order

pub fn order(lhs: Version, rhs: Version) std.math.Order {
    if (lhs.major < rhs.major) return .lt;
    if (lhs.major > rhs.major) return .gt;
    if (lhs.minor < rhs.minor) return .lt;
    if (lhs.minor > rhs.minor) return .gt;
    if (lhs.patch < rhs.patch) return .lt;
    if (lhs.patch > rhs.patch) return .gt;
    if (lhs.pre != null and rhs.pre == null) return .lt;
    if (lhs.pre == null and rhs.pre == null) return .eq;
    if (lhs.pre == null and rhs.pre != null) return .gt;

    // Iterate over pre-release identifiers until a difference is found.
    var lhs_pre_it = std.mem.splitScalar(u8, lhs.pre.?, '.');
    var rhs_pre_it = std.mem.splitScalar(u8, rhs.pre.?, '.');
    while (true) {
        const next_lid = lhs_pre_it.next();
        const next_rid = rhs_pre_it.next();

        // A larger set of pre-release fields has a higher precedence than a smaller set.
        if (next_lid == null and next_rid != null) return .lt;
        if (next_lid == null and next_rid == null) return .eq;
        if (next_lid != null and next_rid == null) return .gt;

        const lid = next_lid.?; // Left identifier
        const rid = next_rid.?; // Right identifier

        // Attempt to parse identifiers as numbers. Overflows are checked by parse.
        const lnum: ?usize = std.fmt.parseUnsigned(usize, lid, 10) catch |err| switch (err) {
            error.InvalidCharacter => null,
            error.Overflow => unreachable,
        };
        const rnum: ?usize = std.fmt.parseUnsigned(usize, rid, 10) catch |err| switch (err) {
            error.InvalidCharacter => null,
            error.Overflow => unreachable,
        };

        // Numeric identifiers always have lower precedence than non-numeric identifiers.
        if (lnum != null and rnum == null) return .lt;
        if (lnum == null and rnum != null) return .gt;

        // Identifiers consisting of only digits are compared numerically.
        // Identifiers with letters or hyphens are compared lexically in ASCII sort order.
        if (lnum != null and rnum != null) {
            if (lnum.? < rnum.?) return .lt;
            if (lnum.? > rnum.?) return .gt;
        } else {
            const ord = std.mem.order(u8, lid, rid);
            if (ord != .eq) return ord;
        }
    }
}