clippy_lints/src/vec_resize_to_zero.rs

   1 use crate::utils::span_lint_and_then;
   2 use if_chain::if_chain;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::{Expr, ExprKind};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::source_map::Spanned;
   8
   9 use crate::utils::{match_def_path, paths};
  10 use rustc_ast::ast::LitKind;
  11 use rustc_hir as hir;
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Finds occurences of `Vec::resize(0, an_int)`
  15     ///
  16     /// **Why is this bad?** This is probably an argument inversion mistake.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// vec!(1, 2, 3, 4, 5).resize(0, 5)
  23     /// ```
  24     pub VEC_RESIZE_TO_ZERO,
  25     correctness,
  26     "emptying a vector with `resize(0, an_int)` instead of `clear()` is probably an argument inversion mistake"
  27 }
  28
  29 declare_lint_pass!(VecResizeToZero => [VEC_RESIZE_TO_ZERO]);
  30
  31 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for VecResizeToZero {
  32     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
  33         if_chain! {
  34             if let hir::ExprKind::MethodCall(path_segment, _, ref args, _) = expr.kind;
  35             if let Some(method_def_id) = cx.tables.type_dependent_def_id(expr.hir_id);
  36             if match_def_path(cx, method_def_id, &paths::VEC_RESIZE) && args.len() == 3;
  37             if let ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = args[1].kind;
  38             if let ExprKind::Lit(Spanned { node: LitKind::Int(..), .. }) = args[2].kind;
  39             then {
  40                 let method_call_span = expr.span.with_lo(path_segment.ident.span.lo());
  41                 span_lint_and_then(
  42                     cx,
  43                     VEC_RESIZE_TO_ZERO,
  44                     expr.span,
  45                     "emptying a vector with `resize`",
  46                     |db| {
  47                         db.help("the arguments may be inverted...");
  48                         db.span_suggestion(
  49                             method_call_span,
  50                             "...or you can empty the vector with",
  51                             "clear()".to_string(),
  52                             Applicability::MaybeIncorrect,
  53                         );
  54                     },
  55                 );
  56             }
  57         }
  58     }
  59 }