clippy_lints/src/assertions_on_constants.rs

   1 use if_chain::if_chain;
   2 use rustc::hir::{Expr, ExprKind};
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::{declare_lint_pass, declare_tool_lint};
   5
   6 use crate::consts::{constant, Constant};
   7 use crate::utils::{in_macro, is_direct_expn_of, span_help_and_lint};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for `assert!(true)` and `assert!(false)` calls.
  11     ///
  12     /// **Why is this bad?** Will be optimized out by the compiler or should probably be replaced by a
  13     /// panic!() or unreachable!()
  14     ///
  15     /// **Known problems:** None
  16     ///
  17     /// **Example:**
  18     /// ```rust,ignore
  19     /// assert!(false)
  20     /// // or
  21     /// assert!(true)
  22     /// // or
  23     /// const B: bool = false;
  24     /// assert!(B)
  25     /// ```
  26     pub ASSERTIONS_ON_CONSTANTS,
  27     style,
  28     "`assert!(true)` / `assert!(false)` will be optimized out by the compiler, and should probably be replaced by a `panic!()` or `unreachable!()`"
  29 }
  30
  31 declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
  32
  33 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
  34     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  35         let mut is_debug_assert = false;
  36         if_chain! {
  37             if let Some(assert_span) = is_direct_expn_of(e.span, "assert");
  38             if !in_macro(assert_span)
  39                 || is_direct_expn_of(assert_span, "debug_assert").map_or(false, |span| {
  40                     is_debug_assert = true;
  41                     // Check that `debug_assert!` itself is not inside a macro
  42                     !in_macro(span)
  43                 });
  44             if let ExprKind::Unary(_, ref lit) = e.node;
  45             if let Some(bool_const) = constant(cx, cx.tables, lit);
  46             then {
  47                 match bool_const.0 {
  48                     Constant::Bool(true) => {
  49                         span_help_and_lint(
  50                             cx,
  51                             ASSERTIONS_ON_CONSTANTS,
  52                             e.span,
  53                             "`assert!(true)` will be optimized out by the compiler",
  54                             "remove it"
  55                         );
  56                     },
  57                     Constant::Bool(false) if !is_debug_assert => {
  58                         span_help_and_lint(
  59                             cx,
  60                             ASSERTIONS_ON_CONSTANTS,
  61                             e.span,
  62                             "`assert!(false)` should probably be replaced",
  63                             "use `panic!()` or `unreachable!()`"
  64                         );
  65                     },
  66                     _ => (),
  67                 }
  68             }
  69         }
  70     }
  71 }