clippy_lints/src/vec_resize_to_zero.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::{match_def_path, paths};
   3 use if_chain::if_chain;
   4 use rustc_ast::LitKind;
   5 use rustc_errors::Applicability;
   6 use rustc_hir as hir;
   7 use rustc_hir::{Expr, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::source_map::Spanned;
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Finds occurrences of `Vec::resize(0, an_int)`
  15     ///
  16     /// ### Why is this bad?
  17     /// This is probably an argument inversion mistake.
  18     ///
  19     /// ### Example
  20     /// ```rust
  21     /// vec!(1, 2, 3, 4, 5).resize(0, 5)
  22     /// ```
  23     ///
  24     /// Use instead:
  25     /// ```rust
  26     /// vec!(1, 2, 3, 4, 5).clear()
  27     /// ```
  28     #[clippy::version = "1.46.0"]
  29     pub VEC_RESIZE_TO_ZERO,
  30     correctness,
  31     "emptying a vector with `resize(0, an_int)` instead of `clear()` is probably an argument inversion mistake"
  32 }
  33
  34 declare_lint_pass!(VecResizeToZero => [VEC_RESIZE_TO_ZERO]);
  35
  36 impl<'tcx> LateLintPass<'tcx> for VecResizeToZero {
  37     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  38         if_chain! {
  39             if let hir::ExprKind::MethodCall(path_segment, args, _) = expr.kind;
  40             if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  41             if match_def_path(cx, method_def_id, &paths::VEC_RESIZE) && args.len() == 3;
  42             if let ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = args[1].kind;
  43             if let ExprKind::Lit(Spanned { node: LitKind::Int(..), .. }) = args[2].kind;
  44             then {
  45                 let method_call_span = expr.span.with_lo(path_segment.ident.span.lo());
  46                 span_lint_and_then(
  47                     cx,
  48                     VEC_RESIZE_TO_ZERO,
  49                     expr.span,
  50                     "emptying a vector with `resize`",
  51                     |db| {
  52                         db.help("the arguments may be inverted...");
  53                         db.span_suggestion(
  54                             method_call_span,
  55                             "...or you can empty the vector with",
  56                             "clear()".to_string(),
  57                             Applicability::MaybeIncorrect,
  58                         );
  59                     },
  60                 );
  61             }
  62         }
  63     }
  64 }