[tests] Add net6.0 TargetFramework.

[jpobst]

Today, even when building and testing on .NET 6, most of our test suites are still building and running with net472. Fix this by adding the net6.0 <TargetFramework> and updating CI to run the net6.0 version instead of the net472 version.

Fixes were required to account for differences between net472 and net6.0 behavior.

[jonpryor]

What error is being observed that requires disabling this fixture?

[jpobst]

Compile errors:

error CS0117: 'AssemblyBuilderAccess' does not contain a definition for 'Save'
error CS1061: 'AppDomain' does not contain a definition for 'DefineDynamicAssembly' and no accessible extension method 'DefineDynamicAssembly' accepting a first argument of type 'AppDomain' could be found (are you missing a using directive or an assembly reference?)
error CS1061: 'LambdaExpression' does not contain a definition for 'CompileToMethod' and no accessible extension method 'CompileToMethod' accepting a first argument of type 'LambdaExpression' could be found (are you missing a using directive or an assembly reference?)

[jonpryor]

I think the .NET rounding algorithm changed?

I think this might be better addressed by "forcing" the rounding mode within the ConstantPoolItem subclasses, e.g.

diff --git a/src/Xamarin.Android.Tools.Bytecode/ConstantPool.cs b/src/Xamarin.Android.Tools.Bytecode/ConstantPool.cs
index a030f37f..59eda31f 100644
--- a/src/Xamarin.Android.Tools.Bytecode/ConstantPool.cs
+++ b/src/Xamarin.Android.Tools.Bytecode/ConstantPool.cs
@@ -260,7 +260,7 @@ namespace Xamarin.Android.Tools.Bytecode {
 
 		public override string ToString ()
 		{
-			return string.Format (CultureInfo.InvariantCulture, "Float({0})", Value);
+			return string.Format (CultureInfo.InvariantCulture, "Float({0:E6})", Value);
 		}
 	}
 
@@ -329,7 +329,7 @@ namespace Xamarin.Android.Tools.Bytecode {
 
 		public override string ToString ()
 		{
-			return string.Format (CultureInfo.InvariantCulture, "Double({0})", Value);
+			return string.Format (CultureInfo.InvariantCulture, "Double({0:E14})", Value);
 		}
 	}
 

[jpobst]

The actual output we are writing to XML files is using the "R" format specifier, which is producing different values based on target framework. The documentation suggests using "G9" and "G17" instead for roundtripping.

I have updated our code to use this and tests pass. This is technically a functional change, but it seems like it should not cause any issues.

[jonpryor]

I'm not fond that this file exists, as it (again) suggests differing output based on whether net6 or mono is used.

Without running diff -u JavaType.xml JavaType-net.xml, I'm going to assume that the diffs are due to float/double representation differences. If this is the case, the solution is to as done above, and force a consistent rounding length, so that Mono & net6 produce identical output.

[jonpryor]

Why is this reference required? It doesn't appear to have anything:

 % monodis --typedef /usr/local/share/dotnet/shared/Microsoft.NETCore.App/6.0.0-preview.7.21377.19/System.Runtime.dll       
Typedef Table
1: (null) (flist=1, mlist=1, flags=0x0, extends=0x0)

[jpobst]

CS0012: The type 'Enum' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. (SourceFile([871..891)))
CS0012: The type 'ValueType' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. (SourceFile([944..962)))
CS0012: The type 'IDisposable' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. (SourceFile([312..321)))

[jonpryor]

Today, even when building and testing on .NET 6, most of our test
suites are still building and running with `net472`.

Fix this by adding `net6.0` to `$(TargetFrameworks)` and updating CI
to run the `net6.0` version instead of the `net472` version.

Fixes were required to account for differences between `net472` and
`net6.0` behavior, in particular:

  * The semantics for the [Round-trip format specifier `R`][0]
    changed between .NET Framework and .NET 6.
    Update `ConstantPoolFloatItem.ToString()` and
    `ConstantPoolDoubleItem.ToString()` to use the G9 and G17
    format specifiers, respectively, so that behavior is consistent.

  * Types such as `System.String` moved from `mscorlib.dll` to
    `System.Private.CoreLib.dll`, which impacts the output of
    `JavaNativeTypeManager.GetPackageName()`, as the assembly name
    is taken consideration.  Assertions around
    `JavaNativeTypeManager.GetPackageName()` need to be based on the
    target framework.

  * When using `CSharpCompilation.Create()`, `System.Runtime.dll`
    must now be referenced when building on net6+, otherwise certain
    types won't be resolved:

        error CS0012: The type 'Enum' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. (SourceFile([871..891)))
        error CS0012: The type 'ValueType' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. (SourceFile([944..962)))
        error CS0012: The type 'IDisposable' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. (SourceFile([312..321)))

  * `MarshalMemberBuilderTest.cs` must be disabled when building for
    .NET 6+, as `AssemblyBuilderAccess.Save` doesn't exist, nor does
    `AppDomain.DefineDynamicAssembly()`, nor
    `LambdaExpression.CompileToMethod()`.
    Related: https://github.com/xamarin/java.interop/issues/616

        error CS0117: 'AssemblyBuilderAccess' does not contain a definition for 'Save'
        error CS1061: 'AppDomain' does not contain a definition for 'DefineDynamicAssembly' and no accessible extension method 'DefineDynamicAssembly' accepting a first argument of type 'AppDomain' could be found (are you missing a using directive or an assembly reference?)
        error CS1061: 'LambdaExpression' does not contain a definition for 'CompileToMethod' and no accessible extension method 'CompileToMethod' accepting a first argument of type 'LambdaExpression' could be found (are you missing a using directive or an assembly reference?)

[0]: https://docs.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings#round-trip-format-specifier-r