open_exception gem: auto open exceptions in your editor

Posted: Monday April 26, 2010
Tags:  emacs, gems, ruby

open_exception opens an exception in your favorite editor when developing locally. It works by parsing the backtrace, and opening the offending file at the offending line in your favorite editor (assuming your favorite editor supports remote open commands).

You can add filters that allow you to ignore some exceptions, and filters that allow you to scope the backtrace search. The backtrace scoping is useful for opening the last call in your application code when the exception occurs in a framework or lib.

If you are on MacOSX and have the growl gem installed, you will get a growl notification with the exception message when the file is opened.

Editors

Out if the box, the gem supports three editors (with the following open commands):

:emacs => '/usr/bin/emacsclient -n +{line} {file}',
:textmate => '/usr/local/bin/mate -a -d -l {line} {file}',
:macvim => '/usr/local/bin/mvim +{line} {file}'

Note: if using emacs, you will need to be running emacsserver. To start the server: M-x server-start

or add (server-start) to your init.

Configuration

To configure, pass a block to the configure method:

OpenException.configure do |oe|
    # open_with can be one of the built in editors (:emacs, :macvim, :textmate)
    # or a command to execute to open the file, where {file} and {line} will be replaced
    # with the file path and line number, respectively. See 'Editors' above for an example.
    # The default editor is :emacs.
     
    oe.open_with = :emacs
     
    # you can add exclusion filters to ignore exceptions. A filter can be an exception class to 
    # ignore, or a proc that is passed the exception, and should evaluate to true if the exception 
    # should be ignored. Be careful with using a class - it uses is_a?, so any subclasses of the
    # passed class will be ignored as well. The list of filters is [] by default.
     
    oe.exclusion_filters << SomeErrorClass
    oe.exclusion_filters << lambda { |exception| true if exception_should_be_excluded }
     
    # you can scope the search for the file:line to open with a filter as well. A filter can be a 
    # regular expression that is matched against the line, or a proc that is passed the line and 
    # should evaluate to true if the line should be used. The first line that any filter passes for 
    # will be the file:line that is opened. This is useful for opening the point in the stack just
    # before control passes out of your app code when the exception occurs in an external 
    # lib/framework. The list of filters is [] by default. 
     
    oe.backtrace_line_filters << %r{/app/root/(app|lib)} 
    oe.backtrace_line_filters << lambda { |backtrace_line| true if line_should_be_used }
     
end

Rails Integration

The gem also alias chains in to rails’ ActionController#rescue_action_locally method to automatically open exceptions in development mode. The gem also adds the following filter to the :backtrace_line_filters to scope the opened files to the app:

%r{#{Rails.root}/(app|lib)}

To replace or remove this filter, you will need to reset the :backtrace_line_filters in your configure block:

OpenException.configure do |oe|
    oe.backtrace_line_filters = []
    oe.backtrace_line_filters << my_new_filter
end

This has been tested with rails v2.3.5, but should work fine with 2.1 <= rails < 3. It may work with rails 3 as well, I just haven’t yet looked at rails 3.

Standalone/Other Frameworks

# To manually open an exception, or wire it up in another framework, you call:
OpenException.open(exception)
 
# You can override the default (or configured) options by passing a hash as the second arg:
OpenException.open(exception, {:open_with => :textmate, :backtrace_line_filters => [filter, another_filter])

The source is on github, and the gem is on rubygems.