src/tools/clippy/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(cx: &LateContext<'_>, expr: &hir::Expr<'_>, count_recv: &hir::Expr<'_>, map_arg: &hir::Expr<'_>) {
  12     if_chain! {
  13         if is_trait_method(cx, count_recv, sym::Iterator);
  14         let closure = expr_or_init(cx, map_arg);
  15         if let Some(def_id) = cx.tcx.hir().opt_local_def_id(closure.hir_id);
  16         if let Some(body_id) = cx.tcx.hir().maybe_body_owned_by(def_id);
  17         let closure_body = cx.tcx.hir().body(body_id);
  18         if !cx.typeck_results().expr_ty(closure_body.value).is_unit();
  19         then {
  20             if let Some(map_mutated_vars) = mutated_variables(closure_body.value, cx) {
  21                 // A variable is used mutably inside of the closure. Suppress the lint.
  22                 if !map_mutated_vars.is_empty() {
  23                     return;
  24                 }
  25             }
  26             span_lint_and_help(
  27                 cx,
  28                 SUSPICIOUS_MAP,
  29                 expr.span,
  30                 "this call to `map()` won't have an effect on the call to `count()`",
  31                 None,
  32                 "make sure you did not confuse `map` with `filter`, `for_each` or `inspect`",
  33             );
  34         }
  35     }
  36 }