src/tools/clippy/clippy_lints/src/bool_assert_comparison.rs

   1 use clippy_utils::{diagnostics::span_lint_and_sugg, higher, is_direct_expn_of, ty::implements_trait};
   2 use rustc_ast::ast::LitKind;
   3 use rustc_errors::Applicability;
   4 use rustc_hir::{Expr, ExprKind, Lit};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_middle::ty;
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::symbol::Ident;
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// This lint warns about boolean comparisons in assert-like macros.
  13     ///
  14     /// ### Why is this bad?
  15     /// It is shorter to use the equivalent.
  16     ///
  17     /// ### Example
  18     /// ```rust
  19     /// // Bad
  20     /// assert_eq!("a".is_empty(), false);
  21     /// assert_ne!("a".is_empty(), true);
  22     ///
  23     /// // Good
  24     /// assert!(!"a".is_empty());
  25     /// ```
  26     pub BOOL_ASSERT_COMPARISON,
  27     style,
  28     "Using a boolean as comparison value in an assert_* macro when there is no need"
  29 }
  30
  31 declare_lint_pass!(BoolAssertComparison => [BOOL_ASSERT_COMPARISON]);
  32
  33 fn is_bool_lit(e: &Expr<'_>) -> bool {
  34     matches!(
  35         e.kind,
  36         ExprKind::Lit(Lit {
  37             node: LitKind::Bool(_),
  38             ..
  39         })
  40     ) && !e.span.from_expansion()
  41 }
  42
  43 fn is_impl_not_trait_with_bool_out(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> bool {
  44     let ty = cx.typeck_results().expr_ty(e);
  45
  46     cx.tcx
  47         .lang_items()
  48         .not_trait()
  49         .filter(|trait_id| implements_trait(cx, ty, *trait_id, &[]))
  50         .and_then(|trait_id| {
  51             cx.tcx.associated_items(trait_id).find_by_name_and_kind(
  52                 cx.tcx,
  53                 Ident::from_str("Output"),
  54                 ty::AssocKind::Type,
  55                 trait_id,
  56             )
  57         })
  58         .map_or(false, |assoc_item| {
  59             let proj = cx.tcx.mk_projection(assoc_item.def_id, cx.tcx.mk_substs_trait(ty, &[]));
  60             let nty = cx.tcx.normalize_erasing_regions(cx.param_env, proj);
  61
  62             nty.is_bool()
  63         })
  64 }
  65
  66 impl<'tcx> LateLintPass<'tcx> for BoolAssertComparison {
  67     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  68         let macros = ["assert_eq", "debug_assert_eq"];
  69         let inverted_macros = ["assert_ne", "debug_assert_ne"];
  70
  71         for mac in macros.iter().chain(inverted_macros.iter()) {
  72             if let Some(span) = is_direct_expn_of(expr.span, mac) {
  73                 if let Some(args) = higher::extract_assert_macro_args(expr) {
  74                     if let [a, b, ..] = args[..] {
  75                         let nb_bool_args = is_bool_lit(a) as usize + is_bool_lit(b) as usize;
  76
  77                         if nb_bool_args != 1 {
  78                             // If there are two boolean arguments, we definitely don't understand
  79                             // what's going on, so better leave things as is...
  80                             //
  81                             // Or there is simply no boolean and then we can leave things as is!
  82                             return;
  83                         }
  84
  85                         if !is_impl_not_trait_with_bool_out(cx, a) || !is_impl_not_trait_with_bool_out(cx, b) {
  86                             // At this point the expression which is not a boolean
  87                             // literal does not implement Not trait with a bool output,
  88                             // so we cannot suggest to rewrite our code
  89                             return;
  90                         }
  91
  92                         let non_eq_mac = &mac[..mac.len() - 3];
  93                         span_lint_and_sugg(
  94                             cx,
  95                             BOOL_ASSERT_COMPARISON,
  96                             span,
  97                             &format!("used `{}!` with a literal bool", mac),
  98                             "replace it with",
  99                             format!("{}!(..)", non_eq_mac),
 100                             Applicability::MaybeIncorrect,
 101                         );
 102                         return;
 103                     }
 104                 }
 105             }
 106         }
 107     }
 108 }