src/tools/clippy/clippy_lints/src/needless_bitwise_bool.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet_opt;
   3 use if_chain::if_chain;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{BinOpKind, Expr, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_middle::ty;
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9
  10 declare_clippy_lint! {
  11     /// ### What it does
  12     /// Checks for uses of bitwise and/or operators between booleans, where performance may be improved by using
  13     /// a lazy and.
  14     ///
  15     /// ### Why is this bad?
  16     /// The bitwise operators do not support short-circuiting, so it may hinder code performance.
  17     /// Additionally, boolean logic "masked" as bitwise logic is not caught by lints like `unnecessary_fold`
  18     ///
  19     /// ### Known problems
  20     /// This lint evaluates only when the right side is determined to have no side effects. At this time, that
  21     /// determination is quite conservative.
  22     ///
  23     /// ### Example
  24     /// ```rust
  25     /// let (x,y) = (true, false);
  26     /// if x & !y {} // where both x and y are booleans
  27     /// ```
  28     /// Use instead:
  29     /// ```rust
  30     /// let (x,y) = (true, false);
  31     /// if x && !y {}
  32     /// ```
  33     #[clippy::version = "1.54.0"]
  34     pub NEEDLESS_BITWISE_BOOL,
  35     pedantic,
  36     "Boolean expressions that use bitwise rather than lazy operators"
  37 }
  38
  39 declare_lint_pass!(NeedlessBitwiseBool => [NEEDLESS_BITWISE_BOOL]);
  40
  41 fn is_bitwise_operation(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
  42     let ty = cx.typeck_results().expr_ty(expr);
  43     if_chain! {
  44         if !expr.span.from_expansion();
  45         if let (&ExprKind::Binary(ref op, _, right), &ty::Bool) = (&expr.kind, &ty.kind());
  46         if op.node == BinOpKind::BitAnd || op.node == BinOpKind::BitOr;
  47         if let ExprKind::Call(..) | ExprKind::MethodCall(..) | ExprKind::Binary(..) | ExprKind::Unary(..) = right.kind;
  48         if !right.can_have_side_effects();
  49         then {
  50             return true;
  51         }
  52     }
  53     false
  54 }
  55
  56 fn suggesstion_snippet(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<String> {
  57     if let ExprKind::Binary(ref op, left, right) = expr.kind {
  58         if let (Some(l_snippet), Some(r_snippet)) = (snippet_opt(cx, left.span), snippet_opt(cx, right.span)) {
  59             let op_snippet = match op.node {
  60                 BinOpKind::BitAnd => "&&",
  61                 _ => "||",
  62             };
  63             return Some(format!("{} {} {}", l_snippet, op_snippet, r_snippet));
  64         }
  65     }
  66     None
  67 }
  68
  69 impl LateLintPass<'_> for NeedlessBitwiseBool {
  70     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
  71         if is_bitwise_operation(cx, expr) {
  72             span_lint_and_then(
  73                 cx,
  74                 NEEDLESS_BITWISE_BOOL,
  75                 expr.span,
  76                 "use of bitwise operator instead of lazy operator between booleans",
  77                 |diag| {
  78                     if let Some(sugg) = suggesstion_snippet(cx, expr) {
  79                         diag.span_suggestion(expr.span, "try", sugg, Applicability::MachineApplicable);
  80                     }
  81                 },
  82             );
  83         }
  84     }
  85 }