Panic inside sort

[worldly creek]

I am encountring a panic inside the zig std lib sort code when I use a custom sort function. Normally the cause of a panic seems reasonably obvious, but in this case it is not. What would you suspect the cause of this bug to be?

(I am using a custom comparator cmp, and its only failing when I use one specific comparator but not the other. The comparator seems rather innocuous, so I dont think that is the problem. But I could be wrong )

thread 49651731 panic: integer overflow
/zig/zig-macos-aarch64-0.14.0/lib/std/sort/block.zig:520:73: 0x10046da4f in block__anon_31336 (praxis)
                        index = findFirstBackward(T, items, items[index - 1], Range.init(pull[pull_index].to, pull[pull_index].from - (count - 1)), length - count, context, lessThan);
                                                                        ^
/zig/zig-macos-aarch64-0.14.0/lib/std/mem.zig:601:19: 0x1004229f7 in sort__anon_24055 (praxis)
    std.sort.block(T, items, context, lessThanFn);
                  ^
/zig/praxis/src/search_index.zig:119:29: 0x100422667 in sort (praxis)
                std.mem.sort(T, sr.*.partial_match.items, {}, cmp);
                            ^
/zig/praxis/src/dictionary.zig:356:30: 0x1004234c3 in sort_search_results (praxis)
        try self.by_form.sort();
                             ^
/zig/praxis/src/dictionary.zig:220:37: 0x10042476f in load_text_data (praxis)
        try self.sort_search_results();

[silk cloak]

is the comparator strictly less than or greater than?

ie. can comp(a, b) == comp(b, a) ever be true

[worldly creek]

It shouldn't be possible, but perhaps, I can double check more carefully.

[tough glade]

from the integer overflow error on index - 1: do you have any special case code for when index is 0?