Confusing hint on missing parentheses after collect<>

[CohenArthur]

The following code produces a quite unhelpful error from the compiler:

use std::io;                                               
use std::fs;
use std::path::{Path, PathBuf};

pub fn build<P: AsRef<Path>>(path: P) -> Result<Vec<PathBuf>, io::Error> {
    let entries = fs::read_dir(path)?;

    let filevec = entries.map(| res | res.map(| e | e.path()))
                         .collect::<Result<Vec<_>, io::Error>>?;

    Ok(filevec)
}

The error in question being .collect::<Result<Vec<_>, io::Error>>?; instead of .collect::<Result<Vec<_>, io::Error>>()?;.

Compiler output:

   Compiling playground v0.0.1 (/playground)
error: field expressions may not have generic arguments
 --> src/lib.rs:9:36
  |
9 |                          .collect::<Result<Vec<_>, io::Error>>?;
  |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

error: could not compile `playground`.

To learn more, run the command again with --verbose.

It's quite a simple mistake, but I got confused by the error message and tried different type-related fixes which didn't work (obviously).

This might be related to #54521

[estebank]

Current full output:

error: field expressions cannot have generic arguments
  --> src/lib.rs:11:36
   |
11 |                          .collect::<Result<Vec<_>, io::Error>>?;
   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0615]: attempted to take value of method `collect` on type `std::iter::Map<std::fs::ReadDir, [closure@src/lib.rs:10:31: 10:62]>`
  --> src/lib.rs:11:27
   |
11 |                          .collect::<Result<Vec<_>, io::Error>>?;
   |                           ^^^^^^^ method, not a field
   |
help: use parentheses to call the method
   |
11 |                          .collect::<Result<Vec<_>, io::Error>>()?;
   |                                                               ^^

[estebank]

No change, only outstanding work is to emit only one of the two errors along with the existing suggestion on E0615.

[oriongonza]

@rustbot claim