From a purist perspective, you're right - the contract has been broken, and a major version should've been incremented.
However, Go has always been more of a pragmatic than a purist language. For example, they've analyzed tons of code and found that most of them had bugs caused by having `for` loop with a single variable being mutated. So they changed the `for` loop (in a technically backwards incompatible way) in order to make all those bugs disappear. In a way, they modified the formal contract to make it more aligned with the de-facto contract that users were expecting.
I personally think that kind of pragmatism beats purism any day. Maybe the fact that I've never personally been affected by Go backwards incompatibilities also plays a role... But I've yet to find a single person who has :)
However, Go has always been more of a pragmatic than a purist language. For example, they've analyzed tons of code and found that most of them had bugs caused by having `for` loop with a single variable being mutated. So they changed the `for` loop (in a technically backwards incompatible way) in order to make all those bugs disappear. In a way, they modified the formal contract to make it more aligned with the de-facto contract that users were expecting.
I personally think that kind of pragmatism beats purism any day. Maybe the fact that I've never personally been affected by Go backwards incompatibilities also plays a role... But I've yet to find a single person who has :)