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_tool_lint, lint_array};
   5
   6 use crate::consts::{constant, Constant};
   7 use crate::syntax::ast::LitKind;
   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 pub struct AssertionsOnConstants;
  33
  34 impl LintPass for AssertionsOnConstants {
  35     fn get_lints(&self) -> LintArray {
  36         lint_array![ASSERTIONS_ON_CONSTANTS]
  37     }
  38
  39     fn name(&self) -> &'static str {
  40         "AssertionsOnConstants"
  41     }
  42 }
  43
  44 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
  45     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  46         if_chain! {
  47             if let Some(assert_span) = is_direct_expn_of(e.span, "assert");
  48             if !in_macro(assert_span)
  49                 || is_direct_expn_of(assert_span, "debug_assert").map_or(false, |span| !in_macro(span));
  50             if let ExprKind::Unary(_, ref lit) = e.node;
  51             then {
  52                 if let ExprKind::Lit(ref inner) = lit.node {
  53                     match inner.node {
  54                         LitKind::Bool(true) => {
  55                             span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
  56                                 "assert!(true) will be optimized out by the compiler",
  57                                 "remove it");
  58                         },
  59                         LitKind::Bool(false) => {
  60                             span_help_and_lint(
  61                                 cx, ASSERTIONS_ON_CONSTANTS, e.span,
  62                                 "assert!(false) should probably be replaced",
  63                                 "use panic!() or unreachable!()");
  64                         },
  65                         _ => (),
  66                     }
  67                 } else if let Some(bool_const) = constant(cx, cx.tables, lit) {
  68                     match bool_const.0 {
  69                         Constant::Bool(true) => {
  70                             span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
  71                                 "assert!(const: true) will be optimized out by the compiler",
  72                                 "remove it");
  73                         },
  74                         Constant::Bool(false) => {
  75                             span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
  76                                 "assert!(const: false) should probably be replaced",
  77                                 "use panic!() or unreachable!()");
  78                         },
  79                         _ => (),
  80                     }
  81                 }
  82             }
  83         }
  84     }
  85 }