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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::{ast_utils, is_direct_expn_of};
   3 use rustc_ast::ast::{Expr, ExprKind, Lit, LitKind};
   4 use rustc_errors::Applicability;
   5 use rustc_lint::{EarlyContext, EarlyLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// ### What it does
  10     /// This lint warns about boolean comparisons in assert-like macros.
  11     ///
  12     /// ### Why is this bad?
  13     /// It is shorter to use the equivalent.
  14     ///
  15     /// ### Example
  16     /// ```rust
  17     /// // Bad
  18     /// assert_eq!("a".is_empty(), false);
  19     /// assert_ne!("a".is_empty(), true);
  20     ///
  21     /// // Good
  22     /// assert!(!"a".is_empty());
  23     /// ```
  24     pub BOOL_ASSERT_COMPARISON,
  25     style,
  26     "Using a boolean as comparison value in an assert_* macro when there is no need"
  27 }
  28
  29 declare_lint_pass!(BoolAssertComparison => [BOOL_ASSERT_COMPARISON]);
  30
  31 fn is_bool_lit(e: &Expr) -> bool {
  32     matches!(
  33         e.kind,
  34         ExprKind::Lit(Lit {
  35             kind: LitKind::Bool(_),
  36             ..
  37         })
  38     ) && !e.span.from_expansion()
  39 }
  40
  41 impl EarlyLintPass for BoolAssertComparison {
  42     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
  43         let macros = ["assert_eq", "debug_assert_eq"];
  44         let inverted_macros = ["assert_ne", "debug_assert_ne"];
  45
  46         for mac in macros.iter().chain(inverted_macros.iter()) {
  47             if let Some(span) = is_direct_expn_of(e.span, mac) {
  48                 if let Some([a, b]) = ast_utils::extract_assert_macro_args(e) {
  49                     let nb_bool_args = is_bool_lit(a) as usize + is_bool_lit(b) as usize;
  50
  51                     if nb_bool_args != 1 {
  52                         // If there are two boolean arguments, we definitely don't understand
  53                         // what's going on, so better leave things as is...
  54                         //
  55                         // Or there is simply no boolean and then we can leave things as is!
  56                         return;
  57                     }
  58
  59                     let non_eq_mac = &mac[..mac.len() - 3];
  60                     span_lint_and_sugg(
  61                         cx,
  62                         BOOL_ASSERT_COMPARISON,
  63                         span,
  64                         &format!("used `{}!` with a literal bool", mac),
  65                         "replace it with",
  66                         format!("{}!(..)", non_eq_mac),
  67                         Applicability::MaybeIncorrect,
  68                     );
  69                     return;
  70                 }
  71             }
  72         }
  73     }
  74 }