Use serialize_precision for printing floats in var_dump()

[nikic]

var_dump() is debugging functionality, so it should print floating-point numbers accurately. We do this by switching to serialize_precision, which (by default) will print with as much precision as necessary to preserve the exact value of the float.

[claudepache]

print_r() should also be modified, I think.

[hikari-no-yume]

Thank you so much for doing this! I had worked on a patch for this but never finished it.

[nikic]

@claudepache Agreed, going to do that in a separate PR.

@hikari-no-yume Doing this kind of change has gotten a lot easier, thanks to the magic of bless_tests.php.

[hikari-no-yume]

@claudepache @nikic Personally I think updating print_r() is a less obviously good idea. I just wrote my objections on internals, but will quote it here for convenience:

The one that gave me pause before and now is print_r(). In principle, it is just print but recursive (I assume that's whence the name comes), but unfortunately some people use it for debugging, so there might be a case for changing it. With that said, it's already a very bad choice for debugging due to other things ("1", 1, 1.0 and TRUE look the same, "0", 0.0, and 0 look the same, "", FALSE and NULL look the same…) that precision is the least of the developer's problems if they choose print_r(), and it's also not in the spirit of "print but recursive". So, it is probably unreasonable to change print_r() here. Maybe we should put a massive red "DO NOT USE THIS FOR DEBUGGING" warning on its documentation page…

[nikic]

@hikari-no-yume Yeah, just saw your mail. I agree with your assessment there, print_r should follow print semantics.

To be honest, I have no idea why that function even exists, it seems like a strictly inferior version of var_dump.

[hikari-no-yume]

(Hope not to sidetrack things too much…) It seems like its niche is meant to be a way to “print” arrays and objects and have it be nicer for humans to read than var_dump. But if you're a developer then you have var_dump which is more informative for you, and if you're not a developer, a nicely-formatted table is probably clearer?