[Java.Interop] Use PublicApiAnalyzers to ensure we do not break API (#1170)

Fixes: #1169

Context: dotnet/android@76ab8b2

dotnet/android@76ab8b2c mentions:

> Now that we are in the .NET `TargetFramework` world we also need
> to ensure we do not *add* any new API to a Target Framework once it
> has shipped.  A `TargetFramework` is essentially a contract that we
> cannot change.  (Imagine if you had different minor versions of .NET
> on your local machine and CI machine, what works on one should work
> on the other.)

This prevents an issue where a user on `.NET 8.0.300` uses a method
that isn't available to their coworker or CI on `.NET 8.0.100`.

This logical argument also applies to `Java.Interop.dll`.

Enable Microsoft's [PublicApiAnalyzers][0] for `Java.Interop.dll`.
([PublicApiAnalyzers documentation][1].)  This ensures that we don't
add new API once we've shipped `Java.Interop.dll` for a given
.NET version.

Update `build-tools/jnienv-gen` so that `JniEnvironment.g.cs` enables
nullable reference types.  This allows us to *avoid* disabling RS0041.

Co-authored-by: Jonathan Pryor <jonpryor@vt.edu>

[0]: https://github.com/dotnet/roslyn-analyzers/tree/ace28a1039d09626a94d3b0f8ce69e547ca2bcbf/src/PublicApiAnalyzers
[1]: https://github.com/dotnet/roslyn-analyzers/blob/ace28a1039d09626a94d3b0f8ce69e547ca2bcbf/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md

Author: jpobst

build-tools/jnienv-gen/Generator.cs

@@ -86,6 +86,7 @@ static void GenerateFile (TextWriter o)
 			o.WriteLine ("// Generated file; DO NOT EDIT!");
 			o.WriteLine ("//");
 			o.WriteLine ("// To make changes, edit monodroid/tools/jnienv-gen-interop and rerun");
+			o.WriteLine ("#nullable enable");
 			o.WriteLine ();
 			o.WriteLine ("#if !FEATURE_JNIENVIRONMENT_SAFEHANDLES && !FEATURE_JNIENVIRONMENT_JI_INTPTRS && !FEATURE_JNIENVIRONMENT_JI_PINVOKES && !FEATURE_JNIENVIRONMENT_XA_INTPTRS && !FEATURE_JNIENVIRONMENT_JI_FUNCTION_POINTERS");
 			o.WriteLine ("#define FEATURE_JNIENVIRONMENT_JI_PINVOKES");
@@ -255,7 +256,7 @@ static void GenerateJniNativeInterfaceInvoker (TextWriter o, HandleStyle style)
 				if (e.Prebind)
 					o.WriteLine ("\t\tpublic readonly {0} {1};\n", d, e.Name);
 				else {
-					o.WriteLine ("\t\t{0} _{1};", d, e.Name);
+					o.WriteLine ("\t\t{0}? _{1};", d, e.Name);
 					o.WriteLine ("\t\tpublic {0} {1} {{", d, e.Name);
 					o.WriteLine ("\t\t\tget {");
 					o.WriteLine ("\t\t\t\tif (_{0} == null)\n\t\t\t\t\t{1}", e.Name, Initialize (e, "_", d));
@@ -551,7 +552,7 @@ static void RaiseException (TextWriter o, JniFunction entry, HandleStyle style)
 				return;
 
 			o.WriteLine ();
-			o.WriteLine ("\t\t\tException __e = JniEnvironment.GetExceptionForLastThrowable ({0});",
+			o.WriteLine ("\t\t\tException? __e = JniEnvironment.GetExceptionForLastThrowable ({0});",
 					(style == HandleStyle.JIIntPtrPinvokeWithErrors || style == HandleStyle.JIFunctionPtrWithErrors)
 					? "thrown"
 					: "");
@@ -1127,7 +1128,7 @@ public override string[] GetMarshalToManagedStatements (HandleStyle style, strin
 			case HandleStyle.JIFunctionPtrWithErrors:
 				return new[] {
 					string.Format ("if ({0} == IntPtr.Zero)", variable),
-					string.Format ("\treturn null;"),
+					string.Format ($"\tthrow new InvalidOperationException (\"Should not be reached; `{entry.Name}` should have thrown!\");"),
 					string.Format ("return new {0} ({1}, {2}, {3}, isStatic: {4});", type, entry.Parameters [1].Name, entry.Parameters [2].Name, variable, IsStatic ? "true" : "false"),
 				};
 			case HandleStyle.XAIntPtr:

src/Java.Interop/Java.Interop.csproj

@@ -88,18 +88,11 @@
       <DependentUpon>JniPeerMembers.JniInstanceMethods_Invoke.tt</DependentUpon>
     </Compile>
   </ItemGroup>
-  <ProjectExtensions>
-    <MonoDevelop>
-      <Properties>
-        <Policies>
-          <VersionControlPolicy>
-            <CommitMessageStyle Indent="&#x9;" LineAlign="0" IncludeDirectoryPaths="True" />
-          </VersionControlPolicy>
-        </Policies>
-      </Properties>
-    </MonoDevelop>
-  </ProjectExtensions>
   <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.PublicApiAnalyzers" Version="3.3.4">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
     <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="All" />
   </ItemGroup>
   <Import Project="Java.Interop.targets" />

src/Java.Interop/Java.Interop/JavaObjectArray.cs

@@ -11,6 +11,7 @@ public class JavaObjectArray<T> : JavaArray<T>
 	{
 		internal    static  readonly    ValueMarshaler   Instance           = new ValueMarshaler ();
 
+		[SuppressMessage ("ApiDesign", "RS0022:Constructor make noninheritable base class inheritable", Justification = "Existing public API")]
 		public JavaObjectArray (ref JniObjectReference handle, JniObjectReferenceOptions options)
 			: base (ref handle, options)
 		{
@@ -29,20 +30,23 @@ static JniObjectReference NewArray (int length)
 			}
 		}
 
+		[SuppressMessage ("ApiDesign", "RS0022:Constructor make noninheritable base class inheritable", Justification = "Existing public API")]
 		public unsafe JavaObjectArray (int length)
 			: this (ref *InvalidJniObjectReference, JniObjectReferenceOptions.None)
 		{
 			var peer    = NewArray (CheckLength (length));
 			Construct (ref peer, JniObjectReferenceOptions.CopyAndDispose);
 		}
 
+		[SuppressMessage ("ApiDesign", "RS0022:Constructor make noninheritable base class inheritable", Justification = "Existing public API")]
 		public JavaObjectArray (IList<T> value)
 			: this (CheckLength (value))
 		{
 			for (int i = 0; i < value.Count; ++i)
 				SetElementAt (i, value [i]);
 		}
 
+		[SuppressMessage ("ApiDesign", "RS0022:Constructor make noninheritable base class inheritable", Justification = "Existing public API")]
 		public JavaObjectArray (IEnumerable<T> value)
 			: this (ToList (value))
 		{

src/Java.Interop/Java.Interop/JniEnvironment.Types.cs

@@ -262,7 +262,7 @@ public static void RegisterNatives (JniObjectReference type, JniNativeMethodRegi
 				}
 #endif  // DEBUG && NETCOREAPP
 
-				int r   = _RegisterNatives (type, methods, numMethods);
+				int r   = _RegisterNatives (type, methods ?? Array.Empty<JniNativeMethodRegistration>(), numMethods);
 
 				if (r != 0) {
 					throw new InvalidOperationException (

src/Java.Interop/Java.Interop/JniValueMarshaler.cs

@@ -49,6 +49,7 @@ public struct JniValueMarshalerState : IEquatable<JniValueMarshalerState> {
 		public  IJavaPeerable?          PeerableValue       {get; private set;}
 		public  object?                 Extra               {get; private set;}
 
+		[SuppressMessage ("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "Existing public API")]
 		public JniValueMarshalerState (JniArgumentValue jniArgumentValue, object? extra = null)
 		{
 			JniArgumentValue    = jniArgumentValue;
@@ -57,6 +58,7 @@ public JniValueMarshalerState (JniArgumentValue jniArgumentValue, object? extra
 			Extra               = extra;
 		}
 
+		[SuppressMessage ("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "Existing public API")]
 		public JniValueMarshalerState (JniObjectReference referenceValue, object? extra = null)
 		{
 			JniArgumentValue    = new JniArgumentValue (referenceValue);
@@ -65,6 +67,7 @@ public JniValueMarshalerState (JniObjectReference referenceValue, object? extra
 			Extra               = extra;
 		}
 
+		[SuppressMessage ("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "Existing public API")]
 		public JniValueMarshalerState (IJavaPeerable? peerableValue, object? extra = null)
 		{
 			PeerableValue       = peerableValue;