bench::mark results with a long unnamed expression don't print

[nealrichardson]

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If the expression you're benchmarking is sufficiently long, tibble's print method won't be able to fit it on screen, and it doesn't know how to ellipsize it like it would a regular character vector, so it just prints nothing. Here's a trivial example:

> bench::mark(as.character(as.character(as.character(as.character(as.character(letters))))))
# A tibble: 1 x 13
  expression                                                                   
  <bch:expr>                                                                   
1 as.character(as.character(as.character(as.character(as.character(letters)))))
# … with 12 more variables: min <bch:tm>, median <bch:tm>, `itr/sec` <dbl>,
#   mem_alloc <bch:byt>, `gc/sec` <dbl>, n_itr <int>, n_gc <dbl>,
#   total_time <bch:tm>, result <list>, memory <list>, time <list>, gc <list>

> bench::mark(as.character(as.character(as.character(as.character(as.character(as.character(letters)))))))
# A tibble: 1 x 13
# … with 13 more variables: expression <bch:expr>, min <bch:tm>,
#   median <bch:tm>, `itr/sec` <dbl>, mem_alloc <bch:byt>, `gc/sec` <dbl>,
#   n_itr <int>, n_gc <dbl>, total_time <bch:tm>, result <list>, memory <list>,
#   time <list>, gc <list>
>

The workaround is to name the expression, like I did here.

I'm not sure if this is something that can be solved with a print method for bench_expr, or if there should be an acknowledgement of the issue and a recommendation to name the expressions, or something else.