clippy_lints/src/reference.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
  11 use crate::rustc::{declare_tool_lint, lint_array};
  12 use crate::rustc_errors::Applicability;
  13 use crate::syntax::ast::{Expr, ExprKind, UnOp};
  14 use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
  15 use if_chain::if_chain;
  16
  17 /// **What it does:** Checks for usage of `*&` and `*&mut` in expressions.
  18 ///
  19 /// **Why is this bad?** Immediately dereferencing a reference is no-op and
  20 /// makes the code less clear.
  21 ///
  22 /// **Known problems:** Multiple dereference/addrof pairs are not handled so
  23 /// the suggested fix for `x = **&&y` is `x = *&y`, which is still incorrect.
  24 ///
  25 /// **Example:**
  26 /// ```rust
  27 /// let a = f(*&mut b);
  28 /// let c = *&d;
  29 /// ```
  30 declare_clippy_lint! {
  31     pub DEREF_ADDROF,
  32     complexity,
  33     "use of `*&` or `*&mut` in an expression"
  34 }
  35
  36 pub struct Pass;
  37
  38 impl LintPass for Pass {
  39     fn get_lints(&self) -> LintArray {
  40         lint_array!(DEREF_ADDROF)
  41     }
  42 }
  43
  44 fn without_parens(mut e: &Expr) -> &Expr {
  45     while let ExprKind::Paren(ref child_e) = e.node {
  46         e = child_e;
  47     }
  48     e
  49 }
  50
  51 impl EarlyLintPass for Pass {
  52     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
  53         if_chain! {
  54             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.node;
  55             if let ExprKind::AddrOf(_, ref addrof_target) = without_parens(deref_target).node;
  56             then {
  57                 let mut applicability = Applicability::MachineApplicable;
  58                 span_lint_and_sugg(
  59                     cx,
  60                     DEREF_ADDROF,
  61                     e.span,
  62                     "immediately dereferencing a reference",
  63                     "try this",
  64                     format!("{}", snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability)),
  65                     applicability,
  66                 );
  67             }
  68         }
  69     }
  70 }
  71
  72 /// **What it does:** Checks for references in expressions that use
  73 /// auto dereference.
  74 ///
  75 /// **Why is this bad?** The reference is a no-op and is automatically
  76 /// dereferenced by the compiler and makes the code less clear.
  77 ///
  78 /// **Example:**
  79 /// ```rust
  80 /// struct Point(u32, u32);
  81 /// let point = Foo(30, 20);
  82 /// let x = (&point).x;
  83 /// ```
  84 declare_clippy_lint! {
  85     pub REF_IN_DEREF,
  86     complexity,
  87     "Use of reference in auto dereference expression."
  88 }
  89
  90 pub struct DerefPass;
  91
  92 impl LintPass for DerefPass {
  93     fn get_lints(&self) -> LintArray {
  94         lint_array!(REF_IN_DEREF)
  95     }
  96 }
  97
  98 impl EarlyLintPass for DerefPass {
  99     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
 100         if_chain! {
 101             if let ExprKind::Field(ref object, ref field_name) = e.node;
 102             if let ExprKind::Paren(ref parened) = object.node;
 103             if let ExprKind::AddrOf(_, ref inner) = parened.node;
 104             then {
 105                 let mut applicability = Applicability::MachineApplicable;
 106                 span_lint_and_sugg(
 107                     cx,
 108                     REF_IN_DEREF,
 109                     object.span,
 110                     "Creating a reference that is immediately dereferenced.",
 111                     "try this",
 112                     format!(
 113                         "{}.{}",
 114                         snippet_with_applicability(cx, inner.span, "_", &mut applicability),
 115                         snippet_with_applicability(cx, field_name.span, "_", &mut applicability)
 116                     ),
 117                     applicability,
 118                 );
 119             }
 120         }
 121     }
 122 }