Update test templates for V9 (#1451)

* Update test templates for V9

Update the language version in all our testing templates for C# 9.

Required for testing PRs for V9 features.

* revert changes where global usings

are in force.

* note changed C# 9 behavior

* one more test failure.

* Use V9 in this template

* Change expected error.

Author: BillWagner

standard/attributes.md

@@ -20,7 +20,7 @@ A generic class declaration shall not use `System.Attribute` as a direct or indi
 
 > *Example*:
 >
-> <!-- Example: {template:"standalone-lib", name:"AttributeCantBeGeneric", expectedErrors:["CS8400"], ignoredWarnings:["CS0169"]} -->
+> <!-- Example: {template:"standalone-lib", name:"AttributeCantBeGeneric", expectedErrors:["CS8773"], ignoredWarnings:["CS0169"]} -->
 > ```csharp
 > public class B : Attribute {}
 > public class C<T> : B {} // Error – generic cannot be an attribute
@@ -982,7 +982,8 @@ Specifies that a non-nullable return value may be null.
 
 > *Example*: Consider the following generic method:
 >
-> <!-- Example: {template:"code-in-class-lib", name:"MaybeNull1Attribute", replaceEllipsis:true, customEllipsisReplacements: ["return default;"], expectedErrors:["CS8627"]} -->
+> <!-- TODO:  This sample no longer generates the error in C# 9. This could be part of the new nullable constraints. Was: , expectedErrors:["CS8627"]-->
+> <!-- Example: {template:"code-in-class-lib", name:"MaybeNull1Attribute", replaceEllipsis:true, customEllipsisReplacements: ["return default;"]} -->
 > ```csharp
 > #nullable enable
 > public T? Find<T>(IEnumerable<T> sequence, Func<T, bool> predicate) { ... }

tools/example-templates/code-in-class-lib-without-using/Project.csproj

@@ -5,7 +5,7 @@
     <AssemblyName>$example-name</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
 </Project>

tools/example-templates/code-in-class-lib/Project.csproj

@@ -5,7 +5,7 @@
     <AssemblyName>$example-name</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
 </Project>

tools/example-templates/code-in-main-without-using/Project.csproj

@@ -6,7 +6,7 @@
     <Nullable>annotations</Nullable>
     <AssemblyName>$example-name</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
 </Project>

tools/example-templates/code-in-main/Project.csproj

@@ -6,7 +6,7 @@
     <Nullable>annotations</Nullable>
     <AssemblyName>$example-name</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
 </Project>

tools/example-templates/code-in-partial-class/Project.csproj

@@ -6,7 +6,7 @@
     <AssemblyName>$example-name</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
 </Project>

tools/example-templates/extern-lib/ExampleProject.csproj

@@ -5,7 +5,7 @@
     <EnableDefaultItems>false</EnableDefaultItems>
     <NoWarn>CS0169</NoWarn>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

tools/example-templates/extern-lib/ExternN2.csproj

@@ -4,7 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <EnableDefaultItems>false</EnableDefaultItems>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

tools/example-templates/extern-lib/ExternR1.csproj

@@ -4,7 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <EnableDefaultItems>false</EnableDefaultItems>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

tools/example-templates/extern-lib/ExternX.csproj

@@ -4,7 +4,7 @@
     <TargetFramework>net6.0</TargetFramework>
     <EnableDefaultItems>false</EnableDefaultItems>
     <Nullable>annotations</Nullable>
-    <LangVersion>8</LangVersion>
+    <LangVersion>9</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>