribute.
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