src/tools/clippy/clippy_lints/src/mut_reference.rs

   1 use rustc::lint::*;
   2 use rustc::ty::{self, Ty};
   3 use rustc::ty::subst::Subst;
   4 use rustc::hir::*;
   5 use utils::span_lint;
   6
   7 /// **What it does:** Detects giving a mutable reference to a function that only
   8 /// requires an immutable reference.
   9 ///
  10 /// **Why is this bad?** The immutable reference rules out all other references
  11 /// to the value. Also the code misleads about the intent of the call site.
  12 ///
  13 /// **Known problems:** None.
  14 ///
  15 /// **Example:**
  16 /// ```rust
  17 /// my_vec.push(&mut value)
  18 /// ```
  19 declare_clippy_lint! {
  20     pub UNNECESSARY_MUT_PASSED,
  21     style,
  22     "an argument passed as a mutable reference although the callee only demands an \
  23      immutable reference"
  24 }
  25
  26
  27 #[derive(Copy, Clone)]
  28 pub struct UnnecessaryMutPassed;
  29
  30 impl LintPass for UnnecessaryMutPassed {
  31     fn get_lints(&self) -> LintArray {
  32         lint_array!(UNNECESSARY_MUT_PASSED)
  33     }
  34 }
  35
  36 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnecessaryMutPassed {
  37     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  38         match e.node {
  39             ExprCall(ref fn_expr, ref arguments) => if let ExprPath(ref path) = fn_expr.node {
  40                 check_arguments(
  41                     cx,
  42                     arguments,
  43                     cx.tables.expr_ty(fn_expr),
  44                     &print::to_string(print::NO_ANN, |s| s.print_qpath(path, false)),
  45                 );
  46             },
  47             ExprMethodCall(ref path, _, ref arguments) => {
  48                 let def_id = cx.tables.type_dependent_defs()[e.hir_id].def_id();
  49                 let substs = cx.tables.node_substs(e.hir_id);
  50                 let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
  51                 check_arguments(cx, arguments, method_type, &path.name.as_str())
  52             },
  53             _ => (),
  54         }
  55     }
  56 }
  57
  58 fn check_arguments<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arguments: &[Expr], type_definition: Ty<'tcx>, name: &str) {
  59     match type_definition.sty {
  60         ty::TyFnDef(..) | ty::TyFnPtr(_) => {
  61             let parameters = type_definition.fn_sig(cx.tcx).skip_binder().inputs();
  62             for (argument, parameter) in arguments.iter().zip(parameters.iter()) {
  63                 match parameter.sty {
  64                     ty::TyRef(
  65                         _,
  66                         _,
  67                         MutImmutable,
  68                     ) |
  69                     ty::TyRawPtr(ty::TypeAndMut {
  70                         mutbl: MutImmutable,
  71                         ..
  72                     }) => if let ExprAddrOf(MutMutable, _) = argument.node {
  73                         span_lint(
  74                             cx,
  75                             UNNECESSARY_MUT_PASSED,
  76                             argument.span,
  77                             &format!("The function/method `{}` doesn't need a mutable reference", name),
  78                         );
  79                     },
  80                     _ => (),
  81                 }
  82             }
  83         },
  84         _ => (),
  85     }
  86 }