Provide refined type for the int range returned by intdiv #15347

Feature request

https://phpstan.org/r/98ff7c32-c78d-4f60-b7fa-acac1bbcf1ac

Computing intdiv on values currently only returns int as type in phpstan. However, we could have more precise types. A typical pattern where this happens is when dealing with pagination settings. The code snippet shared above is taken almost verbatim from doctrine/orm#12643 ("almost" because I reduced it to the bare minimum reproducer).

The mathematical rules give us those guarantees:

• the result is 0 iff the first argument is 0
• if both operands are the same sign, the result is positive
• if both operands are of opposite signs, the result is negative

This could allow a return type extension to inspect the int range of operands so that the return type is one of those:

• 0 (if num1 is known to be 0)
• int<1, max> (if num1 is not 0 and both operands are ranges that are of a same known sign)
• int<min, -1> (if num1 is not 0 and both operands are ranges that are of a opposite known sign)
• int<0, max> (if num1 can be 0 and both operands are ranges that are of a same known sign for non-zero values of num1)
• int<min, 0> (if num1 can be 0 and both operands are ranges that are of a opposite known sign for non-zero values of num1)
• int<min, -1>|int<1, max> when num1 cannot be 0 without guarantees on the signs of operands
• int for other cases

Did PHPStan help you today? Did it make you happy in any way?

No response