PR feedback.

Closes dotnet#29683
Closes dotnet#29662

docs/features/nullable-reference-types.md

@@ -8,7 +8,7 @@ In source, nullable reference types are annotated with `?`.
 string? OptString; // may be null
 Dictionary<string, object?>? OptDictionaryOptValues; // dictionary may be null, values may be null
 ```
-A warning is reported when annotating a reference type or unconstrained generic type with `?` outside a `#nullable` context.
+A warning is reported when annotating a reference type with `?` outside a `#nullable` context.
 
 In metadata, nullable reference types are annotated with a `[Nullable]` attribute.
 ```c#
@@ -28,7 +28,8 @@ namespace System.Runtime.CompilerServices
 }
 ```
 
-Each type reference is accompanied by a NullableAttribute with an array of bytes, where 0 is Oblivious, 1 is NotAnnotated and 2 is Annotated. 
+Each type reference is accompanied by a NullableAttribute with an array of bytes, where 0 is Oblivious, 1 is NotAnnotated and 2 is Annotated.
+All value types are marked with flag 0 (oblivious).
 
 To optimize trivial cases the attribute can be omitted, or instead can be replaced with an attribute that takes a single byte value rather than an array.  
 
@@ -41,7 +42,7 @@ Trivial/optimized cases:
 
 NullableAttribute(1) should be placed on a type parameter definition that has a `class!` constraint.
 NullableAttribute(2) should be placed on a type parameter definition that has a `class?` constraint.
-Other forms of NullableAttribute ar not emitted on type parameter definitions and are not specially recognized on them.
+Other forms of NullableAttribute are not emitted on type parameter definitions and are not specially recognized on them.
 
 The `NullableAttribute` type declaration is synthesized by the compiler if it is not included in the compilation, but is needed to produce the output.
 
@@ -58,6 +59,8 @@ string[] Oblivious1; // string~[]~
 [Nullable(new[] { 1, 1 })] string[] NotNull2; // string![]!
 [Nullable(new[] { 0, 2 })] string[] ObliviousMaybeNull; // string?[]~
 [Nullable(new[] { 1, 2 })] string[] NotNullMaybeNull; // string?[]!
+int Int; // int
+Nullable<int> NullableInt1; // Nullable<int>
 ```
 ## Declaration warnings
 _Describe warnings reported for declarations in initial binding._

src/Compilers/CSharp/Portable/Symbols/TypeSymbolWithAnnotations.cs

@@ -967,8 +967,8 @@ public bool ApplyNullableTransforms(byte defaultTransformFlag, ImmutableArray<by
                     break;
 
                 case NullableAnnotation.Unknown:
-                    Debug.Assert((NullableAnnotation)transformFlag == NullableAnnotation.Unknown);
-                    if (result.NullableAnnotation != NullableAnnotation.Unknown && (!result.NullableAnnotation.IsAnyNullable() || !oldTypeSymbol.IsNullableType()))
+                    if (result.NullableAnnotation != NullableAnnotation.Unknown &&
+                        !(result.NullableAnnotation.IsAnyNullable() && oldTypeSymbol.IsNullableType())) // Preserve nullable annotation on Nullable<T>.
                     {
                         result = CreateNonLazyType(newTypeSymbol, NullableAnnotation.Unknown, result.CustomModifiers);
                     }

src/Compilers/CSharp/Test/Emit/Emit/EditAndContinue/EditAndContinueStateMachineTests.cs

@@ -4814,7 +4814,7 @@ public IEnumerable<int> F()
                 Diagnostic(ErrorCode.ERR_EncUpdateFailedMissingAttribute, "F").WithArguments("C.F()", "System.Runtime.CompilerServices.IteratorStateMachineAttribute").WithLocation(12, 29));
         }
 
-        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/29662")]
+        [Fact]
         public void AddedIteratorStateMachineAttribute()
         {
             var source0 = MarkedSource(@"
@@ -4999,7 +4999,7 @@ public async Task<int> F()
                 Diagnostic(ErrorCode.ERR_EncUpdateFailedMissingAttribute, "F").WithArguments("C.F()", "System.Runtime.CompilerServices.AsyncStateMachineAttribute").WithLocation(6, 28));
         }
 
-        [Fact(Skip = "https://github.com/dotnet/roslyn/issues/29662")]
+        [Fact]
         public void AddedAsyncStateMachineAttribute()
         {
             var source0 = MarkedSource(@"