src/tools/clippy/clippy_lints/src/assertions_on_constants.rs

   1 use clippy_utils::consts::{constant, Constant};
   2 use clippy_utils::diagnostics::span_lint_and_help;
   3 use clippy_utils::higher;
   4 use clippy_utils::source::snippet_opt;
   5 use clippy_utils::{is_direct_expn_of, is_expn_of, match_panic_call};
   6 use if_chain::if_chain;
   7 use rustc_hir::{Expr, ExprKind, UnOp};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10
  11 declare_clippy_lint! {
  12     /// ### What it does
  13     /// Checks for `assert!(true)` and `assert!(false)` calls.
  14     ///
  15     /// ### Why is this bad?
  16     /// Will be optimized out by the compiler or should probably be replaced by a
  17     /// `panic!()` or `unreachable!()`
  18     ///
  19     /// ### Known problems
  20     /// None
  21     ///
  22     /// ### Example
  23     /// ```rust,ignore
  24     /// assert!(false)
  25     /// assert!(true)
  26     /// const B: bool = false;
  27     /// assert!(B)
  28     /// ```
  29     pub ASSERTIONS_ON_CONSTANTS,
  30     style,
  31     "`assert!(true)` / `assert!(false)` will be optimized out by the compiler, and should probably be replaced by a `panic!()` or `unreachable!()`"
  32 }
  33
  34 declare_lint_pass!(AssertionsOnConstants => [ASSERTIONS_ON_CONSTANTS]);
  35
  36 impl<'tcx> LateLintPass<'tcx> for AssertionsOnConstants {
  37     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
  38         let lint_true = |is_debug: bool| {
  39             span_lint_and_help(
  40                 cx,
  41                 ASSERTIONS_ON_CONSTANTS,
  42                 e.span,
  43                 if is_debug {
  44                     "`debug_assert!(true)` will be optimized out by the compiler"
  45                 } else {
  46                     "`assert!(true)` will be optimized out by the compiler"
  47                 },
  48                 None,
  49                 "remove it",
  50             );
  51         };
  52         let lint_false_without_message = || {
  53             span_lint_and_help(
  54                 cx,
  55                 ASSERTIONS_ON_CONSTANTS,
  56                 e.span,
  57                 "`assert!(false)` should probably be replaced",
  58                 None,
  59                 "use `panic!()` or `unreachable!()`",
  60             );
  61         };
  62         let lint_false_with_message = |panic_message: String| {
  63             span_lint_and_help(
  64                 cx,
  65                 ASSERTIONS_ON_CONSTANTS,
  66                 e.span,
  67                 &format!("`assert!(false, {})` should probably be replaced", panic_message),
  68                 None,
  69                 &format!("use `panic!({})` or `unreachable!({})`", panic_message, panic_message),
  70             );
  71         };
  72
  73         if let Some(debug_assert_span) = is_expn_of(e.span, "debug_assert") {
  74             if debug_assert_span.from_expansion() {
  75                 return;
  76             }
  77             if_chain! {
  78                 if let ExprKind::Unary(_, lit) = e.kind;
  79                 if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.typeck_results(), lit);
  80                 if is_true;
  81                 then {
  82                     lint_true(true);
  83                 }
  84             };
  85         } else if let Some(assert_span) = is_direct_expn_of(e.span, "assert") {
  86             if assert_span.from_expansion() {
  87                 return;
  88             }
  89             if let Some(assert_match) = match_assert_with_message(cx, e) {
  90                 match assert_match {
  91                     // matched assert but not message
  92                     AssertKind::WithoutMessage(false) => lint_false_without_message(),
  93                     AssertKind::WithoutMessage(true) | AssertKind::WithMessage(_, true) => lint_true(false),
  94                     AssertKind::WithMessage(panic_message, false) => lint_false_with_message(panic_message),
  95                 };
  96             }
  97         }
  98     }
  99 }
 100
 101 /// Result of calling `match_assert_with_message`.
 102 enum AssertKind {
 103     WithMessage(String, bool),
 104     WithoutMessage(bool),
 105 }
 106
 107 /// Check if the expression matches
 108 ///
 109 /// ```rust,ignore
 110 /// if !c {
 111 ///   {
 112 ///     ::std::rt::begin_panic(message, _)
 113 ///   }
 114 /// }
 115 /// ```
 116 ///
 117 /// where `message` is any expression and `c` is a constant bool.
 118 fn match_assert_with_message<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<AssertKind> {
 119     if_chain! {
 120         if let Some(higher::If { cond, then, .. }) = higher::If::hir(expr);
 121         if let ExprKind::Unary(UnOp::Not, expr) = cond.kind;
 122         // bind the first argument of the `assert!` macro
 123         if let Some((Constant::Bool(is_true), _)) = constant(cx, cx.typeck_results(), expr);
 124         // block
 125         if let ExprKind::Block(block, _) = then.kind;
 126         if block.stmts.is_empty();
 127         if let Some(block_expr) = &block.expr;
 128         // inner block is optional. unwrap it if it exists, or use the expression as is otherwise.
 129         if let Some(begin_panic_call) = match block_expr.kind {
 130             ExprKind::Block(inner_block, _) => &inner_block.expr,
 131             _ => &block.expr,
 132         };
 133         // function call
 134         if let Some(arg) = match_panic_call(cx, begin_panic_call);
 135         // bind the second argument of the `assert!` macro if it exists
 136         if let panic_message = snippet_opt(cx, arg.span);
 137         // second argument of begin_panic is irrelevant
 138         // as is the second match arm
 139         then {
 140             // an empty message occurs when it was generated by the macro
 141             // (and not passed by the user)
 142             return panic_message
 143                 .filter(|msg| !msg.is_empty())
 144                 .map(|msg| AssertKind::WithMessage(msg, is_true))
 145                 .or(Some(AssertKind::WithoutMessage(is_true)));
 146         }
 147     }
 148     None
 149 }