Compiler Breaking Changes Post VS2019

This document lists known breaking changes in Roslyn in Visual Studio 2019 Update 1 and beyond compared to Visual Studio 2019.

Breaks are formatted with a monotonically increasing numbered list to allow them to referenced via shorthand (i.e., "known break #1"). Each entry should include a short description of the break, followed by either a link to the issue describing the full details of the break or the full details of the break inline.

1. https://github.com/dotnet/roslyn/issues/38305

Compiler used to generate incorrect code when a built-in comparison operator producing Boolean? was used as an operand of a logical short-circuiting operator used as a Boolean expression. For example, for an expression

    GetBool3() = True AndAlso GetBool2()

and functions

    Function GetBool2() As Boolean
        System.Console.WriteLine("GetBool2")
        Return True
    End Function
    Shared Function GetBool3() As Boolean?
         Return Nothing
    End Function

it is expected that GetBool2 function going to be called. This is also the expected behavior outside of a Boolean expression, but in context of a Boolean expression the GetBool2 function was not called. Compiler now generates code that follows language semantics and calls GetBool2 function for the expression above.