AggregateException.ToString() prints terrible message

[Denis535]

Let's throw )

throw new AggregateException(
    "Error",
    new Exception( "Error 1" ),
    new AggregateException( "Error 2", new Exception( "Error 3" ) ) );

If we catch and print this exception then we get a such message:

System.AggregateException: Error (Error 1) (Error 2 (Error 3)) ---> System.Exception: Error 1
   --- End of inner exception stack trace ---
   at ConsoleApp2.Program.Main(String[] args) in C:\Users\Den\Desktop\ConsoleApp2\ConsoleApp2\Program.cs:line 17
---> (Inner Exception #0) System.Exception: Error 1<---

---> (Inner Exception dotnet/corefx#1) System.AggregateException: Error 2 (Error 3) ---> System.Exception: Error 3
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.Exception: Error 3<---
<---

May be for you it's good format, but in my opinion it is terrible.
I'd like to see something like following:

 System.AggregateException: Error
 stack-trace ...
 |-- System.Exception: Error 1
 |   stack-trace ...
 |-- System.AggregateException: Error 2
 |   stack-trace ...
     |-- System.Exception: Error 3
     |   stack-trace ...

[danmoseley]

@deni35 we're open to improvements if they are clearly better. Could you find one or two real-world examples, and show what they look like before and after your proposal? They could be from other issues or elsewhere but I think it would be best to look at real ones.

[pentp]

On .NET Framework AggregateException.Message behaves like any other exception and usually returns the default message "One or more errors occurred". On .NET Core however it tries to be helpful and adds the messages of all inner exceptions on top of this which leads to these overly verbose/repeating messages.

Even worse, after calling AggregateException.Flatten() this aggregated message is set as the new flattened exception's message which ends up doubling everything again:

var ex = new AggregateException("Error", new Exception("Error1"), new AggregateException("Error2", new Exception("Error3")));
Console.WriteLine(ex.Message);
// output: "Error (Error1) (Error2 (Error3))"
Console.WriteLine(ex.Flatten().Message);
// output: "Error (Error1) (Error2 (Error3)) (Error1) (Error3)"

As a real world example, we try to de-aggregate exception messages when rendering them in places where they should be human readable. And for detailed logging we try to do something similar to @deni35's proposal (with reverse ordering and different style). In both cases when moving to .NET Core 3.0 we discovered that these messages are basically unreadable/repeating multiple times.

[stephentoub]

On .NET Core however it tries to be helpful and adds the messages of all inner exceptions on top of this which leads to these overly verbose/repeating messages.

Everyone has their own opinion 😄... the change was made in .NET Core in response to feedback that it should include all of this.
https://github.com/dotnet/corefx/issues/5364

[pentp]

At least we should fix Flatten() then to use base.Message instead of repeating everything twice.

[pentp]

The Flatten() issue was mostly resolved with #605

[stephentoub]

Thanks

[danmoseley]

Partly related, last year I made two failed attempts to improve ToString() for nested exceptions

dotnet/coreclr#25045
dotnet/coreclr#27333

I'm not planning to have another go for 5.0 although I do think it's worthy of improvement. I don't think there is an active issue tracking this so anyond reading this should feel free to open one if they care about it.