Use 3 argument Array.Copy, as it is more optimized in .NET5

[Therzok]

No description provided.

[jkotas]

ImmutableArray tests are failing:

    System.Collections.Immutable.Tests.ImmutableArrayTest.CopyToInvalid(source: []) [FAIL]
      Assert.Equal() Failure
                    � (pos 4)
      Expected: dest
      Actual:   destinationArray
                    � (pos 4)
      Stack Trace:
        /_/src/libraries/Common/tests/CoreFx.Private.TestUtilities/System/AssertExtensions.cs(46,0): at System.AssertExtensions.Throws[T](String netCoreParamName, String netFxParamName, Action action)
        /_/src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs(1635,0): at System.Collections.Immutable.Tests.ImmutableArrayTest.CopyToInvalid(IEnumerable`1 source)
    System.Collections.Immutable.Tests.ImmutableArrayTest.CopyToInvalid(source: [1]) [FAIL]

[jkotas]

It should be fine to fix the test failures by relaxing the argument name validation in this test.

[Therzok]

@jkotas Do you mean something like:

// Skip checking .NETFramework parameter name is either 'destinationArray' or 'dest'
AssertExtensions.Throws<ArgumentNullException>("destinationArray", netFxParamName: null, () => array.CopyTo(null));
AssertExtensions.Throws<ArgumentNullException>("destinationArray", netFxParamName: null, () => array.CopyTo(null, 0));
AssertExtensions.Throws<ArgumentNullException>("destinationArray", netFxParamName: null, () => array.CopyTo(0, null, 0, 0));
AssertExtensions.Throws<ArgumentNullException>("destinationArray", netFxParamName: null, () => array.CopyTo(-1, null, -1, -1)); // The destination should be validated first.

[stephentoub]

@Therzok, still working on this?

[Therzok]

@stephentoub I'll setup the repo on a Windows machine to see why it's failing, the tests passed locally on OS X. Sorry for the delays.

[stephentoub]

If you need help, let me know (and if I have push permissions to your branch, I can just fix it for you, too).

[Therzok]

I've had a few hoops and hurdles. If you have MSBuild Build Tools installed and they don';t have the required pre-reqs, you could end up opening the wrong developer command prompt to build. I'm trying to get the in-VS tests to run right now, looking at the test explorer, it doesn't seem to run them. Although it seems the top menu run seems to work.

[Therzok]

Okay, so, I've managed to get it setup and run it on .netcore. Whenever I try to run the .NET Framework config, I'm getting Illegal characters in path., with no extra explanation from VS.

[stephentoub]

I fixed up the commit. Thanks for the contribution.

[Therzok]

Thanks for that!