Invalid Code Generation & Potential Parsing Error

Version Used: VS 17.2.6

Steps to Reproduce:

Write this code:


public class Foo {
protected virtual T? Serialization_Remove<T>(string Value) {
    return default;
}
}

public class Foo1 : Foo {

}


2.  Then go inside Foo1 and type ```override ser``` and press ```TAB``` and then Foo1 will have the following code:

public class Foo1 : Foo {

protected override T? Serialization_Remove<T>(string Value) {
    return base.Serialization_Remove<T>(Value);
}

}


3.  The auto-generated code does not compile!  Oddly, however, altering the code as follows causes it to work:

public class Foo1 : Foo { protected override T? Serialization_Remove(string Value) where T : default { // Note the new where clause here return base.Serialization_Remove(Value); } }



**Expected Behavior**:
I believe there are two separate-but-related issues.

***Issue 1***
2. According to the [docs](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/where-generic-type-constraint) the ```where T : default``` is necessary ```...when a base class or interface declares two overloads of a method, one that specifies the struct constraint, and one that doesn't have either the struct or class constraint applied```, however, as you see in the code above, there are not two overloads of a method.  Because of this, I believe that the ```T : default``` should not be necessary.

***Issue 2***
The auto-generated code does not work.  It should, regardless of how Issue1 is dealt with.

**Actual Behavior**:
Auto-generated code should work; ideally without needing the ```T : default``` constraint.

dotnet / roslyn

Invalid Code Generation & Potential Parsing Error #62997