clippy::fallible_impl_from: consider implementing `TryFrom` instead

What you see

warning: consider implementing `TryFrom` instead
 --> main.rs:5:1
  |
5 | / impl From<String> for Foo {
6 | |     fn from(s: String) -> Self {
7 | |         Foo(s.parse().unwrap())
8 | |     }
9 | | }
  | |_^
  |
  = help: `From` is intended for infallible conversions only. Use `TryFrom` if there's a possibility for the conversion to fail
note: potential failure(s)
 --> main.rs:7:13
  |
7 |         Foo(s.parse().unwrap())
  |             ^^^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#fallible_impl_from
  = note: `-W clippy::fallible-impl-from` implied by `-W clippy::nursery`

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

TryFrom should be used if there’s a possibility of failure.

New lints still being finished. Off by default and may have false positives.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

struct Foo(i32);

impl From<String> for Foo {
    fn from(s: String) -> Self {
        Foo(s.parse().unwrap())
    }
}

Write this instead

struct Foo(i32);

impl TryFrom<String> for Foo {
    type Error = ();
    fn try_from(s: String) -> Result<Self, Self::Error> {
        if let Ok(parsed) = s.parse() {
            Ok(Foo(parsed))
        } else {
            Err(())
        }
    }
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

[lints.clippy]
fallible_impl_from = "warn"

#![warn(clippy::fallible_impl_from)]

cargo clippy -- -W clippy::fallible-impl-from

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.