[Dlang-internal] Regression control & breaking changes policies

[Walter Bright via Dlang-internal]

On 12/4/2016 3:52 PM, Dicebot wrote:
> before change  |  after change | transition process
> ===================================================
> valid          | invalid       | deprecate-then-error
> invalid        | valid         | none
> invalid        | invalid       | none
> valid          | valid         | -transition=feature to find semantic changes
>
> One key thing about this is that adding deprecation is in most cases trivial and
> adds no extra effort if done right from the beginning.

The table makes sense and looks right. But there's a problem with the return 
scope changes. It's just too much to just wholesale deprecate things all at 
once. People need time to ease into it, not be faced with a pile of diverse 
deprecation messages.

Having -transition=safe makes that practical, and also ensures time to correct 
any unrecognized issues with it.