A recent question on the ruby newsgroup asked about getting line and file information when using the #warn method. The standard #warn method is really just equivelant to:
$stderr.puts "Some warning message"
While the #raise method includes a full traceback including the filename, linenumber, and the stack of calls that got to this point. The #caller method provides all the needed traceback information — here’s the relevant portion of the ri generated docs:
Kernel#caller
caller(start=1) => array
Returns the current execution stack---an array containing
strings in the form ``_file:line_'' or ``_file:line: in
`method'_''. The optional _start_ parameter determines the
number of initial stack entries to omit from the result.
So we just need to redefine the Kernel#warn method to use this information.
module Kernel
alias :oldwarn :warn
def warn (msg = "", fulltrace = false)
trace = caller(1)
where = trace[0].sub(/:in.*/,'')
$stderr.puts "#{where}: Warning: #{msg}"
$stderr.puts trace.map {|t| "\tfrom #{t}"} if fulltrace
end
end
Now we have a method that will provide the file and linenumber, and optionally (if you supply a true second argument), a stacktrace like #raise does. Here we have a simple example script:
~$ nl -w3 -ba -s" " -nrn warn.rb
1 module Kernel
2 alias :oldwarn :warn
3 def warn (msg = "", fulltrace = false)
4 trace = caller(1)
5 where = trace[0].sub(/:in.*/,'')
6 $stderr.puts "#{where}: Warning: #{msg}"
7 $stderr.puts trace.map {|t| "\tfrom #{t}"} if fulltrace
8 end
9 end
10
11 class Foo
12 def bar
13 warn "just a warning"
14 end
15 def qux
16 warn "warning with trace", true
17 end
18 end
19
20 obj = Foo.new
21 obj.bar
22 obj.qux
Which produces:
~$ ruby warn.rb
warn.rb:13: Warning: just a warning
warn.rb:16: Warning: warning with trace
from warn.rb:16:in `qux'
from warn.rb:22
Simple, but effective.