Add Solution.WithProjectInfo API

[tmat]

Returns a new Solution snapshot with the target project updated to values specified in ProjectInfo.

Makes it possible for dotnet-watch to incrementally update Solution based on information loaded from MSBuild.

[tmat]

@dotnet/roslyn-ide @ToddGrun @CyrusNajmabadi @jasonmalinowski ptal

[CyrusNajmabadi]

overall this change seems ok. i def have some questions, and some small suggestions.

I'm not a fan of seeing null becoming first class in these codepaths :) but i can be convinced it's ok if we talk about it.

[CyrusNajmabadi]

high level preference, if we can disallow null (or moving from non-null to null), that would be my STRONG preference.

[tmat]

high level preference, if we can disallow null (or moving from non-null to null), that would be my STRONG preference.

The issue is that our APIs are inconsistent. We allow nulls in some public APIs such as ProjectInfo and disallow in others (WithCompilationOptions, WithParseOptions). I assume this is to support non-C#/VB projects.

[CyrusNajmabadi]

The issue is that our APIs are inconsistent. We allow nulls in some public APIs such as ProjectInfo and disallow in others (WithCompilationOptions, WithParseOptions). I assume this is to support non-C#/VB projects.

My feeling is that this should be like 'language' (which cannot be changed). If you hve a language with options, then you have options, and they should not be null. If you have a language without options, then you don't have options, and it should only be null. The change between (especially non-null to null) feels broken and confusing to me.

[CyrusNajmabadi]

tnx.