Mismatched types should suggest From/Into conversions

[gnzlbg]

This program (Playground):

use std::{process::Stdio, fs::File};
pub fn foo(_x: Stdio) {}
pub fn bar(x: File) { foo(x) }

errors with

error[E0308]: mismatched types
 --> src/lib.rs:3:27
  |
3 | pub fn bar(x: File) { foo(x) }
  |                           ^ expected struct `std::process::Stdio`, found struct `std::fs::File`
  |
  = note: expected type `std::process::Stdio`
             found type `std::fs::File`

error: aborting due to previous error

but there is an impl of From<File> for Stdio, such that this code (Playground):

use std::{process::Stdio, fs::File};
pub fn foo(_x: Stdio) {}
pub fn bar(x: File) { foo(x.into()) }

compiles and works as expected.

The error message should have a note stating that there is a conversion available, and a fix suggestion. That would be a huge boon for API discoverability. If there are multiple APIs that take File and return Stdio, the error message should suggest some of them with some sort of prioritization (From/TryFrom traits, ::from/::new methods, .as_... methods, etc.)

[estebank]

CC #37384, #42499

[kadiwa4]

Fixed (nightly 2023-01-27):

error[E0308]: mismatched types
 --> src/lib.rs:3:27
  |
3 | pub fn bar(x: File) { foo(x) }
  |                       --- ^ expected struct `Stdio`, found struct `File`
  |                       |
  |                       arguments to this function are incorrect
  |
note: function defined here
 --> src/lib.rs:2:8
  |
2 | pub fn foo(_x: Stdio) {}
  |        ^^^ ---------
help: call `Into::into` on this expression to convert `File` into `Stdio`
  |
3 | pub fn bar(x: File) { foo(x.into()) }
  |                            +++++++

For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground` due to previous error