False positive on standard read!() usage

[EverlastingBugstopper]

Hey! I've recently been getting this strange error for (what I think) is a fairly common usage of the text_io crate's read macro:

fn interactive_delete(prompt_string: &str) -> Result<bool, failure::Error> {
    println!("{} [y/n]", prompt_string);
    let mut response: String = read!("{}\n");
    response = response.split_whitespace().collect(); // remove whitespace
    response.make_ascii_lowercase(); // ensure response is all lowercase
    response.truncate(INTERACTIVE_RESPONSE_LEN); // at this point, all valid input will be "y" or "n"
    match response.as_ref() {
        YES => Ok(true),
        NO => Ok(false),
        _ => failure::bail!("Response must either be \"y\" for yes or \"n\" for no"),
    }
}

When running clippy I get the following warning:

$ cargo clippy
   Compiling wrangler v1.5.0-rc.0 (/Users/me/wrangler)
warning: returning an `Err(_)` with the `?` operator
   --> src/commands/kv/mod.rs:106:32
    |
106 |     let mut response: String = read!("{}\n");
    |                                ^^^^^^^^^^^^^
    |
    = note: `#[warn(clippy::try_err)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#try_err
    = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

If I then use nightly and run with the recommend backtrace, I get this which is rather unintelligible to me. It seems as if clippy wants me to fix something in an external crate?

$ cargo clippy -- -Z external-macro-backtrace
warning: returning an `Err(_)` with the `?` operator
   --> <::text_io::try_scan macros>:8:45
    |
1   |  /     ($ pattern : expr, $ ($ arg : expr), *) =>
2   |  |     {
3   |  |         use :: std :: io :: Read ; try_scan !
    |  |____________________________________-
4   | ||         (:: std :: io :: stdin () . bytes () . map (| c | c . unwrap ()) => $
5   | ||          pattern, $ ($ arg), *) ; format_args ! ($ pattern, $ ($ arg), *) ;
    | ||_________________________________- in this macro invocation (#4)
6   |  |     } ; ($ input : expr => $ pattern : expr, $ ($ arg : expr), *) =>
7   |  |     { { try_scan ! (@ impl question_mark ; $ input => $ pattern, $ ($ arg), *) } }
    |  |         ---------------------------------------------------------------------- in this macro invocation (#5)
8   |  |     ; (@ question_mark : $ ($ e : tt) +) => { { ($ ($ e) +) ? } } ;
    |  |                                                 ^^^^^^^^^^^^^
...    |
31  |  |                          return try_scan !
    |  |_________________________________-
32  | ||                          (@ $ action : Err (Error :: MissingClosingBrace)),
    | ||__________________________________________________________________________- in this macro invocation (#6)
...    |
38  |  |         }
39  |  |     } ;
    |  |       -
    |  |       |
    |  |       in this expansion of `try_scan!` (#3)
    |  |       in this expansion of `try_scan!` (#4)
    |  |_______in this expansion of `try_scan!` (#5)
    |          in this expansion of `try_scan!` (#6)
    | 
   ::: src/commands/kv/mod.rs:106:32
    |
106 |            let mut response: String = read!("{}\n");
    |                                       ------------- in this macro invocation (#1)
    | 
   ::: <::text_io::try_read macros>:1:1
    |
1   |      / () => { try_read ! ("{}") } ; ($ text : expr) =>
2   |      | {
3   |      |     {
4   |      |         (|| -> Result < _, $ crate :: Error >
5   |      |          {
6   |      |              let __try_read_var__ ; try_scan ! ($ text, __try_read_var__) ; Ok
    |      |                                     --------------------------------------- in this macro invocation (#3)
...        |
18  |      |     }
19  |      | } ;
    |      |___- in this expansion of `try_read!` (#2)
    | 
   ::: <::text_io::read macros>:1:1
    |
1   |        ($ ($ arg : tt) *) => { try_read ! ($ ($ arg) *) . unwrap () } ;
    |        ----------------------------------------------------------------
    |        |                       |
    |        |                       in this macro invocation (#2)
    |        in this expansion of `read!` (#1)
    |
    = note: `#[warn(clippy::try_err)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#try_err

If you would like to reproduce this easily, the repo is here: https://github.com/cloudflare/wrangler

Thanks so much for reading this and please let me know if I'm being silly or y'all need more information :)

[phansch]

Thanks for the report! This is a bug and we should not emit the lint in this case.