Fully update CompilationOptions when project files change.

[SirIntruder]

When .csproj files change, o# gets fully updated CSharpCompilationOptions from MSBuild, but it doesn't apply them to the workspace. Because of this, o# completely ignores changes to AllowUnsafeCode, Nullable, DefineConstants, LangVersion etc. after the initial project load.

Fortunately, o# was updating CSharpCompilationOptions already, for the purpose of updating analyzer rulesets. So fix amounted to passing

projectFileInfo.CreateCompilationOptions()

instead of

project.CompilationOptions.WithSpecificDiagnosticOptions(projectFileInfo.GetDiagnosticOptions())

Problem with the old code was that project.CompilationOptions was essentially old compiler options. ProjectFileInfo is fresh data, and with this PR the whole CompilerOptions object will be fresh, not just the DiagnosticsOptions part.

[SirIntruder]

I will make a test when I catch some more time this week, need to check how FileChanges are handled in the testHost.

[filipw]

thanks a lot this very helpful.

Because of this, o# completely ignores changes to AllowUnsafeCode, Nullable, DefineConstants, LangVersion etc. after the initial project load.

this is not entirely true, because OmniSharp already automatically updates parse options (like DefineConstants, LangVersion). Only compilation options are ignored.

[filipw]

IMHO this is ok to take as-is, we can add the test in a separate PR

[JoeRobich]

@SirIntruder Thanks!