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 use syntax_pos::Span;
   6
   7 use crate::consts::{constant, Constant};
   8 use crate::utils::{in_macro, is_direct_expn_of, span_help_and_lint};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for `assert!(true)` and `assert!(false)` calls.
  12     ///
  13     /// **Why is this bad?** Will be optimized out by the compiler or should probably be replaced by a
  14     /// panic!() or unreachable!()
  15     ///
  16     /// **Known problems:** None
  17     ///
  18     /// **Example:**
  19     /// ```rust,ignore
  20     /// assert!(false)
  21     /// // or
  22     /// assert!(true)
  23     /// // or
  24     /// const B: bool = false;
  25     /// assert!(B)
  26     /// ```
  27     pub ASSERTIONS_ON_CONSTANTS,
  28     style,
  29     "`assert!(true)` / `assert!(false)` will be optimized out by the compiler, and should probably be replaced by a `panic!()` or `unreachable!()`"
  30 }
  31
  32 declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
  33
  34 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
  35     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  36         let mut is_debug_assert = false;
  37         let debug_assert_not_in_macro = |span: Span| {
  38             is_debug_assert = true;
  39             // Check that `debug_assert!` itself is not inside a macro
  40             !in_macro(span)
  41         };
  42         if_chain! {
  43             if let Some(assert_span) = is_direct_expn_of(e.span, "assert");
  44             if !in_macro(assert_span)
  45                 || is_direct_expn_of(assert_span, "debug_assert")
  46                     .map_or(false, debug_assert_not_in_macro);
  47             if let ExprKind::Unary(_, ref lit) = e.node;
  48             if let Some(bool_const) = constant(cx, cx.tables, lit);
  49             then {
  50                 match bool_const.0 {
  51                     Constant::Bool(true) => {
  52                         span_help_and_lint(
  53                             cx,
  54                             ASSERTIONS_ON_CONSTANTS,
  55                             e.span,
  56                             "`assert!(true)` will be optimized out by the compiler",
  57                             "remove it"
  58                         );
  59                     },
  60                     Constant::Bool(false) if !is_debug_assert => {
  61                         span_help_and_lint(
  62                             cx,
  63                             ASSERTIONS_ON_CONSTANTS,
  64                             e.span,
  65                             "`assert!(false)` should probably be replaced",
  66                             "use `panic!()` or `unreachable!()`"
  67                         );
  68                     },
  69                     _ => (),
  70                 }
  71             }
  72         }
  73     }
  74 }