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Document breaking change for #46044 #51070

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Mar 9, 2021
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Document breaking change for #46044 #51070

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Document breaking change for #46044
cston Feb 8, 2021
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Rename file
cston Mar 5, 2021
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cston Mar 5, 2021
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13 changes: 13 additions & 0 deletions docs/compilers/CSharp/Compiler Breaking Changes - DotNet 6.md
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## This document lists known breaking changes in Roslyn in C# 9.0 introduced with .NET 6.
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@Youssef1313 Youssef1313 Feb 8, 2021 •
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Consider adding a link for this document in https://github.com/dotnet/docs/blob/main/docs/csharp/whats-new/breaking-changes.md.


1. https://github.com/dotnet/roslyn/issues/46044 In C# 9.0 (Visual Studio 16.9), a warning is reported when assigning `default` to, or when casting a possibly `null` value to a type parameter type that is not constrained to value types or reference types. To avoid the warning, the type can be annotated with `?`.
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@jcouv jcouv Feb 9, 2021 •
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In C# 9.0 [](start = 49, length = 9)

I think this warning is now produced even for LangVer=8, right? If so we should just say "In Visual Studio 16.9, ..."

I didn't understand why start a new document. There is no .NET 6 yet (we just shipped .NET 5).
Our file structure got a bit confused. The latest file is DotNet 5 (for 16.8). So we could start a new document for post-DotNet 5. #Resolved

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I think this warning is now produced even for LangVer=8, right?

No, the warnings are not reported with /langversion:8.

So we could start a new document for post-DotNet 5.

I've renamed the document to "Compiler Breaking Changes - post DotNet 5.md" based on our discussion.

In reply to: 572483433 [](ancestors = 572483433)

```C#
static void F1<T>(object? obj)
{
T t1 = default; // warning CS8600: Converting possible null value to non-nullable type
t1 = (T)obj; // warning CS8600: Converting possible null value to non-nullable type

T? t2 = default; // ok
t2 = (T?)obj; // ok
}
```
12 changes: 12 additions & 0 deletions docs/compilers/CSharp/Compiler Breaking Changes - post VS2019.md
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Expand Up @@ -142,3 +142,15 @@ class C

22. https://github.com/dotnet/roslyn/issues/49596 In *Visual Studio 2019 version 16.9* and greater, conversions from `sbyte` or `short` to `nuint` require explicit casts,
and binary operations with `sbyte` or `short` and `nuint` arguments require explicit casts for one or both operands for `+`, `-`, `*`, `/`, `%`, `<`, `>`, `<=`, `>=`, `==`, `!=`, `|`, `&`, and `^`.

23. https://github.com/dotnet/roslyn/issues/46044 In *Visual Studio 2019 version 16.9* and greater, a warning is reported when assigning `default` to, or when casting a possibly `null` value to a type parameter type that is not constrained to value types or reference types. To avoid the warning, the type can be annotated with `?`.
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I'm a little bit lost here. The title of this document is:

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

I'm expecting this to be documented in the new file only. Am I missing something?

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Indeed, it looks like we messed up with some recent breaking changes.
The latest file is https://github.com/dotnet/roslyn/blob/master/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20DotNet%205.md and corresponds to VS 16.8 / .NET 5.
We should probably start a new file for post-.NET 5.

```C#
static void F1<T>(object? obj)
{
T t1 = default; // warning CS8600: Converting possible null value to non-nullable type
t1 = (T)obj; // warning CS8600: Converting possible null value to non-nullable type

T? t2 = default; // ok
t2 = (T?)obj; // ok
}
```