src/tools/clippy/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     pub VEC_RESIZE_TO_ZERO,
  24     correctness,
  25     "emptying a vector with `resize(0, an_int)` instead of `clear()` is probably an argument inversion mistake"
  26 }
  27
  28 declare_lint_pass!(VecResizeToZero => [VEC_RESIZE_TO_ZERO]);
  29
  30 impl<'tcx> LateLintPass<'tcx> for VecResizeToZero {
  31     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  32         if_chain! {
  33             if let hir::ExprKind::MethodCall(path_segment, _, args, _) = expr.kind;
  34             if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
  35             if match_def_path(cx, method_def_id, &paths::VEC_RESIZE) && args.len() == 3;
  36             if let ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = args[1].kind;
  37             if let ExprKind::Lit(Spanned { node: LitKind::Int(..), .. }) = args[2].kind;
  38             then {
  39                 let method_call_span = expr.span.with_lo(path_segment.ident.span.lo());
  40                 span_lint_and_then(
  41                     cx,
  42                     VEC_RESIZE_TO_ZERO,
  43                     expr.span,
  44                     "emptying a vector with `resize`",
  45                     |db| {
  46                         db.help("the arguments may be inverted...");
  47                         db.span_suggestion(
  48                             method_call_span,
  49                             "...or you can empty the vector with",
  50                             "clear()".to_string(),
  51                             Applicability::MaybeIncorrect,
  52                         );
  53                     },
  54                 );
  55             }
  56         }
  57     }
  58 }