Keep a rational allocation amount exact

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Fix `Money::Allocation.generate` converting a Rational with unlimited `to_d` precision. It now uses `Money.conversion_precision`
 - Fix `Money::Currency.reset!` keeping the cached key set, so a currency registered before the reset was still accepted by `Money::Currency.new` and raised `NoMethodError` instead of `UnknownCurrency`
 - Fix `Money::Bank::VariableExchange#import_rates` parsing `:json` with `JSON.load`, which instantiates any class named by a `json_class` key; it now uses `JSON.parse`
 - Fix deprecation warning for eql?

lib/money/money/allocation.rb

@@ -79,7 +79,7 @@ def self.convert_to_big_decimal(number)
       if number.is_a? BigDecimal
         number
       elsif number.is_a? Rational
-        BigDecimal(number.to_f.to_s)
+        number.to_d(Money.conversion_precision)
       else
         BigDecimal(number.to_s)
       end

spec/money/allocation_spec.rb

@@ -42,6 +42,12 @@
         expect(described_class.generate(BigDecimal(5), 4, false)).to eq([1.25, 1.25, 1.25, 1.25])
       end
 
+      it "converts a rational with Money.conversion_precision instead of through a float" do
+        expect(described_class.generate(Rational(2, 3), 1, false)).to eq([BigDecimal("0.6666666666666667")])
+        expect(described_class.generate(Rational(10**400, 1), 1, false)).to eq([BigDecimal("1e400")])
+        expect(described_class.generate(Rational(1, 10**400), 1, false)).to eq([BigDecimal("1e-400")])
+      end
+
       it "handles splits into repeating decimals" do
         amount = BigDecimal(100)
         parts = described_class.generate(amount, 3, false)