src/tools/clippy/clippy_lints/src/loops/explicit_counter_loop.rs

   1 use super::{
   2     get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP,
   3 };
   4 use clippy_utils::diagnostics::span_lint_and_sugg;
   5 use clippy_utils::source::snippet_with_applicability;
   6 use clippy_utils::{get_enclosing_block, is_integer_const};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::intravisit::{walk_block, walk_expr};
  10 use rustc_hir::{Expr, Pat};
  11 use rustc_lint::LateContext;
  12
  13 // To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
  14 // incremented exactly once in the loop body, and initialized to zero
  15 // at the start of the loop.
  16 pub(super) fn check<'tcx>(
  17     cx: &LateContext<'tcx>,
  18     pat: &'tcx Pat<'_>,
  19     arg: &'tcx Expr<'_>,
  20     body: &'tcx Expr<'_>,
  21     expr: &'tcx Expr<'_>,
  22 ) {
  23     // Look for variables that are incremented once per loop iteration.
  24     let mut increment_visitor = IncrementVisitor::new(cx);
  25     walk_expr(&mut increment_visitor, body);
  26
  27     // For each candidate, check the parent block to see if
  28     // it's initialized to zero at the start of the loop.
  29     if let Some(block) = get_enclosing_block(cx, expr.hir_id) {
  30         for id in increment_visitor.into_results() {
  31             let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
  32             walk_block(&mut initialize_visitor, block);
  33
  34             if_chain! {
  35                 if let Some((name, initializer)) = initialize_visitor.get_result();
  36                 if is_integer_const(cx, initializer, 0);
  37                 then {
  38                     let mut applicability = Applicability::MachineApplicable;
  39
  40                     let for_span = get_span_of_entire_for_loop(expr);
  41
  42                     span_lint_and_sugg(
  43                         cx,
  44                         EXPLICIT_COUNTER_LOOP,
  45                         for_span.with_hi(arg.span.hi()),
  46                         &format!("the variable `{}` is used as a loop counter", name),
  47                         "consider using",
  48                         format!(
  49                             "for ({}, {}) in {}.enumerate()",
  50                             name,
  51                             snippet_with_applicability(cx, pat.span, "item", &mut applicability),
  52                             make_iterator_snippet(cx, arg, &mut applicability),
  53                         ),
  54                         applicability,
  55                     );
  56                 }
  57             }
  58         }
  59     }
  60 }