Use integer comparison for equality

If we are comparing 2 numbers that are even integers, compare them via
big.Int values rather than formatted strings. This avoids problems with
large integers stored in big.Float with different precisions which could
format differently.

cty/primitive_type.go

@@ -1,6 +1,8 @@
 package cty
 
-import "math/big"
+import (
+	"math/big"
+)
 
 // primitiveType is the hidden implementation of the various primitive types
 // that are exposed as variables in this package.
@@ -77,6 +79,18 @@ func rawNumberEqual(a, b *big.Float) bool {
 	case a.Sign() != b.Sign():
 		return false
 	default:
+		// First check if these are integers, and compare them directly. Floats
+		// need a more nuanced approach.
+		aInt, aAcc := a.Int(nil)
+		bInt, bAcc := b.Int(nil)
+		if aAcc != bAcc {
+			// only one is an exact integer value, so they can't be equal
+			return false
+		}
+		if aAcc == big.Exact {
+			return aInt.Cmp(bInt) == 0
+		}
+
 		// This format and precision matches that used by cty/json.Marshal,
 		// and thus achieves our definition of "two numbers are equal if
 		// we'd use the same JSON serialization for both of them".

cty/value_ops_test.go

@@ -91,6 +91,11 @@ func TestValueEquals(t *testing.T) {
 			NumberFloatVal(1.22222),
 			BoolVal(true),
 		},
+		{
+			MustParseNumberVal("9223372036854775808"),
+			NumberFloatVal(float64(9223372036854775808)),
+			BoolVal(true),
+		},
 
 		// Strings
 		{