[ruby-core:73924] [Ruby trunk Bug#12100] CSV converters fail when using single arg proc

Issue #12100 has been reported by Matthew Daubert.

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Bug #12100: CSV converters fail when using single arg proc
https://bugs.ruby-lang.org/issues/12100

* Author: Matthew Daubert
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: all versions 2.0, 2.1, 2.2, 2.3, trunk
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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CSV#parse (and others) throw an ArgumentError when passing a single argument Proc as a converter because of a performance optimization check that assumes Proc#arity is always positive. Lambdas with one argument work fine as do Procs and lambdas with two arguments. The documentation suggests to me that either should work. Supporting the Proc variant is trivial and allows to_proc and to_proc shortcut syntax to be used eliminating the surprising behavior and uninformative error message. Illustration of the problem is below and a patch with tests is attached. I'm also creating a PR on Github because I think this is a minor enough change to be merged quickly. Thank you.

~~~
require 'csv'
puts CSV.parse("  foo  ,  bar  ", converters: -> f { f.strip }).inspect
puts CSV.parse("  foo  ,  bar  ", converters: :strip.to_proc).inspect

# Without patch this outputs:
# [["foo", "bar"]]
# /home/mdaubert/.rbenv/versions/2.3.0/lib/ruby/2.3.0/csv.rb:2205:in `strip': wrong number of arguments (given 1, expected 0) (ArgumentError)

# With patch this outputs:
# [["foo", "bar"]]
# [["foo", "bar"]]
~~~

---Files--------------------------------
fix_csv_converter_single_arg_proc.patch (1.78 KB)


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