[ruby-core:32096] [Ruby 1.9.1-Backport#3795][Open] Date._valid_civil? in 1.9.1 raises exception for some invalid dates instead of returning false

Backport #3795: Date._valid_civil? in 1.9.1 raises exception for some invalid dates instead of returning false
http://redmine.ruby-lang.org/issues/show/3795

Author: Colin Bartlett
Status: Open, Priority: Normal

possible_bug = <<_possible_bug
  Date._valid_civil? in 1.9.1 raises exception for some invalid dates
  instead of returning false.

  This is a possible bug in 1.9.1 Date._valid_civil? found while
  I was testing changes to some methods in Date to make them faster.
  I tried a search but couldn't find a bug report for this.

  If it is a bug, then there are implications for other methods
  in 1.9.1 Date, and I would be more than happy to elaborate.

  For versions of Date.valid_civil? before Ruby 1.9.1, if the date
  is valid then the return value is the julian day number, else nil.

  In 1.9.1 Date my understanding is that the intended behaviour is
  if the date is valid then the return value is true, else false.
  But in the 1.9.1 version on my computer, for example:
    month = -14, day = -1 returns false;
    month = -13, day = -1 raises a NoMethodError exception.
  The behaviour is the same on http://tryruby.org:
    RUBY_VERSION                     #=> "1.9.1"                                                              
    Date.valid_civil? 2010, -14, -1  #=> false                                                                
    Date.valid_civil? 2010, -13, -1  #=>                                    
         #=> NoMethodError: undefined method `+' for nil:NilClass                    

  The problem seems to be in the private method Date._valid_civil?
  which as currently written seems not to cater for the possibility
  that Date.find_ldom might return nil.
  The following code shows the behaviour on my computer:
    (a) using the current 1.9.1 Date._valid_civil?;
    (b) after a one line patch to Date._valid_civil?
_possible_bug

puts
puts "Ruby #{RUBY_VERSION}"
puts "defined?( Date.find_ldom() )"
p defined?( Date.find_ldom() )

puts possible_bug

require "date"

def test_date_valid_civil()
  y = 2010
  sg = Date::ITALY
  mm = [ -12, -14, -25, -13, -26, 0 ]
  dd = [ -1 ]
  mm.each do |m|
    dd.each do |d|
      print "* y=#{y}, m=#{m}, d=#{d}; sg=#{sg.inspect};"
      begin
        rr = Date.valid_civil?( y, m, d, sg )
        puts "  #=> #{rr.inspect}"
      rescue
        puts "  #=> " + $!.inspect
      end
    end
  end
end

puts
puts "(a) use Ruby 1.9.1 to test current 1.9.1 Date._valid_civil?"
test_date_valid_civil()

puts; puts "(b) patch and test patched Date._valid_civil?"

class Date
  t = Module.new do
    private

    def _valid_civil? (y, m, d, sg=GREGORIAN) # :nodoc:
      if m < 0
        m += 13
      end
      if d < 0
     #  j = find_ldom(y, m, sg)   #-
        return unless j = find_ldom(y, m, sg)  #+ patch by CWB 2010-09-06
        ny, nm, nd = jd_to_civil(j + d + 1, sg)
        return unless [ny, nm] == [y, m]
        d = nd
      end
      jd = civil_to_jd(y, m, d, sg)
      return unless [y, m, d] == jd_to_civil(jd, sg)
      jd
    end
  end

  extend  t
  include t
end

test_date_valid_civil()


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