src/tools/clippy/clippy_lints/src/methods/vec_resize_to_zero.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use if_chain::if_chain;
   4 use rustc_ast::LitKind;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{Expr, ExprKind};
   7 use rustc_lint::LateContext;
   8 use rustc_span::source_map::Spanned;
   9 use rustc_span::{sym, Span};
  10
  11 use super::VEC_RESIZE_TO_ZERO;
  12
  13 pub(super) fn check<'tcx>(
  14     cx: &LateContext<'tcx>,
  15     expr: &'tcx Expr<'_>,
  16     count_arg: &'tcx Expr<'_>,
  17     default_arg: &'tcx Expr<'_>,
  18     name_span: Span,
  19 ) {
  20     if_chain! {
  21         if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  22         if let Some(impl_id) = cx.tcx.impl_of_method(method_id);
  23         if is_type_diagnostic_item(cx, cx.tcx.type_of(impl_id), sym::Vec);
  24         if let ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = count_arg.kind;
  25         if let ExprKind::Lit(Spanned { node: LitKind::Int(..), .. }) = default_arg.kind;
  26         then {
  27             let method_call_span = expr.span.with_lo(name_span.lo());
  28             span_lint_and_then(
  29                 cx,
  30                 VEC_RESIZE_TO_ZERO,
  31                 expr.span,
  32                 "emptying a vector with `resize`",
  33                 |db| {
  34                     db.help("the arguments may be inverted...");
  35                     db.span_suggestion(
  36                         method_call_span,
  37                         "...or you can empty the vector with",
  38                         "clear()".to_string(),
  39                         Applicability::MaybeIncorrect,
  40                     );
  41                 },
  42             );
  43         }
  44     }
  45 }