addOtherSourceLocation

    fn addOtherSourceLocation(
        wip: *Wip,
        other: ErrorBundle,
        index: SourceLocationIndex,
    ) !SourceLocationIndex {
        if (index == .none) return .none;
        const other_sl = other.getSourceLocation(index);

        var ref_traces: std.ArrayList(ReferenceTrace) = .empty;
        defer ref_traces.deinit(wip.gpa);

        if (other_sl.reference_trace_len > 0) {
            var ref_index = other.extraData(SourceLocation, @backingInt(index)).end;
            for (0..other_sl.reference_trace_len) |_| {
                const other_ref_trace_ed = other.extraData(ReferenceTrace, ref_index);
                const other_ref_trace = other_ref_trace_ed.data;
                ref_index = other_ref_trace_ed.end;

                const ref_trace: ReferenceTrace = if (other_ref_trace.src_loc == .none) .{
                    // sentinel ReferenceTrace does not store a string index in decl_name
                    .decl_name = other_ref_trace.decl_name,
                    .src_loc = .none,
                } else .{
                    .decl_name = try wip.addString(other.nullTerminatedString(other_ref_trace.decl_name)),
                    .src_loc = try wip.addOtherSourceLocation(other, other_ref_trace.src_loc),
                };
                try ref_traces.append(wip.gpa, ref_trace);
            }
        }

        const src_loc = try wip.addSourceLocation(.{
            .src_path = try wip.addString(other.nullTerminatedString(other_sl.src_path)),
            .line = other_sl.line,
            .column = other_sl.column,
            .span_start = other_sl.span_start,
            .span_main = other_sl.span_main,
            .span_end = other_sl.span_end,
            .source_line = if (other_sl.source_line != 0)
                try wip.addString(other.nullTerminatedString(other_sl.source_line))
            else
                0,
            .reference_trace_len = other_sl.reference_trace_len,
        });

        for (ref_traces.items) |ref_trace| {
            try wip.addReferenceTrace(ref_trace);
        }

        return src_loc;
    }