fix `number_to_percentage` with `Float::NAN`, `Float::INFINITY`.

Closes #14405.

This is a follow-up to 9e997e9039435617b6a844158f5437e97f6bc107 to restore
the documented behavior.

2 files changed, 4 insertions, 2 deletions

diff --git a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
index c42354fc83..c45f6cdcfa 100644
--- a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
@@ -32,8 +32,7 @@ module ActiveSupport
         end
 
         formatted_string =
-          case rounded_number
-          when BigDecimal
+          if BigDecimal === rounded_number && rounded_number.finite?
             s = rounded_number.to_s('F') + '0'*precision
             a, b = s.split('.', 2)
             a + '.' + b[0, precision]
diff --git a/activesupport/test/number_helper_test.rb b/activesupport/test/number_helper_test.rb
index 6d8d835de7..9bdb92024e 100644
--- a/activesupport/test/number_helper_test.rb
+++ b/activesupport/test/number_helper_test.rb
@@ -79,6 +79,9 @@ module ActiveSupport
           assert_equal("123.4%", number_helper.number_to_percentage(123.400, :precision => 3, :strip_insignificant_zeros => true))
           assert_equal("1.000,000%", number_helper.number_to_percentage(1000, :delimiter => '.', :separator => ','))
           assert_equal("1000.000  %", number_helper.number_to_percentage(1000, :format => "%n  %"))
+          assert_equal("98a%", number_helper.number_to_percentage("98a"))
+          assert_equal("NaN%", number_helper.number_to_percentage(Float::NAN))
+          assert_equal("Inf%", number_helper.number_to_percentage(Float::INFINITY))
         end
       end