Merge pull request #706 from lauxjpn/float_conversion

Explicitly cast double values down to float in Row.GetFloat().

Author: bgrainger

src/MySqlConnector/Core/Row.cs

@@ -353,8 +353,15 @@ public double GetDouble(int ordinal)
 		public float GetFloat(int ordinal)
 		{
 			var value = GetValue(ordinal);
-			return value is decimal decimalValue ? (float) decimalValue :
-				(float) value;
+
+			// Loss of precision is expected, significant loss of information is not.
+			// Use explicit range checks to guard against that.
+			return value switch
+			{
+				double doubleValue => (doubleValue >= float.MinValue && doubleValue <= float.MaxValue ? (float) doubleValue : throw new InvalidCastException("The value cannot be safely cast to Single.")),
+				decimal decimalValue => (float) decimalValue,
+				_ => (float) value
+			};
 		}
 
 		public MySqlDateTime GetMySqlDateTime(int ordinal)

tests/Conformance.Tests/GetValueConversionTests.cs

@@ -82,5 +82,13 @@ public GetValueConversionTests(SelectValueFixture fixture)
 		// the minimum date permitted by MySQL is 1000-01-01; override the minimum value for DateTime tests
 		public override void GetDateTime_for_minimum_Date() => TestGetValue(DbType.Date, ValueKind.Minimum, x => x.GetDateTime(0), new DateTime(1000, 1, 1));
 		public override void GetDateTime_for_minimum_DateTime() => TestGetValue(DbType.Date, ValueKind.Minimum, x => x.GetDateTime(0), new DateTime(1000, 1, 1));
+
+		// The GetFloat() implementation allows for conversions from double to float.
+		// The minimum tests for float and double do not test for the smallest possible value (as the tests for integer values do),
+		// but test for the largest value smaller than 0 (Epsilon).
+		// If double.Epsilon is converted to float, it will result in 0.
+		public override void GetFloat_throws_for_minimum_Double() => TestGetValue(DbType.Double, ValueKind.Minimum, x => x.GetFloat(0), 0);
+		public override void GetFloat_throws_for_one_Double() => TestGetValue(DbType.Double, ValueKind.One, x => x.GetFloat(0), 1);
+		public override void GetFloat_throws_for_zero_Double() => TestGetValue(DbType.Double, ValueKind.Zero, x => x.GetFloat(0), 0);
 	}
 }