clippy_lints/src/needless_borrow.rs

   1 //! Checks for needless address of operations (`&`)
   2 //!
   3 //! This lint is **warn** by default
   4
   5 use rustc::lint::*;
   6 use rustc::hir::{ExprAddrOf, Expr, MutImmutable};
   7 use rustc::ty::TyRef;
   8 use utils::{span_lint, in_macro};
   9 use rustc::ty::adjustment::AutoAdjustment::AdjustDerefRef;
  10
  11 /// **What it does:** This lint checks for address of operations (`&`) that are going to be dereferenced immediately by the compiler
  12 ///
  13 /// **Why is this bad?** Suggests that the receiver of the expression borrows the expression
  14 ///
  15 /// **Known problems:**
  16 ///
  17 /// **Example:** `let x: &i32 = &&&&&&5;`
  18 declare_lint! {
  19     pub NEEDLESS_BORROW,
  20     Warn,
  21     "taking a reference that is going to be automatically dereferenced"
  22 }
  23
  24 #[derive(Copy,Clone)]
  25 pub struct NeedlessBorrow;
  26
  27 impl LintPass for NeedlessBorrow {
  28     fn get_lints(&self) -> LintArray {
  29         lint_array!(NEEDLESS_BORROW)
  30     }
  31 }
  32
  33 impl LateLintPass for NeedlessBorrow {
  34     fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
  35         if in_macro(cx, e.span) {
  36             return;
  37         }
  38         if let ExprAddrOf(MutImmutable, ref inner) = e.node {
  39             if let TyRef(..) = cx.tcx.expr_ty(inner).sty {
  40                 if let Some(&AdjustDerefRef(ref deref)) = cx.tcx.tables.borrow().adjustments.get(&e.id) {
  41                     if deref.autoderefs > 1 && deref.autoref.is_some() {
  42                         span_lint(cx,
  43                                   NEEDLESS_BORROW,
  44                                   e.span,
  45                                   "this expression borrows a reference that is immediately dereferenced by the compiler");
  46                     }
  47                 }
  48             }
  49         }
  50     }
  51 }