Invalid code for bool? to bool conversion in return

[bahusoid]

If you change the code below:
https://github.com/nhibernate/nhibernate-core/blob/4d887d8796e7c4e56cf88f52b5748826d6255c18/src/NHibernate/Engine/ISessionImplementor.cs#L47-L50

to the following:

internal static bool AutoFlushIfRequired(this ISessionImplementor implementor, ISet<string> querySpaces)
{
	return (implementor as AbstractSessionImpl)?.AutoFlushIfRequired(querySpaces) ?? false;
}

Iinvalid code is generated:

internal static async Task<bool> AutoFlushIfRequiredAsync(this ISessionImplementor implementor, ISet<string> querySpaces, CancellationToken cancellationToken)
{
	cancellationToken.ThrowIfCancellationRequested();
	var autoFlushIfRequiredTask = (implementor as AbstractSessionImpl)?.AutoFlushIfRequiredAsync(querySpaces, cancellationToken);
	if (autoFlushIfRequiredTask != null)
	{
		return await (autoFlushIfRequiredTask).ConfigureAwait(false) ?? false;
	}
	return (implementor as AbstractSessionImpl)?.AutoFlushIfRequiredAsync(querySpaces, cancellationToken) ?? false;
}

Compilation error:
error CS0019: Operator '??' cannot be applied to operands of type 'bool' and 'bool'

P.S. It's not something that I really need just noticed when tested some stuff

[maca88]

I've changed the generation logic for a Null-conditional operator when the return value is used afterwards.
The problem of generating an if statement in this case is that without knowing the end value type that will be used afterwards is not always possible to create a valid code.
Example:

public int? Test()
{
  var number = GetReader()?.ReadContentAsString().Length;
  // A lot of code that may use the number variable...
  return number > 5 ? number : 0;
}

The old behavior copied the whole code after the invocation statement, but as we can see below the code is invalid because of duplicate variable names:

// Old method - not working
public async Task<int?> TestAsync()
{
  var task = GetReader()?.ReadContentAsStringAsync();
  if (task != null)
  {
    var number = (await task).Length;
    // A lot of code that may use the number variable...
    return number > 5 ? number : 0;
  }
  var number = GetReader()?.ReadContentAsString().Length; // Error: number already declared
  // A lot of code that may use the number variable...
  return number > 5 ? number : 0;
}

The only solution that I found and implement to solve the above problem without knowing the type of the number variable is to use a ternary if:

// Current solution
public async Task<int?> TestAsync()
{
  var reader = GetReader();
  var number = (reader == null ? null : await reader.ReadContentAsStringAsync())?.Length;
  // A lot of code that may use the number variable...
  return number > 5 ? number : 0;
}

In your example the following code will be generated:

var autoFlushIfRequired0 = (implementor as AbstractSessionImpl);
return (autoFlushIfRequired0 == null ? (bool?) null : await (autoFlushIfRequired0.AutoFlushIfRequiredAsync(querySpaces, cancellationToken)).ConfigureAwait(false)) ?? false;

I know that it is not ideal, but due to the current limitations of the transformation process it is the only solution for now.
The ideal solution would be:

public async Task<int?> TestAsync()
{
  int? number = null;
  var task = GetReader()?.ReadContentAsStringAsync();
  if (task != null)
  {
    number = (await task)?.Length;
  }
  // A lot of code that may use the number variable...
  return number > 5 ? number : 0;
}

Also having multiple async invocation with a Null-conditional operator in the same statement is currently not supported even with the new logic. Example:

// Will not work if GetReader and ReadContentAsString have an async counterpart 
var number = instance?.GetReader()?.ReadContentAsString().Length;