createPosixBlock

    pub fn createPosixBlock(
        map: *const Map,
        gpa: Allocator,
        options: CreatePosixBlockOptions,
    ) Allocator.Error!PosixBlock {
        const ZigProgressAction = enum { nothing, edit, delete, add };
        const zig_progress_action: ZigProgressAction = action: {
            const fd = options.zig_progress_fd orelse break :action .nothing;
            const exists = map.contains("ZIG_PROGRESS");
            if (fd >= 0) {
                break :action if (exists) .edit else .add;
            } else {
                if (exists) break :action .delete;
            }
            break :action .nothing;
        };

        const envp = try gpa.allocSentinel(?[*:0]u8, len: {
            var len: usize = map.count();
            switch (zig_progress_action) {
                .add => len += 1,
                .delete => len -= 1,
                .nothing, .edit => {},
            }
            break :len len;
        }, null);
        var envp_len: usize = 0;
        errdefer {
            envp[envp_len] = null;
            PosixBlock.deinit(.{ .slice = envp[0..envp_len :null] }, gpa);
        }

        if (zig_progress_action == .add) {
            envp[envp_len] = try std.fmt.allocPrintSentinel(gpa, "ZIG_PROGRESS={d}", .{options.zig_progress_fd.?}, 0);
            envp_len += 1;
        }

        for (map.keys(), map.values()) |key, value| {
            if (mem.eql(u8, key, "ZIG_PROGRESS")) switch (zig_progress_action) {
                .add => unreachable,
                .delete => continue,
                .edit => {
                    envp[envp_len] = try std.fmt.allocPrintSentinel(gpa, "{s}={d}", .{
                        key, options.zig_progress_fd.?,
                    }, 0);
                    envp_len += 1;
                    continue;
                },
                .nothing => {},
            };

            envp[envp_len] = try std.fmt.allocPrintSentinel(gpa, "{s}={s}", .{ key, value }, 0);
            envp_len += 1;
        }

        assert(envp_len == envp.len);
        return .{ .slice = envp };
    }