clippy_lints/src/methods/suspicious_map.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::usage::mutated_variables;
   3 use clippy_utils::{expr_or_init, is_trait_method};
   4 use if_chain::if_chain;
   5 use rustc_hir as hir;
   6 use rustc_lint::LateContext;
   7 use rustc_span::sym;
   8
   9 use super::SUSPICIOUS_MAP;
  10
  11 pub fn check<'tcx>(
  12     cx: &LateContext<'tcx>,
  13     expr: &hir::Expr<'_>,
  14     map_args: &[hir::Expr<'_>],
  15     count_args: &[hir::Expr<'_>],
  16 ) {
  17     if_chain! {
  18         if let [count_recv] = count_args;
  19         if let [_, map_arg] = map_args;
  20         if is_trait_method(cx, count_recv, sym::Iterator);
  21         let closure = expr_or_init(cx, map_arg);
  22         if let Some(body_id) = cx.tcx.hir().maybe_body_owned_by(closure.hir_id);
  23         let closure_body = cx.tcx.hir().body(body_id);
  24         if !cx.typeck_results().expr_ty(&closure_body.value).is_unit();
  25         then {
  26             if let Some(map_mutated_vars) = mutated_variables(&closure_body.value, cx) {
  27                 // A variable is used mutably inside of the closure. Suppress the lint.
  28                 if !map_mutated_vars.is_empty() {
  29                     return;
  30                 }
  31             }
  32             span_lint_and_help(
  33                 cx,
  34                 SUSPICIOUS_MAP,
  35                 expr.span,
  36                 "this call to `map()` won't have an effect on the call to `count()`",
  37                 None,
  38                 "make sure you did not confuse `map` with `filter` or `for_each`",
  39             );
  40         }
  41     }
  42 }