[Mono.Android] Use PublicApiAnalyzers to ensure we do not break API. (#8171)

Fixes: #7421

Context: #1118
Context: 07e7477

We currently have our internal `<CheckApiCompatibility/>` task
(07e7477), which ensures that we do not break backwards compatibility
between Android API levels.

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.)

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

Running the `PublicApiAnalyzer` adds about 25 seconds to a local build.
One can use our existing `$(DisableApiCompatibilityCheck)` property to
also disable them to facilitate faster local build if desired.

Additionally, disable [`RS0041`][2] ("Public members should not use
oblivious types").  We should look at getting
`Android.Runtime.JniEnv.g.cs` properly annotated with nullable
reference types, and then we could enable this analyzer.

***Note***: PublicApiAnalyzers cannot be the *only* mechanism that is
used to track API compatibility for `Mono.Android.dll`, because some
binding constructs can result in compatible APIs while breaking
*semantics*.  See also Issue #1118.  We thus need to continue using
`<CheckApiCompatibility/>` (or some equivalent) to ensure that our
`[Register]` attribute values do not change without review.

[0]: https://github.com/dotnet/roslyn-analyzers/tree/40a3ec17a7507b8767b4ac806f29b6df179cf627/src/PublicApiAnalyzers
[1]: https://github.com/dotnet/roslyn-analyzers/blob/40a3ec17a7507b8767b4ac806f29b6df179cf627/src/PublicApiAnalyzers/PublicApiAnalyzers.Help.md
[2]: https://github.com/dotnet/roslyn-analyzers/blob/40a3ec17a7507b8767b4ac806f29b6df179cf627/src/PublicApiAnalyzers/Microsoft.CodeAnalysis.PublicApiAnalyzers.md#rs0041-public-members-should-not-use-oblivious-types

Author: jpobst

build-tools/automation/guardian/PoliCheck.Exclusions.xml

@@ -1,9 +1,9 @@
 <PoliCheckExclusions>
+  <!-- Reminder: you are only allowed one exclusion element of each type, to have multiple values you must pipe separate them in a single element -->
   <!-- Each of these exclusions is a folder name - if \[name]\ exists in the file path, it will be skipped -->
   <Exclusion Type="FolderPathFull">LICENSE-DATA|NREFACTORY|LOCALIZE</Exclusion>
-  <Exclusion Type="FolderPathStart">src\Mono.Android\Profiles</Exclusion>
   <!-- Each of these exclusions is a folder name - if any folder or file starts with "\[name]", it will be skipped -->
-  <!--<Exclusion Type="FolderPathStart">ABC|XYZ</Exclusion>-->
+  <Exclusion Type="FolderPathStart">src\Mono.Android\Profiles|src\Mono.Android\PublicAPI</Exclusion>
   <!-- Each of these file types will be completely skipped for the entire scan -->
   <!--<Exclusion Type="FileType">.ABC|.XYZ</Exclusion>-->
   <!-- The specified file names will be skipped during the scan regardless which folder they are in -->

src/Mono.Android/Android.Runtime/JNIEnv.cs

@@ -835,7 +835,9 @@ static unsafe void _GetDoubleArrayRegion (IntPtr array, int start, int length, d
 				JniEnvironment.Arrays.GetDoubleArrayRegion (new JniObjectReference (array), start, length, p);
 		}
 
+#pragma warning disable RS0027 // API with optional parameter(s) should have the most parameters amongst its public overloads
 		public static void CopyArray (IntPtr src, Array dest, Type? elementType = null)
+#pragma warning restore RS0027 // API with optional parameter(s) should have the most parameters amongst its public overloads
 		{
 			if (dest == null)
 				throw new ArgumentNullException ("dest");

src/Mono.Android/Android/IncludeAndroidResourcesFromAttribute.cs

@@ -6,7 +6,9 @@ namespace Android {
 	[Obsolete ("This attribute is no longer supported.", error: true)]
 	public class IncludeAndroidResourcesFromAttribute : ReferenceFilesAttribute
 	{
+#pragma warning disable RS0022 // Constructor make noninheritable base class inheritable
 		public IncludeAndroidResourcesFromAttribute (string path)
+#pragma warning restore RS0022 // Constructor make noninheritable base class inheritable
 		{
 			ResourceDirectory = path;
 		}

src/Mono.Android/Java.Interop/JavaLibraryReferenceAttribute.cs

@@ -6,7 +6,9 @@ namespace Java.Interop {
 	[Obsolete ("This attribute is no longer supported.", error: true)]
 	public class JavaLibraryReferenceAttribute : Android.ReferenceFilesAttribute
 	{
+#pragma warning disable RS0022 // Constructor make noninheritable base class inheritable
 		public JavaLibraryReferenceAttribute (string filename)
+#pragma warning restore RS0022 // Constructor make noninheritable base class inheritable
 		{
 			LibraryFileName = filename;
 		}

src/Mono.Android/Java.Interop/JavaTypeParametersAttribute.cs

@@ -3,7 +3,10 @@
 #if NET
 using System.Runtime.CompilerServices;
 
+// PublicApiAnalyzers doesn't like TypeForwards
+#pragma warning disable RS0016 // Symbol is not part of the declared API
 [assembly: TypeForwardedTo (typeof (Java.Interop.JavaTypeParametersAttribute))]
+#pragma warning restore RS0016 // Symbol is not part of the declared API
 
 #else   // !NET
 

src/Mono.Android/Mono.Android.csproj

@@ -9,7 +9,7 @@
     <RootNamespace>Android</RootNamespace>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
-    <NoWarn>0618;0809;0108;0114;0465;8609;8610;8614;8617;8613;8764;8765;8766;8767</NoWarn>
+    <NoWarn>0618;0809;0108;0114;0465;8609;8610;8614;8617;8613;8764;8765;8766;8767;RS0041</NoWarn>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);JAVA_INTEROP</DefineConstants>
     <IntermediateOutputPath>$(BaseIntermediateOutputPath)$(Configuration)\$(TargetFramework)\android-$(AndroidPlatformId)\</IntermediateOutputPath>
@@ -27,6 +27,7 @@
   <PropertyGroup>
     <DefineConstants Condition=" '$(AndroidApiLevel)' &gt; '$(AndroidLatestStableApiLevel)' ">$(DefineConstants);ANDROID_UNSTABLE</DefineConstants>
     <OutputPath>$(_MonoAndroidNETDefaultOutDir)</OutputPath>
+    <RunAnalyzers Condition=" '$(DisableApiCompatibilityCheck)' == 'True' ">false</RunAnalyzers>
   </PropertyGroup>
 
   <PropertyGroup Condition=" '$(IncludeAndroidJavadoc)' == 'True' ">
@@ -39,6 +40,11 @@
     <NoWarn>$(NoWarn);CA1422;CA1416</NoWarn>
   </PropertyGroup>
 
+  <ItemGroup>
+    <AdditionalFiles Include="PublicAPI\API-$(AndroidApiLevel)\PublicAPI.Shipped.txt" />
+    <AdditionalFiles Include="PublicAPI\API-$(AndroidApiLevel)\PublicAPI.Unshipped.txt" />
+  </ItemGroup>
+  
   <PropertyGroup>
     <JavaCallableWrapperAbsAssembly>$([System.IO.Path]::GetFullPath ('$(OutputPath)$(AssemblyName).dll'))</JavaCallableWrapperAbsAssembly>
   </PropertyGroup>
@@ -338,6 +344,13 @@
     <Compile Include="Xamarin.Android.Net\NegotiateAuthenticationHelper.cs" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.PublicApiAnalyzers" Version="3.3.4">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\build-tools\create-android-api\create-android-api.csproj" ReferenceOutputAssembly="false" />
     <!-- Explicitly pass the target framework of the project so we don't have conflicts with the multiple targets in this file. -->

src/Mono.Android/Properties/AssemblyInfo.cs.in

@@ -7,6 +7,7 @@
 // Copyright 2014 Xamarin, Inc.
 // Copyright 2016 Microsoft Corporation.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.Versioning;
@@ -26,6 +27,8 @@ using System.Runtime.Versioning;
 [assembly: SupportedOSPlatform("Android@[email protected]")]
 #endif
 
+// PublicApiAnalyzers doesn't like TypeForwards
+#pragma warning disable RS0016 // Symbol is not part of the declared API
 [assembly: System.Runtime.CompilerServices.TypeForwardedToAttribute(typeof(System.Drawing.Color))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedToAttribute(typeof(System.Drawing.ColorConverter))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedToAttribute(typeof(System.Drawing.KnownColor))]
@@ -36,9 +39,13 @@ using System.Runtime.Versioning;
 [assembly: System.Runtime.CompilerServices.TypeForwardedToAttribute(typeof(System.Drawing.Size))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedToAttribute(typeof(System.Drawing.SizeF))]
 [assembly: System.Runtime.CompilerServices.TypeForwardedToAttribute(typeof(System.Drawing.SystemColors))]
+#pragma warning restore RS0016 // Symbol is not part of the declared API
+
 [assembly: InternalsVisibleTo("Mono.Android.Export, PublicKey=0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf16cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b2c9733db")]
 [assembly: InternalsVisibleTo("Mono.Android-Tests, PublicKey=0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf16cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b2c9733db")]
 [assembly: InternalsVisibleTo("Java.Interop-Tests, PublicKey=0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf16cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b2c9733db")]
 [assembly: InternalsVisibleTo("Mono.Android-TestsMultiDex, PublicKey=0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf16cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b2c9733db")]
 [assembly: InternalsVisibleTo("Mono.Android-TestsAppBundle, PublicKey=0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf16cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b2c9733db")]
 [assembly: InternalsVisibleTo("Mono.Android.NET-Tests, PublicKey=0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf16cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b2c9733db")]
+
+[assembly: SuppressMessage ("ApiDesign", "RS0016:Add public types and members to the declared API", Justification = "Analyzer fails due to extended characters.", Scope = "member", Target = "~F:Android.Util.Patterns.GoodIriChar")]

src/Mono.Android/PublicAPI/API-34/PublicAPI.Shipped.txt

@@ -0,0 +1 @@
+#nullable enable