rust/tests/ui/unnecessary_fold.rs

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

/// Calls which should trigger the `UNNECESSARY_FOLD` lint
fn unnecessary_fold() {
    // Can be replaced by .any
    let _ = (0..3).fold(false, |acc, x| acc || x > 2);
    // Can be replaced by .all
    let _ = (0..3).fold(true, |acc, x| acc && x > 2);
    // Can be replaced by .sum
    let _ = (0..3).fold(0, |acc, x| acc + x);
    // Can be replaced by .product
    let _ = (0..3).fold(1, |acc, x| acc * x);
}

/// Should trigger the `UNNECESSARY_FOLD` lint, with an error span including exactly `.fold(...)`
fn unnecessary_fold_span_for_multi_element_chain() {
    let _ = (0..3).map(|x| 2 * x).fold(false, |acc, x| acc || x > 2);
}

/// Calls which should not trigger the `UNNECESSARY_FOLD` lint
fn unnecessary_fold_should_ignore() {
    let _ = (0..3).fold(true, |acc, x| acc || x > 2);
    let _ = (0..3).fold(false, |acc, x| acc && x > 2);
    let _ = (0..3).fold(1, |acc, x| acc + x);
    let _ = (0..3).fold(0, |acc, x| acc * x);
    let _ = (0..3).fold(0, |acc, x| 1 + acc + x);

    // We only match against an accumulator on the left
    // hand side. We could lint for .sum and .product when
    // it's on the right, but don't for now (and this wouldn't
    // be valid if we extended the lint to cover arbitrary numeric
    // types).
    let _ = (0..3).fold(false, |acc, x| x > 2 || acc);
    let _ = (0..3).fold(true, |acc, x| x > 2 && acc);
    let _ = (0..3).fold(0, |acc, x| x + acc);
    let _ = (0..3).fold(1, |acc, x| x * acc);

    let _ = [(0..2), (0..3)].iter().fold(0, |a, b| a + b.len());
    let _ = [(0..2), (0..3)].iter().fold(1, |a, b| a * b.len());
}

fn main() {}