Confusing error message for methods in formatting.

[ckarmann]

Someone asked this question on StackOverflow: http://stackoverflow.com/questions/21273648/how-do-you-use-the-plural-method-in-rust/21274149#21274149

I'm just learning Rust, so I tried to research the subject and I was confused by the error message from rustc:

error: argument used to format with `d` was attempted to not be used for formatting

While I'm not a native English speaker, I can usually understand any technical english text. However I find this error message very difficult to parse. What does "attempted to not be used" mean ?

So, this issue is mainly about the error message: can it be made clearer? or am I just lacking more context to understand it?

As for the StackOverflow problem itself, shouldn't an argument be usable for both format tokens {:d} and {0, format, ... } ?

[huonw]

Still an issue:

fn main() {
    println!("This page has been visited {} {:0$}.", 1, 2);
}

<anon>:2:54: 2:55 error: argument used to format with `` was attempted to not be used for formatting
<anon>:2     println!("This page has been visited {} {:0$}.", 1, 2);
                                                              ^

(NB. the {plural} and {select} forms have now been removed from the formatter, so this requires using a dynamic width parameter or some such.)

Explanation:

At the moment a formatting parameter can only be used for one style of printing, e.g. argument 0 can be formatted with {0} as many times as wanted or with {0:d} arbitrarily many times, but cannot be used in two contexts, e.g. you can't have "{0} {0:d}" (a somewhat artificial restriction, I guess). This error message is saying "you used it for some style of printing, and now are trying to use it for not-formatting" (using it in {plural} or as a dynamic width 0$ is using it for something other than actual printing).

I guess it could be rephrased to something like

argumented used for format with `...` was attempted to be used in a non-formatting role.

[steveklabnik]

Triage: same message today.

[steveklabnik]

Triage: no change

[doppioslash]

Still there...

[sophiajt]

I don't get an error with this:

fn main() {
    println!("This page has been visited {} {:0$}.", 1, 2);
}

And for the original from so, I get:

error: invalid format string: expected `'}'`, found `','`
 --> /Users/jturner/Source/bad_error.rs:9:22
  |
9 |     let s1 = format!("This page has been visited {:d} {0, plural, one{time} other{times}}.", count);
  |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Mark-Simulacrum]

I guess this has been fixed now, or at least I can't reproduce. I'm going to go ahead and close this issue.