Feature #14141: Add a method to Exception for retrieving formatted exception for logging purpose (Exception#{formatted,display})

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[sorah (Sorah Fukumori)]

Most people want to log caught exceptions to stderr (or somewhere else) then continues their program as usual.

def the_program
  # ...
  raise "failure!"
  # ...
rescue RuntimeError => e
  $stderr.puts "#{e.message} (#{e.class})\n\t#{e.backtrace.join("\n\t")}"
  retry
end

I'm very bored to write error logging many time...
I want to log errors in the default format of Ruby, just like the following:

rescue RuntimeError => e
  e.display
  # ...

From Ruby 2.5, we've started branching error formatting on TTY-ness of $stderr. It'd be bit more useful if we can log using the same format with the format which Ruby determines.

Ruby already has Object#display.
One consideration is to retrieve formatted String from Exception object, but the current error logging code (eval_error.c) depends on IO,
so I want to start from just having Exception#display. I think most use case is just to log errors into IO.

[matz (Yukihiro Matsumoto)]

Do you really want display that prints to IO or some other method that generates a formatted string?

Matz.

[sorah (Sorah Fukumori)]

At least that satisfies my need. I think advanced error logging can be achieved by existing Exception#{class,message,backtrace}.

[sorah (Sorah Fukumori)]

• File 1.patch added

[sorah (Sorah Fukumori)]

• File 2.patch 2.patch added

[sorah (Sorah Fukumori)]

• File deleted (1.patch)

[nobu (Nobuyoshi Nakada)]

Kernel#display outputs to STDOUT by the default.

https://github.com/nobu/ruby/tree/feature/Exception%23display

[sorah (Sorah Fukumori)]

• File 0001-Add-Exception-formatted-to-get-a-formatted-string.patch 0001-Add-Exception-formatted-to-get-a-formatted-string.patch added
• File 0002-Add-Exception-display-to-log-exception.patch 0002-Add-Exception-display-to-log-exception.patch added

Hmm. Changed my mind. Implemented Exception#formatted with this patch.

I'm not sure this name is proper, suggestions appreciated

[sorah (Sorah Fukumori)]

• Subject changed from Exception#display to display same formatted text for IO to Add a method to Exception for retrieving formatted exception for logging purpose (Exception#{formatted,display})

[sorah (Sorah Fukumori)]

• Status changed from Open to Assigned
• Assignee set to matz (Yukihiro Matsumoto)

[Eregon (Benoit Daloze)]

+1 on an easy way to get a formatted exception.

BTW, "#{e.message} (#{e.class})\n\t#{e.backtrace.join("\n\t")}"
is slightly different than what the C code does, if the message spans multiple lines (then the (#{e.class}) is still on the first line).

[sorah (Sorah Fukumori)]

is slightly different than what the C code does, if the message spans multiple lines (then the (#{e.class}) is still on the first line).

meh, yes, I just gave up to write the exact Ruby code with the C-level behavior...

[matsuda (Akira Matsuda)]

I'm not sure this name is proper, suggestions appreciated

How about "to_formatted_s"?
Active Support has this method for some core classes, and so I guess this name may sound familiar to the Rails people. https://github.com/rails/rails/blob/07788c7/activesupport/lib/active_support/core_ext/time/conversions.rb#L26-L41

[akr (Akira Tanaka)]

How about Exception#long_message or full_message ?

[sorah (Sorah Fukumori)]

In DeveloperMeeting20171212Japan. We concluded to add Exception#formatted in the proposed patch, as #full_message in Ruby 2.5

Several considerations are pointed out:

• Q. Does the method interact with $stderr.tty? ?
  • Yes.
  • Q. Is it imaginable?
  • The motivation is to have a method to retrieve the same formatted string that Ruby prints out in the execution context at the timing of method call (TTY-ishness)
• Q. Naming
  • long_message which follows existing #message
  • full_message is more familiar (Rails has a similarly named method)
• Q. What if the method accepts some arguments to specify formatting option? (e.g., coloring, backtrace direction)
  • (Proposed implementation changes formatting from $stderr.tty?)
  • I'd like to start with the minimum implementation. We can decide to add options afterward.

@matz (Yukihiro Matsumoto): please approve.

[matz (Yukihiro Matsumoto)]

Hi,

full_message is approved.

Matz.

[sorah (Sorah Fukumori)]

• Status changed from Assigned to Closed

Applied in changeset trunk|r61154.

---

error.c(exc_full_message): Exception#full_message

Add a method to retrieve a String expression of an exception,
formatted in the same way that Ruby prints an uncaught exception out.

[Feature #14141]

[Eregon (Benoit Daloze)]

• Related to Bug #14324: Should Exception#full_message include escape sequences? added