clippy_lints/src/assertions_on_constants.rs

   1 use rustc::hir::{Expr, ExprKind};
   2 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use rustc::{declare_lint_pass, declare_tool_lint};
   4
   5 use crate::consts::{constant, Constant};
   6 use crate::utils::{in_macro_or_desugar, is_direct_expn_of, is_expn_of, span_help_and_lint};
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for `assert!(true)` and `assert!(false)` calls.
  10     ///
  11     /// **Why is this bad?** Will be optimized out by the compiler or should probably be replaced by a
  12     /// panic!() or unreachable!()
  13     ///
  14     /// **Known problems:** None
  15     ///
  16     /// **Example:**
  17     /// ```rust,ignore
  18     /// assert!(false)
  19     /// // or
  20     /// assert!(true)
  21     /// // or
  22     /// const B: bool = false;
  23     /// assert!(B)
  24     /// ```
  25     pub ASSERTIONS_ON_CONSTANTS,
  26     style,
  27     "`assert!(true)` / `assert!(false)` will be optimized out by the compiler, and should probably be replaced by a `panic!()` or `unreachable!()`"
  28 }
  29
  30 declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
  31
  32 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
  33     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  34         let lint_assert_cb = |is_debug_assert: bool| {
  35             if let ExprKind::Unary(_, ref lit) = e.node {
  36                 if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.tables, lit) {
  37                     if is_true {
  38                         span_help_and_lint(
  39                             cx,
  40                             ASSERTIONS_ON_CONSTANTS,
  41                             e.span,
  42                             "`assert!(true)` will be optimized out by the compiler",
  43                             "remove it",
  44                         );
  45                     } else if !is_debug_assert {
  46                         span_help_and_lint(
  47                             cx,
  48                             ASSERTIONS_ON_CONSTANTS,
  49                             e.span,
  50                             "`assert!(false)` should probably be replaced",
  51                             "use `panic!()` or `unreachable!()`",
  52                         );
  53                     }
  54                 }
  55             }
  56         };
  57         if let Some(debug_assert_span) = is_expn_of(e.span, "debug_assert") {
  58             if in_macro_or_desugar(debug_assert_span) {
  59                 return;
  60             }
  61             lint_assert_cb(true);
  62         } else if let Some(assert_span) = is_direct_expn_of(e.span, "assert") {
  63             if in_macro_or_desugar(assert_span) {
  64                 return;
  65             }
  66             lint_assert_cb(false);
  67         }
  68     }
  69 }