Hi
I gave this some additional thoughts.
Am 2025-05-09 13:36, schrieb Jakub Zelenka:
- A minor version MUST NOT break syntax compatibility (i.e. every PHP
program that compiles must continue to compile).
Added this one
Thinking about this more, I am not sure if having this as a MUST rule
matches what we did in the past and I'm also not sure if it is useful to
have. This rule prevents the addition of new keywords, since they might
conflict with function names. Adding new symbols and adding a new
keyword is functionally equivalent, both changes would result in a
compile time error. Singling out the syntax change does not appear to be
a useful distinction.
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From my experience in maintaining an old PHP application and upgrading
it to support the latest and greatest PHP every year, I think the
following points would be a good starting point to discuss:
- For backwards compatibility breaks introduced in minor versions there
MUST be a simple (for some appropriate definition of simple) way to
adjust the code to be compatible with both the current PHP version and
the upcoming version. Ideally the change would be compatible with a
wider range of past PHP versions (past 3 or so?). It must be a change
that is simple to perform even with basic tooling (i.e. not requiring an
IDE or static analyzers).
- Backwards compatibility breaks in minor versions MUST NOT result in
silent behavioral differences. Instead any breaking change must be
"obvious" when executing the program, even when having a
less-than-stellar test suite.
Adding new symbols results in a compile time error (immediately obvious)
and is simple to fix (rename or remove your own implementation).
Similarly throwing a ValueError for invalid inputs is reasonably easy to
detect by executing the affected code path (you can't miss an Exception)
and also simple to fix (don't do that). Changing operator precedence is
not easy to detect, thus it is unacceptable. Throwing an error when
single-letter variables (e.g. $i) would be easy to detect, but break
almost every program, thus would be unacceptable.
Best regards
Tim Düsterhus
