[dart-misc] Rethrow a new Exception preserving the cause

[Gonzalo Chumillas]

I would like to rethrow a new exception preserving the original exception.
For example

try {
buggyFunction();
} catch (exception) {
throw new MyCustomException(exception);
}

This way I can provide more specific information, without losing the
original exception (the cause). In the same way that this guy explains:
http://programmers.stackexchange.com/a/278038/173231

Is that possible?
Thanks.

['Kasper Lund' via Dart Misc]

Looks like this might be answered by:

http://stackoverflow.com/questions/16028565/how-do-i-rethrow-an-exception-and-preserve-the-stack-trace

Cheers,
Kasper


On Tue, Aug 9, 2016 at 7:28 PM Gonzalo Chumillas <

Post by Gonzalo Chumillas
I would like to rethrow a new exception preserving the original exception.
For example
try {
buggyFunction();
} catch (exception) {
throw new MyCustomException(exception);
}
This way I can provide more specific information, without losing the
http://programmers.stackexchange.com/a/278038/173231
Is that possible?
Thanks.
--
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[Gonzalo Chumillas]

Thanks. In my case I don't want to rethrow the same exception. I would like
to throw a new custom exception and, at the same time, preserving the cause
(the original exception).

But I think Dart doesn't considers this circumstance, sadly.

Post by 'Kasper Lund' via Dart Misc
http://stackoverflow.com/questions/16028565/how-do-i-rethrow-an-exception-and-preserve-the-stack-trace
Cheers,
Kasper

Post by Gonzalo Chumillas
I would like to rethrow a new exception preserving the original
exception. For example
try {
buggyFunction();
} catch (exception) {
throw new MyCustomException(exception);
}
This way I can provide more specific information, without losing the
http://programmers.stackexchange.com/a/278038/173231
Is that possible?
Thanks.
--
For other discussions, see https://groups.google.com/a/dartlang.org/
For HOWTO questions, visit http://stackoverflow.com/tags/dart
To file a bug report or feature request, go to http://www.dartbug.com/new
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[Günter Zöchbauer]

try {
buggyFunction();
} catch (exception) {
rethrow;
}

Post by Gonzalo Chumillas
I would like to rethrow a new exception preserving the original exception.
For example
try {
buggyFunction();
} catch (exception) {
throw new MyCustomException(exception);
}
This way I can provide more specific information, without losing the
http://programmers.stackexchange.com/a/278038/173231
Is that possible?
Thanks.

[Gonzalo Chumillas]

Thanks GÃŒnter. In my case I don't want to rethrow the same exception. I
would like to throw a new custom exception and preserve the previous
exception (the cause). Doing something like that is possible in other
languages, such as PHP:
http://programmers.stackexchange.com/a/278038/173231

Post by Gonzalo Chumillas
try {
buggyFunction();
} catch (exception) {
rethrow;
}

Post by Gonzalo Chumillas
I would like to rethrow a new exception preserving the original
exception. For example
try {
buggyFunction();
} catch (exception) {
throw new MyCustomException(exception);
}
This way I can provide more specific information, without losing the
http://programmers.stackexchange.com/a/278038/173231
Is that possible?
Thanks.

['Lasse R.H. Nielsen' via Dart Misc]

On Tue, Aug 9, 2016 at 8:08 PM, Gonzalo Chumillas <

Post by Gonzalo Chumillas
Thanks GÃŒnter. In my case I don't want to rethrow the same exception. I
would like to throw a new custom exception and preserve the previous
exception (the cause). Doing something like that is possible in other
http://programmers.stackexchange.com/a/278038/173231

Dart Errors don't have a `cause` field. Errors generally don't have a
different cause, they are "stand-alone" error reports and are not expected
to be intercepted at all, except at a framework level.

Exceptions (any non-error object thrown) represents communication with the
calling code, and it should include exactly the information expected by the
caller. There are no general guide-lines for exceptions any more than there
are general guide-lines for any returned object.

If you make an exception, e.g., thrown from an API layer, that can report
multiple ways something specific could fail, you can add a `cause` field to
that exception - if you think the caller can use that information for
anything.

/L
--
Lasse R.H. Nielsen - ***@google.com
'Faith without judgement merely degrades the spirit divine'
Google Denmark ApS - Frederiksborggade 20B, 1 sal - 1360 KÞbenhavn K
- Denmark - CVR nr. 28 86 69 84

[tatumizer-v0.2]

Quite often, you need to add some context info to exception object on its
way up.
There's no way to do it in java either: it's not a new exception CAUSED BY
low-level exception; it's the same low-level exception with added context
info.

We discussed it a couple of years ago here, but it ended in nothing.
It's possible to implement simple mechanism in java that doesn't even
require intercepting exception. But in dart, because to async calls, you
can't rely on stack, so probably an "attachment" hook is needed in
exception object. Or maybe this is the use case for expando? (which is
currently way too slow for anything).

Not sure. @Lasse: your response doesn't seem to address this feature.

['Lasse R.H. Nielsen' via Dart Misc]

Post by tatumizer-v0.2
Quite often, you need to add some context info to exception object on its
way up.
There's no way to do it in java either: it's not a new exception CAUSED BY
low-level exception; it's the same low-level exception with added context
info.
We discussed it a couple of years ago here, but it ended in nothing.
It's possible to implement simple mechanism in java that doesn't even
require intercepting exception. But in dart, because to async calls, you
can't rely on stack, so probably an "attachment" hook is needed in
exception object. Or maybe this is the use case for expando? (which is
currently way too slow for anything).

No, I was just addressing using a `MyCustomException` to include the cause.

If you want to add more information to an existing error, you need to
either create a new error of the same type with more information or attach
the information on the side of the object. You can do that using an
Expando, but if you know that the exception will be caught shortly after
and the extra information consumed there, you can also just use an identity
map and remove the entry again at the catch point.

/L
--
Lasse R.H. Nielsen - ***@google.com
'Faith without judgement merely degrades the spirit divine'
Google Denmark ApS - Frederiksborggade 20B, 1 sal - 1360 KÞbenhavn K
- Denmark - CVR nr. 28 86 69 84

[tatumizer-v0.2]

It should be a weak map. Not sure dart has weak maps per se, but expando
provides a kind of rough equivalent (based on its description from dartdoc)

[tatumizer-v0.2]

Maybe exception object should have an attached map of names/values.
But this doesn't fully solve the problem.
Writing
var myAttachmentObject=...
try {
...
} catch (ex) {
ex.addAttachment("foo", myAttachmentObject);
rethrow;
}

is very tedious. And the case is quite common to justify supporting it in a
language specifically.
[ Notice that myAttachmentObject has to be declared outside of try{} block
- disgusting! ]


Ideally, there can be and operator like (better name to be found)
on-exception-call-this-function((e)=>doSomething) which doesn't really
catch an exception, just calls a function during unwinding a stack.
This operator should work in a scope of a block. (Exit from block will
remove it from stack).

Not sure why this feature is not supported by any language. Probably,
mundane stuff like that is too lowly for language designers.





.

[tatumizer-v0.2]

Much simpler idea: there should be a way to add information to stack trace.
Not sure how it can look syntactically, and what to do with asynchronous
calls, which create an amorphous mess in runtime (async/await hack making
it even worse).

The whole idea of Circuit (if anyone remembers this promising concept, by
now defunct) was to create a structure to sort out the mess. Sadly, the
idea was not appreciated by contemporaries :(

Does Fuchsia have a message board? These people seem to be more susceptible
to innovative ideas.

[tatumizer-v0.2]

More specifically: would it be possible to add a new field (e.g.,
"attachment" or something) to stack_trace.Frame?
So that we can call stack_trace.currentFrame.addAttachment(name, value)
(because Frame can refer to async "stack frame", then there's no difference
in API between async stack and normal stack).
There's no removeAttachment. Attachment records will be (naturally) cleaned
up when frame goes out of existence.

When stack trace is printed, attachments are printed automatically.

I think it's a cool feature, really. It will eliminate a lot of nonsense
like catching exception just to add stuff to it (java added special
mechanism of suppressed exceptions in 1.7 for that purpose, but it's ugly
anyway: you still have to catch and re-throw).

['Lasse R.H. Nielsen' via Dart Misc]

Post by tatumizer-v0.2
More specifically: would it be possible to add a new field (e.g.,
"attachment" or something) to stack_trace.Frame?
So that we can call stack_trace.currentFrame.addAttachment(name, value)
(because Frame can refer to async "stack frame", then there's no
difference in API between async stack and normal stack).
There's no removeAttachment. Attachment records will be (naturally)
cleaned up when frame goes out of existence.

You can suggest that to the stack_frame package. It won't work if you don't
use that package (the language doesn't represent individual stack frames in
any way, the only primitive is the full StackTrace object).

Which likely also means that it isn't possible to attach anything to the
"current stack frame" in practice. The Frame of the stack_trace package is
created after the fact by parsing the stack trace string.

Post by tatumizer-v0.2
When stack trace is printed, attachments are printed automatically.
I think it's a cool feature, really. It will eliminate a lot of nonsense
like catching exception just to add stuff to it (java added special
mechanism of suppressed exceptions in 1.7 for that purpose, but it's ugly
anyway: you still have to catch and re-throw).

/L
--
Lasse R.H. Nielsen - ***@google.com
'Faith without judgement merely degrades the spirit divine'
Google Denmark ApS - Frederiksborggade 20B, 1 sal - 1360 KÞbenhavn K
- Denmark - CVR nr. 28 86 69 84

Post by tatumizer-v0.2
More specifically: would it be possible to add a new field (e.g.,
"attachment" or something) to stack_trace.Frame?
So that we can call stack_trace.currentFrame.addAttachment(name, value)
(because Frame can refer to async "stack frame", then there's no
difference in API between async stack and normal stack).
There's no removeAttachment. Attachment records will be (naturally)
cleaned up when frame goes out of existence.
When stack trace is printed, attachments are printed automatically.
I think it's a cool feature, really. It will eliminate a lot of nonsense
like catching exception just to add stuff to it (java added special
mechanism of suppressed exceptions in 1.7 for that purpose, but it's ugly
anyway: you still have to catch and re-throw).
--
For other discussions, see https://groups.google.com/a/dartlang.org/
For HOWTO questions, visit http://stackoverflow.com/tags/dart
To file a bug report or feature request, go to http://www.dartbug.com/new
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--
Lasse R.H. Nielsen - ***@google.com
'Faith without judgement merely degrades the spirit divine'
Google Denmark ApS - Frederiksborggade 20B, 1 sal - 1360 KÞbenhavn K
- Denmark - CVR nr. 28 86 69 84

['Bob Nystrom' via Dart Misc]

+Natalie, who is the maintainer of the package in question. :)

– bob

On Wed, Aug 17, 2016 at 10:54 AM, 'Lasse R.H. Nielsen' via Dart Misc <

Post by 'Lasse R.H. Nielsen' via Dart Misc

Post by tatumizer-v0.2
More specifically: would it be possible to add a new field (e.g.,
"attachment" or something) to stack_trace.Frame?
So that we can call stack_trace.currentFrame.addAttachment(name, value)
(because Frame can refer to async "stack frame", then there's no
difference in API between async stack and normal stack).
There's no removeAttachment. Attachment records will be (naturally)
cleaned up when frame goes out of existence.

You can suggest that to the stack_frame package. It won't work if you
don't use that package (the language doesn't represent individual stack
frames in any way, the only primitive is the full StackTrace object).
Which likely also means that it isn't possible to attach anything to the
"current stack frame" in practice. The Frame of the stack_trace package is
created after the fact by parsing the stack trace string.

Post by tatumizer-v0.2
When stack trace is printed, attachments are printed automatically.
I think it's a cool feature, really. It will eliminate a lot of nonsense
like catching exception just to add stuff to it (java added special
mechanism of suppressed exceptions in 1.7 for that purpose, but it's ugly
anyway: you still have to catch and re-throw).

/L
--
'Faith without judgement merely degrades the spirit divine'
Google Denmark ApS - Frederiksborggade 20B, 1 sal - 1360 KÞbenhavn K
- Denmark - CVR nr. 28 86 69 84

Post by tatumizer-v0.2
More specifically: would it be possible to add a new field (e.g.,
"attachment" or something) to stack_trace.Frame?
So that we can call stack_trace.currentFrame.addAttachment(name, value)
(because Frame can refer to async "stack frame", then there's no
difference in API between async stack and normal stack).
There's no removeAttachment. Attachment records will be (naturally)
cleaned up when frame goes out of existence.
When stack trace is printed, attachments are printed automatically.
I think it's a cool feature, really. It will eliminate a lot of nonsense
like catching exception just to add stuff to it (java added special
mechanism of suppressed exceptions in 1.7 for that purpose, but it's ugly
anyway: you still have to catch and re-throw).
--
For other discussions, see https://groups.google.com/a/dartlang.org/
For HOWTO questions, visit http://stackoverflow.com/tags/dart
To file a bug report or feature request, go to http://www.dartbug.com/new
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--
'Faith without judgement merely degrades the spirit divine'
Google Denmark ApS - Frederiksborggade 20B, 1 sal - 1360 KÞbenhavn K
- Denmark - CVR nr. 28 86 69 84
--
For other discussions, see https://groups.google.com/a/dartlang.org/
For HOWTO questions, visit http://stackoverflow.com/tags/dart
To file a bug report or feature request, go to http://www.dartbug.com/new
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[tatumizer-v0.2]

I know it's not easy to implement. But the good news is: all "conceptual"
building blocks are already there, so it's easy to express this in the form
"add attachment to stack frame", and it will look as if it's a simple
operation. Sure, if you don't use the stack_trace package, it won't work -
but that's fine (no stack trace - no attachments obviously)

[tatumizer-v0.2]

As an aside: I can't imagine any production system which deliberately
avoids stack_trace package. You get an exception from deeply nested async -
and you don't even know how program got there, and you don't have any clues
(even from the log) that link said error with its possible cause.

[Alex Tatumizer]

Prior art:
http://blog.honeybadger.io/how-to-add-context-data-to-exceptions-in-ruby/
They use different terminology. In dart's case, it would be equivalent to
stack_trace.addContext(dict) or something