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Date: Mon, 10 Sep 2012 14:23:36 -0400
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To: Pierre Joye <pierre.php@gmail.com>
Cc: jpauli <jpauli@php.net>, PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] What is our definition of a "Backward Compatibility Break"
From: ircmaxell@gmail.com (Anthony Ferrara)

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Pierre,

On Mon, Sep 10, 2012 at 1:54 PM, Pierre Joye <pierre.php@gmail.com> wrote:

> hi,
>
> On Mon, Sep 10, 2012 at 6:28 PM, jpauli <jpauli@php.net> wrote:
> > Based on our recent discussion on #pecl , I'd like we clarify what we
> > think is a "BCB" (Backward Compatibility Break) as well as what "only
> > minor BC breaks" could mean.
>
> Change in phpinfo related stuff are minor. Adding a notice or warning
> is minor or irrelevant. Changing return values (like suddenly
> returning array instead of integer, f.e.), behaviors or similar things
> are not allowed in x.y+1.


I'm not so sure about that. Adding a warning or notice may actually cause a
lot of headaches. See what happened with call-time-pass-by-reference in
5.3... All of a sudden a lot of code that worked fine is flooding logs with
new warnings...

I guess my point is that the line between a BCB and a minor BCB is a
lot finer and a lot more subjective that it seems on the surface. Is adding
a new language feature with a new keyword a BCB (since existing
functionality using that keyword is now a parse error), or is it a minor
BCB since it doesn't change any existing built-in behavior (only adds new
behaviors)?

I think that's what we need to expand upon.

My take on it is this:

If you can solve the "break" using nothing but static analysis and a static
conversion "script", then it's a minor break. So new keywords would be fine
(you could find/replace function yield() with function yield2() really
easily). But changing the semantics of code (returning an array instead of
an int, changing how references are passed, etc) would require developer
interaction to fix, and as such would not be minor.

And one point on what classifies as a BC break: Everything. Any change will
break BC in some way. Even adding a function is a BC break since existing
code may use the same function names. Fixing a segfault is a BC break as
well, as it's changing the way it works. The difference comes in if it's a
minor BC break, or a major one. And that's not trivial...

My $0.02 at least...

Anthony

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