fix(tvix/eval): allow negative substring lengths r/6267

Nix uses string::substr without checking the sign of the length[1].
The NixOS testing infrastructure relies on this[2], and on the
implicit conversion of that to the maximum possible value for a
size_t.

[1]: https://github.com/NixOS/nix/blob/ecae62020b64914d9859a71ce197d03688c6133c/src/libexpr/primops.cc#L3597
[2]: https://github.com/NixOS/nixpkgs/blob/c7c298471676ac1c7789ab3c424fbcebecaa6791/nixos/lib/testing/driver.nix#L29

Change-Id: I6d0caf6830b6bda3fdf44c40c81de6a1befeca7b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8746
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

0 files changed, 0 insertions, 0 deletions