rust-clippy/clippy_lints/src/map_clone.rs

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// 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::rustc::hir;
use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use crate::rustc::{declare_tool_lint, lint_array};
use crate::syntax::source_map::Span;
use crate::utils::paths;
use crate::utils::{
in_macro, match_trait_method, match_type,
remove_blocks, snippet,
span_lint_and_sugg,
};
use if_chain::if_chain;
use crate::syntax::ast::Ident;
#[derive(Clone)]
pub struct Pass;
/// **What it does:** Checks for usage of `iterator.map(|x| x.clone())` and suggests
/// `iterator.cloned()` instead
///
/// **Why is this bad?** Readability, this can be written more concisely
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let x = vec![42, 43];
/// let y = x.iter();
/// let z = y.map(|i| *i);
/// ```
///
/// The correct use would be:
///
/// ```rust
/// let x = vec![42, 43];
/// let y = x.iter();
/// let z = y.cloned();
/// ```
declare_clippy_lint! {
pub MAP_CLONE,
style,
"using `iterator.map(|x| x.clone())`, or dereferencing closures for `Copy` types"
}
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(MAP_CLONE)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
if in_macro(e.span) {
return;
}
if_chain! {
if let hir::ExprKind::MethodCall(ref method, _, ref args) = e.node;
if args.len() == 2;
if method.ident.as_str() == "map";
let ty = cx.tables.expr_ty(&args[0]);
if match_type(cx, ty, &paths::OPTION) || match_trait_method(cx, e, &paths::ITERATOR);
if let hir::ExprKind::Closure(_, _, body_id, _, _) = args[1].node;
let closure_body = cx.tcx.hir.body(body_id);
let closure_expr = remove_blocks(&closure_body.value);
then {
match closure_body.arguments[0].pat.node {
hir::PatKind::Ref(ref inner, _) => if let hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) = inner.node {
lint(cx, e.span, args[0].span, name, closure_expr);
},
hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, name, None) => match closure_expr.node {
hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner) => lint(cx, e.span, args[0].span, name, inner),
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hir::ExprKind::MethodCall(ref method, _, ref obj) => if method.ident.as_str() == "clone" && match_trait_method(cx, closure_expr, &paths::CLONE_TRAIT) {
lint(cx, e.span, args[0].span, name, &obj[0]);
}
_ => {},
},
_ => {},
}
}
}
}
}
fn lint(cx: &LateContext<'_, '_>, replace: Span, root: Span, name: Ident, path: &hir::Expr) {
if let hir::ExprKind::Path(hir::QPath::Resolved(None, ref path)) = path.node {
if path.segments.len() == 1 && path.segments[0].ident == name {
span_lint_and_sugg(
cx,
MAP_CLONE,
replace,
"You are using an explicit closure for cloning elements",
"Consider calling the dedicated `cloned` method",
format!("{}.cloned()", snippet(cx, root, "..")),
)
}
}
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}