[ruby-core:54193] [CommonRuby - Feature #8257] Exception#cause to carry originating exception along with new one

Issue #8257 has been updated by headius (Charles Nutter).


Links to implementation of "cause" rendering and Kernel#raise logic from Rubinius:

"cause" rendering: https://github.com/rubinius/rubinius/blob/master/kernel/common/exception.rb#L72

Kernel#raise: https://github.com/rubinius/rubinius/blob/master/kernel/delta/kernel.rb#L27

Note that the changes almost exclusively affect rendering of exceptions that bubble out; no other visible aspects of exceptions change with this enhancement. This means that libraries can start using the feature without consumers having to change any code.

This feature would also be useful for associate a low-level cause with higher-level exceptions in core classes and standard library, such as wrapping a low-level IO exception in an SSLError or net/* exception.
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Feature #8257: Exception#cause to carry originating exception along with new one
https://bugs.ruby-lang.org/issues/8257#change-38472

Author: headius (Charles Nutter)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


Often when a lower-level API raises an exception, we would like to re-raise a different exception specific to our API or library. Currently in Ruby, only our new exception is ever seen by users; the original exception is lost forever, unless the user decides to dig around our library and log it. We need a way to have an exception carry a "cause" along with it.

Java has getCause/setCause and standard constructors that take a cause exception. Printing out an exception's backtrace then reports both that exception and any "cause" exception.

Rubinius has added a similar feature: https://gist.github.com/dbussink/b2e01e51d0c50b27004f

The changes required for this feature are pretty benign:

* Exception#cause and #cause= accessors.
* A new set of Kernel#raise overloads that accept (as a trailing argument, probably) the "cause" exception.
* Modifications to backtrace-printing logic to also display backtrace information from the "cause" exception (and in turn, from any nested "cause" exceptions).

There's some discussion here about alternatives to #cause, none of which are quite as elegant as having it built in: http://www.skorks.com/2013/04/ruby-why-u-no-have-nested-exceptions/


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