Non-reducible extension nodes are not expanded #95
Description
Describe the bug
First some context: I have written a library which allows creating state machine lambdas with continuations similar to what the C# compiler does for async and iterator methods and lambdas. So you start with a "synchronous" expression tree just like you write an async or iterator method, and some extension nodes are used which represent await X and yield return X. These cannot be reduced, since the cannot be translated to a built-in expression representation.
Now when using the ExpressionTreeToString on these, I get an output like this:
.Lambda #Lambda1<System.Func`3[Xunit.Abstractions.ITestOutputHelper,System.Threading.SemaphoreSlim,System.Threading.Tasks.ValueTask]>(
Xunit.Abstractions.ITestOutputHelper $var1,
System.Threading.SemaphoreSlim $var2) {
.Try {
.Block(System.Threading.SemaphoreSlim $semaphore) {
$semaphore = $var2;
.Extension<bsn.AsyncLambdaExpression.Expressions.AwaitExpression>;
.Try {
.Call $var1.WriteLine("In Lock")
} .Finally {
.Call $semaphore.Release()
};
.Default(System.Threading.Tasks.ValueTask)
}
} .Catch (System.Exception $ex) {
.New System.Threading.Tasks.ValueTask(.Call System.Threading.Tasks.Task.FromException($ex))
}
}
The AwaitExpression here hat a "Body" expression like this:
.Call $semaphore.WaitAsync()
So the bug is: The code writing the extension fails to write out the "Body".
The DebugView in VS outputs the following:
.Extension<bsn.AsyncLambdaExpression.Expressions.AsyncLockExpression> {
.Block(System.Threading.SemaphoreSlim $semaphore) {
$semaphore = $var1;
.Call $semaphore.WaitAsync();
.Try {
.Call $var2.WriteLine("In Lock")
} .Finally {
.Call $semaphore.Release()
}
}
}$var2$var1
Which is also pretty bad, but in a different way (it doesn't mention the await extension).
Note that even though AwaitExpression and YieldReturnExpression cannot be reduced for the reason stated above, they do implement VisitChildren which then does visit the child expressions.
The current implementation of DebugViewWriterVisitor.WriteExtension is like this, which explains the missing traversal of the inner expressions of non-reducible extension methods:
protected override void WriteExtension(Expression node) {
Out(
$".Extension<{node.GetType()}>"
);
if (node.CanReduce) {
[...]
}
}
I think a combination of both would be best, e.g. always writing out the extension name, but then try to traverse the children.