rust-clippy/clippy_lints/src/copy_iterator.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.

use crate::utils::{is_copy, match_path, paths, span_note_and_lint};
use rustc::hir::{Item, ItemKind};
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_tool_lint, lint_array};

/// **What it does:** Checks for types that implement `Copy` as well as
/// `Iterator`.
///
/// **Why is this bad?** Implicit copies can be confusing when working with
/// iterator combinators.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// #[derive(Copy, Clone)]
/// struct Countdown(u8);
///
/// impl Iterator for Countdown {
///     // ...
/// }
///
/// let a: Vec<_> = my_iterator.take(1).collect();
/// let b: Vec<_> = my_iterator.collect();
/// ```
declare_clippy_lint! {
    pub COPY_ITERATOR,
    pedantic,
    "implementing `Iterator` on a `Copy` type"
}

pub struct CopyIterator;

impl LintPass for CopyIterator {
    fn get_lints(&self) -> LintArray {
        lint_array![COPY_ITERATOR]
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CopyIterator {
    fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
        if let ItemKind::Impl(_, _, _, _, Some(ref trait_ref), _, _) = item.node {
            let ty = cx.tcx.type_of(cx.tcx.hir().local_def_id(item.id));

            if is_copy(cx, ty) && match_path(&trait_ref.path, &paths::ITERATOR) {
                span_note_and_lint(
                    cx,
                    COPY_ITERATOR,
                    item.span,
                    "you are implementing `Iterator` on a `Copy` type",
                    item.span,
                    "consider implementing `IntoIterator` instead",
                );
            }
        }
    }
}