tidy evaluation in tidyr

This is a question about the codes in vignette("in-packages")

The dataset is below.

(mini_iris <- iris %>% 
    as_tibble() %>% 
    .[c(1, 2, 51, 52, 101, 102), ])
#> # A tibble: 6 x 5
#>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species   
#>          <dbl>       <dbl>        <dbl>       <dbl> <fct>     
#> 1          5.1         3.5          1.4         0.2 setosa    
#> 2          4.9         3            1.4         0.2 setosa    
#> 3          7           3.2          4.7         1.4 versicolor
#> 4          6.4         3.2          4.5         1.5 versicolor
#> 5          6.3         3.3          6           2.5 virginica 
#> 6          5.8         2.7          5.1         1.9 virginica

If the column names are in a character vector (possibly from a function call), you can provide that to one_of()

nest_egg <- function(data, cols) {
  nest(data, egg = one_of(cols))
}

nest_egg(mini_iris, c("Petal.Length", "Petal.Width", "Sepal.Length", "Sepal.Width"))
#> # A tibble: 3 x 2
#>   Species               egg
#>   <fct>      <list<df[,4]>>
#> 1 setosa            [2 × 4]
#> 2 versicolor        [2 × 4]
#> 3 virginica         [2 × 4]

And then, vignette describes that

The use of one_of() here is important; if you don’t use it, and data contains a column named cols, nest() will nest it instead of the columns named in cols.

I think it can be solved in using tidy evaluation.

library(rlang)
nest_egg2 <- function(data, cols) {
  cols <- enexprs(cols)
  nest(data, egg = !!!cols)
}
nest_egg2(mini_iris, c("Petal.Length", "Petal.Width", "Sepal.Length", "Sepal.Width"))

but it shows error

Error: `!!!` can't be supplied with a name. Only the operand's names are retained.

In next section, Vignette describes that

To provide an interface that works like the tidyr function that you’re wrapping, you should pass the argument along using {{ arg }}. {{ }} is a special tidy eval operator that captures the expression supplied by the user and forwards it to another tidy eval-enabled function.

nest_egg <- function(df, cols) {
  nest(df, egg = {{ cols }})
}

nest_egg(mini_iris, -Species)

But I wonder what my nest_egg2 has problem in