We choose to throw an error in the invalid-input space where we *can*
produce a valid (but wrong) result to allow ourselves to, mirroring
CppNix, change the semantics to not corrupt it at all in the future,
while having a middle state where it is an error.
This is a largely-rewritten version of
https://github.com/NixOS/nix/pull/13013.
Co-authored-by: rootile <lix@rootile.de>
Fixes: https://github.com/NixOS/nix/issues/12899
Upstream-PR: https://github.com/NixOS/nix/pull/13013
Change-Id: I6a6a6964cdd1a88714952e80c660d1fa57d1f2d8
Previously, builtins.floor and builtins.ceil always cast the input into a floating point value before running the operation and casting the floating point result back into an integer.
No checks were made for precision loss in either coercing integer inputs or converting the output to an integer (and in fact in the latter case, invoked undefined behaviour).
Now, Lix checks for precision loss on integer input (to avoid a silent eval semantics change if we were to simply pass it through as-is) and on integer output.
If your code fails to evaluate after this change, use --extra-deprecated-features floor-ceil-corrupt-integers.
