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

4 files changed, 20 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
diff --git a/activemodel/test/cases/type/decimal_test.rb b/activemodel/test/cases/type/decimal_test.rb
index 46a913258e..c3b43725cc 100644
--- a/activemodel/test/cases/type/decimal_test.rb
+++ b/activemodel/test/cases/type/decimal_test.rb
@@ -11,6 +11,14 @@ module ActiveModel
         assert_equal BigDecimal.new("1"), type.cast(:"1")
       end
 
+      def test_type_cast_decimal_from_invalid_string
+        type = Decimal.new
+        assert_nil type.cast("")
+        assert_equal BigDecimal.new("1"), type.cast("1ignore")
+        assert_equal BigDecimal.new("0"), type.cast("bad1")
+        assert_equal BigDecimal.new("0"), type.cast("bad")
+      end
+
       def test_type_cast_decimal_from_float_with_large_precision
         type = Decimal.new(precision: ::Float::DIG + 2)
         assert_equal BigDecimal.new("123.0"), type.cast(123.0)
diff --git a/activemodel/test/cases/type/float_test.rb b/activemodel/test/cases/type/float_test.rb
index 2e34f57f7e..8026d63ad5 100644
--- a/activemodel/test/cases/type/float_test.rb
+++ b/activemodel/test/cases/type/float_test.rb
@@ -9,6 +9,14 @@ module ActiveModel
         assert_equal 1.0, type.cast("1")
       end
 
+      def test_type_cast_float_from_invalid_string
+        type = Type::Float.new
+        assert_nil type.cast("")
+        assert_equal 1.0, type.cast("1ignore")
+        assert_equal 0.0, type.cast("bad1")
+        assert_equal 0.0, type.cast("bad")
+      end
+
       def test_changing_float
         type = Type::Float.new
 
diff --git a/activemodel/test/cases/type/integer_test.rb b/activemodel/test/cases/type/integer_test.rb
index 2b9b03f3cf..a91144036b 100644
--- a/activemodel/test/cases/type/integer_test.rb
+++ b/activemodel/test/cases/type/integer_test.rb
@@ -7,6 +7,7 @@ module ActiveModel
     class IntegerTest < ActiveModel::TestCase
       test "simple values" do
         type = Type::Integer.new
+        assert_nil type.cast("")
         assert_equal 1, type.cast(1)
         assert_equal 1, type.cast("1")
         assert_equal 1, type.cast("1ignore")