[WIP] [Xamarin.Android.Build.Tasks] use hashes as Inputs for _GenerateJavaStubs

[jonathanpeppers]

One of the slower parts of an incremental Android build is:

_GenerateJavaStubs = 978 ms

Currently, this happens when any .NET assembly changes: C# change, .xaml change, etc.

In theory, we could analyze .NET assemblies during the linker and create a "hash" that represents types & members that would invalidate _GenerateJavaStubs's output. We can then save these hashes in a file to be used as Inputs instead of the .NET assemblies themselves.

Example of the hash:

HashAlgorithm hasher = new Microsoft.Android.Build.Tasks.Crc64 ();
foreach (var type in scanner.GetJavaTypes (assembly)) {
    Hash (hasher, type.FullName);
    foreach (var method in type.Methods) {
        Hash (hasher, method.Name);
    }
}

The result is:

Target Name=_GenerateJavaStubs Project=bar.csproj
Skipping target "_GenerateJavaStubs" because all output files are up-to-date with respect to the input files.

Improving the incremental build time about about ~1 second in a dotnet new maui project. _LinkAssembliesNoShrink will be slightly slower, but because it builds partially it will only be creating this hash on a single file most of the time. Currently, this seems to be about ~20ms final numbers TBD.

Things left to do:

• Make sure we are hashing the right things that _GenerateJavaStubs cares about.

• Fix Release builds, they likely aren't setup right.

• Add several tests around this scenario. We need to validate adding new Java.Lang.Object subclasses work as expected.

[jonathanpeppers]

Actually, looks like I have a small code change in java.interop. Looks like this won't build yet...

[jonathanpeppers]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jonathanpeppers]

Due to the various errors trying to use JavaTypeScanner in Microsoft.Android.Sdk.ILLink.csproj.

I'm going to see if I can do this idea for Debug builds only.

[jonathanpeppers]

Closing old PRs, will revisit later if needed.