Add partial method modifier support for Value, From and TryFrom

[DPDmancul]

This solves #845 for Value, From and TryFrom. It could be easily extended to support also TryParse and other methods.

This enables:

• Adding an attribute to a generated method

[ValueObject]
public sealed partial class MyVo
{
    [Obsolete("For internal use only")]
    public static partial MyVo From(int value);
}

• Making a generated method private

[ValueObject]
public sealed partial class MyVo
{
    private static partial MyVo From(int value);
}

[SteveDunn]

Thanks for the PR @DPDmancul . This is for C# 14 right? I guess we'll need to determine the version of Roslyn loaded and or the language version, before generating the partial methods.

[DPDmancul]

This is for C# 14 right?

I ran the tests with C# 12, but it should work also for lower versions. Only for using the partial keyword with properties (e.g. Value) it is required C# 13. But this shouldn't be a problem: if the user is using a language version which doesn't allow the partial keyword, it will be notified with an error in its code.

we'll need to determine the version of Roslyn loaded [..] before generating the partial methods.

Indeed the problem in the CI tests is that the IPropertySymbol.IsPartialDefinition property is not found: this property is available since Roslyn 4.12.2

Since the version of Microsoft.CodeAnalysis.CSharp is not specified, it is taken from the target framework. So maybe this could be solved with preprocessor directives, putting the logic inside an #if NETX_0_OR_GREATER, and otherwise returning always null (as if the partial property was not found).

[DPDmancul]

Since there is no direct correspondence between target framework and Roslyn versions, I added a runtime fallback. Instead of directly calling the property, I try to get the property with reflection and return a fallback value (false) if it does not exist (i.e. we have an old Roslyn).

[SteveDunn]

I think we're nearly there @DPDmancul ! Thanks for your hard work on this one; apologies, I know it's quite difficult even to get the simplest of changes into Vogen!

It looks like the last hurdle is to fix the snapshot tests. You can run them from the IDE, or from the command line. If I'm fairly certain that my changes are all correct, I run .\RunSnapshots.ps1 -v "minimal" -reset in the root. This takes about 30 minutes and rebases the snapshots to what is generated on that run. It's a good gauge of the impact of your change: if you see only a small number of git changes, then your fix is limited and hasn't modified anything else.

[SteveDunn]

LGTM! Thank you for the great contribution!