models: ensure DROM phone numbers are valid

They were accepted before, because they were 'possible' – but now
they are explicitely considered as valid.

app/models/champs/phone_champ.rb

@@ -20,12 +20,33 @@
 #  type_de_champ_id               :integer
 #
 class Champs::PhoneChamp < Champs::TextChamp
+  # We want to allow:
+  # * international (e164) phone numbers
+  # * “french format” (ten digits with a leading 0)
+  # * DROM numbers
+  #
+  # However, we need to special-case some ten-digit numbers,
+  # because the ARCEP assigns some blocks of "O6 XX XX XX XX" numbers to DROM operators.
+  # Guadeloupe          | GP | +590 | 0690XXXXXX, 0691XXXXXX
+  # Guyane              | GF | +594 | 0694XXXXXX
+  # Martinique          | MQ | +596 | 0696XXXXXX, 0697XXXXXX
+  # Réunion             | RE | +262 | 0692XXXXXX, 0693XXXXXX
+  # Mayotte             | YT | +262 | 0692XXXXXX, 0693XXXXXX
+  # Nouvelle-Calédonie  | NC | +687 |
+  # Polynésie française | PF | +689 | 40XXXXXX, 45XXXXXX, 87XXXXXX, 88XXXXXX, 89XXXXXX
+  #
+  # Cf: Plan national de numérotation téléphonique,
+  # https://www.arcep.fr/uploads/tx_gsavis/05-1085.pdf  “Numéros mobiles à 10 chiffres”, page 6
+  #
+  # See issue #6996.
+  DEFAULT_COUNTRY_CODES = [:FR, :GP, :GF, :MQ, :RE, :YT, :NC, :PF].freeze
+
   validates :value,
     phone: {
       possible: true,
       allow_blank: true,
       message: I18n.t(:not_a_phone, scope: 'activerecord.errors.messages')
-    }, unless: -> { Phonelib.valid_for_country?(value, :pf) }
+    }, unless: -> { Phonelib.valid_for_countries?(value, DEFAULT_COUNTRY_CODES) }
 
   def to_s
     value.present? ? Phonelib.parse(value).full_national : ''

lib/core_ext/phonelib.rb

@@ -0,0 +1,14 @@
+# Class extensions to the Phonelib module, which allow parsing using several countries at once.
+module Phonelib
+  # Variation of `.valid_for_country`, that can check several countries at once.
+  def self.valid_for_countries?(value, countries)
+    countries.any? { |country| valid_for_country?(value, country) }
+  end
+
+  # Variation of `Phonelib.parse`, which parses the given string using the first country
+  # for which the phone number is valid.
+  def self.parse_for_countries(value, passed_countries = [])
+    valid_country = passed_countries.find { |country| valid_for_country?(value, country) }
+    parse(value, valid_country)
+  end
+end

spec/models/champs/phone_champ_spec.rb

@@ -22,6 +22,10 @@ describe Champs::PhoneChamp do
       expect(champ_with_value("+1(0) - 123456789")).to be_valid
       expect(champ_with_value("+49 2109 87654321")).to be_valid
       expect(champ_with_value("012345678")).to be_valid
+      # DROM numbers should be valid
+      expect(champ_with_value("06 96 04 78 07")).to be_valid
+      expect(champ_with_value("05 94 22 31 31")).to be_valid
+      expect(champ_with_value("+594 5 94 22 31 31")).to be_valid
       # polynesian numbers should not return errors in any way
       ## landline numbers start with 40 or 45
       expect(champ_with_value("45187272")).to be_valid