rust-clippy/clippy_lints/src/reference.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::utils::{snippet_with_applicability, span_lint_and_sugg};
use if_chain::if_chain;
use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
use syntax::ast::{Expr, ExprKind, UnOp};
/// **What it does:** Checks for usage of `*&` and `*&mut` in expressions.
///
/// **Why is this bad?** Immediately dereferencing a reference is no-op and
/// makes the code less clear.
///
/// **Known problems:** Multiple dereference/addrof pairs are not handled so
/// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
///
/// **Example:**
/// ```rust
/// let a = f(*&mut b);
/// let c = *&d;
/// ```
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declare_clippy_lint! {
pub DEREF_ADDROF,
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complexity,
"use of `*&` or `*&mut` in an expression"
}
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(DEREF_ADDROF)
}
}
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fn without_parens(mut e: &Expr) -> &Expr {
while let ExprKind::Paren(ref child_e) = e.node {
e = child_e;
}
e
}
impl EarlyLintPass for Pass {
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fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
if_chain! {
if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.node;
if let ExprKind::AddrOf(_, ref addrof_target) = without_parens(deref_target).node;
then {
let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
cx,
DEREF_ADDROF,
e.span,
"immediately dereferencing a reference",
"try this",
format!("{}", snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability)),
applicability,
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);
}
}
}
}
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/// **What it does:** Checks for references in expressions that use
/// auto dereference.
///
/// **Why is this bad?** The reference is a no-op and is automatically
/// dereferenced by the compiler and makes the code less clear.
///
/// **Example:**
/// ```rust
/// struct Point(u32, u32);
/// let point = Foo(30, 20);
/// let x = (&point).x;
/// ```
declare_clippy_lint! {
pub REF_IN_DEREF,
complexity,
"Use of reference in auto dereference expression."
}
pub struct DerefPass;
impl LintPass for DerefPass {
fn get_lints(&self) -> LintArray {
lint_array!(REF_IN_DEREF)
}
}
impl EarlyLintPass for DerefPass {
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fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
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if_chain! {
if let ExprKind::Field(ref object, _) = e.node;
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if let ExprKind::Paren(ref parened) = object.node;
if let ExprKind::AddrOf(_, ref inner) = parened.node;
then {
let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
cx,
REF_IN_DEREF,
object.span,
"Creating a reference that is immediately dereferenced.",
"try this",
snippet_with_applicability(cx, inner.span, "_", &mut applicability).to_string(),
applicability,
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);
}
}
}
}