[generator] Don't mark a method as [UnsupportedOSPlatform] if it overrides a supported base method. (#1313)

Context: 1cfb4f4

@jonathanpeppers [noted][0]:

> MAUI noticed this API says `UnsupportedOSPlatform`:
> 
>     // Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065
>     // Android.OS.Bundle
>     [UnsupportedOSPlatform("android21.0")]
>     [Register("putString", "(Ljava/lang/String;Ljava/lang/String;)V", "")]
>     public override void PutString(string? key, string? value) { ... }

In [API-21][1], `android.os.Bundle.putString()` was *moved* to the
new base class [`android.os.BaseBundle`][2].

	<class … name="BaseBundle" … merge.SourceFile="..\..\bin\BuildDebug\api\api-21.xml.in">
	  <method … name="putString" jni-signature="(Ljava/lang/String;Ljava/lang/String;)V" …>
	    <parameter name="key" type="java.lang.String" jni-type="Ljava/lang/String;"></parameter>
	    <parameter name="value" type="java.lang.String" jni-type="Ljava/lang/String;"></parameter>
	  </method>
	</class>
	…
	<class … extends="android.os.BaseBundle" … name="Bundle" …>
	  <method … name="putString" jni-signature="(Ljava/lang/String;Ljava/lang/String;)V" … removed-since="21">
	    <parameter name="key" type="java.lang.String" jni-type="Ljava/lang/String;"></parameter>
	    <parameter name="value" type="java.lang.String" jni-type="Ljava/lang/String;"></parameter>
	  </method>
	</class>

This movement was detected as an API *removal* by `api-merge`,
causing `generator` to emit `[UnsupportedOSPlatform]`:

	partial class Bundle {
	  [UnsupportedOSPlatform("android21.0")]
	  [Register("putString", "(Ljava/lang/String;Ljava/lang/String;)V", "")]
	  public override void PutString(string? key, string? value) => …
	}

While technically correct that `android.os.Bundle.putString()` was
"removed" in API-21, it was really moved to a base class as
`android.os.BaseBundle.putString()`.  We will continue to generate both
methods for binary compatibility, but we should not mark the overriding
method as `[UnsupportedOSPlatform]` because the "supported" base method
is still present.

Fix `generator` to recognize this case and not emit
`[UnsupportedOSPlatform]` here.

With this change, `Android.OS.Bundle.cs` contains:

	partial class Bundle {
	  // Metadata.xml XPath method reference: path="/api/package[@name='android.os']/class[@name='Bundle']/method[@name='putString' and count(parameter)=2 and parameter[1][@type='java.lang.String'] and parameter[2][@type='java.lang.String']]"
	  [Register ("putString", "(Ljava/lang/String;Ljava/lang/String;)V", "")]
	  public override unsafe void PutString (string? key, string? value) { ... }
	}

[0]: https://discord.com/channels/732297728826277939/732297837953679412/1342558634390982666
[1]: https://developer.android.com/sdk/api_diff/21/changes
[2]: https://developer.android.com/reference/android/os/BaseBundle

Author: jpobst

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

@@ -1436,6 +1436,39 @@ public void UnsupportedOSPlatformConstFields ()
 			StringAssert.Contains ("[global::System.Runtime.Versioning.UnsupportedOSPlatformAttribute (\"android30.0\")]", builder.ToString (), "Should contain UnsupportedOSPlatform!");
 		}
 
+
+		[Test]
+		public void UnsupportedOSPlatformIgnoresMethodOverrides ()
+		{
+			// Given:
+			// public class TextView {
+			//   public Object doThing () { ... }
+			// }
+			// public class TextView2 : TextView {
+			//   public Object doThing () { ... }   // removed-since = 30
+			// }
+			// We should not write [UnsupportedOSPlatform] on TextView2.doThing (), because the base method isn't "removed".
+			var xml = @$"<api>
+			  <package name='java.lang' jni-name='java/lang'>
+			    <class abstract='false' deprecated='not deprecated' final='false' name='Object' static='false' visibility='public' jni-signature='Ljava/lang/Object;' />
+			  </package>
+			  <package name='android.widget' jni-name='android/widget'>
+			    <class abstract='false' deprecated='not deprecated' extends='java.lang.Object' extends-generic-aware='java.lang.Object' final='false' name='TextView' static='false' visibility='public'>
+			       <method abstract='false' deprecated='not deprecated' final='false' name='doThing' bridge='false' native='false' return='java.lang.Object' static='false' synchronized='false' synthetic='false' visibility='public' />
+			     </class>
+			    <class abstract='false' deprecated='not deprecated' extends='android.widget.TextView' extends-generic-aware='java.lang.Object' final='false' name='TextView2' static='false' visibility='public'>
+			       <method abstract='false' deprecated='not deprecated' final='false' name='doThing' bridge='false' native='false' return='java.lang.Object' static='false' synchronized='false' synthetic='false' visibility='public' removed-since='30' />
+			     </class>
+			  </package>
+			</api>";
+
+			var gens = ParseApiDefinition (xml);
+			var klass = gens.Single (g => g.Name == "TextView2");
+			var actual = GetGeneratedTypeOutput (klass);
+
+			StringAssert.DoesNotContain ("[global::System.Runtime.Versioning.UnsupportedOSPlatformAttribute (\"android30.0\")]", actual, "Should contain UnsupportedOSPlatform!");
+		}
+
 		[Test]
 		public void StringPropertyOverride ([Values ("true", "false")] string final)
 		{

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

@@ -323,6 +323,11 @@ public void FixupMethodOverrides (CodeGenerationOptions opt)
 								m.DeprecatedSince = bm.DeprecatedSince;
 						}
 
+						// If a "removed" method overrides a "not removed" method, the method was
+						// likely moved to a base class, so don't mark it as removed.
+						if (m.ApiRemovedSince > 0 && bm.ApiRemovedSince == 0)
+							m.ApiRemovedSince = 0;
+
 						break;
 					}
 				}