W1007

Warning

W1007 — An as cast that widens, such as x as i64 when x is an i32. It cannot lose a value, and i64::from(x) says so.

What the compiler reports

Warning[W1007] at {{.*}}warning_for_a_widening_cast.vx:20:16: this cast only widens, so it cannot lose a value; `i64::from(..)`
Warning[W1007] at {{.*}}warning_for_a_widening_cast.vx:22:18: this cast only widens, so it cannot lose a value; `f64::from(..)`

The fragments the test suite holds the compiler to. An ellipsis marks text the test does not constrain; the emitted message also carries a source location.

A program that triggers it

//
// Part of the Vx Project, under the Apache License v2.0 with LLVM Exceptions.
// See LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//
// A cast that only widens, such as `i32` to `i64`, cannot lose a value, and `i64::from(..)` says
// so (W1007). Casts that can lose a value get no W1007: `i64` to `f64` and `i32` to `f32` can
// round, and a narrowing can cut. A cast of a literal gets none either.

fn main() -> i32 {
  let x : i32 = 1;
  let wide = x as i64;
  let f : f32 = 1.5;
  let double = f as f64;
  let big : i64 = 5;
  let rounded = big as f64;
  let single = x as f32;
  let narrow = big as i32;
  let literal = 3 as i64;
  print(wide);
  print(double);
  print(rounded);
  print(single);
  print(literal);
  return narrow;
}

From tests/frontend/pass/warning_for_a_widening_cast.vx, which asserts this diagnostic on every commit.

Related