Fix invalid string Decimal casting under ruby 2.4

In Ruby 2.4, BigDecimal(), as used by the Decimal cast, was changed so
that it will raise ArgumentError when passed an invalid string, in order
to be more consistent with Integer(), Float(), etc. The other numeric
types use ex. to_i and to_f.

Unfortunately, we can't simply change BigDecimal() to to_d. String#to_d
raises errors like BigDecimal(), unlike all the other to_* methods (this
should probably be filed as a ruby bug).

Instead, this simulates the existing behaviour and the behaviour of the
other to_* methods by finding a numeric string at the start of the
passed in value, and parsing that using BigDecimal().

See also
https://bugs.ruby-lang.org/issues/10286
https://github.com/ruby/bigdecimal/commit/3081a627cebdc1fc119425c7a9f009dbb6bec8e8

1 files changed, 3 insertions, 1 deletions

diff --git a/activemodel/lib/active_model/type/decimal.rb b/activemodel/lib/active_model/type/decimal.rb
index 541a12c8a1..b4ba8d4b1f 100644
--- a/activemodel/lib/active_model/type/decimal.rb
+++ b/activemodel/lib/active_model/type/decimal.rb
@@ -21,8 +21,10 @@ module ActiveModel
             case value
             when ::Float
               convert_float_to_big_decimal(value)
-            when ::Numeric, ::String
+            when ::Numeric
               BigDecimal(value, precision || BIGDECIMAL_PRECISION)
+            when ::String
+              value.to_d rescue BigDecimal(0)
             else
               if value.respond_to?(:to_d)
                 value.to_d