[generator] Add support for emitting [UnsupportedOSPlatform] (#1307)

Fixes: #1309
Context: dotnet/android@944d306
Sometimes, Android *removes* APIs. For example, API-23 *removed* the
`android.Manifest.permission.CLEAR_APP_USER_DATA` field.
We still list this field, though:
[`Android.Manifest.Permission.ClearAppUserData` field][0].
> [Android.Runtime.Register("CLEAR_APP_USER_DATA")]
> public const string ClearAppUserData;
In dotnet/android@944d3061 we updated `api-merge` to emit
`//*/@#removed-since`. Consider this snippet from
[`android/src/Mono.Android/Profiles/api-35.xml`][1]:
<field
deprecated="not deprecated" final="true"
name="CLEAR_APP_USER_DATA" jni-signature="Ljava/lang/String;"
static="true" transient="false" type="java.lang.String" type-generic-aware="java.lang.String"
value="&quot;android.permission.CLEAR_APP_USER_DATA&quot;"
visibility="public" volatile="false"
removed-since="23"
/>
Modify `generator` to consume this information and emit
`[UnsupportedOSPlatformAttribute ("androidXX.0")]` as needed for API
that has been removed from `Mono.Android`. This would update
`Android.Manifest.Permission.ClearAppUserData` to be:
[Android.Runtime.Register("CLEAR_APP_USER_DATA")]
[System.Runtime.Versioning.UnsupportedOSPlatformAttribute ("android23.0")]
public const string ClearAppUserData;
[0]: https://learn.microsoft.com/en-us/dotnet/api/android.manifest.permission.clearappuserdata?view=net-android-34.0
[1]: https://github.com/dotnet/android/blob/d012fb811b4bcebe260400f5fc7a0287108336d7/src/Mono.Android/Profiles/api-35.xml

Author: jpobst

tests/generator-Tests/Unit-Tests/CodeGeneratorTests.cs

@@ -1406,6 +1406,36 @@ public void SupportedOSPlatformConstFields ()
 StringAssert.Contains("[global::System.Runtime.Versioning.SupportedOSPlatformAttribute (\"android30.0\")]",builder.ToString(),"Should contain SupportedOSPlatform!");
 }
 
+[Test]
+publicvoidUnsupportedOSPlatform()
+{
+varklass=SupportTypeBuilder.CreateClass("java.code.MyClass",options);
+klass.ApiRemovedSince=30;
+
+generator.Context.ContextTypes.Push(klass);
+generator.WriteType(klass,string.Empty,newGenerationInfo("","","MyAssembly"));
+generator.Context.ContextTypes.Pop();
+
+StringAssert.Contains("[global::System.Runtime.Versioning.UnsupportedOSPlatformAttribute (\"android30.0\")]",builder.ToString(),"Should contain UnsupportedOSPlatform!");
+}
+
+[Test]
+publicvoidUnsupportedOSPlatformConstFields()
+{
+varklass=newTestClass("java.lang.Object","com.mypackage.foo");
+varfield=newTestField("java.lang.String","bar").SetConstant("MY_VALUE");
+
+field.ApiRemovedSince=30;
+
+klass.Fields.Add(field);
+
+generator.Context.ContextTypes.Push(klass);
+generator.WriteType(klass,string.Empty,newGenerationInfo("","","MyAssembly"));
+generator.Context.ContextTypes.Pop();
+
+StringAssert.Contains("[global::System.Runtime.Versioning.UnsupportedOSPlatformAttribute (\"android30.0\")]",builder.ToString(),"Should contain UnsupportedOSPlatform!");
+}
+
 [Test]
 publicvoidStringPropertyOverride([Values("true","false")]stringfinal)
 {

tests/generator-Tests/Unit-Tests/XmlApiImporterTests.cs

@@ -51,6 +51,15 @@ public void CreateClass_CorrectApiSinceOverridePackage ()
 Assert.AreEqual(9,klass.ApiAvailableSince);
 }
 
+[Test]
+publicvoidCreateClass_CorrectApiRemoved()
+{
+varxml=XDocument.Parse("<package name='com.example.test' jni-name='com/example/test'><class name='myclass' removed-since='7' /></package>");
+varklass=XmlApiImporter.CreateClass(xml.Root,xml.Root.Element("class"),opt);
+
+Assert.AreEqual(7,klass.ApiRemovedSince);
+}
+
 [Test]
 publicvoidCreateCtor_EnsureValidName()
 {

tools/generator/ApiVersionsSupport.cs

@@ -18,6 +18,7 @@ public static class ApiVersionsSupport
 publicinterfaceIApiAvailability
 {
 intApiAvailableSince{get;set;}
+intApiRemovedSince{get;set;}
 }
 
 staticIEnumerable<GenBase>FlattenGens(IEnumerable<GenBase>gens)

tools/generator/Java.Interop.Tools.Generator.Importers/XmlApiImporter.cs

@@ -159,6 +159,7 @@ public static Ctor CreateCtor (GenBase declaringType, XElement elem, CodeGenerat
 varctor=newCtor(declaringType){
 AnnotatedVisibility=elem.XGetAttribute("annotated-visibility"),
 ApiAvailableSince=declaringType.ApiAvailableSince,
+ApiRemovedSince=declaringType.ApiRemovedSince,
 CustomAttributes=elem.XGetAttribute("customAttributes"),
 Deprecated=elem.Deprecated(),
 DeprecatedSince=elem.XGetAttributeAsIntOrNull("deprecated-since"),
@@ -211,6 +212,7 @@ public static Field CreateField (GenBase declaringType, XElement elem, CodeGener
 varfield=newField{
 AnnotatedVisibility=elem.XGetAttribute("annotated-visibility"),
 ApiAvailableSince=declaringType.ApiAvailableSince,
+ApiRemovedSince=declaringType.ApiRemovedSince,
 DeprecatedComment=elem.XGetAttribute("deprecated"),
 DeprecatedSince=elem.XGetAttributeAsIntOrNull("deprecated-since"),
 IsAcw=true,
@@ -369,6 +371,7 @@ public static Method CreateMethod (GenBase declaringType, XElement elem, CodeGen
 varmethod=newMethod(declaringType){
 AnnotatedVisibility=elem.XGetAttribute("annotated-visibility"),
 ApiAvailableSince=declaringType.ApiAvailableSince,
+ApiRemovedSince=declaringType.ApiRemovedSince,
 ArgsType=elem.Attribute("argsType")?.Value,
 CustomAttributes=elem.XGetAttribute("customAttributes"),
 Deprecated=elem.Deprecated(),
@@ -515,9 +518,12 @@ static XElement GetPreviousClass (XNode n, string nameValue)
 // Elements need to be passed in the above order. (package, class, member)
 staticvoidFillApiSince(ApiVersionsSupport.IApiAvailabilitymodel,paramsXElement[]elems)
 {
-foreach(vareleminelems)
+foreach(vareleminelems){
 if(int.TryParse(elem.XGetAttribute("api-since"),outvarresult))
 model.ApiAvailableSince=result;
+if(int.TryParse(elem.XGetAttribute("removed-since"),outvarremoved))
+model.ApiRemovedSince=removed;
+}
 }
 
 staticboolIsObfuscatedName(intthreshold,stringname)

tools/generator/Java.Interop.Tools.Generator.ObjectModel/Field.cs

@@ -9,6 +9,7 @@ public class Field : ApiVersionsSupport.IApiAvailability, ISourceLineInfo
 publicstringAnnotatedVisibility{get;set;}
 publicstringAnnotation{get;set;}
 publicintApiAvailableSince{get;set;}
+publicintApiRemovedSince{get;set;}
 publicstringDeprecatedComment{get;set;}
 publicint?DeprecatedSince{get;set;}
 publicboolIsAcw{get;set;}

tools/generator/Java.Interop.Tools.Generator.ObjectModel/GenBase.cs

@@ -188,6 +188,8 @@ IEnumerable<GenBase> Ancestors ()
 
 publicintApiAvailableSince{get;set;}
 
+publicintApiRemovedSince{get;set;}
+
 publicvirtualClassGenBaseGen=>null;
 
 publicGenBaseBaseSymbol=>

tools/generator/Java.Interop.Tools.Generator.ObjectModel/MethodBase.cs

@@ -16,6 +16,7 @@ protected MethodBase (GenBase declaringType)
 publicstringAnnotatedVisibility{get;set;}
 publicstringAnnotation{get;internalset;}
 publicintApiAvailableSince{get;set;}
+publicintApiRemovedSince{get;set;}
 publicstringAssemblyName{get;set;}
 publicGenBaseDeclaringType{get;}
 publicstringDeprecated{get;set;}

tools/generator/SourceWriters/Attributes/UnsupportedOSPlatformAttr.cs

@@ -0,0 +1,21 @@
+usingSystem;
+usingSystem.Collections.Generic;
+usingSystem.Linq;
+usingSystem.Text;
+usingSystem.Threading.Tasks;
+usingXamarin.SourceWriter;
+
+namespacegenerator.SourceWriters
+{
+publicclassUnsupportedOSPlatformAttr:AttributeWriter
+{
+publicintVersion{get;}
+
+publicUnsupportedOSPlatformAttr(intversion)=>Version=version;
+
+publicoverridevoidWriteAttribute(CodeWriterwriter)
+{
+writer.WriteLine($"[global::System.Runtime.Versioning.UnsupportedOSPlatformAttribute (\"android{Version}.0\")]");
+}
+}
+}

tools/generator/SourceWriters/Extensions/SourceWriterExtensions.cs

@@ -12,6 +12,8 @@ namespace generator.SourceWriters
 {
 publicstaticclassSourceWriterExtensions
 {
+constintMINIMUM_API_LEVEL=21;
+
 publicstaticvoidAddField(TypeWritertw,GenBasetype,Fieldfield,CodeGenerationOptionsopt)
 {
 if(field.NeedsProperty)
@@ -306,16 +308,26 @@ public static void AddParameterListCallArgs (List<string> body, ParameterList pa
 }
 
 publicstaticvoidAddSupportedOSPlatform(List<AttributeWriter>attributes,ApiVersionsSupport.IApiAvailabilitymember,CodeGenerationOptionsopt)
-=>AddSupportedOSPlatform(attributes,member.ApiAvailableSince,opt);
+{
+AddSupportedOSPlatform(attributes,member.ApiAvailableSince,opt);
+AddUnsupportedOSPlatform(attributes,member.ApiRemovedSince,opt);
+}
 
 publicstaticvoidAddSupportedOSPlatform(List<AttributeWriter>attributes,intsince,CodeGenerationOptionsopt)
 {
 // There's no sense in writing say 'android15' because we do not support older APIs,
 // so those APIs will be available in all of our versions.
-if(since>21&&opt.CodeGenerationTarget==Xamarin.Android.Binder.CodeGenerationTarget.XAJavaInterop1)
+if(since>MINIMUM_API_LEVEL&&opt.CodeGenerationTarget==Xamarin.Android.Binder.CodeGenerationTarget.XAJavaInterop1)
 attributes.Add(newSupportedOSPlatformAttr(since));
 }
 
+publicstaticvoidAddUnsupportedOSPlatform(List<AttributeWriter>attributes,intsince,CodeGenerationOptionsopt)
+{
+// Here it makes sense to still write 'android15' because it will be missing in later versions like `android35`.
+if(since>0&&opt.CodeGenerationTarget==CodeGenerationTarget.XAJavaInterop1)
+attributes.Add(newUnsupportedOSPlatformAttr(since));
+}
+
 publicstaticvoidAddObsolete(List<AttributeWriter>attributes,stringmessage,CodeGenerationOptionsopt,boolforceDeprecate=false,boolisError=false,int?deprecatedSince=null)
 {
 // Bail if we're not obsolete
@@ -336,7 +348,7 @@ static bool AddObsoletedOSPlatformAttribute (List<AttributeWriter> attributes, s
 returnfalse;
 
 // If it was obsoleted in a version earlier than we support (like 15), use a regular [Obsolete] instead
-if(!deprecatedSince.HasValue||deprecatedSince<=21)
+if(!deprecatedSince.HasValue||deprecatedSince<=MINIMUM_API_LEVEL)
 returnfalse;
 
 // This is the default Android message, but it isn't useful so remove it