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
  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, \
  30      and should probably be replaced by a `panic!()` or `unreachable!()`"
  31 }
  32
  33 pub struct AssertionsOnConstants;
  34
  35 impl LintPass for AssertionsOnConstants {
  36     fn get_lints(&self) -> LintArray {
  37         lint_array![ASSERTIONS_ON_CONSTANTS]
  38     }
  39
  40     fn name(&self) -> &'static str {
  41         "AssertionsOnConstants"
  42     }
  43 }
  44
  45 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssertionsOnConstants {
  46     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  47         if_chain! {
  48             if let Some(assert_span) = is_direct_expn_of(e.span, "assert");
  49             if !in_macro(assert_span)
  50                 || is_direct_expn_of(assert_span, "debug_assert").map_or(false, |span| !in_macro(span));
  51             if let ExprKind::Unary(_, ref lit) = e.node;
  52             then {
  53                 if let ExprKind::Lit(ref inner) = lit.node {
  54                     match inner.node {
  55                         LitKind::Bool(true) => {
  56                             span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
  57                                 "assert!(true) will be optimized out by the compiler",
  58                                 "remove it");
  59                         },
  60                         LitKind::Bool(false) => {
  61                             span_help_and_lint(
  62                                 cx, ASSERTIONS_ON_CONSTANTS, e.span,
  63                                 "assert!(false) should probably be replaced",
  64                                 "use panic!() or unreachable!()");
  65                         },
  66                         _ => (),
  67                     }
  68                 } else if let Some(bool_const) = constant(cx, cx.tables, lit) {
  69                     match bool_const.0 {
  70                         Constant::Bool(true) => {
  71                             span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
  72                                 "assert!(const: true) will be optimized out by the compiler",
  73                                 "remove it");
  74                         },
  75                         Constant::Bool(false) => {
  76                             span_help_and_lint(cx, ASSERTIONS_ON_CONSTANTS, e.span,
  77                                 "assert!(const: false) should probably be replaced",
  78                                 "use panic!() or unreachable!()");
  79                         },
  80                         _ => (),
  81                     }
  82                 }
  83             }
  84         }
  85     }
  86 }