Use generic Marshal.SizeOf when possible

[ThadHouse]

85507b9 introduced a new call to Marshal.Sizeof(Type). This call is not AOT compatible, which is a regression as prior versions were AOT compatible, even if not directly supported.

This conditionally uses the generic version of Marshal.SizeOf, which is AOT compatible to fix the issue.

Closes #21824

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[eerhardt]

@JasonLunn @YarinOmesi - it looks like #19667 caused this regression with native AOT. Is there any way this PR could get merged to unblock the AOT issue?

[snailcatcher]

I think this is a pretty good solution.
I understand that you not officially support AoT.
But, if someone wants to use AoT on his own risk, why not let them do that?

[eerhardt]

@JasonLunn - What is the process for getting this change merged? Are there C# owners/contributors in this project that could review and get the change merged?

[jskeet]

I can't speak to whether this will fix any AOT issues, but it at worst looks harmless.

[jskeet]

(Assigned back to @googleberg for the next step.)

[googleberg]

@ThadHouse Tests seem to be failing. You may need to rebase.

[martincostello]

This pull request is from an unsafe fork and hasn't been approved to run tests.
A protobuf team member will need to review the PR and add the 'safe for tests' tag.

[ThadHouse]

Rebased anyway, but as said it seems like tests were just not running due to being external.

[zhangskz]

Looks like this got stuck at some point after it was approved and likely got garbage collected. Giving this a kick now to see if we can get this submitted. Feel free to follow up if this seems to get stuck again.

[martincostello]

Was the fix for this expected to be in the 3.33.0 release?

After getting a renovate PR for the version bump, I'm still getting this error in CI:

/_/csharp/src/Google.Protobuf/Collections/RepeatedField.cs(714): AOT analysis error IL3050: Google.Protobuf.Collections.RepeatedField`1.TryGetArrayAsSpanPinnedUnsafe(FieldCodec`1<T>,Span`1<Byte>&,GCHandle&): Using member 'System.Runtime.InteropServices.Marshal.SizeOf(Type)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. Marshalling code for the object might not be available. Use the SizeOf<T> overload instead. [/home/runner/work/api/api/src/API/API.csproj]

[martincostello]

Looks like it didn't. The NuGet package was built from a79f2d2, and that line of code is still:

protobuf/csharp/src/Google.Protobuf/Collections/RepeatedField.cs

Line 714 in a79f2d2

if (BitConverter.IsLittleEndian && (codec.FixedSize > 0 && Marshal.SizeOf(typeof(T)) == codec.FixedSize))

[zhangskz]

Looks like this just barely missed the branch cut for v33.0 unforutnately, but I'll flag this for the v33.2 patch.

[zhangskz]

We should be patching this in v33.2 ~this week.